THE WESTERN PORT MARINE ENVIRONMENT Based on a Report to the Environment Protection Authority by Consulting Environmental Engineers

l-he Western Port Marine Environment

ENViRONMENT PROTEcnON AUTHORITY

Making a difference ----... ~ .. -.-

THE WESTERN PORT MARINE ENVIRONMENT Based on a report to the Environment Protection Authority by Consulting Environmental Engineers

Environment Protection Authority State Government of Victor'

March 1996 333.9164 The Western Port 099452 marine environment WES oopy 1 THE WESTERN PORT MARThTE ENVIRONMENT

Based on a report to the Environment Protection Authority by Consulting Environmental Engineers

Edited by: David May and Andy Stephens

Catchment and Marine Studies Unit

EnVironment Protection Authority Olderfleet Buildings 477 Collins Street Melbourne Victoria 3000 Australia

Printed on recycled paper

Publication 493

ISBN 0 7306 7509 2 FORE\VORD

Western Port and its surrounding catchment are highly regarded as a recreational and commercial resource, and is one of Victorias most valuable assets. The terrestrial and marine ecosystems found in this area contain a large variety of plant and animal communities on a scale not found in other parts of Australia. The Western Port catchment supports a large agricultural industry and is one of the most important and productive agricultural areas in the State. Western Port provides a large recreational amenity for fishing, boating and other activities, supports commercial fisheries and is an important deep water port linking industry with Australian and overseas markets.

The marine aod coastal environment of Western Port consists of a large number of interdependent ecosystems. The loss of about 170km2 of intertidal seagrass during the late 1970s caused a major ecological change to the marine environment. A reduction in commercial and recreational fishing followed this event and highlights the dependence of healthy ecosystems on the maintenance of others.

The long term management of the Western Port marine environment and catchment are important issues for Victoria. Rapidly expanding urban development in the catchment will increase the demands for a quality environment, while at the same time placing significant pressure on Western Port. This is critical for the long tenn viability of the area as an environmental and commercial resource and a recreational asset for all Victoria.

This report has been prepared following a review of current and historical literature on the Western Port marine environment. It represents the fIrst large scale review of monitoring and research since the Westernport Bay Environmental Study was conducted in 1973-1974. The information presented provides an assessment ofthe current environmental condition of the Western Port marine environment and integrates a pool of knowledge that is essential for the sustainable management of Western Port in the future.. ACKNOWLEDGMENTS

This report is based on a Review o/the Western Port Marine Environmentprepared for the Environment Protection Authority by Consulting Environmental Engineers Pty. Ltd.

The conduct of the review has been greatly assisted by the enthusiasm and concern of many people for the health of Western Port, in particular: Bruce Ridgeway; Marc Marsden; Dr Brian Cuming; Richard Hawkins; Ren Milsorn; Ian Bunton; Dr Jan Watson; Garry Mabon and AM. Swan.

Dr Eric Bird, Dr Kerry Black, Dr Brian Robinson, Pat Condina, David Baird, Scott Chidgey and Andy Stephens contributed presentations to the workshop, as did Bruce Ridgeway, Dr Brian Cuming, Richard Hawkins and Ren Milsom.

All attendees ofthe workshop provided information and opinions which assisted the identification and critical discussion of environmental issues in Western Port. Dr Graeme Watson, Dr Graeme Edgar, Dr Greg Jenkins, Dr Murray MacDonald, Malcolm Hull (BHP), Victorian Institute of Marine Sciences, Melbourne Water, Marine Science and Ecology, Bird Observers Club ofAustralia and South Gippsland Conservation Society also contributed to the review.

The assistance of Lisa Dixon, Chris Bell, Dr Colin Gibbs, Gus Fabris, Maree Bethel, Rebecca McGuigan, Ian Harris, Robyn Starkey, David Tiller, Jan Barton and Kate Greenlees with editorial comments are gratefully acknowledged. [ Environment Protection Authority The Western Port Marine Environment il 'I TABLE OF CONTENTS

PAGE

CHAPTER l ...... uuu ...... _ ....,...... ,.... ~ ...... u ...... u ...... u .. u 1

INTRODUCTION •.•...• .-...... 1 Review of the Western Port Marine Environment...... I Workshop ...... 2 1 Scientific review ...... 2 CHAPTER 2 ...... UHU.... U...... u ...... un ...... u ...... n ...... 3

., STATUS OF THE WESTERN PORT MARINE ENVIROl'.. 'MENT ...... 3 PHYSICAL CHARACTERISTICS ...... 3 TIDES AND CURRENTS 7 ...... 4 PHYSICO-CHEMICAL INDICATORS ...... 4 CATCHMENT INPUTS ...... 5 TURBIDITY ...... 6 PLANKTON COMMUNITIES ...... 6 /tvfANGROVE AND SALTMARSH COMMUNITIES ...... 6 SEAGRASS AND ASSOCIATED COMMUNITIES ...... 7 INVERTEBRA TES ...... 7 SUMMARY OF THE STATUS OF THE WESTERN PORT MARlh'E ENVIRONMENT ...... 8

PHYSICAL CHARACTERISTICS OF THE WESTERN PORT MARINE ENVIRONMENT... 9 INTRODUCTION ...... 9 GEOLOGy ...... 9 COASTAL FEATURES AND PROCESSES ...... 11 Bluffs and cliffs ...... 14 Sandy shorelines ...... 14 Mudflats ...... 15 Swamp ...... 16 Development...... 17 BATHYMETRY ...... 17 SEDIMENTS ...... 18 Dredging and sediment sources ...... 21 Catchment Sources of Sediment...... 23 Resuspension of sediments from mudflats ...... 24

CHAPTER 4 .... ~ .... ~ •••••.••••.. u_.... u •• u ...... u ...... ~ ...... _ ...... " ...... "...... _ ...... 25

TIDES AI\'D CURRENTS OF WESTERN PORT ...... 25 TIDES IN WESTERN PORT ...... 25 CURRENTS IN "''ESTERN PORT ...... 27 Environment Protection Authority The Western Port Marine Environment

PAGE

CHAPTER 5 ...•••..•••..••...... •.•..••..•••...••..•.••...•.••.•.....•.••...•••..•..••...••.. _...... _....•.••.... m ...... 32

PHYSICO-CHEMICAL MONITORING OF THE WESTER"'I PORT MAR.Il'o-.E El'.'VIROl'.'MENT A.""D CATCHMENT INPUT STREAMS ...... _ ...... 32 INTRODUCTION ...... 32 REVIEW OF THE PHYSICO-CHE1-IISTRY OF WESTERN PORT ...... 32 Monitoring programs undertaken in Western Port...... 32 General physico-chemical monitoring ...... 33 Nutrients ...... 35 Metals in Waters ...... 37 Metals in sediments ...... 38 Metals in biota ...... 40 Organics ...... 41 Hydrocarbons ...... 41 Biocides ...... 42 AVAILABILITY OF BACKGROUND CONTAMINANT CONCENTRATIONS IN WATER, SEDIMENT AND BIOTA ...... 42 CATCHMENT INPUTS ...... 43 Physico-chemical monitoring ...... 44 Long term programs ...... 44 Intensive investigations ...... 46 Metals in input streams ...... 47 Biocides ...... 47 Industry ...... 48 SUMMARy ...... 49 CHAPTER 6 ...... 54

PLANKTON COMMUNITIES ...... _••. 54 INTRODUCTION ...... 54 PHYTOPLANKTON ...... 54 Phytoplankton popuJations ...... 54 Phytoplankton biomass ...... 54 Phytoplankton productivity ...... 57 ZOOPLANKTON ...... 57

CHAP'fER 7...... -n...... ~ ...... " .... ~ ...... u.~"' ...... u .....~ ...u ...... u.~ .....~ ...... 58

SALTMARSH A."1D MANGROVE COMMUNITIES ...... 58 INTRODUCTION ...... 58 SALTMARSH COMMUNITIES ...... 59 MANGROVE COMMlJI','ITIES ...... 60 DISTRIBUTION OF MANGROVE AND SALTMARSH COMMIJ1\'1TIES, ...... 61 CHAPTER 8 ...... 65

SEAGRASS COM.i'\flJ.!'\'ITIES ...... 65 INTRODUCTION ...... 65 SEA GRASS DISTRIBuTION ...... 65 DECLINE OF SEA GRASS ...... 70 Possible Causes of the Decline oflntertidal Seagrass Beds in Western Port ...... 74 Environment Protection Authority The Westem Port Marine Eovironment 1I !

PAGE Physical Blanketing by Sediments ...... 76 Turbidity and Shading ...... 77 Desiccation ...... 78 Industrial Waste Releases ...... 79 Tributyl Tin (TBT) ...... 79 Biocide Runoff from Catchment ...... 80 Natural Events ...... 80 Summary ...... 80

MARINE INVERTEBRATE FAUNA ...... 81 INTRODUCTION ...... 81 I INVERTEBRATE FAUNA OF WESTBR.J>:j PORT ...... 81 ~ Seagrasses and mudflats ...... 82 Channels ...... 83 Sandy Beaches ...... 85 Reefs and Hard Substrates ...... 85 The San Remo Marine Community ...... 86 Monitoring Program at BHP-Lysaght ...... 86 SUMMARy...... 87

FISH AND FISHERIES ...... 88 INTRODUCTION ...... 88 FISH COMMUNITIES IN WESTERi"1 PORT ...... :...... 88 COMMERCIAL AND RECREATIONAL FISHERIES IN WESTERt'l PORT ...... 93 BIBLIOGRAPHY...... 96 PERSONAL COMMUNICATIONS ...... 123 Environment Protection Authority The Western Port Marine Environment

LIST OF FIGURES i

PAGE f Figure 3, I Geology and physiography of Western Port------~ 0 ! Figure 3.2 Major morphological feature".------12 Figure 3.3 Shoreline features of Western Port ------13 1 Figure 3.4 Sites of geological and geomorphological significance in Western------13 , Figure 3.5 Distribution of textural sediment types in Western Port------19 J Figure 3.6 General pattern of sediment transport in Western Port------20 Figure 4.1 Half-tidal fluxes in Western Port------·--27 I Figure 4.2 Western Port showing I Jan grid used in Hinwood hydrodynamic model--·-····------28 Figure 4.3 Typical velocity vectors from Hinwood hydrodynamic model------·--·---·--..·-----·------29 1 Figure 4.4 Independently derived circulation patterns in Western POl1i------·---·------30 Figure 4.5 Instantanecus currents for VIMS localised Bass Strait hydrod)lIamic model------31 ! Figure 5.1 EPA water quality monitoring sites in Western POrl------34 Figure 5.2 Total nitrogen concentrations for EPA monitoring sites for the period 1984-1994------36 Figure 5.3 Total Phosphorous at EPA monitoring sites for the period 1984-1994------36 Figure 5.4 Stream monitoring in west section of Western Port 1973 to 1986------51 Figure 5.5 Stream monitoring in north section of Western Port 1973 to 1986------S2 Figure 5.6 Stream monitoring in east section of Western Port 1973 to 1986------·------53 Figure 6.1 Chlorophyll-a concentrations (I'gl.;') at EPA fixed sites------56 Figure 7, I Generalised pattern of saltmarsh and mangrove zones in Western Port------58 Figure 7.2a Mangrove distribution in Western Port in 1842------62 Figure 7.2b Mangrove distribution in Western Port 193~------,------62 Figure 7.2c Mangrove distribution in Western Port 1984------·------63 Figure 8.1 Sampling locations for vegetation mapping in Western POrt in 1973}------66 Figure 8.2 Seagrass and macrophytic algae distribution in Western Port in 1974 from the Westernport Bay Environmental SlUdy--.------_·------67 Figure 8.3 Seagrass and macrophytic algae distribution in Western Port in 1974. based 01>------68 surveys by Bulthuis in 1974------,------68 Figure 8.4 Seagrass coverage in Western Port from Western Port Bay Strategy------·------_·------69 Figure 8.5 Standing crop of subtidal Heterozostera tasmanica and Caulerpa cactoides at BHP 1972 to 1989---'15 Figure 9.1 Simplified food web of the seagrass ecosystem at Crib Point------84 Figure 10.1 Food web for fish groups associated with seagrass communities ------·---89 Figure 10.2 Commercial fish catches in Western Port------·------94 ;1 Environment Protection The Western Port Marme Environment I ~4uihority [ 'I LIST OF TABLES

PAGE Table 3.1 Program of dredging in Western Port from 1921 to present-·----··-···-·-·------·-··--·---22 Table 4.1 Tidal amplification in Western Port------·------·------26 Table 4.2 Comparisons of velocities in Western Port segments------·.. ------28 Table 5.1 Indicators measured in Western Port for the Environment Protection Authority marine monitoring program - •• -----•• -.----•• - •••• - ••••••• - •• --.---...... ---- ••• --••• - ••• - .....- ••.•• -.-...- ••• 3 3 Table 5.2 Metal concentrations in seawater from Environment Protection Authority monitoring stations-····•• 38 Table 5.3 Summary of results of sediment analyses from Statham (1977) ..------..•• ..-·-·-·-·------· .. -·-··-39 Table 5.4 Annual frequency of monitoring at EPA water quality monitoring stations--·······----·····-···---43 Table 5.5 Input monitOring investigations in the Western Port catchment.·-····-·-·----·-·······-···---..45 Table 5.6 EPA licensed discharges to Western Port catcbment·----·--·-·.. -··------·--···--·-··-48 Table 5.7 Approximate unit loads from Western Port catcbments Data from 1973 to 1985--·--·-······-··--49 1 Table 6.1 Cbloropbyll·a measured in September 1974----···.. ···--·-·------··-·-·-··-·-·----·····-·-55 J Table 6.2 Cblorophyll-a (flg L") data collected by Bulthuis--·· ..-·····-···-· .. ·········-·····- ..·-·_············-55 Table 7.1 Saltmarsh communities from Western Port.) ••••••• ..·····-·-----··-·· .. ······----····--·· .. -·-··-·-59 Table 8.1 Monthly standing crop estimate for Heterozostera tasmanica in Western Port and Port Phillip 1978· 1979 ..-- ..- ...- •• - ..- ....- .....-- ...... -.- ...... -.-.-- ..--- ....- ..-- ..- ..-- ..·····---· .. ··--·-69 Table 8.2 Summary of local information on seagrass loss and related events---..• .. ---- ..---·----·----- ..·-72 Table 8.3 Area of seagrasses for 1974 and 1984·----..• .. •• ....• .. ·--···- ..- ..•• ..-- ....• ...... •• ...... -72 Table 8.4 Above ground biomass of seagrasses 1975 and 1984 glm2 dry weigh.-....·- ...... • .... ·-·- ..• ..... 73 Table 10.1 Common fish assemblages in Western Port ------··.. ·--· .. -· .. ·----··---· .. -·-- ....·--- ..90 Table 10.1 (continued) Common fish assemblages in Western Port·----·--·.. • .. - ..------..-· .... -----91 Table 10.2 Species recorded from commercial and recreational catches in Western Port ..--- ....• .... -·- ..--93 Environment Protection Authority The Western Port Marine Environment

CHAPTER!

INTRODUCTION

The marine ecosystems in Western Port are widely recognised to be of regional, national and international importance. The range of habitats and communities in Western Port includes mangroves, salt marshes, seagrass, reef and soft seabed communities.

Mangroves in Western Port are close to their worldwide southern limit of distribution. The deep channels I (a major reason for the port related industrial development) contain unusual fauna, including living fossils such as the articulated brachiopod Magellania australis and the bivalve Neotrigonia j margaritacea. The bird habitats of Western Port are listed in the Ramsar convention as being of international significance to \\'literbirds and waders, and the northern part of Western Port is included on 1 the Register ofthe National Estate.

There are numerous links and interrelationships between the marine plants and animals, and the peculiar physical characteristics of Western Port. The habitats and communities have been the focus of research for many years. The most intensive study was undertaken in 1973 and 1974, and involved a mUlti-disciplinary research program. Its aim was to examine a wide variety of the biological and physical aspects -of Western Port and its catchment. The westernport Bay Environmental Study 1973-1974 (Ministry for Conservation 1975) provided baseline scientific information for development of the State Environment Protection Policy No. w-28 (The Waters o/Western Port Bay and Catchment) (1979).

Community interest in the quality ofthe Western Port environment and concern about potential impacts of development has been strong for many years. This interest \\'!is a major reason for the Victorian Government funding of the Westernport Bay Environmental Study (1973-1974). The loss of intertidal seagrass habitat in Western Port was firs! reported in the "north eastern sector of the bay during the early 1970s. Continued reduction in seagrass habitat since then has made this the highest profile environmental issue in Western Port. Subsequent changes in catches of commercial fish, bird life, water quality and habitat value have been linked to seagrass decline and there is a great deal of concern in the community about the decline of marine ecosystems in Western Port.

Review of the Western Port Marine Environment

In December 1994 EPA commissioned the consultants, Consulting Environmental Engineers, to conduct an investigation of the Western Port marine environment The review required a critical assessment and interpretation of marine environmental information on Western Port. The information contained in this report includes both published and unpublished works. Relevant anecdotal evidence was also considered and incorporated into the review.

The central focus of the investigation were studies examining marine biological communities and physico-chemical (waters and sediments) parameters. The influence of factors such as: diffuse and point source (industrial, urban and agricultural runoff) discharges, dredging, catchment activities and natoral processes were also assessed.

j Environment Protection Authority The Western Pori Marine Ellvironment

The objectives of the review were to provide:

I. A critical analysis of historical environmental data and investigations in the Western Port marine environment; and 2. An assessment of the present state of the Western Port marine environment, identifying critical gaps in knowledge.

In September 1995, Consulting Environmental Engineers submitted their report to EPA which provides the basis for this publication.

Workshop

To begin the review EPA sponsored a workshop attended by researchers and members of the public who had particular experience or expertise in Western Port. The objective of the workshop was to identify information which may not have been available through conventional literature and data searches. The workshop was held on 13 February 1995, and attendees had a wide range of backgrounds and interests.

Formal presentations at the workshop provided a stimulus for subsequent discussions of anecdotal and historical information. Substantial information was provided on areas such as fisheries, catchment erosion, seagtass loss, bird life, and industrial inputs which complemented the review of scientific information.

Speakers at the workshop were: Dr Brian Robinson, Dr Kerry Black, Dr Eric Bird, Scott Chidgey, Andy Stephens, Ren Millsom, David Baird, Pat Condina, Dr Brian Cuming, Richard Hawkins and Bruce Ridgeway.

The workshop participants concluded that Western Port was a valuable natural asset, and identified the public authorities and age:"cies, private companies and, landholders which were responsible for maintenance and protection of various components of the Western Port environment.

Scientific review

In preparation of this report EPA had each chapter reviewed by specialist reviewers for scientific relevance, accuracy and interpretation of the information.

Reviewers for each of the chapters were: Chapters 3 and 4, Dr Eric Bird; Chapter 5, Gus Fabris; Chapter 6, Dr Rick Royle and Dr Dave McKinnon; Chapter 7, Dr Paul Boon; Chapter 8, Dr Hugh K.irkman; Chapter 9, Dr Graeme Watson; Chapter 10, Dr Murray McDonald and Dr Graeme Watson.

2 Environment Protection Authority The Western Pori Marine Environment

CHAPTER 2

STATUS OF THE WESTERN PORT MARIl~E ENVIRO~MENT

The aim of this chapter is to provide an assessment of the major biological, physical and chemical elements of the Western Port marine environment. The tenn "environmental condition or status" as used in the context of this investigation, is an assessment of the environmental quality or health of the Western Port marine environment. The assessment of condition has been based on the review and interpretation of current environmental literature. Where current data is not available historical data has been used as a basis for a preliminary statement of condition.

The need to detennine the environmental condition of Western Port is a result of concern about important issues such as the protection of the ecological values of the ecosystems. At issue are specific components of the environment such as seagrasses, mangroves, saltmarshes, and other flora and fauna; and the balance of needs including: management of anthropogenic inputs; sustainable use of ruitural resources (fisheries); protection of human health; and recreation. l This chapter individually assesses, where possible, the environmental condition of subjects reviewed in the following chapters 3-10 and are presented in the same topic order. More detailed discussion of investigations and data can be found within the appropriate chapter. The final section Status of the Western Port Marine Environment presents an integrated assessment of all chapters to provide a statement ofthe environmental condition of Western Port.

PHYSICAL CHARACTERISTICS

The northern catchment of Western Port was substantially modified by construction of drains through the Koo-wee-rup swamp from the I 880s to the 1930s. Prior to this drainage work, there were few streams which discharged directly into the Upper North Ann. Since construction of the drains, large volumes of sediment have been transported by floodwaters through the catchment into Western Port. The input of sediment from the catchment during the period from the l880s to the 1970s has formed zones of sand and mud around the mouths of the artificial drains, and along the northern shore of Western Port from The Inlets to Stockyard Point.

Extensive dredging of channels and shipping basins occurred in Western Port during the late 1960s and early 1970s. Maintenance and some capital dredging programs are proceeding at present, and will continue in the future. Limited data are available on the characteristics of sediments in spoil grounds and infonnation is insufficient to determine the long tenn redistribution of the spoil within and beyond the spoil grounds. As a result long tenn effects of dredge spoil on water quality and biota outside the immediate area of the disposal site cannot be assessed.

Major coastal works undertaken in Western Port involved dredging, reclamation, and wharf and marina construction. Most of the activity has focussed on the western coastline from Hanns Inlet to Tyabb, and inclodes Hastings, Cribb Point, Umg Island, and the wharf development at BHPlLysaght. Extensive dredging has been associated with these developments. Although the coastal structures have pennanently

3 Environment Protection Authority The Western Port Marine Environment --~

changed the coastline, there are no obvious impacts on the broader physical characteristics of Western Port.

The majority of information on physical conditions in the marine environment of Western Port including sediment characteristics and sediment transport, was coJlected almost 20 years ago. These data are suitable for a general description of the geology and sediment transport mechanisms in Western Port. No recent investigations have been conducred. No data have been collecred on sediments or sedimentation within embayments or at the mouths of creeks, rivers or drains.

TIDES AND CURRENTS

The broad scale of tides and currents of Wesrem Port are well documented. Computer models with cell sizes of I km and 1.5 km have been developed which adequately describe currents at a scale of two to five kilometres. Major changes to the physical shape of Western Port such as causeways, broadening or narrowing channels, large wharves, or large breakwaters would be required to change the general tidal and current characteristics. Smaller scale current characteristics are poorly understood, particularly flow on mudflats, and there are few measurements of currents outside the main shipping channels. Modelling of currents on a scale suitable to determine the effects of marinas, wharves, breakwaters or groynes would require measurement oflocal currents and documentation of the local seabed.

PHYSICO-CHEMICAL INDICATORS

Limited investigations have been conducted since the Westernport Bay Environmental Study (1973- 1974). The Environment Protection Authority has sampled three sires in Wesrern Port since 1984. Direct comparisons of EPA data and Westernport Bay Environmental Study (1973-1974) data are difficult as the EPA program was designed to detcct long term trends in indicators rather than short term temporal and spatial changes. Detection of trends are difficult without conducting appropriate statistical analyses. Data from the entire EPA marine monitoring network (Western Port, Port Phillip Bay, Gippsland Lakes) are currently being analysed for trends.

Environment Protection Authority water quality data for nutrients and other general physico-chemical indicators suggest concentrations do not appear to have changed substantially since 1984. The monitoring site at Corinel1a has consistently higher nutrients, chlorophyl1-a and turbidity than sites at Barrallier Island and Hastings. This is probably a function of its location and the higher detrital and fine sediment content in the warer column. Preliminary comparison between EPA data for nutrients and chlorophyll-a and data from Westernport Bay Environmental Study (1973-1974) investigations suggest concentrations remain largely unchanged.

Monitoring data indicare metal concentrations in water are low and remain unchanged. Metals such as cadmium, lead, zinc and mercury are often below the limit of derection. Monitoring of metals in mussels, conducted by Marine Science and Ecology for BHP, indicate that concentrations of cadmium, iron and zinc are present at levels higher than background concentrations. Chromium, mercury and lead were not detected. There does not appear to have been an increase in these levels since data was first reported in the 1970s.

Baseline data for the majority of Wesrem Port exist for some physico-chemical parameters (Robinson and Harris 1974) and metals in sediments (Statham 1977; Harris et al. 1979). Recent data for metals in sediment are limited to sampling conducred by EPA since 1990. Sediment concentrations of metals are

4 i Environment Protection Authority The Western Port Marine Environment

low, but it should be noted that EPA sites are not in high depositional areas. No recent data are available for biocide concentrations in waters, sediment or biota.

Investigations conducted during the mid-Iatc 1970s were conducted mainly in the Lower North Ann and western side of the Upper North Arm. Data available for other indicators are: metals in waters (Fabris and Harris 1974; Canterford et al. 1978); metals in biota (Fabris and Harris 1974; Canterfordet al. 1978; Harris et al. 1979; MSE 1990, 1991, 1992); organics in waters and sediments (Robinson 1975; Bums and Smith 1977, 1978, 1982); biocides (Bryant et al. 1975).

I 4 CATCHMEl'II'T INPUTS

Current monitoring of input streams by Melbourne Water and EPA indicate water quality is degraded. All sites, particularly those in the lower areas of the catchment have high levels of nutrients which are above nutrient objectives (EPA 1995). Turbidity levels in these streams are also high. Species diversity at biological monitoring sites is low.

Catchment monitoring generally lacks continuity. Relatively few sites have data from the mid-I 970s to present. Data were most often limited to general in situ indicators (pH, dissolved oxygen, flow, discharge, tnrbidity, colour). Nutrients were sampled at a limited number of sites. Since the Stream Watch monitoring program commenced in 1993, sites sampled by Melbourne Water in the northern section of the catchment have included nutrient analyses. A review of the Victorian Water Quality Monitoring Network in 1991 recommended that a number of sites should be added to the lower reaches of inputs to Western Port. These recommendations have not been implemented to date.

Contaminants are considered a concern, however, they have not been monitored since the 1970s investigations. Data are based on three investigations conducted during the mid to late 1970s (Dale 1974; Fabris et at. 1977; Dale and Pooley 1979). The lack of recent data on metal and biocide concentrations remains a concern due to continuing development and intensive agriculture in the area. Levels of biocides in the Western Port catchment are currently unknown. In intensive horticultural areas, it is likely that biocide use is still high.

Contaminants loads entering Western Port and input streams from point source discharges (i.e. licensed industrial discharges) have been reduced since the mid 19705 through the intreduction of licence conditions administered by EPA, and the requirement to direct discharges to sewer.

Diffuse catchment inputs have substantially increased since European settlement and are currently considered to be the most serious threat to the health of the Western Port marine environment. Inputs contain high loads of nutrients and sediment which enter Western Port. Derived from a large variety of sources within the catchment, inputs are increased by factors such as: urbanisation; removal of native forest and riparian vegetation; inadequately managed land; stream bank erosion; drainage of swamp areas and alteration and straightening of watercourses.

Marine (and freshwater) habitats are adapted to low levels of nutrients. Nutrient levels are elevated by runoff from the catchment from areas such as intensive agriculture (which generally requires a high application rate of nutrients); clearing of native vegetation (which acts as a nutrient trap); erosion and inputs such as sewage which contain high concentrations of nutrients. High nutrient inputs have a deleterious impact on biota in :freshwater and marine environments. Appropriate actions are required to minimise runoff from all areas within the catchment. Catchment runoff from rapidly developing urban areas (eg. Pakenham, Berwick and Cranboume) must be appropriately planned and managed to reduce flows and loads at their source.

5 Environment Protection Authority The Western Port Marine Environment

TURBIDITY

Turbidity in Western Port has increased since European settlement. The draining of swamps and cutting of channels through coastal barriers such as the Koo-wee-rup swamp destroyed a natural sediment filter and resulted in a substantial increase in sediment load. Other catchment activities such as: dam construction; urbanisation; inappropriate land use; removal of native forest and riparian vegetation; and unmade roads have contributed to a substantial increase in sediment load (Commissioner for the Environment 1988).

Water clarity data (Secchi depth) collected during the Westernport Bay Environmental Study (1973- 1974) was not published. The earliest published data date back to 1984 when EPA began regular monitoring of Western Port. This data suggests that turbidity has decreased in the western area of Western Port since 1989. The data also indicates that turbidity remains consistently higher at the Corinella site than other sites.

Increased turbidity from sources such as dredging and catchment inputs is thought to have been one of the causal factors contributing to seagrass loss in the Upper North Arm of Western Port (EPA 1993a, b, c). Seagrass has been shown to playa major role in the stabilisation of intertidal and subtidal sediments and its loss accentuated turbidity problems. Dredging continues to be a potentially threatening process. Large scale dredging programs during the I 970s made a significant contribution to turbidity levels encountered in Western Port. Monitoring has shown that sediments can be remobilised by dredging operations, or after disposal to spoil grounds (MSE 1995).

PLANKTON COMMUNITIES

Environment Protection Authority data for chlorophylJ.-a (phytoplankton biomass estimate) from 1984 to the prej)ent are collected at three sites. It is not possihle to discero trends in the data without appropriate statistical analyses but it is clear that chlorophyll-a is consistently higher at the Corinella site. This is probably a feature of the high concentrations of suspended solids and the proximity to the mudflats in the Upper North Ann. In addition, chlorophyll-a concentrations at Corinella have peaked at over 5 fl.gL-l a number of times since 1990. Data for biomass, productivity and composition of phytoplankton communities are limited to the mid 1970s (Robinson and Harris 1974; Bulthuis 1976; Gibbs et al. 1976; Harris and Vlasich 1976; Bulthuis 1977) and early 1980s (Kimmerer and McKinnon 1985).

The status of zooplankton communities are unknown. The most recent investigations of zooplankton communities were undertaken during the early 1980s. These studies found that copepod biomass appeared to be correlated with phytoplankton productivity and little change in populations had occurred since the 1973-74 survey.

MANGROVE AND SALT MARSH COMMUNITIES

The distribution and area occupied by mangrove and salt marsh communities was last surveyed in detail in 1974, however, distribution (based on aerial photographs taken in 1984) is included on the Victorian Institute of Marine Sciences, Oil Spill Geographic Information System (GIS). Data from the GIS indicates that the total area of both communities between 1974 and 1984 may have marginally

6 Environment Protectitm Authority The Western Port Marine Environment

increased. Current distribution data is not available. Mangrove and salt marsh communities have been degraded considerably since European settlement. Prior to settlement these communities fonned an almost continuous fringe around the northern part of the Western Port coastline. The total area covered by these communities has been reduced through land reclamation of the intertidal area, harvesting of mangroves and erosion.

The co-existence of mangrove and saltmarsh communities are unusual. Mangroves are primarily a tropical flora and saltmarsh communities are found only in temperate regions. Opieet al. (1984) considered the saltmarsh communities to be of national significance, due to the extensive nature of these communities in Western Port, and their floristic diversity in comparison to other saltmarsh communities in southern Australia.

The mangrove populations of Avicennia marina are close to the southern most limit of their worldwide distribution. In comparison to more southerly populations, mangroves in Western Port are large trees rather than smaller stunted shrubs. However, they are smaller than populations in tropical regions. The reproductive periodicity of Avicennia marina at this latitude is considerably longer (every 2-3 years rather than I year) than popUlations in wanner temperate and tropical regions. These popUlations are considered to be ecologically stressed and extremely sensitive to disturbance and other impacts.

SEAGRASS AND ASSOCIATED COMMUNIDES

Intertidal seagrass in Western Port remains heavily degraded and largely unchanged since the early 1980s. Recent investigations by Stephens (1995) indicate that there has been limited recovery (a total of 30% increase in area but limited increase in biomass) in the Upper North Ann, Lower North Ann and Rhyll segments. Little recovery has occurred in the Corine!la segment or the tidal divide, near where large seale losses were first reportcd.

Seagrass beds support large and diverse invertebrate macrofaunal and fish communities. The loss of 70% of the total cover and 85% of the biomass ofseagrass (Bulthuis 1976) has resulted in a major impact on these communities (Edgar et al. 1994). Macrofaunal communities in seagrass habitats are highly productive with a higher biomass and species diversity than communities in unvegetated or channel habitats.

Both commercial and non-commercial fish species inhabit seagrass communities. Of these, the non commercial species are the most abundant and diverse. The loss of seagrass is also thought to have reduced the commercial and recreational fish catches since the early 1980s (MacDonald 1991). The species most notably affected were King George whiting, rock flathead and blue rock whiting. It is uncertain if commercial and nOn commercial fish populations have increased with the observed increase in seagrass cover in Western Port.

INVERTEBRATES

Soft sediment beds (particularly fine sediments) not associated with seagrass in Western Port have a large diversity of infaunal species. No investigations have been recently conducted and their current status is unknown. "''hen last surveyed in 1975 "living fossils" Neotrigonia margaritacea, Anadara trapezia and Magellania australis were present in far greater proportions than other areas of Victoria. The current status of invertebrate species, particularly the opisthobranch molluscsPlatydorzS galbana and Rhodope sp. of the San Remo Marine Community are unknown (listed under Schedule 2 of the

7 Environment Protection Authority The Western Port Marine Elt1'ironment

Flora and Fauna Guarantee Act 1988). The status of this community is due for review by the Flora and Fauna Branch of the Department of Conservation and Natural Resources in 1997.

SUMMARY OF THE STATUS OF THE WESTERN PORT MARINE ENVIRONMENT

The Western Port marine environment and catchment have been substantially modified over the 130 years since European settlement. Recent mapping of intertidal seagrass in Western Port indicates that the total area of seagrass has increased by 30% since 1984, however, biomass is still very low. While cover of mangrove and salt marsh communities have decreased during the past 100 years, data suggest there was a small increase in total area of populations between 1974 and 1984. These communities do not appear to be under any immediate threat from existing activities. Despite these changes to the . environment the concentration of contaminants are very low in water and sediment samples. Elevated levels of some metals and hydrocarbons are found in localised areas adjacent to areas of industrial and urban input.

Parts of the Western Port environment have been significantly altered since European settlement. Some of the changes have adversely affected the marine flora, fauna and physical processes. The largest and most conspicuous changes to the marine environment are:

1. loss of seagrass over an extensive area of the intertidal zone and the resultant impacts on macro invertebrate communities, as well as on commercial and non-commercial fish communities 2. the reduction of salt marsh and mangrove communities, particularly in the northern part of Western Port 3. increase in the turbidity of marine waters and input streams due to catchment activities, dredging and physical changes to the marine environment 4. increased loads of nutrients, sediment, contaminants and freshwater to Western Port from the catchment 5. elevated contaminant concentrations adjacent to areas of urban, industrial and catchment inputs

Increased loads of freshwater, sediments, nutrients and contaminants from the catchment to Western Port continue to place stress on the marine environment. The rapidly expanding development of the catchment's urban areas such as Pakenham, Berwick and Cranbourne will further increase stress on the catchment's input streams and Western Port if these areas are not adequately monitored and sustainably managed.

8 Environment Protet:tWn Authority Tile Western Port Marine Environment

CHAPTER 3

PHYSICAL CHARACTERISTICS OF THE WESTERN PORT MARINE ENVIRONMENT

INTRODUCTION

The physical characteristics of Western Port include processes "hich determine the shape of Western Port above and below the water. Changes to the shape of Western Port are due to accretion in some areas and erosion in others. These changes may be rapid or slow, large scale or small scale. Most unplanned changes to the shape of Western Port whether due to natural or human processes are considered undesirable since they alter boundaries and affect the amenity of the coastline. Groynes i and seawalls are often constructed to prevent erosion, and dredging programs are undertaken to 1 maintain or deepen boating and shipping channels. This section presents a critical review of information on the existing physical condition of Western Port, particularly in relation to bay-wide and local environmental change. The review covers information on geology, coastal features and processes, bathymetry, sediments, sediment transport, and sediment sources.

GEOLOGY

Aspects of the geology and geomorphology of Western Port have been investigated and discussed by many researchers since the shoreline was originally SlJfveyed by George Smythe in 1842 (Selwyn 1856; Edwards 1942; Hills 1942; Edwards 1945; Keble 1950; Jenkin 1962, 1974; Marsden and Mallett 1975; Spencer-Jones et at. 1975; Marsden et at. 1979; Bird 1993) (Figure 3.1). Natural changes to the geology and geomorphology are very slow, and expressed in terms of geological time which is in the order of millions of years.

Most ofthe very slow natural changes acting on the geology of the Western Port are generally beyond the scale of this review. One of these changes which may affect the overall appearance of Western Port is the potential rise in sea level. This is discussed in more detail in chapter 4.

The geology of the Western Port area has been described by Marsdenet al. (1979) and is summarised below:

Geology in the Western Port region is associated with the pattern of rifting and sedimentation along the southern margin of the Australian continent, repeated since the initial separation of the Australian and Antarctic plates in the Mesozoic (Veevers and McIlhinny 1976).

Associated Early to Middle Tertiary volcanic activity resulted in basalts up to 400m thick, and their outcrop is important in determining much ofthe coastline of West em Port (Spencer-Jones et at. 1975).

\ 9 1 Environment Protection Authority The Western Pori Marine Environment

, A QUA~ 0 ~1~1'-It_.'I') A

MESOZOIC ~ =~.!=~::.~ : rn;-'-~$ WI.'LtOZOIC IDlklllia-.- ...... 9 ~.:-'!.:;- lid_I>

S .... Uilll,T.Uil'fl o I$"unn: IV....,.. o.U_11 PWI./.II'

•

".. ,. f 1j) ~t .. L... ____ n • •

- -t_, bIIIJ 01 Wrnmll.u _. "'Ii. -....-~l!

Figure 3.1 Geology and physiography a/Western Port (from Marsden et aL 1979)

Development of Port Phillip, Western Port and their catchments was initiated by downfaulting in the Quaternary.

The mosaic of faulted blocks in southern Victoria extends into Bass Strait with major faults striking north-northeast. The Western Port sunkland is bounded by pronounced topographic fault scarps (Figure 3.1), and is separated from Port Phillip by the Mornington Peninsula. The northern limit of the sunkland is not sharply defined and probably developed by dOV'iTIwarping towards the south. Within the sunkland, minor faulting forms a central uplifted block, which forms Phillip Island and French Island, and also considerably influences the shape of Western Port.

Although the Quaternary history is not known in detail, four main phases have been recognised (Marsden and Mallett 1975).

(l) Sunkland development, with the initiation and entrenchment of the present drainage patterns and channel systems. (2) Extensive fluvial and lacustrine deposition, particularly across the northern part of the sunkland and the Bass River flood plain.

10 Environment Protection Authority The Western Port Marine Environment

(3) Stream entrenchment at low sea level (Late Pleistocene). This was probably an important erosion phase during which sediments from the catchment were transported to the outer areas of the present bay and Bass Strait. Aeolian activity deposited irregular quartzose sand dunes and sand sheets in a well defined belt across the north-west comer of Western Port (Cranhourne Sands). This deposition probably connected the present North Ann to French Island, and deposition possibly even occurred near Lang Lang, north east of Western Port. (4) Holocene sea-level rise allowed water encroachment through the Western Entrance about 10,000 years B.P. (Gill 1973). Major consequences have been the drowning of relict topography; tidal scour of fluvial channels; coastal erosion; the reworking of sediment into extensive intertidal and coastal depositional environments; and development of extensive dense peripheral vegetation with consequent inhibition of stream inflow.

There is evidence in parts of Western Port that sea level was about 1.5 - 2m above the present high water level in the mid-Holocene (5,000 - 6,000 B. P.) (Marsden and Mallett 1975). The narrow Eastern Entrance to Western Port was probably not breached until about this time. Rapid progradation of coastal zones, particularly associated with channel and bank systems at the head of the Western Entrance Segment and around the Confluence Zone, also probably began in the mid-Holocene.

Individual geological and landform features have been the subject of several student theses (Ge11 1974; Miles 1974; Nicholson 1974; Miles 1976a). Rosengren (1984) listed numerous sites of geological and. geomorphological significance in the Western Port catchment.

Other changes documented in Western Port and its catchment relevant to geology are the effects of: erosion of coastal features such as the Lang Lang Cliffs and Somers Beach (Bird 1993); increased deposition of sediments from the catchment (Marsden ef aT. 1979) and infilling of shipping channels; and sedimentation from material derived from Western Port itself (dredging, or resuspension of sediments from mudflats) as discussed below.

COASTAL FEATURES AND PROCESSES

In general, the Western Port coastline comprises bluffs, steep cliffS, dunes, sandy beaches, swamps, saltrnarshes, mangroves, mudflats and river mouths (Marsden and Mallett 1974, 1975). The major morphological features of Western Port are shown in Figure 3.2. Figure 3.3 shows the coastal landforms of Western Port from Bird and Barson (1975) which are based on aerial photographs taken in 1974.

Coastal features form the interface between the land and sea environments. The coastal strip is often the focus of human activities and is subject to relatively rapid changes due to natural and human influences on coastal processes. Rapid changes to the coastal features and boundaries affect coastal properties and buildings, boating access and the habitats of plants and animals.

Maps and lists of coastal features in Western Port have been compiled for various purposes. Most have been prepared from aerial photograph series at scales of approximately I :\0,000. The Atlas of Biological and Recreational Resources of the Victorian Coast (Ministry for Conservation 1980a) presents coastal features in Western Port on charts at a scale of 1: 100,000. These are hased on aerial photographs and ground truthing surveys conducted during the period up to 1972. The shoreline of Western Port contains a large number of sites of geological and geomorphological significance (Rosengren 1984) (Figure 3.4).

II Environment Proteetion Authority The Western Port Marine Environment

, ~ ... t:<_IM!", . e:c:::Ei'3 F3 ...... E3

FN)och Is. ;l =-:'~!IIld~~

[;;'j ::"_~~:IWw~).

Figure 3.2 Major morphologicaljeatures (from Marsden and Mallett 1975)

In 1989, the Victorian Institute of Marine Sciences (VlMS) compiled information on the coastal features of Western Port as part of its oil spill geographic information system (GIS) for Western Port, The features were identified from aerial photographs (1984 series), topographic maps, and ground surveys of coastal infrastructure features in 1990 (hoat ramps, shoreline assembly areas, storage buildings, temporary field accommodation). The purpose of the VIMS GIS is to assist oil spill controllers to identify sensitive environmental areas (eg. sites of geological and geomorphological significance, Figure 3.4) and habitats, and access points for vehicles and small boats during spills under a variety of weather and tide conditions.

Bird and Barson (1975) describe shoreline changes in Western Port at "selected sectors that show features of particular interest". When discussing the effects of mangrove disturbance. Bird and Barson (1975) concluded that changes identified in the mangrove fringe were primarily due to human activities. In areas where mangroves had died back or been removed, the system became unstsble and resulted in the erosion of salt marshes and drifting of sand. Areas where mangroves persisted were considered to be stable.

12 Environment Protection Authority The Western Port Marine Environment

~_ Sandy .~" .. .-.

Figure 3.3 Slwrelinefeatures of Western Port (from Bird and Barson 1975)

KEY ~ SITE OF t '..::::J SIGNIFl¢~

I 1 Figure 3.4 Sites of geological and geomorphological significance in Western Port (from VIMS GIS \ after Rosengren 1984) I 13 - Environment Protection Authority The Western Port Marine Environment

Bird (1993) reviewed the coastal processes which fonned and continue to shape the Western Port coastline. The review was based on a range of publications, post-graduate studies, surveys and student excursions and deseribed the coastline in tenns of its past and present characteristics. Discussion of the processes affucting the coastline included: river inputs; ocean swell; longshore currents; offshore sources of sand; and the influence of vegetation, I.e. mangroves, saltmarsh and seagrass.

Bluffs and cliffs

The bluffs and cliffs in Western Port are associated with the geological events described by Marsden et al. (1979). Bird (1993) described the cliffs as they occur intennittently along the Western Port shoreline (West Head to Somers, Stony Point, Warneet, Red Bluff near Lang Lang, and along the Settlement Point peninsula to Stony Point ncar Bass). The San Remo peninsula incorporates bluffs along both Western Port and Bass Strait. Bluffs and cliffs occur along the south side of French Island and along much of the coast of Phillip Island. Bird (1993) notes a number of changes to these features: coastal bluffs are slumping in the vicinity of Flinders; the clay cliffs at Lang Lang are cracking and receding; Red Bluff at Lang Lang is undercutting and collapsing; and the weathered basalt cliff at Corinella is receding. The rate at which these coastal features are receding is not known.

Sandy shorelines

Sandy shorelines are mostly found between the rockY bluffs and headlands along the Western Entrance, the western and northern shores of Phillip Island, and parts of the southern and western coasts of French Island (Bird 1993). Sandy beaches are often backed by dunes and associated vegetation. The sands of the beaches in Western Port are predominantly quartzose. They originate from past (Late Quaternary) wave induced transport from the seabed of Bass Strait, and deposition in Western Port, particularly the Western Entrance (Gell 1978; Bird 1993). The beaches and dunes are changing in profile and outline in both the short-term and long-tenn.

The predominant south-westerly waves have caused eastward drifting of sand along the coast from Balnarring, past Somers to Sandy Point Drifting results in the fonnation and migration of successive beach lobes, as at Connorant Point. The pattern of intersecting beach and dune ridges behind the coast east of Somers shows that there has been a long history of such lobe fonnation, migration and truncation. This process resulted in a major foreland developing south of Hann's Inlet in Holocene times. There was local progradation on Sandy Point during the 1980s when a beach lobe arrived. Sand has also been swept northward from the Point, out on to the floor of Western Port by inflowing tidal currents. Sand movement onto Middle Bank is caused by south-westward ebb currents.

Concern has been expressed by residents about beach erosion at Somers. Groynes and rock walls have been constructed in an attempt to stop the erosion of sand and the threat tu shoreline amenity and buildings (i.e. Somers Yacht Club). The Somers Yacht Club appears to have been built on a transitory lobe, and the natural onward migration of the lobe has caused erosion of the beach towards the yacht club. Bird (1993) considered that the erosion had become severe due to the indirect effects of armouring the beach with boulders, which increased reflected wave scour and moved sand off the beacho

On the north coast of Phillip Island, successive beach lobes have formed and migrated eastward past Cowes, to Observation Point (Phillip Island Conservation Society 1987). Comparison of maps and charts since 1826 indicate historical oscillations of the sandy shoreline. The present eastward extent of

14 Environlnellt Protection Autllorlty Tile Western Pori Marine environment

Observation Point is less than it was in 1826, but recently this spit has begun to grow again, partly sbeltering Rhyll Inlet.

The erosion of Red Bluff at Lang Lang has resulted in sand being transported northward to Lang Lang jetty and southward to renourish the spit at Stockyard Point (Bird 1993). This is similar to the changes at Cowes Bank and Observation Point. Dark organic clay cliffs extend north from Lang Lang pier to the mouth of Lang Lang River, and intermittently beyond. These cliffs are scalloped in outline, steep to vertical, up to 2 metres high, fronted by a gently-sloping wave-cut ramp in firm clay, passing seaward beneath softer mud deposits (Gell 1974). The swamp margin was evidently cut back during the later stages ofthe Holocene marine transgression, and erosion of the dark organic clays contributed muddy sediments to the northern part of Western Port.

The Lang Lang boat ramp Was constructed in the 1950s as a concrete ramp across soft mudflats (Ridgeway 1995). Today the ramp has to be cleared periodically of sand which covers the ramp during storms and a channel dug to allow boats access to deep water from the ramp. There is further anecdotal information on changes to the characteristics of the shoreline from the historic viewpoint at the Lang Lang Foreshore Reserve:

The first bathing area of the beach was the Red Bluff (being the only sandy part) and access to this beach was by a path of steps cut down tbe cliff face. Along the top of the Bluff was a good stand of tea tree which enabled the horses to be tied up in the shade for the day ...

After the disastrous flood of 1934, patches of sand appeared along sections of the foreshore from the jetty to the Bluff, as well as Stockyard Point. These areas became popular with fishermen, with plenty of mullet, whiting, bay trout, sbark and rays being caught off the jetty and along the foreshore (Coghlan 1988).

Ridgeway (1995) reported that the easternmost channel at Stockyard Point has infiHed with coarse sediments over the past 20 years. There appears to have been a substantial change in the composition oftbe shoreline in tbe area from muds to sands in the Lang Lang area since approximately 1934.

Mudflats

Extensive intertidal mudflats characterise the northern and eastern parts of Western Port. Much of the seabed in the north of Western Port is exposed during low spring tides, revealing a pattern of dendritic channels which drain into increasingly larger main channels. This is a tide-dominated morphology, shaped by ebb and flow currents. Comparisons of nautical charts indicate little change in the morphology since Cox made the first bathymetric survey in 1865. The muddy deposits contain shell beds (Miles 1976b), some of which have been washed out to form shelly strips along the edges of intertidal shoals, and shelly beaches on the northern and north-eastern shores (Gell 1978).

The channels of tbe North Arm and East Arm are separated at low tide by a natural barrier known as the "tidal divide" (Marsden and Mallett 1975) or "'tidal watershed" (Miles 1974, 1976b). The tidal divide extends across the north-eastern segment of Western Port from just north of the Lang Lang River to Palmer Point on French Island. Surveys of the tidal divide in ] 973 showed it to be a faint low ridge with an S-shaped alignment. The central part between the top of the tidal channels is between 0 and 20 centimetres above Western Port Chart Datum, rising laterally towards Palmer Point and the Lang Lang shore (Bird 1974a).

15 Environment Protection Authority Tile Western Port Marine Environment 1r

The tidal divide is submerged to a depth of about 3 metres at high spring tides. As the tide ebbs the channels emerge, fringed by faint intermittent levees, often with a waterfall up to 50cm high near the channel head. Water remains in shallow depressions on the intervening soft mudflats, draining slowly into the channel through gaps in the levees. The channels heading westward into Bourchier Channel have 'cauliflower' heads, while those heading southward end more sharply, perhaps indicating that the tidal divide is migrating south-eastward.

Bird and Barson (1975) and Bird (1993) have described near-shore changes to the soft sediments in the north of Western Port in terms of removal of mangroves, erosion of saltmarsh and infilling for industrial development and dredging for boat channels. Bird (1993) stresses the importance of mangroves in stabilising fine sediments, and their role in the seaward progression of the land/sea interface. The distribution of mangroves and saltmarsh in Western Port has been affected by harvesting of mangroves, clearing for coastal access, removal or infilling for coastal construction, and possibly smothering of aerial roots by increased sedimentation from the catchment Removal of mangroves has contributed to erosion of saltmarsh and soft sediments in many parts of Western Port (eg. Hastings, Yaringa, Pioneer Bay, Queensferry, and Tankerton). However, mangroves appear to be recovering and advancing in some areas including Yaringa and Watson Bay (Bird 1993).

The introduction of the tussock grass Spartina to saltmarshes in Victoria includes areas of Western Port. Spartina can stabilise sediments, however, it can also effectively choke streams and inhibit dispersion of floodwaters. Spartina is present in a meander cut-off on the Bass River delta, in patches off the river mouth, and is also found in Moody's Creek.

Swamp

The northern catchment of Western Port has been substantially modified by drainage of the Koo-wee rup swamp which formed an extensive and complex hydrological and biological system (Roberts 1985). The mudflats and northern coastline of Western Port have been affected by modifications to the catchment. Drainage of Koo-wee-rup swamp from 1885 to the 1930s had a major impact on the region It resulted in some areas ofland in the catchment dropping by 2.5m in the first 30 years after drainage as the extensive peat deposits of the swamp dried out (Hills 1942).

Swamp drainage and flood control schemes began on a small scale in the 1870s, with intermittent phases of improvement and extension of drainage channels through to the present day. The swamp was drained by the excavation of large permanent channels aeross the flat of the swamp into Western Port. Drains were cut to open into inlets on the swampy northern shore, and outflow channels excavated to improve the outflow from the Bunyip and Lang Lang Rivers (Key 1968). Prior to excavation of these channels, there were no permanent watercourses flowing into the north of Western Port. Minor ephemeral creeks existed, but most floodwaters would have dispersed across the area of the swamp and slowly drained into Western Port through small creeks and temporary outlets. The outcome of these drainage schemes was to concentrate previously diffuse runoff at particular points and increase the discharge of sediment, especially sand and silt, into Western Port (Marsden and Mallett 1975).

i6 Environment Protection Authority The Western Port Marine Environment

Development

Examination of charts, maps, aerial photographs and Port Melbourne Authority dredging history (see below) shows that over the years from the 1880s to present there have been major coastal works in Western Port. These works have involved dredging, infilling (reclamation), wharf and marina construction. Wharves or marinas have been constructed at Hanns Inlet, Stony Point, Crib Point, Hastings, Long Island, Old Tyabb (BHPlLysaght), Watsons Inlet, Yaringa, Blind Bight, Tooradin, Tankerton, Sawtell Inlet, Corinella, San Remo and RhyIL

Development plans for Western Port were proposed by the Bolte Government in the late 1960s to construct the Ruhr Valley of Australia. The plans incorporated large scale modification to the western coast of Western Port by extensive dredging for shipping channels and infilling of a substantial proportion of the western coastline for wharves and industry. Other developments suggested were in the 1970s for French Island involved infilling and substantial modification to the coastline and channels, construction of a second major airport for Melbourne, and construction of a nuclear powered electricity station. These visions for Western Port appear to have faded, while shipping oriented industry such as the ESSO development at Long Island, the BHP steel mill at Old Tyabb, and the oil refinery/terminal at Crib Point have become a reality.

In spite of development proposals, the multi-disciplinary study in 1973-1974 (Ministry for Conservation 1975), various management reports (eg. WPRPCC 1992), recommendations for a Phase II environmental study (Mahon 1979) and the State Environment Protection Policy, No. W-28 The Waters of Western Port Bay and Catchment (1979), there is no long term management plan for coastal development and industry in Western Port.

BATHYMETRY

The bathymetry of Western Port is the pattern of depth contours which describe the change in depth of the seabed from the spring high water mark (approximately 3m above Chart Datum at Stony Point), to the spring low water mark (approximately O.2m above Chart Datum at Stony Point) (Chart AUS 151 - Hydrographic Service of the Royal Australian Navy 1988). It includes the deep channels in northern Western Port (greater than 20m in places such as Crawfish Rock), and offshore from Seal Rocks (> 30m). The channels, banks and tidal flats are major influences on the strength and direction of tidal currents (Harris et ai. 1979a), and the nature of habitats for plants and animals. The presence of the deep natural channels in proximity to flat land is a characteristic of Western Port which is fundamental to the past, present and proposed shipping related development in the region.

Bird and Barson (1975) indicated that at least parts of the bathymetry of Western Port have been documented since the beginning of the 19th Century. Charts were made by Bass in 1798, Barrallier in 1801, Faure in 1802, D'Urville in 1826 and Wetherall in 1827. Cox produced a chart of "Port Western" in 1865. The present bathymetry of Western Port is documented on a series of nautical charts published by a number of sources including: Hydrographic Service of the Royal Australian Navy (AUS 151 - western side of Western Port only); British Admiralty charts (eg. BA 149Y); survey records of shipping channels collected by the Port of Melbourne Authority; local sailors (Hawkins 1993) and fishing publications. The Hydrographic Service released a chart of the whole of Western Port (AUS 150) in June 1995, which is based on data from earlier surveys by the Royal Australian Navy and Port of Melbourne Authority.

17 Environment Proteclion Authority The Western Port Marine Environment

The accuracy of most of these charts is sufficient for navigation, identification of major seabed features, and detection of large scale changes in shipping channels and turning basins. The Port of Melbourne Authority also has a program in operation to survey the shipping channels from the Lysaght turning basin to the Nobbies. Soundings are taken along sections 25m apart from the 5m depth contour of the channels. The surveys are repeated every five years. Some areas are surveyed more frequently, for example the sand wave field between channel markers 19 and 21. Special surveys are also carried out pre and post-dredging and monitoring of dredge spoil locations. Measurements have a vertical accuracy of better than O.3m and horizontal accuracy of 3 to 4m.

Information on bathymetry at a finer resolution, and for areas outside shipping lanes, is limited to localised sections measured during hydrodynamic and geological studies over twenty years ago (Miles 1976a, b; Hinwood 1979). These studies may not include a required reference to a recognised, fixed datum to describe the feature or zone being studied (Donaldson Marsden 1977; Bulthuis unpublished). Aerial photographs taken during low tides show the extent of creek deltas and relatively small channels through the intertidal mudflats (Miles 1974). Crawfish Rock, Eagle Rock, and Schnapper Rock are outcrops awash at high tide, while Barralier Island and Pelican Island are slightly higher areas of sand and gravel accretion. Details of small changes in the level of the seabed may provide significant information On the amount of material being carried into Western Port from the catchment and may indicate factors affecting biological assemblages in Western Port. Compilation of these data into useful charts would require considerable effort.

SEDIMENTS

Sediments and sediment transport characteristics of Western Port were studied in detail in the Westernport Bay Environmental Study (1973-1974) (Ministry for Conservation 1975) and subsequent investigations by Marsden and co-workers at the University of Melbourne between 1973 and 1978. Many of these studies (Miles 1974; Marsden and Mallett 1975; Miles 1976b; Seedsmanand Marsden 1977; Marsden et al. 1979) recognised the importance of intertidal seagrasses in stabilising and accreting vast areas of intertidal fine sediments on the flats in the northern part of Western Port. It was during investigations in 1976 that concern for the apparent decline of the intertidal seagrasses in the northern part of Western Port was raised by Marsden and recorded by Wilk et al. (1979).

The main sources of sediment to Western Port have been: I. oceanic sand from the floor of Bass Strait, washed into the wide Western Entrance, and to a lesser extent the narrow Eastern Entrance (at San Remo) 2. sand eroded from cliffed sections, as at Red Bluff (Lang Lang) and on the south-east coast of French Island 3. sand, silt and clay carried in by rivers, notably the Bass River 4. silt and clay from weathered basalt exposed in cliffs between Flinders and Balnarring, Phillip Island and at Corinella 5. organic clay from erosion of bordering swamp land, particularly on the north-eastern shores

Sediment is also delivered into Western Port as the result of drainage and reclamation of the e>.1ensive swamps to the north of the catchment. Clearing, construction of roads and dams (Cardinia Dam from 1970 to 1973) and the resultant massive erosion (East 1935; Roberts 1985; Candina 1995) in the catchment contributes to sediment runoff into the channelised and eroding rivers. The coarse sediments are deposited in the lower segments of the rivers and at the mouths of the rivers in northern and eastern Western Port (Roberts 1985). Recent depositional fans have formed at the mouths of drains into The Inlets at Bunyip, Yallock, Lang Lang and Bass Rivers and as a strip of sand extending south-east along the coast from the Lang Lang River to Stockyard Point (Bird and Barson 1975;

18 Environment Protection Authority The Western Port Marine Environment

Spencer-Jones et al. 1975; Marsden et al. 1979; Wilk et al. 1979; Bird 1993). The fine silts and muds have been covered by coarser material near the shoreline. The changes in elevation due to this process and possible impacts on intertidal biota such as mangroves are not known.

Coarse {Very coarse! Sand

G] COlfser Ihl .. 1+

Medium Sand o 1101.4+

[] 1.4 lit 2,

Fine Saud 10 Silt o 210 S+

Clay

• finer thin S+

PHIL(;P IStAND

o 12l'" 5 Jail

Figure 3.5 Distribution of textural sediment types in Western Port (from Marsden, Mallett and Donaldson 1979)

Marsden and Mallett (1975) first described the general pattern of movement of sediments in Western Port. They mapped the distribution of textural sediment types from aerial photographs and bottom sediment samples collected throughout Western Port from 1970 to 1974. Further studies were carried out, and the results mapped and described by Marsden et al. (1979) (Figure 3.5). Data from the sediment sampling programs including position fixes, core descriptions and grain size analyses are available from the University of Melbourne Archives. There has been limited grain size analysis of sediments in Western Port since the studies in the 1970s (Edgar et al. 1994). The character of the intertidal sediments have changed in the northern parts of Western Port; nearshore fine, muddy sediments have been replaced by coarser sands from river inputs, however there is insufficient recent data to assess the changes over the past 20 years.

Sediment transport in Western Port has been described by a number of researchers (Sternberg and Marsden 1974; Harris et al. 1979a; Marsden 1979; Marsdenet al. 1979; Seedsman and Marsden 1980; Bird 1993). The general pattern of sediment transport is shown in Figure 3.6 (more detailed analyses may be found in Sternberg and Marsden 1974). Bird (1971, 1986) described the process of sediment accumulation by mangroves and the consequent progradation of the mangrove and saltmarsh zones.

19 Environment Protection Authority The Wefilern Port Marine Environment

Incoming wave action from the south-westerly ocean swell and waves generated locally by westerly, south-westerly and southerly winds moves sand in drifts from the Western Entrance along the adjacent shores. Occasional easterly or north-easterly winds over waters south of French Island generate a westward drift of sand along the north coast of Phillip Island and the shore between Sandy Point and Somers; this is much weaker than the other drifts, and the effects are only temporary.

The studies of sediment transport in Western Port in the 1970s adequately describe the general patterns of sediment transport, and these are expected to be similar in the 1990s. The information collected previously is sufficient to describe the paths of transport of coarse material along the channels and on sand banks, and the general characteristics of sediment accomulation on intertidal mudflats and mangrove zones.

Concern was expressed at the EPA workshop (February 1995) and the Australian Coastal Engineering Conference 1995 about the lack of detailed information on sediments. It was felt that there was insufficient fine scale «1 Okm grid) infOffilation or long term data on sediment transport, sediment bed levels and turbidity plume behaviour. This compromises any assessment of the extent of potential changes that may result from dredge spoil disposal in Western Port.

m[§J ...... '''''' ...... "", __ ",_,

o ~ .. IMII ...... II 1<11 ~ tl.,

~ Bub,,,,,, _I"" CItIIoo .. Moht ...... ". ~ C,'-"... :5Hd , ...... _._, ._, ~ tll_ ,q,",I_~

I / l ....1 __ ••• "-"iP> i_ dr"u

I! -".IW etI!t Old ~r "'_ ,.u.. " •..0 $rut_ tao_"".,

Figure 3.6 General pattern ojsediment transport in Western Port (from HarriS et aL J979a)

There is widespread concern that external and internal sources of sediment to Western Port contributed to the decline of seagrasses in the early 19705, and continue to contribute to high levels of turbidity and sediment deposition. The high concentration of suspended sediments may affect the ability of seagrass to re-establish. In addition, other biota in Western Port may be affected. There is also concern

20 Environment Protection Authority The Western Port Marine Environment

that disturbance of sediments may release contaminants (eg. metals and organic compounds) into the marine environment of Western Port.

Activities in Western Port and its catchment which have increased the load of suspended solids in Western Port include: extensive dredging of turning basins and shipping channels in North Ann, particularly in the 1970s and disposal of spci1; major erosion in the headwaters of input streams and drains of the catchment (Condina 1995); the construction of coastal structures; and resuspension of sediments on mudflats, previously retained by the seagrass which receded drastically in the late 1970s. The pattern or amount of sedimentation around Western Port is not fully understood and the relative contribution of possible sources cannot be assessed.

Dredging and sediment sources

In the past, dredging primarily involved excavation of new shipping channels and swing basins (capital dredging). Recent dredging tends to be directed to maintaining or deepening existing channels and swing basin depths (maintenance dredging). The volumes and disposal locations of dredging programs in Western Port since 1921 are presented in Table 3.1. The largest volumes of materials were dredged in the late 19605 and early 1970s, and considerable volumes of spoil were disposed within Western Port.

Approximately 1.2 mjllion cubic metres of sediment was dredged for turning basins at Long Island Point (1968 to 1970) and at John Lysaght (1971-72). The dredge spoil was disposed in three different ways. More than IS0,000m3 was dredged and pumped to the point of land south of Long Island Point in 1969; approximately 300,00Orn3 of spoil was dumped from hopper barges at a spoil ground bet:ween Peck Point and Tortoise Head. Almost 700,OOOm' of sediment was pumped with associated seawater to land at the Lysaght site at Old Tyabb in 1972. The volume of material displaced was substantially greater than these figures indicate, since cutter suction dredges also pump large volumes of water with the dredged material.

According to the operator of Yaringa, extensive retention basins were required to allow settlement of fme spoil material prior to discharge of supernatant during the 1988 Yaringa dredging program. Runoff control (if any) from spoil disposal sites on land during the 1960s and 1970s programs appears to have been inadequate. Watson (1974) reported that, while the impact of the dredging at John Lysaght in the early 1970s was relatively confined to the dredging site, plumes of turbid water from the disposal of spoil were extensive. Turbid runoff from land disposal sites continued over several years after completion of the two year dredging program.

Watson (1974) also reported runoff in Sawtell's Inlet of sediment from clay in spoil disposed on land at Tooradin in 1974. Watson (1974) provided this description of the sediment: The peculiar weathering characteristics of the Western Port (dredged) clay. When disturbed, in certain instances, this clay under both submarine and subaerial weathering breaks down to a glutinous consistency, followed, at least in the subtidal to a finely divided floc ... the spoil dump, levelled in anticipation of further work, has not been further developed because of lack of consolidation.

21 Environment Protection Au/horiO' The Western Port .Marine Environment

Table 3,1 Program qfdredging in Western Port from 1921 to present (Port ofMelbourne Authority)

Year Location Disposal site Volume to shore, m' Volume to sea, m' dredged 1921 Hanns Inlet Shore 760000 1965 Stony Point Shore 142000 Crib Point Tankerton 324000 1969 LIP Pecks Point 295000 LIP Hastings Bight 157000 Watsons Inlet Shore 15000 1970 Yaringa Shore 76500 1971 Sawtell Inlet MudFlats 2300 Hanns Inlet Shore 50000 1972 BHP Old Tyabb 676000 Rutherford Inlet Mud Bank 2700 Wameet Local 1500 Blind Bight Beach 11000 Son Remo Shore 2600 Tooradin Island 19100 1973 Hastings Shore 1975 Ship Channel Grossard Point 10000 1980 Ship Channel Tankerton 10000 1988 Ship Channel Tankerton 24000 Yaringa Shore 35000 1990 Stony Point Shore 500 1991 Toor.din Shore 500 1994 Stony Point MudFlats 500 Tankerton Tankerton 12500 Hastings Island 4000 Ship Channel Tankerton 35000 Total 1921 to 1994 I 1915100 I 751600

There have been numerous reports discussing the impacts of dredging in Western Port (Watson 1974; Marsden 1976a; Lakey and Tiekell 1980; Bulthuis 1981e; MSE 199.)1. The State Environment Protection Policy for Western Port (1979) states inter alia:

Dredging, Spoil Disposal and Other Works Section 30 Dredging, reclamation, building of port facilities and other works should be carried out in a manner which causes minimal disturbance of plant and animal habitats, particularly in the case of saltmarsbes, mangroves and seagrass meadows, Where practicable, the disposal of dredged spoil shall be at external marine sites or on land above the salt marsh zones.

This requirement was developed as a consequence of the Westernport Bay Environmental Study (1973- 1974) (Ministry for Conservation 1975). More recently, in 1991 EPA developed a Trial Dredge Protocol (EPA 1992) to minimise the environmental impacts of dredging. This is now being used as the basis for programming dredging activities in Western Port and other parts of Victoria.

The most recent dredging in Western Port was undertaken by the Port of Melbourne Authority in late 1994, at Tankerton jetty and the main shipping channeL The program involved community consultation, use of EPA Trial Dredge Protocol, consultation with EPA and DCNR, and initiation of an environmental monitoring program. \Vhile there have been marine biological and bathymetric surveys of the marine biota on the seabed within the spoil disposal area, there appears to be no information available on the extent or persistence of turbidity plumes from the dredging or disposal

22 Environment Protection Authority The Western Port Marine Environment

areas, or on the redistribution of sediments over time at the disposal locations. The existing monitoring program does not appear to be designed to detect changes in deposition due to sedimentation of suspended material.

Catchment Sources of Sediment

There is very little recent quantitative information on the volumes of sediment entering Western Port from the catchment. Massive erosion in the Western Port catchment has been widely reported and documented, primarily by photography(State Rivers and Water Supply Commission 1983; Roberts 1985; Condina 1995). Sargeant (1977) compiled information and data on the sources and effects of erosion in the Western Port catchment. He determined that erosion has been widening and deepening drains and river channels, particularly in their middle and lower courses, rather in the headwater regions. Although much of the drainage works in the lower catchment had been completed in the 1930s, clearing of land in the upper catchment appears to have accelerated in the late 1960s and 1970s, and was accompanied by massive erosion (Sargeant 1977).

On the Lang Lang River, Bird (1980a) related episodes of channel erosion cutting an outlet to Western Port in the 1880s, and subsequent channel diversion and straightening, snagging (clearing of fallen trees and branches), and failures of weirs (drop structures). These changes have led to channel incision, then widening, resulting in the movement of more than four mi Ilion cubic metres of sediment (mainly sift and clay, with some sand) down the river. Most of the sediment moving down Cardinia Creek has come from the deepening and widening of the channel well below the dam, where there are features similar to those on the Lang Lang River (Warner and Bird 1988).

In response to the massive erosion problems in the headwaters of the Western Port tributaries, Melbourne Water undertook erosion control measures in the catchment in 1980, 1989 and 1993-94. Melbourne Water is responsible only for the rivers and streams in the north and west of the Western Port catchment (does not include the Bass River). It is estimated by Melbourne Water that the erosion control measures have reduced the volume of sediment loads carried by the rivers and drains into Western Port by over 50 per cent. Data from the Melbourne Water monitoring program do not appear to confirm these estimates. Melbourne Water estimated that prior to the completion of erosion mitigation works in the northern Western Port catchment in the 199Os, rivers and drains discharged approximately 100,00Om3 of sediment into the north of Western Port annually (Condina 1995). The basis for these estimates was not available during this review.

In spite of the concern for sediment erosion and runoff into Western Port, there has been no monitoring of streams or catchments during high flow events to estimate loads entering Western Port, or the contribution of individual catchments and streams. Estimates appear have been based on short term, infrequent or discontinued monitoring data (CEE 1986; Wallis 1988).

The Bass River discharges into the poorly flushed Rhyll segment of Western Port, and has a mean annual flow equal to 30 per cent of the flow of all rivers in the northern catchments of Western Port (CEE I 986a). Information of sedimentation in this area is unavailable.

23 Environmeni Protection Authority The Western Port Marine Environmeni

Resuspension of sediments from mudflats

Resuspension offine sediments on mudflats which were previously protected by overlying seagrasses appears to have increased turbidity of waters in the Upper North Arm. Brand and Bulthuis (1977) showed that the concentration of suspended solids in water draining from intertidal areas covered with .eagrass was substantially lower than water draining from denuded areas. EPA water quality monitoring in Western Port since 1984 indicates high turbidity in the northern part of Western Port, but there are insufficient measurements available for the period prior to or during the seagrass loss to compare with EPA data. There are no data on sedimentation rates anywhere for Western Port.

Sargeant (1977) speculated that loss of seagrass could lead to intertidal flat instability. and local and widespread erosion of mudflats. There is no sufficiently detailed information on the topography or shape of mudflats to determine whether changes have or are occurring.

24 Environment Protection AutJlOrity The Western Port Marine Environment

1 CHAPTER 4 1i i TIDES AND CURRENTS OF WESTERN PORT

Tides and currents ofWe~tern Port are key processes which detennine the morphology of Western Port, sediment transport, water quality, habitats and nutrition for plants and animals. They also affect shipping, boating and recreational amenity. Proposals in the early 19105 to construct causeways, fill large areas of intertidal area and dredge expansive shipping channels and basins would have changed the tidal character of Western Port. Those proposals are no longer considered likely (Bate and MarIes 1978), and developments which may affect wster currents are more likely to be localised such as marina wharves and dredged channels.

TIDES IN WESTERN PORT

Tides in Western Port are influenced by several facrors: ocean tides in Bass Strait at the entrance to Western Port; the shape and bed topography of Western Port; bed characteristics, roughness and 1 resistance to flow; meteorological factors (particularly winds and barometric pressure); and river inflows. I The ocean tides are descnbed for Stony Point in the annual edition of the Australian Tide Tables (Hydrographic Office 1995). The Victorian Tide Tables published by the Port of Melbourne Authority provides times for high and low waters relative to Stony Point and tidal ranges for Flinders Pier, Cowes Pier, Newhaven Pier, Spit Point, Bouchier Channel, Tooradin Pier, Wameet Pier, Eagle Rock and Hastings Pier. Descriptions of the patterns of the tides in Bass Strait have been presented by a number of authors (pollock 1973; Fandry 1985; Hinwood and Wallis 1989; Black and Hatton 1994).

Examination of the tidal pattern in Bass Strait show that the tides in the Western Entrance to Bass Strait are similar to those at the entrance of Port Phillip Bay. The most significant difference is that the M2 (principal diurnal) tidal component has a range of 104m at the entrance ro Port Phillip Bay, but a range of 1.6m at the entrance to Western Port.

However, the large tides in Western Port are markedly different from the small tides in Port Phillip Bay. This is because Port Phillip Bay has a small entrance area (The Rip) and a large surface area while Western Port has a large entrance (Western Channel plus Eastern Channel) and a relatively smhll surface area. As a consequence, the tidal wave at the Western Entrance is able ro travel with very little attenuation throughout the whole of Western Port.

The shape of Western Port has a secondary influence on tides. The cross-sectional area of the major channels, decreases significantly north of Sandy Point with a slight amplification of tides with distance north (Table 4.1). The diurnal tide (M2+S2 constituents) at Tooradin is 24% greater than the diurnal tide at Flinders (Table 4.1).

25 Environment Protection Authority The Western Port Marine Environment

Table 4.1 Tidal amplification in Western Port (from Hinwood 1979)

Site Amplitude of tidal constituents, metres

M2 82 M2+S2 Distance from Flinders (km) Flinders 0.80 0.21 1.01 0 Cowes 0.86 0.24 1.10 17 Stony Point 0.90 0.22 1.12 23.5 San Remo 0.93 0.22 1.15 27 Elizabeth Island 0.94 0.23 1.37 30.5 Eagle Rock 0.97 0.24 1.21 26.5 Sandy Point LOO 0.24 1.24 45 Bourch L01 0.26 1.27 49 Tooradin 0.99 0.26 1.25 49 Point Lonsdale 0.44 0.13 0.57 45

The roughness of the seabed creates shear and can reduce the extent of water movement. Substantial changes in seabed composition from seagrass to mud and sand over the past two 'decades should have been reflected in a small change in tidal pattern at Tooradin and other sites in the north of Western Port. Measurements have not been made to confirm this hypothesis. Changes in bed roughness following the loss of seagras8 would have a minor effect on the tides, but this is unlikely to be measured by the Stony Point gauge. In view of the large tidal range in Western Port, it would be a relatively small effect.

Winds have a short term (a few hours to a few days) influence on the tides in Western Port because of its large surface area and generally shallow depth. For example, a strong northerly wind can reduce the tidal rise substantially in the northern zone of Western Port. Conversely, a strong south westerly wind increases the tidal rise. Meteorological pressure variations have a minor influence, with high pressure resulting in lower tides, and lower pressure resulting in higher tides.

Tides are recorded continuously at Stony Point, and tidal conditions have been recorded at other sites in Western Port. Adequate information exists on tidal patterns in Western Port for navigation and shipping. From the tide levels recorded at Stony Point it is possible to predict tidal levels (and to a slightly lower accuracy, tidal currents) throughout Western Port (Black and Hatton 1994). Published papers on these models provide adequate information on tidal patterns under the existing topography of Western Port.

Large changes in the shape of Western Port would have a major effect on the tides. As an illustration, the extravagant development proposal for Western Port in the mid 19608 envisaged reclamation of the whole of the northern area of mudflats into a port served by a single deep channel. This development would have had a major effect on tidal conditions throughout Western Port, with a lower tidal range in the northern channel and substantiaIiy weaker tidal currents in the entrance channels and around Phillip Island. Other associated and environmental changes would occur, as was pointed out by many observers at the time (Wallis 1968).

Factors affecting tides are: sea level change; bed level change; shape of Western POrt; and bed roughness. Sea level has been rising between 1 and 2 mm/year for a century and may rise more rapidly in the next century as a result of the enhanced Greenhouse effect. The effect of seabed changes on tides should be negligible over the next two decades, as natuml changes in seabed level in Western Port and short-term variations in sea level due to winds and meteorological pressure will overwhelm the effect of rising sea level. Dredging to date has not had a significant effect on tides in Western Port. The major pressures on tidal pattern are: large scale dredging; infilling and reclamation of mudflats; and natural accretion of

26 Environment ProtectionAuthorily The Western Port Marine Environment

mudflats and progradation of mangroves and salt marshes (Bird 1993). Hinwood (1979) predicted that there would be little change in tides or tidal current if there was a barrier across the tidal divide.

AU yclwtmlln ml x 1t1' o ~nnuntbtr ~_-,-_--,'!"'" .. PoorqUlIlltydllf.a

Figure 4.1 Half-tidal fluxes in Western Port (from Hinwood and O'Brien 1974)

CURRENTS IN WESTERN PORT

The general pattern of water currents and circulation in Western Port is well known from oceanographic, chemical and sedimentological investigations undertaken in Western Port during the Westernport Bay ElrVironmental Stuc(y (1973-1974) (Ministly for Conservation 1975), and earlier studies (Hinwood 1970; Hinwood and O'Brien 1973; Harris et al. 1979a; Harris and Robinson 1979; Hinwood 1979; Hinwood and Jones 1979; Marsden 1979a, b, c; Sternberg 1979).

Hinwood and O'Brien (1974) developed a transport model on the basis of extensive current, tide, dispersion and bathymetric measurements made during Westernport Bay i;nvironmental Stuc(y (1973- 1974). Half-tidal fluxes calculated by Hinwood and O'Brien at seven sections around Western Port are shown in Figure 4.1. Hinwood & O'Brien concluded that velocity data demonstrated that the lunar semi diurnal tide is the principal driving mechanism for Western Port; under pure tidal motion (i.e. excluding winds) there is a clockwise circulation around Phillip Island and possibly also round French Island.

27 Environment Protection Authority The Western Port Marine Environment

Figure 4.2 Western Port showing 1 km grid used in Hinwood hydrodynamic rtWdel (from Hinwood 1979)

Table 4.2 Comparisons ofvelocities in Western Port segments (from Hinwood 1979)

Location or Section Comments Western Entrance Flood flow greater and maximum velocity higher on west side, ebb flow greater and maximum velocity higher on east side. Western Entrance Segment 3 km Weak net flood flow on west side and ebb flow against Phillip Island. west of Sandy Point Flow across Middle Bank is perpendicular to the bank and net flow is in flood direction but at northern end is in ebb direction.

Lower North Arm near Current at deepest part of channel is faster and turns about 30 minutes Confluence Zone behind the rest of the section. For about 20 minutes at the end of the ebb there is a flow from East Arm into North Arm and near the end of the flood there is a flow in the opposite direction for about 20 minutes.

Lower North Arm at Middle Net flow small, flood predominates in main channel (west of Middle Spit Spit). Current turns earlier in eastern channel and velocities are lower. North Arm at Eagle Rock Velocities higher and net ebb flow on south side, net flood flow on north side. Current starts to flood on north side I hour ahead of the rest of the section, but starts to ebb at same time. Eastern Basin Current starts to ebb at Eastern Entrance end and during first hour currents in basin are directed generally towards that end. Then a strong current develops along Phillip Island towards the East Arm and currents in the basin swing more in that direction for most of the ebb. Flood starts at Eastern Entrance end and flows strongly north against the east shore while weak ebb currents persist in the rest of the basin. The main flood pattern is a strong south east current near Phillip Island from the Lower East Arm with currents over most of the basin directed towards the Corinella Segment. The flood current from the East Arm persists about 1 hour after that from the Eastern Entrance. Carinella Segment Ebb current lasts for a shorter time than the flood, has higher velocities and a slight dominance in flow.

28 Environment Protection Authority The Western Port Marine Environment

{ ,! Hinwood (1979) provide a good description of tidal currents in Western Port (summarised in Table 4.2). i He described hydrodynamic and pollutant transport models developed for Western Port. The models are ! based on a 1 km grid (Figure 42), and bathymetric, current, tide height and simulated waste dispersion 1, measurements were made specifically in order to develop the models. Typical velocity vectors for model I "1 runs with a simulated barrier on the tidal divide are shown in Figure 4.3. The pattern of net water j movement can be seen from the hydrodynamic model (Figure 4.4). I Measurements by Hinwood and O'Brien (1974) and Sternberg (1979) demonstrated that water currents in J the channels of Western Port are strong, and can reach I.3m1s in the water column and O.7m1s on the i seabed. Hinwood (l979) concluded that; "In most channels, the depth-mean velocity attains a maximum of about O.6m1s on the mean tide, which for the sandy sediment, is probably the velocity at I which the channel is self-maintaining". The vector plots from the model (Figure 4.3) show that the 1 currents are strongest in the main channels, with weaker currents in the bays and inlets, over intertidal I areas and in the south east of Western Port Wind exerts only a small influence over ebb and flood 1 currents, although strong and persistent winds affect the net circulation (Hinwood 1979). ! A

Figure 4.3 Typical velocity vectors from Hinwood hydrodynamic model (from lIinwood 1979)

29 -"~"~".~~~-~...... ------

Environment Protection Authority Tile Western Port Marine Environment

Harris et al. (1979a) compared information on water circulation in Western Port from a variety of sources (Figure 4.4), and derived a general circulation pattern which indicates clockwise circulation. \\'bile net movement for Western Port is generally cloch.'Wise, there is variation in net movement across channels.

More recently (19905), PMA has measured currents in the main shipping channel and has developed a predictive model of water current in the channel to assist in management of ship traffic. VIMS extended the Bass Strait hydrodynamic model (IOkm grid) into Western Port on a 1,500m grid. Instantaneous predicted current vectors for typical runs of the Bass Strait hydrodynamic model are shown in Figure 4.5 (Black and Hatton 1994). The model suggests that there is little net longshore movement past the entrances to Western Port.

Current meter measurements near Cape Schanck (Chidgey and Wallis 1992) indicated that local wind . patterns strongly influence net nearshore drift. For data collected in March 1992 when winds were predominantly from the south west near Cape Schanck, the net water movement was about 3 per cent of the net daily wind Measurements of bottom currents by Sternberg and Marsden (1974 a, b) and Sternberg (1979) show that there is net drift along the bottom to the north and east of Western Port. The currents are sufficiently strong to transport most sandy sediments (Marsden et al. 1979), although cohesive sediments ( clays) or those protected by seagrasses would be less affected by such currents.

Figure 4.4 Independently derived circulation patterns in Western Port (from Harris et aL 1979a)

Although residence times for certain locations were calculated during calibration and validation of the hydrodynamic and transport models (Hinwood 1979), data was not published. Residence times may be inferred from existing data (Hinwood and O'Brien 1974; Hinwood 1979), and it is generally acknowledged that residence times in Western Port range from months in the north and east, to days and half days near the Western Entrance (Hinwood pers comm.). However, calculation of more precise residence times would require modification of existing models, use of detailed submodels (WiIliams

30 Environment Protection Authority The Western Port Marine Environment

1978), reduction in grid size to 100m, and more information on bath)n1etry of the intertidal areas (Hinwoodpers comm.).

Even with sophisticated modelling and measurement technology of the 1990s, we have little more information on the pattern of water movement past and around Western Port than was documented by Hinwood and O'Brien in August 1974. The existing models of water movement are adequate to describe general movement patterns and to defme boundary conditions for smaller scale models. However, in order to describe accurate finer scale water movement (such as within Hastings Bight, Watson's Inlet or dredge disposal areas), additional current and bath)n1etric measurements would be required in those areas.

BOAOS ROCKS SOUTH EASTERN OUTFALL 2-D NESTED MODEL RUN PPWPWTLF.OUT 109*66 GRID NESTED RUN PORTLAND RESIDUAl+OUNNAMATTA PREDICTED TIDES AND AIREYS WINDS TIME OO:OOhrs on 16/3192 HYDRODYNAMIC. MODe.. 300 TIME 432.()() hrz; L...... I 600U metr- ~ 0.50 mlr.

BOADS ROCKS SOUTH EASTERN OUTFAll 2-0 NESTED MODEL RUN PPWPWTLF.OUT 1OS~5& GRID NESTED RUN, PORTLAND RESIDUAl+OUNNAMATTA PREDICTED nDES AND AlREYS WINOS TIME OO:OOhrs on 19/3192 H'ItlROOYNAMlC MOOEL:)oo TIMe SG4.GO hI"$: I---J 6BOO metre!; l-..l 0.50.m/$

Figure 4.5 Instantaneous currents for VIMS localised Bass Strait hydrodynamic model (from Black and Hatton 1994)

3i Environment Protection Authority The Western Port Marine Environment

CHAPTERS

PHYSICO-CHEMICAL MONITORING OF THE WESTERN PORT MARINE ENVIRONMENT AND CATCHMENT INPUT STREAMS

INTRODUCTION

Water quality is generally assessed in terms of indicators which are applied to ecosystem"health" and hwnan usage. Water quality in Western Port is influenced by internal processes, inputs from the catchment, and quality of ocean water entering from Bass Strait Water quality of Western Port described in this chapter represents the composition of the water, sediment and biota in terms of indicators which are relevant to maintenance of natural ecosystems and desirable hwnan uses.

REVIEW OF THE PHYSICO-CHEMISTRY OF WESTERN PORT

Monitoring programs undertaken in Western Port

Investigations during the 1970s (Ministry for. Conservation 1975; Gibbset al. 1976; Bums and Smith 1977; Harris et al. 1979b) and the Environment Protection Authority marine monitoring network (which is an ongoing project) are the only programs that have attempted to assess the relative physico-chemical status ofthe Western Port marine environment.

The Westernport Bay Environmental SIu0'(1973-1974) was the most extensive monitoring investigation undertaken in Western Port. Investigations undertaken by the study provided substantial information on the biological, chemical and physical characteristics of the system. The ability of marine chemistry investigations to assess background concentrations are widely varied, with the majority of data collected in the Lower North Arm and western section ofthe Upper North Arm.

The Environment Protection Authority marine monitoring program differs from previous investigations as the primary aim is to detect long term trends in surface waters. Collection of physico-chemical water quality data from three sites in Western Port has been ongoing since 1984 (Table 5.1; Figure 5.1). Quarterly sediment samples (analysed for metals and organics) were added to the program in 1990. The three sites were selected on the basis that they were representative of conditions in Western Port. The significance of a program designed to determine long term trends is that it aims to detect if the physico chemistry of the water body (compared to site specific studies) are changing over time. For example, whether there are significant increases or decreases in indicators (nutrients, metals or temperature). This type of program can provide a reasonable indication of the long term impact of catchment and other activities over time. Analysis oflong term trends are currently being undertaken by EPA

The disadvantage of this program is that it provides no indication of pulse inputs from pollution and catchment events or fine scale temporal and spatial variation in a water body. Ideally these investigations should also be undertaken in conjunction with a monitoring program to detect long term trends.

32 • environment Protection Authority The Western Port Murine Environment

CHAPTERS

PHYSICO-CHEMICAL MONITORING OF THE WESTERN PORT MARINE ENVIRONMENT AND CATCHMENTINPUTSTRE~S

INTRODUCTION

Water quality is generally assessed in terms of indicators which are applied to ecosystem"health" and human usage. Water quality in Western Port is influenced by internal processes, inputs from the catchment, and quality of ocean water entering from Bass Strait Water quality of Western Port described in this chapter represents the composition of the water, sediment and biota in terms of indicators which are relevant to maintenance of natural ecosystems and desirable human uses.

REVIEW OF THE PHYSICO-CHEMISTRY OF WESTERN PORT

Monitoring programs undertaken in Western Port

Investigations during the 1970s (Ministry for. Conservation 1975; Gibbset al. 1976; Burns and Smith 1977; Harris et af. 1979b) and the Environment Protection Authority marine monitoring network (which is an ongoing project) are the only programs that have attempted to assess the relative physico-chemical status of the Western Port marine environment

The Westernport Bay Environmental Study(1973-1974) was the most extensive monitoring investigation undertaken in Western Port. Investigations undertaken by the study provided substantial information on the biological, chemical and physical characteristics of the system. 'The ability of marine chemistry investigations to assess background concentrations are widely varied, with the majority of data collected in the Lower North Arm and western section of the Upper North Arm.

The Environment Protection Authority marine monitoring program differs from previous investigations as the primary aim is to detect long term trends in sutface waters. Collection of physico-chemical water quality data from three sites in Western Port has been ongoing since 1984 (Table 5.1; Figure 5.1). Quarterly sediment samples (analysed for metals and organics) were added to the program in 1990. The three sites were selected on the basis that they were representative of conditions in Western Port. The significance of a program designed to determine long term trends is that it aims to detect if the physico chemistry of the water body (compared to site specific studies) are changing over time. For example, whether there are significant increases or decreases in indicators (nutrients, metals or temperature). This type of program can provide a reasonable indication of the long term impact of catchment and other activities over time. Analysis oflong term trends are currently being undertaken by EPA.

32 Environment Protectinn Autltority The Westem POri ]Warille Environment

Table 5.1 Indicators measured in Western Port jor the Environment Protection Authority marine 1 monitoring program i i, Indicator

Dissolved oxygen Chlorophyll a Oxygen saturati on Chlorophyll b 1 Salinity Chlorophyll c pH Living Chlorophyll a Temperature Phaeophytin l[ Secchi disk depth carorenoids I Total phosphorus Arsenic 1 Reactive phosphorus Cadmium Reactive silica ,I Copper Total nitrogen Lead I Total Kjeldahl nitrogen Mercury Nitrate nitrogen Nickel Oxidised nitrogen Zinc Ammoniacal nitrogen Iron Manganese

General physico-cbemical monitoring

The most common type of monitoring undertaken in a water body is the analysis of basic physico chemical indicators. Some of these indicators are easy to collect and relatively inexpensive, and are often used to provide a general indication of the "health" of the water body. The most ccmmon parameters sampled are: dissolved oxygen, saIinity; suspended solids; turbidity; and pH. More detailed and expensive investigations also measure nutrients and contaminants (metals and organic ccmpounds) (Table 5.1).

The first large scale data set for Western Port was collected during 1973-1974 as part of the Westernport Bay .8nvironmental Study. The most extensive investigation of water quality during this period (Robinson and Harris 1974) collected data from 90 sites over 23 time periods between June 1973 and October 1974. This investigation monitored temperature, salinity, Secchi depth, silicate, phosphorous, inorganic nitrogen and dissolved oxygen at the majority of sites per cruise. In addition, depending on field and analytical equipment, chlorophyll-a, pH and total organic carbon were measured on a limited number of samples.

In order to facilitate analysis of data in the limited time available, Robinson and Harris (1974) divided cruises into a series of eight sampling periods. Sites were grouped into six different areas of Western Port which reflected similar hydrodynamic conditions. Data were presented as average values for each segment and sampling period. The investigation determined that many indicators were significantly influenced by seasonal, spatial and tidal events. This study was particularly valuable as enough data were collected to provide a useful assessment on background conditions of these indicators at the time.

Gibbs et al. (1976) ccntinued to sample the same indicators and sites in Western Port sampled by Robinson and Harris (1974). Several sites were added to the program during the period of October 1974 to September 1976. Gibbs et al. (1976) summarised data in an interim report to the Marine Chemistry Unit, conclusions were similar to those of Robinson and Harris (1974). No further analysis of data was conducted.

33 I

Environment Protection Authority The Western Pori Marine Environment

SiteN". ~t.i"" 709 lLI:alnV' 7.16 BarriHar Nand n4 Corintlb

Figure 5.1 EPA water quality monitoring sites in Western Port

The only monitoring program at present in Western Port is the Environment Protection Authority marine ambient water quality monitoring network. This program commenced in 1984 and was designed to sample three sites on a monthly hasis. The EPA program monitors general physico chemical indicators, metals and nutrients in water, as well as metals and limited organics in sediment on a quarterly basis (Table 5.1). Results from this program for indicators such as dissolved oxygen, temperature, pH and salinity indicate there has been minimal change during the past ten years. Data reflect typical fluctuations that can be attributed to seasonal, diurnal, tidal or climatic variation.

Turbidity of Western Port has been a serious issue for some time. It is influenced by the resuspension of fine sediments from wave action on intertidal mudflats and inputs from creeks and rivers (Marsden and Mallett 1975; Bulthuis et al. 1984). Turbidity in Western Port is thought to have increased through dredging programs in the 1970s and loss of seagrass. Physico-chemical investigations conducted during the Westernport Bay Environmental Study did not report any measurements of turbidity or water clarity. Although the investigation conducted by Harris and Robinson (1974) measured Secchi depth at all stations, data was not reported (Robinson pers comm.). The only published data for Western Port has been collected by EPA. EPA monitors turbidity (suspended solids) by measuring the concentration ofNFR (non-filtrable residue), and water clarity by Secchi disk measurements.

NFR analyses suggest that turbidity has decreased since 1986. Corresponding measurements ofSecchi depth indicates clarity has increased since 1989 in the west of Western Port. Further analysis of data is currently in progress to determine whether there is a trend.

34 ~ Environment Protection Authority The Western Port Marine Environment i 1 ~ I I Nutrients i Robinson and Harris (1974) included nutrients in their June 1973-0ctober 1974 investigation. I Orthophosphate, total phosphorous, ammonia, Kjeldahl nitrogen, nitrate and nitrite were routinely measured in the majority of samples. The report was the most comprehensive water quality data-set collected during the Westernport Bay Environmental Study. II I Data collected by Robinson and Harris (1974) indicated there was substantial spatial and temporal , variation in nutrient concentrations. Their data clearly demonstrated that variation in nutrients was 1 strongly influenced by catchment inputs, seasonal parameters and the tidal cycle. Robinson and Harris (1974) also discussed in general tenns the cycling of nutrients within various areas of Western Port. The role of seagrass beds in causing depletion of orthophosphate in particular was discussed. The role of nitrogen in the water column was limited to a discussion of inorganic nitrogen. The role of seagrass beds, sediments and other areas in cycling nutrients was not experimentally investigated in Western I Port during 1973-74. Therefore the processes discussed should be treated with caution. 1 j Gibbs et al. (1976) continued sampling the same sites and indicators as Robinson and Harris (1974) from October 1974 to September 1976. Limited analyses of data were conducted and all conclusions concurred with Robinson and Harris (1974).

Harris and Vlasich (1976) began a detailed monitoring program of nutrients and chlorophyll-a at approximately six weekly intervals to dctennine if significant concentrations of nutrients from Beags Rocks outfall Were entering Western Port. Harris and Vlasich (1976) concluded that nutrients from Boags Rocks at that time did not pose any immediate threat to Western Port. Nutrient concentrations were decreasing with eastward transport of the plume from Cape Schanck to the Western Entrance. Ammonia and orthophosphate were removed from the water column by increased biological activity before the plume reached the Western Entrance. Harris and Vlasich (1976) found that small amounts of nitrate, nitrite and total phosphorous reach Western Port. These nutrients were undetectable above background concentrations north of Flinders Pier.

Bulthuis (1977) while investigating phytoplankton biomass and productivity in Western Port also included analyses of nutrients. Analytical methods for nutrients were preliminary and data should be treated with caution. He considered nutrient concentrations to be unifonn with depth in all areas of Western Port and all analyses at a single station were treated as replicates. The investigation also considered that there was no apparent seasonal trend for inorganic nitrogen during the period of sampling. Ranges in nutrients were found to be low with nitrate and nitrite tending to be lower in spring and summer. Total phosphorus and orthophosphate was lowest during spring. Nutrient fluctuations due to semi-diurnal, diurnal and seasonal factors are well established in Western Port and other areas (Robinson and Harris 1974; Skyring et at. 1992). The lack of detail of sampling sites, dates and data makes it difficult to assess conclusions made by Bulthuis (1977).

The Environment Protection Authority marine water quality monitoring network has monitored nutrients (total phosphorus, orthophosphate, total nitrogen, Kjeldahl nitrogen, ammonia, nitrite and nitrate) at three sites since 1984 (Fig. 5.1). Data collected during this time indicate regnlar variation in concentrations of nutrients (Figure 5.2). Nutrient concentrations at the Corinella site are consistently higher than other sites (Figure 5.3). Chlorophyll-a (Chapter 6, Figure 6.1) and turbidity are also regularly higher at Corinella. Increased nutrient levels at this site possibly relate to higher nutrient bound sediment particles and seagrass detritus.

35 Environment ProtectioJ1 Authority The Western Port Marine Environment

N N ~ ~ ro N a a a ~ ro a ro ~ ~ ro ~ a a N N ~ N N N N N ~ N ro m N ~ ~ N ~ N ~ N ro ;; a a a a a ;; a a a a a ~ a a ~ ~ ~ ~ ~ ~ w ~ ~ ro m a a N ~ ro ro ro ro ro ro ro ro ro ro ro m m a; a; m m m m m m m m ;'e ;'e ;'e ;'e ;'e ;'e "' "' ;'e "' ;'e DATE Figure 5.2 Total nitrogen concentrations for EPA monitoring sites for the period 1984-1994 (Units mg rl Station Legend 709 Hastings Channel 716 Barallier Island 724 Corinella)

0,25

0.2 V' 709 ---m--- 716 ~7241 i

~ 0.15 - 2 "2: 0

~%o s: 0.1

N N ~ ~ ro N a 0 a ~ ro 0 ro ~ ~ ro ~ a a N ~ N N N N N ;:: ;; w m N ~ ~ ~ N ~ N ~ N ;;; ;; a a a a a a a a a a a ~ a a ~ ;;: ~ cO ~ ~ w ~ ~ ;;; m a a N ~ ro ro ro ro ro ro ro ro ro ro ro m m m a; m 0 ;'e m m m m 0 m m m m ;'e m m 0 m "' "' DATE

·I Figure 5.3 Total Phosphorous at EPA monitoring sites for the period 1984-1994 (Units mg L Station Legend 709 Hastings Channel 716 Barallier Island 724 Corinella)

36 Environment Protection Authority The Western Port Marine Environment

Data collected by Robinson and Harris (1974), Gibbs et al. (1976), Harris and Vlasich (1976) and EPA are the only sources of long term nutrient monitoring in Western Port. These data provide an indication of temporal and spatial nutrient fluctuations. Nutrient cycling processes in Western Port are poorly understood since information is limited to several investigations of nutrient content and turnover in mangroves and seagrass (Attiwill and Clough 1974a,b; NSR 1974; Attiwill and Clough 1978). Nutrient fluxes between marine sediments, water and biota have not been investigated. Some theoretical estimates were made of potential re-cycling of nutrients in these two systems during the Westernport Bay Environmental Stucry (1973-1974) (A ttiwill and Clough 1974a, b).

Metals in Waters

The majority of soluble metals introduced to the marine environment tend to rapidly flocculate or bind to particles and sink to the seabed. A small quantity of soluble metals is taken ur directly by marine biota. In general, the concentration of metals in seawater is low (ng - IJ.g L- ) except in highly contaminated areas. The low concentration of metals in seawater means that accidental external contamination of samples with even small amounts of metals is potentially a problem. Considerable effort in the preparation, collection and storage of samples for metal analysis is required for seawater samples compared to analysis of sediment and biota which can be sub-sampled in a controlled laboratory envirorunent.

Investigations of heavy metals in waters of Western Port are limited. Fabris and Harris (1974) conducted preliminary investigations of a number of metals (cadmium, copper, zinc, lead) at 13 shoreline locations during the Westernport Bay Environmental Study (1973-1974). Fabris and Harris (1974) noted that their results were preliminary and did not represent concentrations in open water. The authors also commented that samples were collected close to input sources and results may have been influenced by these inputs.

Canterford and Ducker (1975) analysed seawater samples from four localities in Western Port for lead, copper, zinc, and cadmium. Results for cadmium, lead, and copper were similar to Fabris and Harris (1974). Concentration of zinc in surface waters was substantially higher than analyses by Fabris and Harris (1974) and present concentrations from EPA monitoring data (EPA 1993a, I 993b, I 993c). Some concern was expressed at the time that contamination of samples had occurred, and data should probably be treated with some caution.

Analytical methods used for analysis of metals in water samples (anodic stripping voltametry) is generally considered to be precise. Fabris (pers comm) considers that sampling and storage procedures used during the Westernport Bay Environmental Stucry may have allowed contamination of samples and resulted in an overestimate of the concentration of some metals in samples.

Since 1984, EPA has monitored metals in surface waters at three sites in Western Port (l993a, b, c) (Fig. 5.1). A more comprehensive range of metals are monitored than previous investigations (cadmium, copper, iron, nickel, lead, zinc, mercury and the metalloid arsenic). The majority of data indicates metals in surface waters are low, with many samples below the limit of detection (Table 5.2). Quality assurance and quality control procedures during analysis indicate contamination of samples is not occurring.

Data collected by Fabris and Harris (1974) were not sufficient to adequately assess background levels

i of metals in seawater during the period of the investigation. EPA data from 1984 to the present is i probably sufficient to reflect concentrations of metals in ambient seawater at the three sites sampled. Data may not be applicable to the Western Entrance Segment or the north-eastern area.

37 1 Environment Protection Authority The Western Port Marine Environment

Daly and Fabris (1993) investigated tributyltin (TBT) concentrations in water and biota in Port Phillip Bay, Western Port and Gippsland Lakes. TBT concentrations were found to be elevated (Hastings 1 I 212ng Sn L- , Newhaven 700 ng Sn L- ) in the vicinity of boat marinas and moorings. Sites outside I these areas were low or below the detection limit (I ng Sn L- ).

Table 5.2 Metal concentrations in seawater from Environment Proteelion Authority moniloring stations (Medians are calculated where possible. NOTE < values indicate concentrations are belcyw the level of detection)

METAL CONCENTRATION, I'g L· Year I Cadmium Copper I Iron I Nickel SITE 709 716 724 709 716 724 709 716 724 709 716 724 1984 <0.05 <0.05 <0.05 0.6 <0.5 1.2 0.5 0.6 l.l 1985 <0.05 0.1 0.1 <0.5 0.3 0.7 0.7 0.9 0.8 1986 <0.05 <0.05 <0.05 0.6 0.7 0.8 0.6 0.7 1.2 1987 <0.05 <0.05 <0.05 0.5 0.5 1.0 0.6 0.7 1.6 1988 <0.05 <0.05 <0.05 0.3 0.4 0.8 0.5 0.6 1.2 1989 <0.05 <0.05 <0.05 <0.5 0.5 1.5 10l.0 1I2.0 1518.5 0.5 0.6 1.4 1990 <0.05 <0.05 <0.05 <0.5 0.5 1.2 88.0 60.0 1029.0 0.5 0.5 1.4 1991 <0.05 <0.05 <0.05 0.5 <0.5 1.0 71.0 89.0 743.0 0.5 0.5 0.9 1992 <0.05 <0.05 <0.05 0.5 <0.5 1.5 130.0 89.0 1215.0 0.4 0.5 1.3 1993 <0.05 <0.05 <0.05 <0.5 <0.5 0.6 36.0 61.0 229.0 0.4 0.5 0.7 1994 <0.05 <0.05

Metals in sediments

The earliest investigation of metals in sediments was conducted during the Westernport Bay Environmental Study (Fabris and Harris 1974). Fabris and Harris (1974) collected three replicate samples from the same intertidal locations as water samples. Analyses indicated that cadmium concentrations were generally below detection limits. Elevated concentrations of other contaminants were found close to larger input sources near Hastings and in tbe north-eastern area of Western Port Fabris and Harris (1974) noted that concentrations should not be considered indicative of background levels in Western Port due to tbeir proximity to input sources and shoreline location.

38 Environment Protection Authority The: Western Port Marine: Environment

Statham (1977) conducted the most intensive investigation to dste of metals in sediments of Western Port Replicated samples were analysed from 153 sites and analysed for zinc, Chromium, cadmium, lead, nickel, cobalt, magnesium, and iron. Statham (1977) investigated correlations between availability of metals and organic complexes, sediment particle size, sediment type and water and sediment movement.

Analytical results were generally lower than other areas of known anthropogenic inputs (eg. Port Phillip Bay) (Table 5.3). Metal concentrations were higher in areas with a high content of silts and clays, also in areas of urban and industrial input (Hastings Bight, Upper North Arm mndflats, . Queensferry embayment and to the west of the Bass River delta). The highest concentration of metals found during the investigation were for lead and zinc, adjacent to industrial areas. lntennediatc values were found in areas with a high clay fraction.

Table 5.3 Summary of results of sediment analyses from Statham (1977) (Where nO mean values are provided, samples were be/(JW detection limit and no mean was calculated All values were I-lg i J dry 'weight)

Metal Mean Range !

I cadmium <0.10-0.67

! cobalt <0.5-7.5 . chromium <1.3-8.0 iron 1871 202-9238 magnesium 42.2 116-346 nickel <0.5-6.1 lead 3.3 <0.5-133 zinc 5.7 <0.7~34.9

Harris et al. (l979b) conducted an investigation of surface sediments from 14 sites distributed throughout Western Port. All samples were analysed for calcium, cadmium, iron, magnesium, lead, zinc and organic carbon. Results from samples indicated cadmium concentrations were very low or below the detection limit. Similar to Fabris and Harris (1974) and Statham (1977), inputs to the North Ann Segment of Western Port (Cardinia Creek and Bunyip River) were considered to have caused lead and zinc contamination of sediments. Samples in the Lower North Arm had elevated zinc concentrations which were thought to have been derived from the nearby steel galvanising mill (Harris et al. 1979b).

Plummer et al. (1975) investigated total mercury in sediments in Western Port at ten sites with a total of26 samples. Results indicated mercury levels were extremely low (ppb I ng gol) 'with no evidence of contamination. Concentrations of methyl mercury would be expected to be significantly lower.

The Environment Protection Authority monitoring program has sampled heavy metals from three sites on a quarterly basis since 1990. Results available indicate concentrations levels are low (EPA 1993b, c). Metal concentrations found in Western Port sediments for this program are similar to results from previous investigations. There do not appear to be any clear trends between the three sites from samples taken in 1990 and 1991. There are some concerns that sites may not accurately reflect sediment concentration in Western Port generally, due to their location. All sites are under a high current regime and the majority of sediment is sand. Fine sediments (silt-clay fraction) at these sites are minimal.

39 Environment Protection Authority The Western Port Marine Environment

Metals in biota

Fabris and Harris (1974) conducted the first investigation of metal concentrations in biota in Western Port. Samples were taken from the same 12 intertidal sample areas as used for waters and sediments. Biota samples were primarily molluscs and crustaceans. Species of biota analysed were variable as it depended on availability at each sample site. Results were considered preliminary due to inherent problems of comparability between species; there were no previous investigations, no replication of analyses and an absence of a temporal sampling regime.

Two other investigations were conducted during the Westernport Bay Environmental Study (1973- 1974) by Canterford and Ducker (197,5) and Plummeret al. (1975). Canterford and Ducker (1974) sampled plankton from four stations over eight time periods for zinc, copper, lead and cadmium. Concentrations of metals in netted samples of plankton were presented in the report. Despite Canterford and Ducker'S comment that results were for phytoplankton, chemical analyses appear to have been conducted on total plankton and all detrital/sediment matter. Concentrations of metals in plankton in this study were generally higher than those found in other biota by Fabris and Harris (1974). It is possible that plankton may accumulate greater concentrations of metals than other biota. However, as samples also included other material it is possible that a substantial error was introduced. The Westernport Bay Environmental Study Repon (Ministry for Conservation 1975) commented that there was some concern about the results and analytical methods. Canterford and Ducker (1975 ) provide no indication of analytical methods.

Canterford et al. (1978) expanded on investigations conducted during the Westernport Bay Environmental Study (1973·1974) and examined the accumulation of four metals (zinc, lead, copper, cadmium) in the diatom Ditylum brightwellii isolated from samples collected in Western Port. The investigation determined that accumulation inDo brightwellii increased with increasing concentration of zinc, lead and cadmium. Results for copper showed no difference between experimental and controls. No measures of productivity were reported, so it is difficult to determine if the reported concentrations had an impact on the physiology of the alga.

Harris et al. (1979b) analysed seagrass (Zostera muelleri and Heterozostera tasmcmica), mud arks (Anadara trapezia) and mud oysters (Ostrea angasi) from a large number of sites in Western Port. Harris et al. (I979b) reported concentrations of lead were higher in biota at sites in the Upper North Arm. Concentrations of zinc were also higher along the west side of the Lower North Arm. Harriset al. (l979b) attributed elevated concentrations to specific input sources. '.Vhile concentrations in these areas were higher at these sites than other localities it should be noted that only four sites were sampled in the Upper North Arm. Sites were relatively remote from input sources (see Harriset al. (l979b) Fig. 3) and attributing elevated concentrations to specific inputs was not justified. Samples from the Lower North Arm were all situated on the western side; no samples were located to the east (see Harris et al. (I979b) Fig. 3). Additional samples should have been collected in both areas to support the conclusions.

A number of investigations have focussed on metal content in wild and translocated mussels in Western Port (Phillips 1976; Harriset al. 1979b; Hefter 1982; MSE 1990, 1991, 1992). Initial work by Phillips (1976) indicated concentrations in mussels were elevated near industrial sources. High concentrations of cadmium were reported in mussels near the BHPfLysaght wharf, however, these data were later found to be erroneous due to analytical error. Harrisel al. (1979b) translocated mussels from Pelican Point to sites in the Lower North Arm for a six month period. After this time mussels were found to have accumulated zinc at all locations. Increased concentrations were attributed to industrial, domestic inputs and shipping activity. This supported earlier findings by Fabris and Harris (1974). Hefter (1982) transplanted mussels from Port Phillip Bay to a location near Stony Point for a

40 J I Environment Protection Authority The Westem Port Marine Environment 1

t period of 30 days, Subsequent analyses of contaminant concentrations in tissues were found to be similar to ambient background levels in the water column.

Further monitoring has been conducted by MSE for BHP Steel at Hastings since 1990 (MSE 1990, 1991, 1992). Mussels were analysed for cadmium, chromium, iron, mercury, lead, and zinc. Lead, chromium and mercury were not detected. Results for the remaining metals were similar to previous investigations in Western Port (MSE 1991, 1992). ~ J ! Elevated concentrations of metals are found in biota in Western Port, particularly in the lower North Arm adjacent to industrial areas and to some extent the Upper North Arm. In the case of the majority of investigations the sampling regime was not extensive enough to adequately detennine input sources.

Ii I Organics I i Hydrocarbons

Early investigations of hydrocarbons in Western Port were conducted during the Westernport Bay Environmental Study. (Robinson 1975) detected low levels of hydrocarbons in sediments and mussels; no hydrocarbons were found in water samples, Robinson (1975) did not fully characterise the compounds, but analyses indicated they were in the CW C21 range, and were likely to be diesel products originating from boating and shipping activities corresponding to local usage. Smith and Burns (1979) found low level contamination in waters in the Lower North Arm. Highest values were found at Hastings (811g L-1 of diesel oil and degraded crude oil). Crude oil was present in all samples collected in the Lower North Arm. No petroleum products were found at the site at Balnarring.

Burns and Smith (1977) conducted an extensive investigation of hydrocarbons in sediments and biota and limited water samples. Results indicated iocalised contamination around areas of industrial, domestic and shipping activities (Hastings, Cribb Point, San Remo, Cowes and Corinella). Mussels collected from refinery influenced areas had high concentrations (600-120011g g-l dry weight) of petroleum hydrocarbons. A gradient of concentration was found with increasing distance from the source (Burns and Smith 1977, Fig. I). Sediment samples also indicated low level contamination in these areas. In addition, Burns and Smith (1977) conducted a qualitative comparison of mussel extracts by gas chromatography (Ge) and fluorescence spectra using standard oils. Mussels close to refinery outfalls showed GC patterns similar to lightly weathered crude oil. Mussels from boating sites had varying proportions of diesel oils and heavier lube oil.

There have been limited investigations of hydrocarbons in sediments in the vicinity of Long Island Point which indicate very low levels of hydrocarbons (less than 5 uglg wet weight) in the intertidal sediments (CEE 1993). ESSO Australia Ltd. is presently undertaking studies of petroleum hydrocarbons in the marine environment, and may include sediment samples from Western Port.

Hydrocarbon analysis and interpretation requires highly specialised laboratories and personnel (Burns and Smith 1977, 1978, 1982). Discrimination between hydrocarbons from sources such as natural waxes (eg. from seagrass leaves) or oils (natural seeps), fuel, lubrication and foreign crude oils; and the degree of weathering is necessary (Murray,pers comm.). Sampling and analytical methods used in the 1978 studies in Western Port are the same as those used by Australian Institute of Marine Science and they are considered to he accurate with a low limit of detection (Burns pers comm.).

41 Environment Protection Authority The Western Port Marine Environment

Sediment samples collected between 1990-1994 from the three penn anent Environment Protection Authority monitoring sites are presently being analysed for total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAH).

Biocides

A single investigation was conducted by Bryant et ai. (1975) on pesticide contamination in Western Port. Bryant et al. (1975) analysed a suite of organochlorine and organophosphate pesticides in waters, sediments and biota. Water samples were analysed from 74 locations around Western Port. Organochlorine pesticides were detected in four of the 74 water samples at very low concentrations. A sample from near The Inlets contained detectable levels of lindane, DOE, DDT and TOE.

Sediments were analysed from 38 locations around Western POrt. Organochlorine pesticides were detected in only one of the 38 sediment samples. A sample near Hastings contained detectable traces of dieldrin. A total of 23 fish, comprising 12 whiting and II mullet were also analysed. Organochlorines were found at very low, but detectable concentrations, in 16 of the 23 fish. DDE appeared to be the most prevalent organochlorine. The limits of detection for the analyses were similar to those for more recent studies in Port Phillip and Corio Bays (EPA 1992). Contamination of the samples does not appear to have occurred since most of the analyses of water samples were below the limits of detection. Hence, the data from the 1973174 surveys may be useful for future comparisons.

AVAILABILITY OF BACKGROUND CONTAMINANT CONCENTRATIONS IN WATER, SEDIMEl\l AND BIOTA

Projects undertaken during the Westernport Bay Enviro1!mental St~ (1973-1974) provided a variety of data on physico-chemical parameters and contaminants in waters, sediments and biota. The ability of data to provide background concentrations during this time is widely variable. Data collected by Robinson and Harris (1974) and Gibbs et at. (1976) adequately assessed-spatial and broad scale temporal changes in dissolved oxygen, temperature, salinity, pH, phosphorus and nitrogen over a sixteen month period in 1973-1974.

No large scale surveys of metals in ..vaters have been undertaken in Western Port Investigations during the Westernport Bay Environmental Study (1973-1 974) were localised or based on shoreline locations. EPA monitoring data are from three sites. Despite a low frequency of sampling there is very little variation in ambient seawater concentrations between 1984-1994. A larger scale spatial investigation is required to determine applicability of Environment Protection Authority data to Western Port as a whole. The survey should include metals such as copper, lead and zinc which have been documented in higher concentrations in sediments and biota near industty and input streams. Tributyltin should also be included in this category.

Background data for hydrocarbons in waters is mainly limited to the L~wer North Arm (Robinson 1974; Burns and Smith 1977, 1978, 1982). Additional sampling was conducted in other areas of Western Port but was generally limited to one or two samples per segment. Investigations are needed to detennine concentrations of organic herbicides near input streams and marinas, particularly as many of these compounds are being used as replacements for traditional metal-based antifouling agents.

The survey of metals in sediments undertaken by Statham (l977) provides a gocd source of background data for all of Western Port although samples are temporally limited. The investigation by Harris et al.

42 Environment Protection Authoril,y The Western Port Marine Environment

I 1 i provides additional background data. Investigations of sediment contamination with a reasonable J temporal and spatial sampling regime are limited to the Lower North Ann, Western Entrance and Rhyll i Segments (Burns and Smith 1977, 1978; Harris et alI979b). Data for the remainder of Western Port are limited to small scale specific investigations (MSE 1992).

EPA monitoring data are currently being assessed to determine if trends are apparent. The monitoring I program is based on regular monthly samples at all sites. The sampling frequency from 1984-1994 has been variable, with the total number of samples sometimes as low as four per year (Table 5.4). Sampling i frequency is also biased towards the months from October to March. As a result of the less than optimal -i sampling regime it may not be possible to adequately assess trends in the data. Sediment monitoring by EPA is currently insufficient to assess background concentrations and long term trends of metals and I hydrocarbons in Western Port due to the short term data-set and low frequency of site monitoring.

J Table 5.4 Annualfrequency o/monitoring at EPA water quality monitoring stations Number of monitoring surveys I Year Station 709 Station 716 Station 724 1984 8 8 9 1985 18 18 17 1986 9 9 8 1987 7 7 6 1988 4 4 4 1989 8 8 8 1990 10 \0 \0 1991 7 7 7 1992 7 7 7 1993 5 5 5 1994 6 I 6 6 i

CATCHMENT lNPUTS

Inputs from urban, rural, and industrial areas of the catchment are a major source of contaminants, nutrients and sediments to the marine environment. Since European settlement substantial modification has occurred to the catchment and this has significantly increased input loads to Western Port. The draining of the Koo-wee-rup swamps, straightening of water courses, removal of native vegetation and urbanisation has also increased the input of freshwater (Weeks 1982; Commissioner for the Environment 1988).

Inputs to the marine environment can be detrimental to water quality and biological communities. The marine environment is generally not adapted to large inputs of freshwater, sediment, nutrients and other contaminants. These inputs can adversely affect existing marine biological communities which may result in disruption of natural processes.

Western Port is an area of concern due to the highly modified nature of the catchment and the increasing pressure placed on all types of drainage systems through development of urban areas such as Cranbourne, Berwick and Pakenham.

43 Environment Protection Authority The Western Port Marine Environment

Physico-chemical monitoring

Long term programs

The majority of catchment monitoring input programs have measured physico-chemical indicators including river discharge (estimation of volume). Prior to theWestemporl Bay Environmental Study (1973-1974), monitoring was conducted by the State Rivers and Water Supply Commission (SRWSC). Data collected from 1907-1964 was for river discharge. The SRWSC began monitoring chemical indicators at the Koo-wee-rup swamp off-take in 1964.

In 1975, the Australian Water Resources Council began the Victorian Water Quality Monitoring Network to monitor water quality in inland streams throughout the state. Sites monitored in Western Port catchment generally sampled in situ parameters such as flow, turbidity, pH, temperature, dissolved oxygen, river discharge (Table 5.5). Several inputs were monitored for a range of nutrient parameters.

Between 1975 and 1993, 17 sites were monitored for various time periods in the Western Port catchment (Hunter and Zampatti J993a, b). Only three sites, two on the Lang Lang River and one on the Bass River have data from 1975176 to the present. By 1993, 13 of the 17 sites had been discontinued (Hunter and Zampatti 1993a). Current monitoring by Water EcoScience (formerly State Water Laboratory) under a state government services contract administered by Conservation and Natural Resources occurs at only four sites in the Western Port catchment (Bunyip River-two sites, Lang Lang River and Bass River).

Monitoring programs up to 1985 were summarised by CEE (19800, b) for the Dandenong Valley Authority (Figures 5.4-5,6). Monitoring was conducted by EPA, Rural Water Commission, Dandenong Valley Authority and Rusden State College. The majority of sites were located between Flinders and Yallock Creek. Minimal monitoring was conducted at the Lang Lang and Bass Rivers. Data collected by these programs were generally in situ with occasional nutrient and chemical analyses. Contaminants such as metals and organics were rarely monitored.

CEE (l986a, b) found that data were generally insufficient to accurately calculate loads for individual streams. This was due to insufficient concurrent flow and water quality measurements, and the short monitoring period. These comments are also applicable to monitoring programs for the last ten years.

CEE (I 986a, b) calculated generalised unit loads for the catchment using the available data (Table 5.7), and found that (with the exception of Kings Creek and North West Main Drain) loads were consistent within catchments, and of the same order as those for the Latrobe Valley and Port Phillip. Due to the infrequency of monitoring flows, the estimate accuracy was considered ±50%. He considered that more accurate load estimates could be calculated from a series of intense monitoring programs undertaken during (J) negligible flow, (2) base flow, and (3) flood flow. CBB also suggested that a hydrological study (and possibly hydrological model) would be an essential precursor to such investigations.

44 Environment Protection Authority The Western Port Marine Environment

Table 5.5 Input monitor·ing investigations in the Western Port catchment (Indicators measured I. Major ions mercury, boron, fluoride, sur/actants. 2. Sites on Bunyip and Lang Lang Rivers 3. Selected ions, iron, manganese, calcium, magnesium, sodium, potassium, sulfate)

Dale (1974) Fabris et al. EPA 1982 Vic. Water quality Stream Watch Dale and Pooley 1977 monitoring (1979) network' Temperature X X X X pH X X X X Flow X X X , River discharge X X Suspended solids X ! X X Volatile suspended . X solids , i i Colour X X Dissolved oxygen X X X , X Conductivity X ! X X X Total dissolved solids X BOD X X Turbidity X X X E. coli X X X Nutrients X X X Metals X X X Major ions X X" Biocides X Selected ions' X- Total organic carbon X· Total hardness X' Reactive silica X X-

Monitoring of other inputs in the catchment was undertaken by the Dandenong Valley Authority (now Melbourne Water). Currently 13 sites are monitored within the Western Port catchment Two monitoring programs sample input streams; these are the original ambient water quality monitoring network (set up by DVA) and the StreamWatch program. StreamWatch commenced in 1993 when Melbourne Water took over the task of sampling EPA metropolitan monitoring sites. Melbourne Water is not responsible for input streams to the south-east of Red Bluff Creek and therefore does not conduct any monitoring in this area.

Six sites are sampled every four weeks, while the remaining seven are sampled every three months. Analyses are conducted on general physico-chemical parameters as well as nutrients and the indicator of faecal contamination (E. coli) (Table 5.5). No sampling for heavy metals or organics is undertaken in the catchment. Results for the Stream Watch program for 1993/1994 indicate that general stream quality in the catchment was in a moderate to poor condition. All sample sites had elevated nitrogen, phosphorous and orthophosphate levels. Suspended solid concentrations were low, although stream turbidity measurements were high.

Limited biological monitoring is also undertaken in the catchment under the Stream Watch program. Two sites on the Lang Lang River are monitored for macro-invertebrates. Results indicate biological communities in the middle to upper reaches of the river are in good condition, while communities in the lower reaches are in a poor condition.

45 Environment Protection Authority The Western Port Marine Environment

The Environment Protection Authority has sampled a number of sites in the Bunyip catchment since December 1993. Monitoring measures general physico-chemical indicators and assesses macro invertebrate stream biota. Recent results indicate there has been a decrease in species numbers over the sampling period of two years. Almost all sites have nutrient levels which exceed EPA nutrient guidelines (EPA 1995) for the region. Cardinia Creek at Beaconsfield was the only site in the catchment to meet EPA nutrient guidelines and supported a healthy invertebrate community. The lower reaches of Cardinia Creek had a very low species richness and levels of nitrogen and phosphorous were 10 and 50 times above the nutrient guidelines for the area, respectively.

Intensive investigations

The first large scale investigation of input streams was conducted during the Westernport Bay Environmental Study (1973-1974). Dale (1974) sampled 17 streams entering Western Port (Figures 5.4-5.6). Inputs were sampled at either weekly, fortnightly or monthly intervals. Monitoring covered a wide range of parameters (Table 5.6); pesticides and metals were also analysed. Harris and Robinson (1974) also sampled the estuarine area of input sources during 1973 and 1974. This data was not included in their report and data was not analysed (Robinson and Cowdell pers comm.).

Flow data during the period of the investigation indicated that the largest inputs Bunyip, Lang Lang and Bass Rivers, contribute 70% of the total freshwater, phosphorus and nitrogen; and 60% of the sediment load to Western Port (Dale 1974). Re-examination of data published by Dale (1974) during this investigation indicates that inputs to the Upper North Arm (Bunyip and Lang Lang Rivers, Yallock, Cardinia, Deep, Toomuc, and Gumscrub Creeks, NWM Catch Drain and McDonalds Drain) contribute approximately 80-90% of the total suspended sediment, nitrogen and phosphorous load to Western Port. The northern part of Western Port has suffered the largest seagrass habitat loss and anecdotal evidence suggests it is higher in turbidity than elsewhere in Western Port

The input stream monitOling program initiated by Dale (1974) was reported by Dale and Pooley (1979) to be part of a five year monitoring program from 1973 to 1978. Monitoring data for 1974-1976 (Dale and Pooley 1979) indicates that a significantly lower frequency of monitoring was undertaken. Data from June 1976-1978 does not appear to have been published.

Dale and Pooley (1979) collated data for 1973-1976. However, minimal analyses of these data were conducted. A brief examination of data during this investigation suggests there was limited variation in parameters but the majority remained largely unchanged between 1973-1976. The most siguificant variation occurred to suspended solids concentration (and sediment load) at the Cardinia Creek site. 1 Dale (1974) reported a suspended solids concentration of 390 mg L· • Data from Dale and Pooley 1 (1979) indicates the concentration had decreased to 47 mg L- • Nutrients and other parameters also decreased during this time, but to a much lesser extent. Flow remained largely unchanged. The high concentration of suspended solids is possibly a result of the 1970-1973 construction of the Cardinia Dam wall.

The Environment Protection Authority conducted a monitoring program of inputs in the Western Port catchment during 1979-1981 (EPA 1982). This program sampled a wide range of indicators at 23 sites on a four weekly basis over the period of the investigation (Table 5.5). Sample sites were distributed on the western, northern and eastern areas of Western Port. The majority of sites were concentrated at the northern inputs associated with the Bunyip River, Yallock Creek and Cardinia. Creek.

The primary aim of the project was to monitor the compliance ofindicators with the objectives stated in the State Environment Protection Policy, The Waters of Western Port Bay and Catchment (1979).

46 Environment Protection Authority The Western Port Marine Environment

The majority of indicators measured were well within the objectives set for the SEPP. The program found that nutrients, particularly Kjeldahl nitrogen was elevated in inputs in the western area of Western Port. Elevated Kjeldahl nitrogen was thought to be from unsewered or incompletely sewered areas. Phosphorous concentrations at all sites (with one exception) were above the objective for ecosystem protection «O.05mg L'; ). Elevated concentrations were attributed to sewage problems.

Other indicators such as dissolved oxygen, pH, turbidity and E .. coli had a certain percentage of readings above the relative SEPP objectives. Higher turbidity and suspended solid measurements were found to be positively correlated with elevated nutrient concentrations(EPA 1982). The investigation also estimated daily loads of nutrients, suspended solids and metals. Calculations of loads had very high standard errors due to the low number of samples taken for indicators and stream flow and the load data is considered inaccurate.

Metals in input streams

Dale (1974) conducted the first survey of metals in input streams. Ten sites were sampled and waters were analysed for zinc, cadmium, lead and copper. Data presented were considered preliminary; indicative of concentrations in inputs rather than mean values. Values were probably an over estimation due to contamination during sampling and storage. Details of the sampling strategy were not provided, however it appears from Dale and Pooley (1979) that sampling occurred only once.

Fabris et at. (1977) sampled the three main inputs (Bunyip, Lang Lang and Bass Rivers) identified by Dale (1974). Samples were collected every three weeks from August 1976 to June 1977 (15 sampling periods). Metal concentrations for cadmium, copper, iron, lead, zinc, and magnesium in river water were determined. Results were generally characteristic of metal concentrations found in other Victorian streams (Fabris et ai. 1977). Estimates of annual metal fluxes were calculated by two different methods in an attempt to compensate for the sman number of samples collected per year over a varied flow regime. Calculations indicated the largest load contributor of copper, iron, lead and zinc to Western Port was the Bunyip River. This supports conclusions made by Fabris and Harris (I 974), Statham (1977) and Harris et al. (1 979b) that inputs to the north of Western Port were contributing to elevated concentrations of some metals in sediment and biota.

The input investigation conducted by EPA (1982) sampled metals (mercury, lead, zinc, chromium, cadmium, nickel) at all sites. The majority of data for mercury, lead, chromium (and some copper) were below the limit of detection. Concentrations of chromium and copper were higher in inputs located in the northern part ofthe catchment as had been found by previous authors (Dale 1974; Fabris et at. 1977; Dale and Pooley 1979). Concentrations were found to be lower than previous investigations. It is uncertain whether the data was a true representation of concentrations in water, particularly as suspended sediment concentrations in all inputs were high.

Biocides

Common pesticides (DDT, dieldrin, endrin, lindane, aldrin, DDE, HCB) were sampled fortnightly at Bass River, Lang Lang River, Bunyip River and YalJock Creek during the investigation (Dale 1974). The remaining inputs were sampled for pesticides on a monthly basis (Dale 1974). Mean pesticide concentrations for the majority of inputs were extremely low, close to or below detection limits. Lindane and dieldrin were the most commonly occurring pesticides. Dale and Pooley (1979) continued to monitor pesticides at a significantly reduced frequency during 1975~1976. Concentrations in waters

47 Environment Protection Authority The Western Pori Marine Environment

were similar to results previously reported by Dale (1974), which indicates that concentrations in stream remained unchanged over this period.

Sediment samples were collected from a number of inputs and analysed for pesticides. The only detectable compounds were endrin (5ng g.l) and dieldrin (4 ng g'!) in the Bunyip River. No further sediment analyses were conducted. The herbicides 2,4-D and 2,4,5-T were analysed on one occasion during 1974 in input streams. Neither compound was detected.

Biocide usage may still pose a problem particularly as there is increasing concern within the scientific community regarding the trend towards pesticides with oestrogen-mimicking compounds.

Industry

Industrial inputs have changed significantly during the past 20 years. The enforcement of EPA licenses on industrial premises has resulted in stricter controls regarding the discharge of pollutants to input streams and Western Port. Data from 1994 indicate that there were approximately 69 licensed premises in the Western Port catchment discharging sewage, waste water and contaminated stormwater to input streams (Table 5.6).

Table 5.6 EPA licensed discharges to Western Port catchment

Shire Total Total Sewage Sewage Wastewater Wastewater licences volume, licences voiume~ licences volume, m3/d m3{d m3{d Flinders 4 115 4 115 Hastings 20 38750 16 730 5 38000 chromiumanbourne 10 2740 10 2740 (part) Bass 6 17 2 12 1 5 Pakenham 20 5300 21 5245 6 55 Buln Buln 3 724 I 14 2 710 Korumburra 3 180 3 180 TOTAL 69 47885 58 8865 18 39020

Discharges from industrial sources may have an impact on input streams, particularly sewage plants which contribute to increased nutrient loads. Other impacts may be increased flows and sediment loads, increased Biochemical Oxygen Demand (BOD) and E. coli.

Western Port receives direct industrial discharges from BHP, ESSO and BP. BHP discharge wastewater contains anum ber of pollutants, including surfactants, phosphorus and sulfides. In the past BP discharged contaminated wastewater that potentially contained sulphides, phosphorus surfactants and phenol, but discharges were discontinued a number of years ago.

All discharges have improved in both quality and quantity (decrease) over the last decade through strict licence controls which encourage waste minimisation, water re-use and implementation of best achievable technologies, such as innovative cleaner production technologies. The amount of sewage discharged indirectly to Western Port has also decreased over the last decade through re-use and land application incentives. Discharged effluent quality has improved through the use of new technology and improved management.

48 Environment Protection Authority The Western Port Morine Environmellt

Table 5.7 Approximate unit loads from Western Port catchments Datafrom 1973 to 1985 (from CEE 1986)

: River or Creek Catchment Mean Loads (kg/d) : Unit Load kglha year"

Area lan' i , Nitrogen Phosphorus Solids Nitrogen Phosphorus Solids Bass 233 220 53 38000 3A 0.8 600 Lang Lang 303 500 31 21000 6.0 OA 250 Yallock 240 300 36 4400 4.6 0.5 70 Bunyip 697 370 66 26000 1.9 0.3 140 NWMDrain 60 160 6 630 9.7 OA 40 McDonald. III 50 S 2000 1.6 0.2 70 Deep 72 70 8 2300 3.5 0.4 120 Toomuc 67 36 3 3100 2.0 0.2 170 Gumscrub 33.5 54 3.5 1300 5.9 0.4 140 Cardinia 117 60 7 10000 1.9 0.2 310 Watsons 40 69 9 710 6.3 0.8 70 Kings 12.S 51 5 115 15 I.S 30 Warrigine 21 13 I 2S0 2.2 0.2 40 East 17.7 6 0.5 183 1.2 0.1 40 Stony 12.9 6 I 165 1.7 0.3 50 Other sites

LaTrobe 4786 2664 248 171000 2.0 0.19 360 Nicholson 530 35 1.3 l1S00 0.2 om 210

Agricultural POri Phillip 3.0 0.7 Bay Urban Runoff Port Phillip 14 0.8 : Bay

SUl\1MARY

Monitoring data suggest that water, sediment and biota in Western Port are not significantly contaminated by metals or organics. Concentrations above background levels have been found close to localised sources such as: areas of shippinglboating activity and close to rivers and creeks in the northern part of Western Port.

Nutrient concentrations are widely variable in Western Port and are strongly influenced by seasonal, tidal and eatchment inputs. Nutrient cycling in tbe Western Port marine environment is poorly understood. There is limited understanding of the roles played by seagrass, phytoplankton, salt marsh and mangrove communities in nutrient cycling within Western Port.

Water clarity data (Secchi depth) collected during the Westernport Bay Environmental Study were not reported; no turbidity measurements were undertaken. Turbidity data from 1984 to the present indieates tbat measurements of water clarity have increased since 1989 with a corresponding decrease in turbidity.

Inereased loads of freshwater, sediments, nutrients and contaminants from the catchment to Western Port pose a further stress on the marine environment. The increasing development of the urban areas such as Pakenham, Berwick and Cranboume are placing considerable stress on the catchment input

49 Environment Protedion Authority The Western Pori Marine Environment

streams and hence Western Port. Appropriate planning and control management strategies must be implemented to reduce storm water flows and loads, particularly in these developing areas.

The water quality of input streams to Western Port is degraded. In particular, high nutrient concentrations are found throughout the middle to lower reaches. Biological communities at the sites monitored are also degraded. Elevated concentrations of some metals (zinc, copper, lead) are found in input streams. Input loads from the catchment have contributed to elevated concentrations of some metals in sediment and biota in the Lower North Arm and Upper North Arm adjacent to input streams. Biocide loads entering from input streams during the 1970s were low. No data are available for current biocide concentrations in water and sediment.

50 '>j 0<;' ~ !.i :;. CONSULTING ENVlffONnEN1AL ENGlrlEEf.6 PlY LT(I '" '"~ " .... OVA - UESTERN~OAT ANALVSIS CATALOGUE OF DATA "O! 51Al10N SQUkt.:£ I-'E If!(JU ------NO OF REAU!NGS ------~ [q' NUMBER OF OATA O~ DATA PHVSII;AL CHEMICAL NUTRIWT SUllO'; FLOIJ ~ ==~=.~===:==~=~~=C~======E==C======~2======~ '" l~NGI,IARR/.,. ~ (RUII ~ O! ,70 EPA 7'3176 38 30 ~ 79/!l3 5 "5 5 , ~ § WArSON EPA 81/83 5 5 5 2 S· (R[tA" '" "". 6.5 kUSUEN !lO/6! 15 15 15 :.. Sl 6. , RUSDEN 60/61 15 15 15 " ~. 6.3 IlUSUEN bO/81 15 15 "So RUSDI::':N 80/81 15 15 "15 1"2671 EPA 73170 68 6<' .." S· 79n3 18 18 " 17 q 6" !jUS DEN bO/lll 15 "15 " I//!{(;S 672 EPA 79/8 ~ 13 " 10 "~ {R(( - " " '"(') EPA 79/83 15 15 14 '" WARRING/II[ 6" 13 EPA 73/76 -. (R{ll( ,. 2. § ." 79183 10 , , - \ •.. " " ~ , " I" RU~UI::N SO/Ill 15 15 15 U. " 1.2 fjU5UEN /lO/81 15 15 15 ~ " 67' EPA 73176 "6 81/83 "2 2 2 "2 , '"

CONSULTJNG £NVlkONMEN1AL £NGINEEHS PlY LiD ~ i OVA - VEST£kNPORT ANALV$JS CATALOGUE OF (lAtA -5 '0 30 3O• :,. '"~ RUSDEN '" .... 3.5 eDitH 15 15 I' So ;;;- S;" 659 E'A nl16 ,. ," N ~ 7'9/63 33 I' " 3J t? /1.7 4-1,U kU~{lEN Hu/SI 15 15 EPA 79/a3 3 "3 , v '" Pa~tI\I'I{ljO> • ... " .. 17 'OC 76/3~ 90 ::l'" e•• OVA 78/eiS ..13 0 13 13 I' , r .03 .,. 79/t13 , , , ;;;l 2.7 :iI.eu HU$O\i:N M/61 15 15 • '" EPA 13176 .." ,. "' S-., 7 , tlt-ti i'~/~3 •• 7 ,u ~ . te. 79/t}3 , I 0' ... I I I -., 2 •• RlJSOEN 81.111.11 "15 I' 15 ~ 6 7'3176 100 9 .....k.~ "A .. ., :;,. ~ . '!'! 19/8:3 24 r2'1ls .. , 1'5/8$ " " '" .2 \ 93 OVA 78/65 "I. 0 t. 16 I. ?l"" (;J f -., Noll Rwt data ~ .adhr tlou vabJu av;ulat>ie rllrtf'l "Vle!cr(an Sl.ltface Uatu' Information 1982" ,.~ ~ Vol I (rr,lll,r'i!I\lt: (l1"\\HH" 11 ea'\.~n'> :2'1·'28 0:;' -2l i'" !:;l rW.., CONSUl. TING ENVI flONnENl'AI. ENG IN££flS PTY l TO /l. OVA - uESTERNrORT ANAlYSIS CATALOGVE OF DATA ~'" '" STATiOO SOURCe f'ERlOl) ~~-~~-~---- NO OF READINGS ~-~-~-~~~-~ Nunsti. OF DATA OF IJA'JA PHVSICAL CHEMltAf.. NuHdENT SOL J rJ$ FLOW '" i~ §f ."' .. "'"''' ...... '''''''' ... .,.''''''''=''''''' ...... '''o:,..".'''''''~=c:"'''''~''''''.,,,'' ... ,. .. ,. .. '''"'''' .... " ... ,,.,~''''''<"=::~,,::= '" ~ ~ " .t ~ !! { '09 Rwe 60/81 21 S' C ." 61> EPA 8!/8:;1 " " " .. '" f{IJSOEN eo/al I> l5 ., :.. ..,~ RVSOEN 60/81 15 15 Si' " "s. ()q ~ kUC 621t$1 ''0 140 " :i' EPA 73116 1" 190 ~ 8J/83 ,I 51 '1 '"51 19 f • la"g lO",) 20• RW' 75161 71 16 16 ). n i;'" ~ ..p. \ '~"~ ) 65' EPA aQ/1;l3 60 60 60 .0 • C· .. '\ ~ )'- '.3 RtJSOEN 80/81 15 15 " ~ J' ,.. kUSOEN t\:0/81 15 ~ " " '"w to flUSOEN 80/1\\ 15 15 15 ~ f~ 5.' ~ W[5Tf«NPOl?f ,.. Jll)SUEN M/81 15 15 \ RU, " cl' ." q 231 75/85 30 '0 112 Oil ~ "'" " ...... '7 EPA ~2/83 • J 3 " '0 .' ~ ;.:J 51 EPA 7'3116 178 175 12' 19/33 3O <5" " " " " ~ ,,' flU$U!::N ~O/'&1 ..... r " " " ~ & 5 •• RUS/IEN 8014) 15 15 " :It ?i'" / Nol. Rue data ~ e.rlltr flov valQtl avallablt r~f.r: ~., ~ "Vielorial'l S.. rhct Vlttar !Mormalion 1982''' .,. VcT I Orainaje Olvl~ICn II Bailn~ 21-2b S' ~ '----' .... !:;l'" ~ ~ ~. ~" ~ Environment Protection Authority The Western Port Marine Environment

CHAPTER 6

PLANKTON COMMUNITIES

INTRODUCTION

Plankton are the very small plants (phytoplankton) and animals (zooplankton) which live most or all of their lives in the water column. The plankton are important components of the food web. The pattern of phytoplankton and zooplankton populations can reflect other environmental factors, including flushing patterns, water body origins and nutrient inputs. Phytoplankton may influence water quality if populations reach very high numbers, i.e. "bloom" proportions.

The earliest documented work on plankton in Western Port was undertaken by Macreadie (1972). Further investigations were undertaken during the 1973-74 Westernport Bay Environmental Study (Ministry for Conservation 1975). Phytoplankton and zooplankton populations were sampled for taxonomic composition, and chlorophyll-a was measured in the water column. Kimmerer and McKinnon (1985, 1987a, b, c) undertook plankton studies in Western Port between 1982 and 1984. The Environment Protection Authority has monitored chlorophyll in Western Port from 1984 to the present. These studies are reviewed below in terms of phytoplankton popUlations, chlorophyll concentration, primary production and zooplankton populations.

PHYTOPLANKTON

Phytoplankton populations

During the 1973 studies (Ministl)' for Conservation 1975), over 90 water samples were analysed from four locations in the Western Entrance and North Arm. Results are limited to a partial species Jist (mainly diatoms) with an estimate of relative abundance for the sampling period. There are no data on phytoplankton popUlations in Western Port since the 1973 investigations.

There have been no reports of algal blooms in Western Port. This may be due to a lack of investigations as has been the case in Port Phillip Bay. Toxic algal blooms in Port Phillip were only discovered when specialist phytoplankton taxonomists collected and anaiysed samples in the late 1980s.

Phytoplankton biomass

Chlorophyll is a pigment unique to the plant kingdom. Through the process of evolution a variety of pigments have formed to enhance the light harvesting capabilities of algae. Chlorophyll is now universally used to estimate phytoplankton abundance (biomass or standing stock) (Jeffrey and Hallegraf 1990). Water quality monitoring programs commonly measure chlorophyll-a since the pigraent is common to all microalgae.

54 Environment Protection Authority TIle Western Port Marine Environment----

Investigations measuring chlorophyll-a in Western Port are severely limited in both the scope and l quality of data. Robinson and Harris (1974) regularly analysed samples from 22 stations from January to October 1974. Limited results were presented graphically for three sites during the period of sampling. Sites were located in the Western Entrance, Rhyll and Corinella and Upper North Arm Segments.

I The Westernport Bay Environmental Study (1973-1974) (Ministry of Conservation 1975) quotes i concentrations of chlorophyll-a in the range of O.03-5.5J.Lg L- . No further details were provided. Bulthuis and Brand (1975) collected data in September 1974 from five sites (Table 6.1), however, no j detailed information was provided.

Table 6. J Chlorophyll-a measured in September j 974 (Bulthuis and Brand j 975)

Location North-west Nth Central Rbyll Corinella Stockyard Pt Station 713 717 720 722 744 ChI-a, IJ-gL-' 1.65 1.4 5.81 7.38 i 7.42

Chlorophyll-a data collected during the Westernport Bay Environmental Study (1973-1974) (Robinson and Harris 1974; Bulthuis and Brand 1975) was not well reported and generally lacking in sufficient detail to assess data and investigations. Gibbs et al. (1976) continued collecting a large range of physico-chemical data including chlorophyll-a from the sites sampled during the Westernport Bay Environmental Study (1973-1974) by Robinson and Harris (1974). No analysis of chlorophyll-a data was conducted by Gibbs et aI. (1976).

Bulthuis (1977) investigated biomass and productivity in Western Port phytoplankton from March 1974 to February 1975. Samples were collected on a monthly basis from all segments in Western Port. Specific sample sites and numbers of sites were not provided. Bulthuis (1977) tabulated data based on averages from each of the three segments (Table 6.2). A large number of samples were collected in the 1 three segments. Data was within the range of0.2-5.9J.!g L- • Bulthuis (l977) also considered that there was no significant temporal trends in chlorophyll-a. Values reported were higher in what he termed the Eastern Arm (Upper North Arm and Corinella Segment).

Table 6.2 Chlorophyll-a (J.!g rl) data collected by Bulthuis (1977)

Mean ehlorophyll-a Range (n) Western Entrance 1.2 ±O.ll 0.6-1.8 16

North Arm 1.3 ±O.O6 ! 0.2-3.9 85 East Arm 2.1 ±0.14 0.3-5.9 60

Harris and Vlasich (1976) monitored a range of marine water quality parameters in Bass Strait and the We stem Entrance to assess the impact of Boags Rocks outfall on nutrients and phytoplankton populations between December 1975 and September 1976 (further discussion is presented in Chapter 5). Harris and V1asich (1976) presented chloroplryll-a contours from Bass Strait into the Western Entrance of Western Port. Chlorophylla concentrations ranged from a minimmn of O.34tg L-1 between Flinders and Somers, to 1.25 and l.35J.Lg L-1 near Ventaor and Cat Bay. They considered that nutrients from Boags Rocks promoted some phytoplankton growth in Bass Strait hut none in Western Port.

55 Environment Protection Authority The Western Port Marine Environment

Kimmerer and McKinnon (1985, 1987a, b, c) collected surface samples from a single site at roughly twice monthly intervals during 1984, and presented these values as a mean for chlorophyH-a and other pigments for that period. Kimmerer and McKinnon (1985) collected samples from central stations in Western Port and Port Phillip Bay over four cruises in 1984 and found chlorophyll was significantly correlated with inverse Secchi depth in Western Port, but not Port Phillip Bay.

The Environment Protection Authority has monitored chlorophyll and phaeopigments since 1984 at three sites in Western Port (Figure 6.1 ).This is the only long term dats set for phytoplankton available for Western Port. Due to the program's design and sampling methods it is unlikely to detect the occurrence of bloom events or other short-term variation in phytoplankton biomass.

Data show seasonal fluctuations, with the Corinella site consistently higher than both Hastings and Barrallier Island. Since 1990 there have been a greater number of peaks above 5/-lgC' at Corinella than other sites, which is worthy of further investigation (Figure 6.1).

M ~ ~ ~ ! ~ I ii ~ ~ " DATE

Figwe 6.1 Chlorophyll-a concentrations (/-lgL'/) at EPAfr.ed sites (Data series from 1984-1994 Station number 709 Hastings; 716 Barraliier Island; 724 Corinella)

A preliminary comparison between EPA data, data from the Westernport Bay Environmental Study, (1973-1974), Gibbs et al. (1976) and reports from the 1980s indicate that chlorophyll-a levels are largely unchanged. However, as data from all investigations are limited, the comparison may be misleading. .

These investigations do not provide sufficient data for accurate estimates of chlorophyll-a due to the limited sampling frequency, number of sites, lack of analyses of other chlorophyIIs and phaeopigments. The majority of samples were based on surface water grab samples; thus the water column was not representatively sampled.

The majority of chlorophyll-a data (Harris and Robinson 1974; Gibbset al. 1976) collected between 1973 and 1978 has not been completely analysed. This program is the most extensive and intensively sampled monitoring program conducted in Western Port. Analysis of this dats set would provide substantial information on tidal, diurnal and seasonal fluctuations of chlorophyll-a and other indicators to which would assist definition of background concentrations for Western Port.

56 , Environment Protection Authority The Western Port Marine Environment 1 J I Phytoplankton productivity J Bulthuis (1976) investigated the impact of nutrient limitation on phytoplankton from Western Port waters. Western Port cultures were incubated for a ten day period with additions of nitrogen and/or phosphorus, or as a controL Bulthuis (1976) reported that the controls exhibited no increased I fluorescence, where as, in experimental cultures, significant additions of both nitrogen and phosphorus were required to increase ph)1oplankton growth. Conclusions made should be treated with caution as additional work was not undertaken and insuffieient details were provided for results, methods, quality control and replication. I Bulthuis (1977) measured phytoplankton productivity during May and June 1974 using anin situ d 4 method. Measurements were made at a variety of depths in the Western Entrance, North Arm and East Arm. Productivity was considered to be significantly lower than Port Phillip Bay in all areas of Western Port except the Western Entrance. Bulthuis (1977) considered that phytoplankton productivity was inhibited by both nitrogen and phosphorous limitation, rather than nitrogen limitation alone as has been documented in other marine systems. Bulthuis (1977) also reported that there was no significant variation in nitrogen and phosphorous in Western Port either spatially or temporally. Data were considered preliminary and conflicted with investigations by Robinson and Harris (1974).

ZOOPLA1~TON

The first study of zooplankton in Western Port was that of Macrcadie (1972). It was followed by those undertaken in 1973-74 for the Westernport Bay Environmental Study (1973-1974) (Arnott 1974, Ministry for Conservation 1975), and those undertaken by Kimmerer and McKinnon from the University of Melbourne in 1982-84 (Kirnmerer and McKinnon 1985, I 987a, b, c, 1989). The 1973-74 study focused on the Western Entrance and North Arm, whereas the 1982-4 studies sampled from stations throughout the bay.

The zooplankton community of Western Port is considerably less diverse than that of Port Phillip, and low by temperate bay standards elsewhere (Kimmerer and McKinnon 1985). The 1973-74 and 1982- 84 zooplankton data for the Western Entrance and North Ann of Western Port were generally similar; the resident zooplankton of Port Phillip Bay was more similar to that of Bass Strait than was that of Western Port (Kirnrnerer and McKinnon 1985).

The zooplankton in Western Port is dominated by Acartia Jancetti (McKinnon et al. 1992). It was recorded as Acania clausie in the 1973-1974 study, and as "medium sized" Acartia tranter! by Kimmerer and McKinnon (1985).A.Jancetti increases in abundance with distance into Western Port (Kimmerer and McKinnon I 987b). as does abundance of other bay-resident taxa such as Pseudodiaptomus comutus and Bestiola similis. Conversely, other species such as Paracalanus indicus. Calanus australis. OitOOna similis, ctenophores and larvaceans decrease in abundance (Kimrnerer and McKinnon 1985, 1987b). These zooplankton distributions were linked to differences in net popUlation growth rate and in behaviour of bay resident and Bass Strait taxa (Kimmerer and McKinnon 1987c). Visual predation by fish is probably the principal agent in the exclusion of Bass Strait residents from within Western Port (Kimmerer and McKinnon 1989).

There are no recent data to describe the present zooplankton populations or distribution in Western Port. It is impossible to determine ifthere have been any changes to the characteristics described in 1973-1974 and 1983-1984.

57 Environment Protection Authority The Westem Port Marine Environment

CHAPTER 7

SALTMARSH AND MANGROVE COMMUNITIES

INTRODUCTION

Saltmarsh and mangrove communities occupy the band of sheltered coastline from the level of highest tides down to just above the mid tide mark (mean sea level). The saltmarsh communities are characterised by a distinct zone of salt tolerant grasses and shrubs which occupy the area occasionally inundated during very high tides. Seaward of the mean high water level, mangrove communities dominate the intertidal mudflat zone to a level just above mean sea level. The band of saltmarsh and mangrove vegetation in northern Western Port provides a transition between the marine and terrestrial environment. The vegetation stabilises the fine sediments and protects them from erosion (Bird 1993). The saltmarsh and mangroves provide a particular habitat for plants and animals, and are considered to play an important role in nutrient cycling in Western Port (Clough and Attiwill 1975; Van def Valk and Attiwill 1983).

The aim of this chapter is to critically review relevant information on saltmarsh and mangrove communities in Western Port, particularly in relation to bay-wide and local scale environmental changes.

The co-existence of saltmarsh and mangrove communities in Western Port is particularly significant. On a global scale, mangroves tend to occupy tropical regions and salt-marshes occupy temperate regions. The co-existence of mangrove forests and floristically diverse and extensive salt-marshes in Western Port is one of the reasons these communities are so valuable and interesting.

Saltmarshes and mangroves are generally closely associated, although they occupy distinct zones (Figure 7.1 from Bird 1993). The available information on saltmarshes and mangroves in Western Port is reviewed in separate sections below.

dune WOOOd,"CI swamp scrub ...... salt marsh _ mangroves

MHT mudflats with Zostera

Figure 7.1 Generalisedpattern ofsaitmarsh and mangrove zones in Western Port (from Bird 1993)

58 Environment Protection Authority The Western Port Marine Environment 1 i j SALTMARSH COMMUNITIES

1 Saltmarsh communities in Western Port are the low, tussock and shrub communities which occupy the flat area between the Melaleuca fringe of the land (extreme high water mark) and the landward edge of the mangrove zone (spring high water mark). They occupied approximately 26,700 ha in 1974 (King' I and Kay 1980). The role of the saltmarsh in the advancement of land into the intertidal area and as a buffer between the mangroves and land has been discussed by Bird (1971, 1993).

The saltmarsh flora comprises a mixture of succulent shrubs and tussock grasses which are tolerant of high salt content in the soils. The saltmarshes in Western Port were mapped in detail by Bridgewater (1975) during the Westernport Bay Environmental Study (1973-1974). Little is known of the fauna associated with the saltmarshes in Western Port.

Saltmarsh communities are common in many temperate regions of the world. These communities display a remarkable floristic and structural similarity from country to country, primarily at the generic level (Bridgewater and Hughes 1974). Bridgewater and Hughes (1974) and Bridgewater (1975) considered saltmarsh communities of Western Port to variants of plant communities found elsewhere in the world. The dominant genera (Salicornia, Spartina, Sueada, Arthrocnemum, Juncus) are usually found in most areas of the world and possibly account for the uniformity in saltmarsh vegetation (Chapman 1977).

Opie et al.(1984) reviewed sites of botanical significance in Western Port. They considered that the saltmarsh communities were not as closely affiliated with the northern hemisphere systems as Bridgewater (1975) believed. Opie et al. (1984) considered that the life strategies, floristic composition, structure and life forms were significantly different in Western Port than elsewhere. Western Port saltmarshes were considered to be very significant in Australia by Opieet al. (1984) for a number of reasons. They are extensive and may extend for a kilometre or more inland from the shoreline. The community is floristically rich in comparison to other saltmarsh communities (Comer Inlet). A large portion is relatively undisturbed by industry and grazing and it also supports a very low weed problem. Opie et al.(l984) consider Western Port represents some of the most significant stands in south-eastern Australia; and are of national importance.

Bridgewater (1975) characterised the communities in terms of dominant plants and their occurrence across the saltmarsh area. Starting from the landward edge of the saltmarsh, the distribution of the community appears below (Table 7.1).

Table 7.1 Saltmarsh communities from Western Port. (Communities rangingfrom landward to seaward extent.) Melaleuca Schoenus-Cotula complex Stipa complex Juncus complex Puccinellia complex Suaeda complex Arthrocnemum complex Sarcocornia complex Spartina complex Avicennia

59 Environment Protection Authority The Western Port Marine Environment

Bridgewater (1975) provided some ecological analysis of saltmarsh communities, which examined spatial and dynamic relationships between species. Bridgewater (1975) considered areas of coast with greater numbers of plant communities to be more stable than areas of fewer communities.

Bridgewater (1975) divided Western Port into 11 regions of more or less equal size in order to assess the contributions of each community to the vegetation of Western Port. Of the 11 areas, the region from Hastings to the Inlets was found to contain the largest number of sub-communities (75-85%) during the investigation. These areas also contained populations of the "more restricted species".

Bridgewater (1975) detennined that grazing by cattle and rabbits was affecting the composition of the saltmarsh communities, particularly by reducing species diversity in the landwardSchoenus-Cotula sub-community. Bridgewater (1975) found that the introduced tussock grass Spartina was predominant in the saltmarsh community at the mouth of the Bass River and the Main Drain. It was also present in the Sarcocornia sub-communities elsewhere and appeared to be "invading" this sub community. Observations during University excursions (Ashtonpers comm.) indicate that Sparlina has increased in density and range in areas outside the mouths of the Bass River and Main Drain, but there have been no investigations to fonnally document the extent of the increase.

MANGROVE COMMUNITIES

Mangrove communities in Western Port comprise the plant and animal assemblages associated with the white mangrove Avicennia marina which grows from the high water mark to approximately mean sea level. Mangrove communities occupied approximately 12,100 ha of the intertidal zone in 1974 (Ministry for Conservation 1975). A. marina in Western Port is very close to the southern limit of its worldwide distribution, and the relatively large area occupied in Western Port is, therefore, of considerable worldwide botanical significance.

Investigations by Bird (1971, 1986), Bird and Barson (1975, 1982) concluded thatAvicennia marina pneumatophores promote accretion of sediment in such a way to promote a depositional terrace at the landward edge of the mangrove community. This terrace is subsequently colonised by the salt-marsh species. These conclusions are supported by observations of areas where mangroves have died or been cleared. The depositional terrace is lowered by current and wave scour and fOnTIS a steep slope. When mangroves regenerate or recolonise such an area the depositional terrace refonns. Bird (1993) supported these observations with experimental work examining accretion of sediment by simulation of pneumatophore networks.

Based on research on mangroves in tropical systems, Spenceley (1987) argued that it was unlikely that •....•.•.•• pneumatophores of Avicennia marina influence accretion of sediment in Western Port. Spenceley 1... (1987) was concerned that experimental data provided by Bird (1986) did not support his concept of sediment accretion by Western Port mangrove communities. Spenceley (1987) supported his claims by detailing research conducted in tropical regions where it bas been demonstrated that mangroves may promote sediment loss. However, he conceded that mangrove systems are widely variable and generalisations regarding their role in sediment loss or accretion may not be relevant in other geographic areas.

The flora and fauna associated with tropical and subtropical mangroves in other parts of Australia has been discussed in detail (Hutchings and Recber 1974; Clough and Attiwill 1982; Hutchings and Saenger 1987). Investigations of infaunal species associated with mangroves in the Sydney region found species were similar to those found in seagrass and other soft sediments.

60 Environment Protection Authority The Western Port Murine Environment

However, there is little infonnation on the flora and fauna associated with mangroves in Western Port. Davey and Woelkerling (1980) surveyed macroalgae associated with mangroves in Victoria including Western Port. There is very little infonnation available on the fauna directly associated with Western Port's mangroves. The general descriptions of invertebrate fauna of Western Port (Smith 1971; Smith et ai. 1975) provide species lists and good qualitative descriptions for most intertidal habitats in Western Port. Only six invertebrate species are described in association with mangrove pneumatophores.

Mangroves are considered to play an important role in nutrient cycling in Western Port (Attiwill and Clough 1974a, b; Van der Valk and Attiwill 1984 a, b). Boon and Cain (1988) compared nitrogen cycling in mangrove and saltmarsh soils from sites near Yaringa, and found that there was no consistent difference between nitrogen metabolism in mangrove or saltmarsh soils in Western Port. They indicated that soluble organic phosphorus may be limiting nitrogen metabolism in these soi Is in Western Port.

The primary productivity of mangroves in Western Port has been compared with mangroves in other regions (Attiwill and Clough 1974b; Clough and Attiwill 1982). Biomass production and turnover in mangroves are substantially lower in Western Port than the same species in warmer climates. Avicennia marina in Western Port produces propagules only every two to three years, in contrast to populations in wanner parts of Australia which reproduce annually (Clough and Attiwill 1982). Attiwill and Clough (1974b) considered these communities were under stress as the mangroves are close to their distributional limit.

The relatively low productivity and slow reproductive cycle ofAvicennia marina in Western Port indicate that studies need to be conducted over periods longer than three years to detect possible changes in productivity and reproductive cycles. It is likely that re-colonisation and establishment of mature mangrove communities in Western Port would be considerably slower than in warm enviromnents.

DISTRIBUTION OF MANGROVE AND SALTMARSH COMMUNITIES

SaImarsh communities in Western Port have been reduced by the deliberate or indirect infilling of sal1marshes for coastal development (eg. Hastings, Long Island, Yaringa and Blind Bight). Grazing has reduced the area of saltmarsh and mangroves in Western Port Further impacts by erosion of salt marshes had occurred by 1939 at Stony Point and the Inlets, and other areas that were used for boat access (Bird and Barson 1975; Bird 1993).

Early charts and maps of Western Port included the distribution of mangroves since they were a dominant and important coastline feature. Bird and Barson (1975) compared maps prepared by Smythe in 1842 with aerial photograph series taken from 1939 to 1975. They found that the distribution of mangroves in Western Port changed substantially between 1842 and 1939 (Figure 7.2a-c), with further changes described between 1939 and 1974. Bird (1986) mapped the distribution of mangroves in 1984 but did not appear to comment on any changes between the 1974 and 1984 distributions.

61 Environment Protection Authority The Western Port Marine Environment

Frenth I$hsnd

Phillij) 1$land

Figure 7.2a Mangrove distribution in Western Port in 1842 (Bird and Barson 1975)

•

WoMiIOtOO fRllIliE _aAT1~UImII ••••• , UAfIl'llll

1 J .. HIIW i Ult ~R; ~~~_Pl.

Phillip 1s.land

•-

Figure 7.2b Mangrove distribution in Western Port 1939 (Bird and Barson 1975)

62 Environment Protection Authority The Western Port Marine Environment

Figure 7.2c Mangrove distribution in Western Port 1984 (Bird and Barson 1975)

Most of the changes to communities have been a reduction in their continuity around the coastline of Western Port and in the extent of the mangrove community between the landward and seaward extent. This has been caused by clearing for coastal access and drainage channels, and smothering of root systems by deposition ·::Jf sand from increased erosion in the catchment Other causes include harvesting of mangroves for barilla ash in the I 840s and episodes of die-back (Bird 1985).

Sand deposition and erosion of the backing sandstone cliffs, together with clearing in the 1800s has substantially reduced the density and extent of mangroves on the north eastern side of Western Port from Red Bluff to Stockyard Point (Bird ·1993). Accumulation of sand from catchment runoff appears to have altered the characteristics of this part of Western Port which was previously fme muds. Photographs near Lang Lang show a few individual mangroves remaining on the now sandy flats (Ridgeway 1995).

There has been no broad scale investigation or mapping of the extent or composition of saltmarsh and mangrove communities in Western Port since investigations were conducted during the Westernport Bay Environmental Study (1973-1974). The most recent data on saltmarsh and mangrove communities are based on aerial photographs taken in 1984. The distribution of these communities was mapped by the Victorian Institute of Marine Sciences (VIMS) for their Oil Spill, Geographic Infonnation System (GIS).

The total area covered by these communlues calculated by the GIS is saltmarsh 31,000ha and mangrove 13,700ha. These figures suggest an increase in distribution of both since 1974 (saltmarsh 26,700ha; mangrove 12,lOOha (Ministry for Conservation 1975; King and Kay 1980». The VIMS data are thought to he accurate to ±10%. The accuracy is not greater as only a few ground surveys were conducted to quantifY data in the photographs. Finer detail was not required for the GIS as area of these communities is not one of the parameters used for oil spill information (Ballpers comm.).

63 Environment Protection Authority The Western Port Marine Environment ----~------~~------

However, data does indicate that there was no reduction in the distribution of the communities during 1974-1984.

The most recent set of aerial photographs were commissioned by EPA in 1994 to map seagrass distribution. These photographs may be suitable to plot present distribution of saltmarsh and mangroves eommunities. To accurately determine saltmarsh distribution intensive ground surveys would be required to determine cover of saltmarsh communities due to their floristic diversity. Mangrove distribution would be substantially easier as mangrove stands in Western Port are monotypic.

64 r

,I En.ironment Protection Authority The Western Port Marine Environment \ 1 CHAPTERS I SEAGRASS COMMUNITIES ~ INTRODUCTION Seagrasses are a group of vascular, flowering plants which live in the marine environment. They may form dense meadows or beds, and provide habitat for a wide range of other plants (algae), and animals ) including fish, crustaceans, molluscs and other invertebrates. Seagrass meadows also provide feeding habitats for birds including swans which feed directly on the seagrass, and cormorants which feed on the fish among tbe seagrasses. There has been major concern over the loss of substantial areas of intertidal seagrasses (both Zostera muelleri and Heterozostera tasmanica) in the north and east of Western Port since 1974. In addition, there is some question about the potential effects of the loss on fisheries and water quality throughout Western Port.

SEAGRASS DISTRIBUTION

The distribution of seagrasses and other macrophytes was initially described during the 1973-74 Westernport Bay Environmental Study (Ministry for Conservation 1975). A series of detailed, I: 15,000 maps were drawn from aerial photographs and ground surveys undertaken by NSR Pty Ltd in 1973 and 1974. The maps show the composition and relative density ofmacrophyte assemblages and were compiled in a report (NSR I974a) to the Westernport Bay Environmental Study (1973-1974).

The surveys of selected areas (Figure 8.1) (NSR 1974a) demonstrated that the macrophyte assemblages were diverse. These ranged from extensive, dense beds of the oceanic, subtidal seagrass Amphibolis antarctica in the west of the Western Entrance, to intertidal meadows comprising mosaics of the seagrasses Heterozostera tasmanica and Zostera muelleri and the algae Caulerpa and Sargassum in the northern and eastern parts of Western Port. The red algaeGracilaria was recorded on sandy silt on the fluvial fans in the northern parts of Western Port. Other areas comprised a mixture of algae, while the seagrass H. tasmanica and algae were also found subtidally in the channels.

NSR (1974a) cautioned that interpretations were difficult at times, and claim they had used their best judgement to identify and plot the distribution of all the vegetation assemblages of Western Port. Interpretation of vegetation is difficult as differences in the appearance of communities can be due to variation in reflection of sunlight at different times of the day, tide, or surface roughness. In addition, the contrast and colour of printing runs can vary substantially.

Examination of the original 1:15,000 map series (CEE 1995) and comparison with photographs taken at the time (Miles 1974, 1976) indicates that some of the interpretations of vegetation assemblages from aerial photographs may not have been accurate. For example, ground level photographs by Miles indicate dense meadows of seagrass along the edges of channels at the tidal divide, whereas the NSR study interpreted the area as being predominantly Cau/erpa spp. from the aerial photographs.

65 Environment Protection Authority The Western Port Marine Environment ~~~~~~~~~------~~~~~

o 5 3

Kilometres

: 2

)( • FRENCH ISLAND

PHILLIP ISLAND

• SURVEY SIT£S ...,.. ... )( 810MASS SAMPLING liTES --

Figure 8.1 Sampling locations jor vegetation mapping in Western Port in 1973 (NSR 1974a)

Observations along the Bass Strait coast of Western Port since 1974 (eEE 1995), indicate the areas of vegetation identified as Amphibolis antarctica along the south coast of Phillip Island and west of Flinders in the NSR maps were predominantly kelps and reefs-associated algae with small beds otA. antarctica. This illustrates the difficulty in interpreting detail of marine vegetation types from aerial photography, without adequate ground surveys to confirm vegetation composition or biomass.

It is probably reasonable to conclude that much of the vegetated areas mapped as seagrass by NSR (1974a) contained a proportion of algae, and that some of the areas of algae (such as the area of CauZerpa spp. on the tidal divide) contained a proportion of seagrass. The NSR (l974a) ground surveys provide some information on species composition and biomass at specific, although limited, locations in Western Port.

66 Environment Protection Authority The Western Port Marine Environment

r::::IIIl ~Zosta"& __1!O_Grwo:l_

~ =-~":,::':;.-:::: __ Itf,_MOlI~··

Figure 8.2 Seagrass and macrophytic algae distribution in Western Port in 1974 from the Westernport Bay Environmental Study (.iWinistry for Conservation 1975)

NSR (I974a) prepared a series of II maps detailing a total of 15 macrophyte assemblages. The final report of the Westernporl Bay Environmental Study (Ministry for Conservation 1975), consolidated the maps by NSR (1974a) into a single, 1:250,000 (approx) map of Western Port detailing only four macrophyte assemblages. The map legend (p358, Ministry for Conservation 1975) had mistakenly transposed the shading key for the distribution ofAmphibolis antarctica and Caulerpa spp. This was corrected by CEE (1995) and is presented in Figure 8.2.

Bulthuis (1976) reported that seagrass maps prepared by NSR (1974a) correctly indicate the distribution of dominant species, but did not provide reliable data for species composition or density. Bulthuis (1976, 1981b, 1982) surveyed seagrass in Western Port during December 1974 and subsequently redefined the areas of dominant species presented by the Westernport Bay Environmental Study to provide a better representation of seagrass and macroalgal distribution (Figure 8.3). This map is considered more accurate due to the greater number of field surveys and a more seientifically rigorous approach. He also quantified the areas of Western Port dominated by the various macrophytes and estimated the summer standing crop. He concluded thatHeterozostera tasmanica was the most important macro-benthic plant in Western Port, covered the greatest area and had the highest standing crop, and that Zostera muelleri generally occurred in the higher intertidal zone. NSR (1974a) comments on northern Western Port considered that in spite of the large area of this zone, the total biomass of seagrass was low due to the large unvegetated areas. In contrast, Bulthuis (1982) found that the largest area of seagrass (H tasmanica) and macroalgae were in the northern section of Western Port.

67 Environment Protection Authority The Western Port Marine Environment

Upper North

Amphibolis anton:tic.a Mm~~~~~H1~UQ~~*~~~\

i~~~~;n Heterllzostero tasmnnica

Zostero muelleri

iIililll CautOl'pn eneloides (orinellll other algae French Islard o l

Figure 8.3 Seagrass and macrophytic algae distribution in Western Port in 1974, based on surveys by Bulthuis in 1974 (Bulthuis 1982)

Subsequently, Bulthuis (l98Ia) carried out a detailed study of variation in seagrass standing crop and growth characteristics from March 1978 to May 1979, and compared three sites in Western Port with one site in Port Phillip. The study showed considerable seasonal variation in standing crop (Table 8.1); with maximum standing crop, leaf growth and productivity in spring and summer, and noted that leaf productivity was considerable even during the winter months (Bulthuis 1981 a).

The original distribution maps have been simplified and modified (eg. WPCCG 1983; WRPCC 1992) so that all of the macrophyte assemblages mapped in 1974 were grouped as "seagrass". This grouping includes areas outside Western Port which are now kelps (Figure 8.4), and they were probably kelps in J 974 however, this is impossible to confirm.

An unusual feature of the intertidal seagrass beds in the north of Western Port is the predominance of the normally subtidal Heterozostera tasmanica. The seagrass H. tasmanica is generally considered to be a subtidal species (Robertson 1984), while Zostera muelleri is considered to be found intertidally (Womersley 1984). In Western Port, Z muelleri was generally found on the higher parts of the mudflats, while H tasmanica occupied the lower areas along the channels or areas of the mudflats where water tends to pool at low tide (NSR 1974a; Bulthuis and Woelkerling 1983). It has been suggested (Stephens 1995) that the high density of intertidal H tasmanica in Western POIt was sufficient to retain large amounts of seawater at low tide, thus minimising desiccation. This process has been shown to occur in seagrass beds in Florida (powell and Schaffner 1991), allowing the seagrass to occupy a zone it could not usually tolerate.

68 Environment Protection AuthoTity The Western Pori Marine EnviTonment

SEAGRASS COVERAGE 1983 SEftGBASSlOSS1913-193a

DENUDED 'RI.O RTO 1973

Figure 8.4 Seagrass coverage in Western Portfrom Western Port Bay Strategy (WRPCC 1992)

Table 8.1 Monthly standing crop estimate jor Heterozostera tasmanica in Western Port and Port Phillip 2 1978-1979 (from Bulthuis 198Jaj Mean (dry weight rri ) ±.s.e.; n= 10, na. = not available

Month Leaf Stem Total above ground Charing Spit San Edwards Chllring Spit San EdWllfds ChIlling Spit San Edwards Cross Point Remo Point Cross Point Remo Point Cross Point Remo Point Mareh 85±12 54 ±7 31 flO 81 ±27 133 ±l6 105 ±IS 49±3S 80 ill 218 ±26 158 ±20 83±52 161 ±49 April S8±S 69±l1 49f5 139±9 121 ±17 69±I2 56±6 147fI5 209±24 138 ±22 JOSflO 286 ±23 May 79f7 54 flO 43±4 87 ±IS 107 flO 59f12 SS±9 87 ±24 186 tiS 113±21 99 tl3 174 ±38 lune 67 ±6 63±9 48±4 80±5 90±9 S9±9 46±4 36'±3 157±14 122±19 94f7 116f7 July 6S±1I 63±l 32 ±5 n.a SOflS 63±5 31 ±S n.a. 145 ±2S 126f7 63f13 n.a. August 73 ±9 41 ±6 28±6 120 ±13 76fl4 30±6 29f7 39±6 148 ±22 71 HZ 56fl3 159 ±IS September n±8 114 ±12 33±6 128 ±17 103 fl9 77±9 26±6 48±9 196±27 191 ±2Q 59±11 176 ±2S October 61fl4 114 ±7 58 f7 100±9 47 flO· 77 ±8 45±S 44±5 107 ill 191 f14 103 ±13 144 ±14 November 103±8 120f8 105 fll 94±11 94±13 70f6 79f13 44±6 197 ±20 190 fl4 184 ±24 138 ±17 December 1I6fl6 96±6 nflO S8±9 94fl4 66±6 71 ±12 33±; 209:1:29 162 ±ll 143 ±21 121 ±13 lanuary 96±IO 173 ±1I S7 ±9 59fl2 75fl0 113 ±13 139±7 39±7 171±18 279 ±21 226 ±25 99f19 February 83 ±13 J3U±12 55 ±7 89 flO 89±16 III ±II 103 ±16 52±6 172 :1:29 241 :1:22 157 ±22 141 ±15 March 8O±12 72±1l 28±4 IQ3 ±14 109 ±16 85±15 50±6 74±9 189±26 157f8 7Sfl0 177 :1:20 April 84±9 44±1l 27±4 121 ±14 111 ±13 SOf7 36±7 SO±IO 195 ±20 94±16 63±11 200 ±24 May 79±10 39±7 47±1O 63 ±12 85±J3 43±5 53 ±IO 42±11 163 ill 82±12 102 :1:20 105 ±22

Clough and Attiwill (1980) estimated the primary productivity of seagrasses in Western Port on the basis of Zostera muelleri productivity and generalised total cover estimates from 1975. They 69 Environment Proteetion Authority The Western Port Marine Environment

concluded that Western Port was a highly productive ecosystem. This is supported by studies of secondary productivity in the seagrass meadows of Western Port, indicating that the seagrass biomass areas of Western Port are amongst the most productive eelgrass systems studied in the world (Watson et al. 1984).

DECLINE OF SEAGRASS

The report of the Westernport Bay Environmental Study (Ministry for Conservation 1975) indicated that seagrasses are of major ecological significance and need to be conserved and protected. It was recommended that steps be taken to minimise the potential for mechanical damage to the seagrass beds by boats which would result in subsequent erosion of the mudflats. However, the report of seagrass die-off noted by NSR (1974a) was not considered to be a serious concern and no further action was taken at that time.

The NSR (l974a) report contains many interesting observations on the seabed, water quality and vegetation in Western Port which, at the time, was considered nonnal for Western Port:

Major constraints were ... and turbidity at high tide which reduced visibility in some places to less than 10 cm, so that even spot dives did not produce much infonnation.

Greatest difficulty was found in mapping the seagrasses in the northern section of Western Port as the water is usually turbid and seagrass is generally sparse and can be confused with large patches of detritus lying on the mud flats.

(Yaringa to Lang Lang River) The quantities of seagrass appeared to decrease on the mud banks with increasing distance from the main tidal channels. Channels were found to be bordered by patches of Heterozostera and Caulerpa with the rest of the mudflat unvegetated or littered with detritus from lignified stems ofHeterozostera. It is possible that the quiet water and high turbidity prevalent in the area contribute to a situation unfavourable to benthic macrophytes on the mudflats ....Die-back reported in the area may prove to be attributable to the marginal nature of this habitat

During the winter surveyseagrass was found to be sparse or absent from these mudflats with seagrass (usually Heterozostera) occurring in quantity only on the edge of tidal channels in patchy bands, where greater tidal velocity could be expected

It is apparent that die-back of seagrass in the north of Western Port had been reported during or just prior to the surveys conducted during the Westernport Bay Environmental Study in 1973-74. NSR (1974a) considered that turbidity, and hence light reduction was a factor limiting the growth of the seagrass in the marginal habitats. At that stage the decline was reported as secondary infonnation of little interest.

Some of the damage to seagrass was attributed to boats being dragged across the edges of the banks (Kirkman 1974, Miles 1974). In the introduction to his reportHeaith of Seagrass in Westernport Bay Kirkman (1974) noted, workers from casual observations, in Westernport Bay indicated that the seagrasses may have been dying back in places. He examined seagrasses for disease, particularly, leaf spots or streaks, leaf fragmentations or weaknesses; no evidence of disease was found on. the basis of these examinations. Kirkman (1974) concluded that the damage to the seagrass banks that he observed was due to boats, or swans feeding on seagrasses, and concluded that all damage was of minor significance and localised.

70 Environment Protection Authority The Western Port Marine Environment

There were substantial and dense meadows of seagrass remaining in the north' and east parts of Western Port during 1975. Photographs taken from the air and ground level of the tidal watershed (Miles 1976a, b) show that, seagrass beds appeared healthy and dense and were elevated above the drainage channels at low tide (Plate 46 in Miles 1976a), Examination of other plates in Miles (plates 65, 67; Miles 1976a) also indicated that in some areas there was a clear demarcation betv.'een vegetated and unvegetated intertidal flats and, in some areas cover appeared to be patchy.

Examination of aerial photographs from 1976 (Miles I 976a) and 1978 (Marsdenet ai, 1979), showed that the denudation in the region appeared to be extending from the Bunyip River area (CEE 1995). Denudation appeared to proceed along individual tidal channcls. The photographs show that while one sub-catchment was denuded, adjacent sub-catchments were vegetated, while another was partially denuded along the edges of the dendritic drainage channel. Miles (1976a, b) described slumping and erosion along the vegetated dendritic channels at the tidal divide.

The issue of seagrass loss began to gain momentum in the late 1970's after sedimentological investigations in the northern part of Western Port found seagrass remains from 2 cm to 10 cm below the surface of a 25km2 to 39km2 area of "bare" mudflat (Donaldson and Marsden 1977), It appeared that this area was covered by sediments from rivers which drained the northern catchment (as discussed below). By the late mid-1970s, the issue of seagrass loss had become a concern to Marsden and co-workers (Sargeant 1977; Wilk et aI. 1979) who were investigating sediments and sediment inputs. Marsden undertook aerial photography at low tides in 1978 using conventional colour and colour infra-red film which dramatically illustrated the extent and pattern of decline of the intertidal seagrass beds (Marsden et al. 1979, Harris et al. 1979a). The photographs clearly showed decline in seagrass distribution along the dendritic channels in the north of Western Port compared with earlier photography, and the demarcation line between denuded and vegetated areas.

Although the importance of seagrass in stabilising the mudflats and maintaining water quality was documented earlier (Brand and Bulthuis 1977), most research directly addressing seagrass decline does not appear to have commenced until the early 1980s (Bulthuis 1981a; Dale 1981; Lyttle 1981; Ministry for Conservation 1982; WPCCG 1983; Bulthuis et aZ. 1984a, b). Historical aerial photographs were used by many of these studies to determine the sequence of seagrass decline. However, care should be taken when interpreting the identity of intertidal macrophyte vegetation from aerial photographs without adequate field checking. For example, Stephens (1995) observed an algal epiphyte on Heterozoste:ra tasmanica at Middle Spit which gave the beds a brown appearance. The brown appearance could have been interpreted as reduced seagrass density from aerial photography. Comparisons between unrectified aerial photographs may not give a true indication of changes. The use of infra-red photography may help to reduce (but not necessarily eliminate) these sources of ambiguity.

There have been anecdotal reports of loss and regrowth of seagrass in Western Port in the 1920s (\VPCCG 1983a), but not on the scale or persistence that occurred from the early 1970s to 1994. The WPCCG (1983a) prepared a table of historic changes in seagrass distribution and fish catches in Western Port. The table was prepared from anecdotal reports and memories of events as far back at the 1920s (Table 8.2). The information was compiled with the benefit of hindsight in a meeting on seagrass die-hack. In spite of inherent limitations on interpretation due to its anecdotal nature, the infonnation appears to be the only consolidated account ofthe distribution and variation seagrass and fish catches over time.

71 Environment Protection Authority The Western Port Marine Environment

Table 8.2 Summary oflocal information on seagrass loss and related events (from WPCCG 1983)

Change Area . Date Source* Fish prolific All areas Prior to 1920's Kevin Hamilton Seagrass die-back Grantville to 1920's Kevin Hamilton Corinella Fish prolific Lang Lang 1934 Bruce Ridgway Seagrass prolific Lang Lang 1948 - 1952 Bruce Ridgway Fish prolific Lang Lang 1948 - 1952 Bruce Ridgway Seagrass die-hack Pelican Island to 1950's and 1960's Kevin Hamilton Rhyll Oyster die-back The Gurdies 1952 Kevin Hamilton Seagrass die-back Lang Lang 1965 - 1966 Bruce Ridgway Seagrass die-back Lang Lang 1967 - 1968 Kevin Hamilton Seagrass die-back Grantville to 1968 Kevin Hamilton Corinella I Seagrass die-back Rhyll to 1971 - 1972 Jim West

! Newhaven John Jansson Seagrass die-back Tortoise Head Area 1976 - 1978 Jim West (Kings and Gardiners Channel) Seagrass die-back Mudbank areas, 1976 Kevin Hamilton south coast of French : Is. (Prison fann area) * The sources were members of the Western Port Catchment Coordmatlon Group - 1983.

From re-examination of the 1973/74 set of photographs (CEE 1995), and aerial photographs taken in 1939, 1967 and 1970 it appears that the macrophyte coverage was greatest in 1970. With the benefit of hind sight it is apparent that, seagrass was receding along the edges of the dendritic channels of the flats on the south and east sides of French Island, and on the north of Phillip Island by 1973/74.

Bulthuis et al. (I 984a) estimated the decline in area of intertidal seagrass beds in Western Port from 1974 and 1984 (Table 8.3). The total area of seagrass beds in Western Port had declined from 250km2 in 1974 to 72km2 in 1984. The total reduction of 178km2 included some reduction in the area of Amphibolis antarctica (subtidal) in the Western Entrance.

Table 8.3 Area ofseagrassesfor 1974 and 1984 (from Bulihuiset al.1984a)

Estimated area dominated by seagrasses and macro-algae, km Segments I Heterozostera Zostera Amphibolis Macro-algae Total . 73n4 83/84 73n4 83/84 73n4 83/84 73n4 83/84 73n4 83/84 Lower North 20.4 3 9.6 15 4.5 I 34.5 19 Upper North 61.6 16 16.2 5 2.8

72 Environment Protection Authority The Western Port Marine Environment

Table 8.4 shows that the mean biomass of seagrass per square metre in the areas where intertidal vegetation remained had decreased at most locations. Exceptions included a substantial increase in the unit biomass of Zostera muelleri in the CorineJla Segment, and a slight increase in the mean unit biomass of Amphibolis antarctica in the Western Entrance.

Table 8.4 Above ground biomass oj seagrasses 1975 and 1984 g/m2 dry weight (from Bulthuis et al. 1984a)

Segments Heterozostera Zostera Amphiholis January January ~,~ January January % change January January % change 1975 1984 change 1975 1984 1975 1984 Lower North 213 76 ·64% 76 40 -47%, Upper North 291 37 -87% 68 32 -53%1 CorineJla 83 26 ·70% 17 45 +165% Rhyll 171 18 -67% 150 14 ·91% Western Entrance 711 753 +6%

Approximately 70 % of the area in Western Port that was covered by sea grass in 1973 is now (1984) bare and denuded of seagrasses. Seagrass biomass has been reduced by about 85% from 1975 to 1984. Bulthuis et al. (1984a) concluded:

Almost all of the seagrass has disappeared from the Corinella Segment, with major losses in the Upper North Arm and Rhyll Segment. Fewer seagrasses have been lost from the lower North Arm Exclusive of the Corinella Segment most of the seagrass has been lost from the intertidal areas while most of the subtidal beds are surviving Within an intertidal mudbank the seagrasses appear to die from the edge towards the centre Surviving intertidal seagrasses are located mainly in undrained pools ... At present intertidal seagrasses are dying because of exposure of the leaves to the air and a covering of fine mud on the leaves

The conclusion (Bulthuis et al. 1984a) that seagrasses appear to die from the edge towards the centre, and that surviving intertidal seagrasses are located mainly in undrained pools is supported by aerial photographs, particularly the infra-red series taken by Marsden in 1977. While Bulthuiset al. (1984a) considered that fewer seagrasses were lost from the lower North Arm, CEE (1995) note that the area of intertidal Heterozostera tasmanica decreased by approximately 20km2 in 1973174 to only 3km2 in 1983/84, while area of Zostera muelleri increased from approximately 10knl in 1973174 to 15km" in 1983/84 (Table 8.3).

There was no further investigation of the decline or distribution of seagrasses in Western Port until 1994 when the Environment Protection Authority commissioned an aerial photographic survey of Western Port. The survey was specifically undertaken to provide information on the extent of seagrasses in Western Port, and provides the basis for mapping the distribution of seagrass in Western Port (Stephens 1995).

A comparison of the aerial photographs taken in 1994 with those taken in 1984 shows that intertidal seagrass is beginning to re-establish in parts of Western Port which were denuded between 1974 and 1984, notably the Upper North Ann. The Corinella Segment and the tidal divide do not appear to have recovered. 'While the aerial photographs indicate the extent of the recovery, the biomass and composition of the vegetation cannot be calculated from the photographs alone.

73 ~----~.~------~

Environment Protection Authority The Western Port Marine Environment

Preliminary results from Stephens (1995) indicates that the density of the recovered seagrass areas is still low, and that some areas formerly occupied by Heterozostera tasmanica have been replaced by Zostera muelleri. The estimate of intertidal seagrass cover in Western Port for May 1994 was 93km2 (Stephens 1995).

While the intertidal seagrass beds in the north, east and south east of Western Port declined drastically between 1974 and 1984, the subtidal seagrasses appear to have been less affected. Bulthuis et al. (1984) noted that the subtidal beds of Heterozostera tasmanica appeared to be surviving along the channels. Monitoring undertaken by Marine Science and Ecology (MSE 1990) at BHP-Lysaght showed that subtidal meadows of H. tasmanica persisted from 1972 to the present. The monitoring at BHP Lysaght includes measurement of the standing crop (above ground biomass) of subtidal seagrass H. tasmanica and the green alga Caulerpa caetoides at least annually. The standing crop measured from 1972 to 1989 is depicted in Figure 8.5.

Figure 8.5 shows that there may have been a slight reduction in biomass from 1975 to 1981 and possibly 1985, although statistical analysis of the raw data would be required to assess whether this apparent trend is significant. Caulerpa cactoides biomass at the monitoring sites also appears to have reduced from late 1975, with total absence at one of the sites from 1981 to 1988. Hence, there may have been a reduction in the biomass of the subtidal seagrasses and algae which persisted in the Lower North Arm of Western Port between 1975 (or earlier) and 1985 when intertidal seagrass loss was most rapid in the Upper North, Corinella and RbyU Arms (Shepherd et al. 1989).

2 In summary, the area of seagrass cover in Western Port is currently around 280km . It has been • 2 assumed by CEE (1995) that the coverage was about 250km when aerial photographs were taken of Western Port for the first time in 1939. The cover inferred from aerial photographs taken between 1939 and 1970 appeared to vary around 250km2 until the early I 970s when a period of major decline commenced. In 1984, intertidal and subtidal seagrass was estimated to cover only 72km2 of Western Port (Bulthuis et al. 1984a). Aerial photographs taken in 1994 show that intertidal seagrass cover has increased slightly to 93km2 (Stephens 1995) compared with about 59km2 for an equivalent area in 1984. The area of subtidal seagrass was not estimated.

Possible Causes of the Decline of Intertidal Seagrass Beds in Western Port

Seagrass loss has been recorded at many other locations in Australia over the past 20 years, including Botany Bay, Cockburn Sound, Gulf of St Vincent, Lake Macquarie and Tuggerah Lakes (Shepherd et al. 1989). The loss has been found to be due to a range offactors (Shepherdet al. 1989, Hamdorf and Kirkman 1995). Shepherd et al. (1989) proposed a unifying hypothesis that may generally explain seagrass loss; namely that a reduction in light reaching seagrass precludes effective seagrass photosynthesis. The cause of seagrass die-back in Cockburn Sound and Gulf of St Vincent has been attributed to reduced light reaching the seagrass leaves due to shading by epiphytes stimulated by increased nutrients (Shepherd et aI1989)_ Reduction in seagrasses in NSW and Queensland estuaries has been attributed to reduction in light reaching seagrasses due to increased suspended sediment from catchment runoff and increased plankton and epiphyte growth The area of seagrass beds lost in Western Port from 1974 to 1984 is almost 50% greater than the sum of the major seagrass losses reported for all bays and estuaries in the rest of southern Australia as listed in Shephardet ai. (1989). Greater losses of more than 1000km2 of seagrass in Queensland and 300km2 in Torres Strait have been recorded but the cause was probably cyclone damage.

74 Environment Protection Authority The Western Pori Marine Environment

6 k"{,:1 Site 1 _ Site 2 5 B i o 4 m • 3 • 2

1 o~~k¥!1~ D Il J S D M J S D ApAu D J D Au J D J F S N D D D D D D D 73 74 75 76 7778 7980 61 83 85 87 69

Survey Yi!ar'

Heterozostera ta:mumica 1972 - 1989 Biomass, kg per sq.m. (Wet Weight) - mean from 6 quadrats of 0.33 m2

6 _ Site 2 5 I'il Site 1 B i ;:: 0 4 m •s 3 ) s· ::: 2 :;. ::: 1 :: 0 D M J S D M J S D_hDJDbJDJFSNDDDDDDD 73 74 75 76 7778. 79BO 8163 85 87 69

Survey Year

Caulerpa cactoides 1972 - 1989 Biomass, kg per sq.m. (Wet Weight) - mean from 6 quadrats of 0.33 m2

Figure 8.5 Standing crop ojsubtidal Heterozostera tasmanica and Caulerpa cactoides at BHP 1972 to 1989 (MSE 1990)

75 Environment Protection Authority The Western Port Marine Environment ~------, The decline of intertidal scagrass in Western Port has been attributed to many causes over the past 15 years (Western Port Catchment Coordination Group 1983; Bulthuiset al. 1984; Shepherd et al. 1989; Stephens 1993, 1995). The most widely quoted hypothesis for the beginning of the decline of intertidal seagrass in Western Port in the 1970's is red\lction of light reaching the leaves due to increased suspended solids deriyed from catchment runoff in the late 1960s and early 1970s (Shepherd et al. 1989). It is hypothesised that the sediment adheres to the leaves of the intertidal scagrasses during low tide, and causes a reduction in light reaching the leaves. There is a lack of evidence supporting this hypothesis due to a lack of data on water quality, contaminant levels, sediment load or erosion characteristics for Western Port or its catchment prior to or during the decline, and the cause may never be scientifically proven.

Other factors have been identified which may have had an impact on seagrass loss. These include: blanketing by sediments (Wilk et al. 1979); industrial waste releases to the east of Western Port (Ridgway 1995); overgro\\1h by epiphytic algae; toxicant runoff from the catchment; natural variation in seagrass biology; simultaneous natural events; and the effects of biocides such as the highly toxic ship antifouling paint Tributyl Tin (TBT). These possible causes of the decline of seagrasses in Western Port are discussed in more detail below.

Physical Blanketing by Sediments

There is strong evidence that physical blanketing of seagrass beds by sediments carried from tbe catchment was the cause for loss of approximately 38 km2 of intertidal seagrass beds adjacent to The InletsiBunyip River Main Drain (Wilk er ai. 1979). Initially, in 1976, Marsden and coworkers identified an area of approximately 25 km 2 of intertidal flat which had been covered by barren sands and silts from the Bunyip and Lang Lang Rivers, Yallock Creek and other artificially cut and straightened drainage channels. The area was clearly discernible from aerial photographs taken in 1939, and seagrass remains were found beneath recent sediments in cores collected from the area.

Subsequently, 47 additional cores and a range of colour and infra-red false colour aerial photographs were taken as part of the study reported by Wilk et al. (1979). The researchers then examined over 50 sediment cores from the combined surveys, comparing them with sediment depth information from East (1935), and maps of features from aerial photographs. Wilke! al. (1979) concluded that 38 km2 of intertidal seagrass beds had been denuded adjacent to the InletslBunyip River Main Drain area since 2 1888, when the Main Drain had been cut to Western Port. Of the 38km , approximately 11km2 had o been covered by sand, and of the remaining 27km", half was covered by muds which were transported further offshore than the sands. The average thickness of the muds was estimated at 2.7cm, and was no greater than 10cm thick. The area covered by the sand sheet had not increased significantly since 1939 when approximately 28km2 of seagrass had been inundated, but the expansion of the mud area had inundated an additional I Okm2 of seagrass between 1939 and 1979 (Wilk et aI. 1979).

While this evidence may explain the mechanism for seagrass loss in this large but confined area, it is apparent from aerial photographs taken in 1967 and 1970 that seagrass was abundant elsewhere in Western Port. Hence blanketing of this area near the Main Drain prior to 1939 does not appear to have been the trigger for the wider decline noted in the mid 1970s.

The expansion ofthe area offine but not coarse sediments from 1939 to 1979 may, however, indicate a change in the source of eroded material in the catchment. A possible shift of erosion to finer material in the catchment could have caused wide spread impacts due to turbidity and reduced light (CEE 1995).

76 Environment Protection Authority The Western Port Marine Environment

Unfortunately, there is no information available on the sequence of erosion or characteristics of eroded material in the catchment. Historical aerial photographs in the catchment could be examined to determine the pattern of land clearing over the past 50 years, soil maps could be used to determine the characteristics of erosion runoff, and runoff volumes could be calculated. Such a study would require considerable effort, and although it may provide more information on inputs of sediments than exists in the available literature, it would not prove a linkage between seagrass decline and sediment runoff from the catchment.

Turbidity and Shading

Experiments using shading screens found that reduction of light toHetcrozostera tasmanica caused a reduction in the quantity of leaves, and it was suggested thatH tasmanica requires a minimum of about 5% of surface irradiance for survival (Bulthuis 1983). The observed loss of seagrass density within Western Port during the decline of intertidal seagrass in Western Port (Bulthuiset al. 1984), therefore, is consistent with the pattern expected for reduction in light reaching the seagrasses.

High turbidity in the northern part of Western Port has been a feature of observations since the early I 970s when records started. Increased turbidity causes low sunlight penetration in the water column and, deposition of sediment onto the leaves of intertidal seagrass could contribute to reducing the amount of light which reaches the seagrass chloroplasts. The persistence of subtidal seagrass in Western Port suggests shading alone was not the cause of intertidal seagrass loss as the reduction in available light to subtidal seagrass would be greater than to intertidal seagrass. It has been suggested that direct adherence of sediment on the leaves of intertidal seagrass blocked enough light to result in the death of the seagrass (Bulthuis et al. 1984a; Shepherd et al. 1989). The adherent and glutinous nature of disturbed clays in northern Western Port has been noted in various reports and letters (Watson 1974; Sargeant 1977; Ridgeway 1995), and (Marsdenpers comm.) which describe the surface sediments observed on the tops of the sediment cores collected in the late 1970s as gelatinous, abiotic sediment overlying sediments containing seagrass material.

Seagrass cover limits or prevents the resuspension of fine sediments from the seabed (Wilk et ai. 1979; WPCCG 1983; Bulthuis et al. 1984). The reduction in biomass or removal of seagrass allows wave action to act directly on the seabed and resuspend the fine sediments which have been previously trapped by seagrass. The initial reduction in seagrass cover appears to have caused an increase in resuspension of fine sediments and increased turbidity in the waters of Western Port. This may in tum have caused further reduction of seagrass and accelerated seagrass loss (Shepherd et al. 1989). This does not indicate the original cause of the decline.

Slumping of mudflats into channels has been described in the dendritic channels of the tidal divide (Miles 1976). Erosion and slumping in the dendritic channels results in direct removal of seagrass growing on the channel edge, and may cause additional suspension of sediments. Reduction of seagrass density along the edges of the channels, where stream velocities are high and wave action may be focussed, would increase the erosion of the bed material in these areas. The extent or significance of this process has not been quantified.

There appears to be no published data on water clarity (data was collected during the Westernport Bay Environmental Study (1973-1974) but not reported) in Western Port prior to the mid-1980's, but anecdotal reports suggest that water in Western Port was relatively clear prior to the late 1960' s at least. Recollections by long time residents indicate that the water in the eastern parts of Western Port was relatively clear until the late 1960's when water became turbid (Ridgeway 1995). Turbidity in the

77 Environment Protection Authority The Western Port Marine Environment ------~--~--~--~~~----- waters near Lang Lang increased in the early 1970's (Wallispers comm.) Seagrass was still abundant in Western Port at that time (Bulthuis 1982).

Dr. Jan Watson noticed the increase in turbidity in Western Port in the early 1970's when underwater photography near Hastings became increasingly difficult through the 1970's, to the point where it was futile in the 1980's due to high turbidity. Watson (MSE 1990) has noticed an improvement ovcr the past few years, so that underwatcr photography is now possible. It is interesting to note that this coincides with the reported regrowth of intertidal seagrasse~ in the north of Western Port.

Another potential cause of shading on seagrass leaves is uncontrolled algal epiphyte growth. Epiphytes on the leaves of seagrass can affect the plant by both reducing the amount of light reaching the chloroplasts and by reducing the rate of diffusion of carbon dioxide (C02) and presumably other nutrients to the seagrass. This inhibition of seagrass photosynthesis by epiphytes has been proposed as a possible rcason for the decline of seagrass populations where epiphyte density increases (Borowitzka and Lethbridge 1989).

Axelrad (1986), in a description of the sudden demise of a large tract of previously luxuriant intertidal Heterozostera tasmanica in Western Port, observed that the seagrass was densely covered with epiphytes, predominantly the pennate diatom Synedra formosa, which had trapped some sediment against the plant. Axelrad (1986) noted that most of the particulate material on the seagrass was epiphytic, not sediment.

The negative effect of high epiphyte load on seagrasses can be reduced when there are abundant grazers that keep the standing crop of epiphytes low even though epiphyte productivity remains high. Gastropods are one such important grazer of epiphytes on seagrass leaves (Watsonet al. 1984; Bulthuis 1986). Daly (1977) found abundant epiphyte grazing gastropods at a Crib Point study site in 1977 while Willoughby (\989) found significantly reduced abundance at the same site in 1989. However, the significance of uncontrolled epiphyte growth on seagrass leaves, or changes to epiphyte grazer popUlations to seagrass decline across Western Port has not been quantified.

Desiccation

Heterozostera tasmanica is usually considered to be a subtidal species (Robertson 1984). Zostera muelleri, on the other hand, is considered to be an intertidal species. An unusual feature of the seagrass beds which existed in Western Port until the 1970's was the predominance ofH. tasmanica rather than Z. muelleri in the intertidal area. Some feature of Western Port or the seagrass beds allowed H. tasmanica to occupy a habitat where it would not normally be found.

The occurrence of dense meadows of Heterozostera tasmanica on the intertidal mudflats in Western Port may be due to the ability of the dense stands to retain significant amounts of water which would reduce the possible effects of desiccation at low tide. This process of water retention has been shown to occur in Thallasia seagrass beds on intertidal banks in Florida Bay (powell and Schaffuer 1991). Thinning of the seagrass (due to shading or other causes) would reduce the capacity of the meadows to retain water and increase the stress of desiccation. The loss of H. tasmanica from the intertidal mudflats, but not from the subtidal area, could implicate thinning followed by desiccation as a possible mechanism for the decline of H. tasmanica On the mudflats.

Zostera muelleri is also found intertidally in Western Port. As an intertidal species, it is capable of withstanding or recovering from desiccation during normal conditions. At certain locations in the Lowcr North Arm of Westem Port where Heterozoslera tasmanica declined between 1974 and 1984, Z. muelleri increased (Bulthuis et al. 1984a). Between 1984 and 1994, Z. muelleri re-colonised some

78 1 1 Environment Protection Authority The Western Port Mariue Environment

denuded areas previously vegetated with H tasmanica (Stephens 1995). However Z. muelleri declined I at most locations in Western Port from 1974 to 1984 which indicates a cause other than desiccation for i the general seagrass decline in Western Port, The possibility of desiccation of seagrasses during very low daytime tides in periods of very hot weather in the early 1970s has also been suggested as a possible cause of death of seagrasses in Western Port; and as a trigger to the ongoing decline into the 1980's (1. Watson, K. Burnspers 1 comm.). While the records for tide height and daytime air temperature probably exist for a considerable period for Western Port, there is no known synthesis of this information in relation to the 1 seagrass decline.

Industrial Waste Releases

There has been considerable local concern over releases of industrial wastewater from sandmining operations near Lang Lang. Locals link the commencement of sand washing operations at Lang Lang in the early 1960s with the commencement of seagrass die-back. They claim that wastewater discharges and releases of wastewater from collapse of storage dams during heavy rains (eg. 1978, 1983) have introduced quantities of wastewater containing detergents and fiocculants into Adams Creek and subsequently into Western Port.

Episodes of shrimp and shellfish kills, and coating of seagrass and foreshore with orange coloured gelatinous substances have been observed along the foreshore at Lang Lang by local residents. Some residents (Ridgeway 1995) believe wastewater releases coat seagrass leaves with flocculant causing the seagrass to die either directly or by reducing the light available to the leaves.

Concern regarding discharges from the sand processing operations continues (Cranbourne Sun, 21 Feb 1995). 'While it is unlikely that releases of wastewater from the Lang Lang River caused the widespread decline of seagrasses throughout the north. of Western Port:, possible local effects of the releases cannot be dismissed. Sand processing in the area will probably continue to be the focus of local attention as long as the potential for releases of wastewater to Western Port remains.

Tributyl Tin (IB1)

TBT is an additive to paints used on the hulls of ships to prevent the growth of marine organisms. It has also been used as a wood preservative, crop spray and in the plastics industry. It is extremely toxic to marine organisms, particularly bivalve shellfish and marine snails (gastropods). In addition to lethal effects, TBT causes a wide range of sublethal effects and was linked with the decline of commercial oyster yields in France and Europe (Daly and Fabris 1993).

Stephens (1993) suggested a mechanism for TBT to affect seagrasses in Western Port and could also apply to other catchment derived pesticides. Small marine snails have been shown to play an important role in cleaning epiphytes from seagrass leaves (Daly 1977; Howard and Short 1986). Removal of these small grazers from seagrass beds by the effect of substances such as TBT could allow excessive growth of epiphytes which could prevent sufficient light reaching the seagrass leaves.

TBT came onto the international market in the 1960's but was not widely used until the early 1970s. The SUCCeSs of TBT in antifouling paints caused a rapid increase in its use from the 19705 to the late J980s. However, in international recognition of the detrimental effects of TBT on the coastal marine

79 Enviromnent Protection Authority The Western Port l'1farine Environment

environment, the use ofTBT in Australia was banned for use on vessels less than 25m in length in the late 19805. It is still used under permit on vessels greater than 25m length. In 1988, EPA found relatively high concentrations of TBT in waters near Hastings marina slipway (212ng SnIL) and Newhaven marina (700ng SnIL) (Daly and Fabris 1993).

TBT has the potential to have been a factor in the decline of seagrasses. However, the widespread decline of seagrasses in areas remote from intense boating and shipping activity (eg. Bunyip to Lang Lang Rivers) and persistence of some seagrasses close to intense boating and shipping activities suggests that the possible contribution ofTBT to the widespread decline of seagrasses in Western Port may be difficult to determine.

Biocide Runofffrom Catchment

There has been no investigation of biocide contamination in the Western Port marine ecosystem since 1973174. Measurements taken during the 1973174 studies (Ministry for Conservation 1975) indicate generally low levels of bincides. The potential impact of persistent low levels of biocides on marine biota in Western Port has not been examined.

Natural Events

It is possible that the decline of seagrasses in the late 1970s early 19805 represents a natural cycle of decline and regrowth. There is no long term record of seagrass distribution or density to determine whether short or long term fluctuations do or do not naturally occur over periods longer than 100 years.

Summary

Seagrass assemblages provided a major link in the Western Port marine ecosystem. There has been a massive decline in the area of seagrass in Western Port between the early 19705 and late 19805, and there are a range of possible reasons for the loss. It is probable that the decline was not due to a single cause, and that high turbidity and desiccation, once decline had starred, played a key role in exacerbating the magnitude of the loss of seagrasses, particularly Heterozostera tasmanica, from the intertidal flats in Western Port.

Seagrass has re-established in some areas of the west, north west and south east of Western Port as reported by local fishermen, (MSE 1990) and documented by Stephens (1995). The areas of revegetation are small and the unit biomass is low. No re-establishment of seagrasses has been reported in the northeast or east of Western Port, where water clarity has remained poor.

All possible factors which may have contributed to the original decline of seagrass and which may impede the regrowth of seagrass should be minimised or eliminated to ensure that regrowth is encouraged.

80 " Environment Protection Authority The Western Port Marine Environment

CHAPTER 9 NUUUNEINVERTEBRATEFAUNA

INTRODUCTION

The invertebrate fauna of Western Pon has several interesting and unique features. This fauna provides an important link in transferring the production of seagrasses, mangroves and other plants to higher trophic levels (such as the fish communities) in the ecosystem. Invertebrates are associated with seagrass habitats, mangrove habitats, mudflats, reefs and the seabeds of the channels.

The aim of this chapter is to provide a critical review of relevant information on marine invertebrates in Western Port, particularly in relation to the loss and recovery of intertidal seagrasses in the north of the bay.

INVERTEBRATE FAUNA OF WESTERN PORT

Numerous investigations of the marine invertebrate fauna of Western Port were made from the first collections by the French Astrolabe voyages in the I 820s through to the I 930s. The majority of these studies were taxonomically related (see review by Smith et al. 1975). Recent studies have had been more ecologically based. Descriptions of invertebrate assemblages have been obtained from surveys by a number of research groups including: the Victorian Fisheries and Wildlife Division in 1965 and 1973-4 (Coleman et al. 1974; Littlejohnet at. 1974); the University of Melbourne, and the Underwater Research Group of Victoria, in association with the National Museum of Victoria. A summary of the various invertebrate assemblages from these studies was compiled by Smith et al. (1975).

The studies by Coleman et at. (1974, 1978) were the first of a series of large scale ecological investigations of the invertebrate benthos in Western Port. These began in MarchiApril 1965 with the sampling of 55 stations near Crib Point. Five sites were sampled seasonally during the following 5 years. In November 1973 and January 1974 Coleman et al. (1974, 1978) sampled 41 sites located throughout Western .Port. In these assays sampling was stratified between intertidal flats, shallow sublittoral areas and deeper sublittoral habitats. The fauna at Crib Point has been examined intensively by several researchers to determine small scale spatial variations in community structure, standing stocks, production and trophic pathways through the community (Littlejohn et al. 1974; Robertson 1978; Watson et al. 1984). These studies involved a series of five samples taken throughout 1974 and monthly samples from May 1975 to May 1976. The ecology of epifaunal gastropods has also been examined (Daly 1977; Willoughby 1989).

Although these studies provided important detail about the ecological relationships between seagrass and its associated fauna, they were generally restricted to localised regions. As noted by Edgaret al. (1994), it is not appropriate to use the information provided hy the studies above for quantitative application, or predictive ability, for other areas in Western Port.

Edgar et ai. (1994) investigated spatial and temporal patterns and trends in the infauna throughout Western Port, and compared these trends with similar studies along the southern Australian coastline (Edgar & Shaw 1995c). Edgar et al. (1994) examined the invertebrate faunas associated with seagrass

81 Envirolflffl?nt Protection Authorio/ The Western Port Marine Environment ------~~------~ and unvegetated habitats (including mudflats and channels) in Western Port over a fifteen month period commencing August 1989. The study sites included Peck Point, Rhyll, Tooradin, Cowes bank and Loelia Shoal. In addition to providing infonnation on the present status of invertebrate fauna, predictive relationships between invertebrate production and seagrass production, and the effects of other environmental variables were determined (Edgar et al. 1994; Edgar & Shaw 1995c).

One of the most substantial investigations of invertebrate fauna in Western Port has been the environmental impact monitoring of effluent from the steelworks of the BHP International Steel Coated Products plant, situated on the north arm of Western Port. This biological monitoring, undertaken by Marine Science & Ecology (MSE), included annual investigations of infauna and epifauna adjacent to the effluent outfall (a swinging basin and berthing area for shipping), and at control sites in the nearby channel. Sessile invertebrates on the wharf pilings were also monitored (MSE 1990, ). The monitoring methods used were rigorous, and sampling has occurred annually since the program began in 1972. Except for fisheries catch returns, this program is the only long term biological monitoring program that has occurred in Western Port.

Western Port can be divided into several general marine habitat types with characteristic invertebrate fauna. These habitats are primarily seagrass and tidal mudflats, channels, beaches and rocky reefs. Differences in faunal species bet\veen habitats is largely a reflection of differences in water movement, tidal exposure, sediment types and the availability of hard substrates for attachment (rocks, pier piles, macrophjtes, shells and other organisms). The remainder of this review is a description of invertebrate assemblages in relation to general habitat types and the long term monitoring program at BHP-Lysaght (MSE 1990).

Seagrasses and mndflats

Invertebrate fauna of the seagrass and mudflat commumtIes comprises infimna (those animals burrowing in the seabed), and epifauna (those animals living On the seabed or on seagrass leaves and stems.

Several investigations have documented a gradual change in the infaunal community strocture from the near shore regions to the shallow channels and inlets and the deep channels (Littlejohnet al. 1974; Smith et al. 1975; Coleman et al. 1978; Edgar et al. 1994). Although species composition is generally similar between the seagrass and mudflat communities, species diversity is generally lower on the un vegetated mudflats than in the seagrass or channel habitats (Coleman et al. 1978, Watson et al. 1984; Edgar et al. 1994). Epifaunal biomass is also higher in seagrass habitats than unvegetated or channel habitats. Infaunal biomass is generally higher in finer sediments (Edgar et al. 1994).

Prominent infaunal species include the bivalves Anadara trapezia, Katelysia rhytiphora, Homalina deltoidalis, H. mariae and Laternula tasmania. Common crustaceans are the mud yabby Callianassa, the shrimp Alpheus sp. and the tanaid Paratanais (Coleman et al. 197&; Watson et al. 19&4; Edgaret al. 1994). Also common are the foraminiferans Ammotium cassis and Trochommina sorsa, the polychaete genera Barantolla, Armandia, Nepthys, Lumbrineris, Platnereis and Pisra, and the gastropods Salinator fragilis, Nassarius burchardi and Polinices sordidus.

The epifauna include a large number of grazing molluscs (families Trochidae and Rissoacea), gammaridean amphipods, the shrimpMacrobrachion sp., the crabs Halicarcinus sp. and Litocheira bispinosa, and occasional sponges, hydroids and ascidians (Littlejohn et al. 1974; Smith et al. 1975; Edgar et al. 1994).

_... .~,,-=. ______•______l1li Environment Protection Authority The Western Port Marine Environment

The infauna and epifauna of seagrass and mudflat habitats arc dominated by selective and non selective deposit feeders with Jew organisms able to graze directly on seagrass. However, most primary production in Western Port is by seagrass. Thus, the organic breakdown and recycling of dead macrophyte material by the microbiota and meiofauna (animals smaller than 1 mm), and the consumption and transfer by the invertebrate macrofauna (animals larger than 1 mm) are important energy transfer processes in the Western Port ecosystem (Littlejohn et al. 1975; Watson et al. 1984). An important component of the ecosystem is the guild of micro-gastropods and amphipods, which consume detritus and epibiota on and around the seagrass leaves (Daly 1977; Watsonet al. 1984). A food web of the seagrass ecosystem developed by Watsonet al. (1984) is shown in Figure 9.1.

Epifaunal production is highest in seagrass habitats, and may be up to several times higher than unvegetated sites. This effect is principally due to large popUlations of grazing molluscs (Robertson 1978; Edgar et al. 1994). Both total macro faunal production and crustacean production are strongly correlated with the proportion of silt to clay in the sediment, and with the biomass of seagrass leaves (Littlejohnet al. 1974; Edgar & Shaw I 995c). Infaunal production is significantly correlated with the amount of organic material in the sediment, and is therefore influenced by detrital production from seagrass (Edgar et al. 1994). Estimates for macrofaunal production in seagrassed areas of Western Port range from 5.3 to I 06g/m2 AFDW (Ash Free Dry Weight). These areas are considered among the most productive systems of the world (Watson et al. 1984; Edgar et al. 1994).

Edgar et al. (1994) compared invertebrate fauna associated with seagrasses and soft seabeds in 1973174 (Coleman et al. 1974) with those surveyed from the same habitats 20 years later. Despite differences in methodology, and a large proportion of macrofaunal taxa left undescribed, Edgaret al. (1994) detected significant changes in the invertebrate fauna between their surveys and those of Coleman et al. (1978). The molluscs Diala suturalis, Styliferina translucida and Pseudoliotia micanus were not collected at all in the 1973174 surveys but were abundant in the 1992/93 surveys. In contrast, the bivalves Notocallisla diemensis and Katelysia rhytiphora were relatively common in the 1973174 surveys, but were rare in the recent studyJEdgaret al. 1994). There appears to be little change in diversity between the surveys, however Edgar et al. (1994) consider that, due to differences in collection methods, it was inappropriate to compare possible differences in species diversity.

Edgar et al. (1994) considered that the substantial seagrass loss would have resulted in the reduction of macrofauna! species in many areas, with a reduction in epifaunal productivity alone from 17gm·2 AFDW ,to 3.3gm-2 AFDW. They estimated that the loss of over 17,000ha of seagrass related communities in Western Port would have reduced the total annual epifaunal production by an estimated 2,SOOtonnes AFDW per year.

Cbannels

The main, deep (10 to 30m) channels of Western Port have a coarser, sandy substrate compared to the intertidal mudflats in the north, and tidal currents are moderate to strong (Littlejohn et al. 1974; Smith et al. 1975; Edgar et al. 1994). Invertebrate fauna ofthe channels comprise an unusually abundant mixture of species not normally found together, present in relatively high abundance. The seapen Virgularia mirabilis (formerly Sarcophyllum sp, see Shepherd and Thomas 1982), which anchors in the substrate by a fleshy stalk, is very abundant in the deepwater channels in Western Port, reaching 2 densities of approximately 200 per m (Edgar et al. 1994).

83 Environmellt Protection Authority The WesteTll Port Marille ElIvirOllment

Figure 9.1 SimplifiedJood web ofthe seagrass ecosystem at Crib Point (from Watson et a1.1984)

84 Environment Protection Authority The Western Port Marine Environ/tumt

Other epifaunal species are generally found attached to rubble, shells and other epifaunal animals (epizoic species). Examples include the gastropod Sigapatella calyptraejormis, the brachiopod Magel/ania australis, the sea stars Nectria ocellata, Patiriella brevispina and Tosia magnifica, the urchin Goniocidaris tub aria and the solitary asci dian Pyura stolonifera. Magellania australis, like V. 2 mirabilis, is also abundant, attaining densities of 250 per m , but is not thought to be common elsewhere in Bass Strait (Smithet al. 1975). Epizoic species include sponges, hydroids and ascidians (Smith et al. 1975).

The most abundant infaunal taxa of the deep channels are polychaetes and crustaceans, the bivalve molluscs, Neotrigonia margaritacea, Pronuncula sp. Notocallista diemensis, Bellucina crassillirata, Venericardia bimaculata, the rock-boring bivalvePholas australasiae, and the carnivorous gastropods Nassarius burchardi, Pterynotus triformis and Amorena undulata (Smith et al. 1975). Macrofaunal prod\lction in the shallow channels is generally lower than in shallower habitats (Edgaret al. 1994); there is no infonnation on the productivity of the deeper channels.

Three species of particular scientific interest in the channels of Western Port are the molluscs Neotrigonia margaritacea and Anadara trapezia, and the brachiopod .Magellania australis. These are living fossil fonns with a long geological history, and are restricted in distribution elsewhere in Victoria. However, these species appear to be abundant within Western Port (Smith et al. 1975).

Sandy Beaches

As with most beaches, the beaches of Western Port are relatively depauperate of invertebrate fauna, particularly when compared to the intertidal mudflats located in the north of Western Port. The coarser, cleaner sands are predominantly inhabited by a few species of the bloodwormAbarenicola. Additional fauna are associated with the seagrassAmphibolis antarctica, which grows on the subtidal sandy seabed in the more oceanic, southern parts of the bay. The fauna are typical of other seagrasses, but include hydroids, bryozoans and colonian ascidians (Smith et al. 1975; Watson et aI1984).

Reefs and Hard Substrates

Subtidal reef surfaces occupy a very small area in Western Port, with most reefs present as scattered outcrops in the North Arm. The best known of these outcrops is Crawfish Rock. The top 10 to 11m of this rock features an algal community dominated by Ecklonia radiata, with Sargassum, Scabaria and Caulerpa in the more sheltered, shallow waters. These algal communities have a strong red algal component, including Claudia elegans, Griffithsia leges,M.yriogramme gunniana and Rhodymenia sp. (Smith et al. 1975). Due to a rapid reduction in light levels with depth, and high current flows around the rock, there is a rapid transition from the algal community to a sessile invertebrate, filter feeding community of sponges, compound ascidians, bryozoans and hydroids. The sponges includeAncorina cor/icata, Geadia sp. and Ircinia sp.; the dominant ascidians are Didemnum patulum and Amphicarpa diptycha. Predominant bryozoans are Amathia bisriata, Bugula dentala, Cellepraria prolifera and Triphyllozoon monolifera. Predominant hydroids are Pennaria sp., Eudendrium generalis, Aglaophenia plumosa, Pumularia selacoides, P. procumbens, Setularia unduiculata, S. lala and Halopteris buskii (Smith et al. 1975).

Although there is no fonnal infurmation available on the character of the assemblages at Crawfish Rock since Smith et al. (1975); there is anecdotal evidence from Dr J. Watson who has frequently dived and made observations at Crawfish Rock over a period of almost 30 years - most recently early in 1995. She noted that many individual sponges observed 20 years ago were still present at Crawfish

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Rock, and that tbe general invertebrate assemblage structure has remained uncbanged. However, the water turbidity has substantially increased over this period (J. Watson pers comm.).

The San Remo Marine Community

An intertidal and subtidal area near San Remo, 600 by 300m, has been listed on Schedule 2 of the Flora and Fauna Guarantee Act 1988 (Department of Conservation & Environment 1992). This area consists of a rich assemblage of flora and fauna, known as the San Remo Marine Community (Kinhi1l Engineers 1988; Marine Research Group of Victoria 1989). The fauna includes a high number of species of opisthobranch molluscs (eg. nudibranchs) and bryozoans, many of which are considered rare (Department of Conservation & Environment 1992). Two opisthobranch species from the San Remo Marine Community have also been listed as threatened taxa on Schedule 2 of the Flora and Fauna Guarantee; these are Platydoris galbana and Rhodope sp. A further eight undescribed species, known only in that area, are likely to be listed when they are formally described (Depertment of Conservation & Environment 1992). Tbe 1988J89 studies at San Remo were intensive, and no similar surveys appear to have been undertaken elsewhere in Victoria. These biota have a relatively high turnover, so the present composition of the community is not known. The status of the San Remo Marine Community is not due for review by the Flora and Fauna Guarantee Unit until 1997 (Department of Conservation & Environment 1992).

Monitoring Program at BHP-Lysaght

Substantial changes in the invertebrate fauna of the north arm of Western Port have been recorded over the 20 years of the BHP monitoring program (Marine Ecology & Science 1990). In the turning basin, the total density of infauna has increased and there has been an apparent change in community structure, while the infauna of the adjacent channel has remained relatively unchanged. The change in the swing basin in fauna has been attributed to sediment changes caused by the winnowing effect of ship propellers (Marine Science & Ecology 1990).

The predominant epibenthic organisms monitored werePyura stolonifera, Magellania jlavescens and Virgularia mirabilis. The abundance of these three species were variable in both the swing basin and channel. Abundances in the channel were highest between approximately 1975 and 1980. The virtual disappearance of V. mirabilis populations since 1981 is correlated with increasing water turbidity (Marine Science & Ecology 1990). Turbidity was extremely high in the 1980s, to the extent that the visual surveys of epibenthos could not be achieved in 1984, 1986 and 1989. V. mirabilis was not observed at all between 1987 and 1992, but was present in low abundances in 1993 (Marine Science & Ecology 1994). Also of concern is the disappearance ofM jlavescens since 1988. Abundances of P. stolonifera bave been low in recent years (Marine Science & Ecology 1994).

The monitoring by Marine Science & Ecology has found no detectable impact resulting from the BHP effluent Rather, shipping disturbances have had an effect on the invertebrate fauna in the swing basin. Other changes in both the swing basin and the channel are likely to be due to the concurrent, large scale changes in Western Port, such as seagrass loss and increasing turbidity (Marine Science & Ecology 1990).

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SlJMI\'lARY

The recent studies by Edgar et al. (1994) and Marine Science & Ecology (1994) provide good descriptions of the current state of invertebrate macrofauna. These results are suitable for comparisons with future surveys using similar methods. Of additional benefit is the predictive model of Edgar & Shaw (1995c) which relates the production of macrofauna, and the macrocrustacean component, with the environmental parameters of seagrass biomass and sediment composition. This model is a useful tool for assessing past and present environmental impacts on the invertebrate fauna.

While most investigations of the invertebrates of Western Port have concentrated on macrofauna (greater than lmm in size), the past and present status of the meiofauna and microfauna is unknown. The status of habitats and regions not studied by Edgar et al. and Marine Science & Ecology (such as channel systems, Crawiish Rock and the San Remo Marine Community) is also unknown.

Information is lacking on the current population status of unusual and possible threatened species, such as Virgularia mirabilis,Magellaniajlavescens and Neotrigonia margaritacea, as well as the San Remo opisthobranchs and other fauna. The observations of Marine Science & Ecology (1990, 1994) suggest the populations of Virgularia mirabilis and Magellania jlavescens may have declined over the past decade.

These problems are closely connected·with the large-scale environmental changes to Western Port and are particularly relevant with regard to the Flora and Fauna Guarantee Act 1988. The principles of this act are:

To guarantee that all taxa of flora and fauna and ecological communities in Victoria can survive, flourish and retain their potential for evolutionary development in the wild (Department of Conservation & Environment, 1992).

On this basis, there is a need to assess the threatened status of invertebrate populations and communities in Western Port, in locations other than the San Remo Marine Community.

87 Environment Protection AuthoriJy The Western Port Marine Environment

CHAPTER 10

FISH AND FISHERIES

INTRODUCTION

Western Port is a very popular area for fishing and other aquatic recreational activities. The fish and fisheries of Western Port are not only an important resource to the community, but are a prominent component of the Western Port marine ecosystem. Commercial and recreational fishers and conservationists have expressed concern over the substantial decline in catches of some fish species in Western Port since the early I 970s. This decline has been attributed to the loss of seagrass habitat in Western Port during the same period.

FISH COl\fMUNITIES IN WESTERN PORT

Three major stndies have examined aspects of the fish communities of Western Port: Negilski (1975),· Robertson (1978) and Edgar et al. (1994).

The earliest stndy, Negilski (1975) was part of the Westernport Bay Environmental Stndy (1973- 1974). Negilski (1975) regularly sampled the fish species at various locations in Western Port between April 1973 and June 1974, in order tn examine species composition and biomass. Negilski (1975) found differences in community structnre between habitat types, particularly between the entrance channel, seagrass areas and the drainage channels. However, only a diversity summary statistic (11') and total biomass for each site was reported.

The second major study was by Robertson (1978), from October 1974 to April 1976. Its aim was to examine the trophic relationships between fishes and other macrofauna of the seagrasses and tidal mudflats of Western Port. This report provided a substantial amount of information on fish community structnres and fish production in the populations sampled. However, due to the comprehensive natnre of the infonnation gathered the investigations were restricted to Cribb Point on the western side of Western Port, and did not provide infonnation on Western Port as a whole.

The most recent stndy was conducted by Edgar et al. (1994), between August 1989 and November 1990. Although the aim of this stndy was to examine the relationships between seagrass habitats and commercial fisheries, a considerable amount of information was obtained on fish assemblages, fish production, spatial differences and the influences of various environmental factors (Edgar & Shaw 1995a, 1995b, 19950).

At least 92 fish species have been recorded in Western Port; the majority are small, economically unimportant species such as gobies (Gobiidae), pipefish (Syngnathidae) and weedfish (Clinidae) (Edgar & Shaw 1995a, 1995b). A list of the common species found in the bay has been compiled for this review (Table 10.1). Most species are widely distributed throughout Western Port, but distinct species assemblages are associated with each of the main marine habitat types (Edgar & Shaw 1995a). These habitats include intertidal mudflats vegetated by seagrasses (Heterozostera tasmanica and Zostera muelleri) and macro-algae (Caulerpa cactoides), unvegetated mudflats, unvegetated drainage channels (4-1 Om deep), beaches and rocky reefs.

88 Environment Protection Authority The Western Port Marine Environment

The seagrass fish assemblages consist predominantly of pipefish, gobies, weedfish, leatheIjackets (Monacanthidae), globefish (Diodon niethemerus), soldierfISh (Gymnapistes marmoratus), blue rock whiting (IIaletta semifaseliata) and adult rock flathead (Platycephalus laevigatus) (Table 10.1). Fishes of the unvegetated mudflats include gobies, flounder (Pleuronectidae), flathead (Platycephalidae), smooth toadfish (Tetractenos glaber) and sandy sprat (IIyperlophus vitlatus). The fauna of channels are typically stingarees (Urolophidae), gurnard perch (Neosebastes scorpaenoides), sand flathead (Platyeephalus bassiensis) and gobies (eg. Favonigobius lateralis). Juvenile King George whiting (Sillaginoides puncta) can be found in seagrass or unvegetated areas which are usually still in the vicinity of vegetated habitat (Robertson 1978; Edgar & Shaw 1995a).

Figure 10.1 Food web for fish groups associated with seagrass communities (from Ministry for Conservation 1975)

Fish diversity, in tenns of species richness, is highest within seagrass habitats. Diversity in seagrass is approximately twice that of unvegetated mudflats, and four times tbat of the channels (Edgar & Shaw 1995a). Most small species, (less than 109 body weight), are found within seagrass habitats, whereas larger species are distributed between habitat types (Edgar & Shaw 1995a). t The fishes of Western Port can be classified by dietary preference into six major trophic groups: benthic crustaceans; planktonic crustacea; seagrass and sessile animals; fish; polychaetes; and molluscs (Edgar & Shaw 1995b). The food web for permanent and transient fish associated with

89 Environment Protection Authority The Western Port Marine Environment

seagrass beds which was identified during the Westernport Bay Environmental Study (1973-1974) reflects a similar set of trophic relationships (Figure 10.1).

Most of the Western Port fish species studied have generalised, broadly overlapping diets with a dominant crustacean component. Only a few species consume algae or seagrass. The diet of crustacean feeders is highly size specific, with shifts from copepods to peracarids at approximately O.lg weight, and to crabs and shrimps at approximately 100g weight. These ontogenetic differences in diet tend to be greater than interspecific differences (Robertson 1978; Edgar & Shaw I 995b ).

The trophic relationships between fishes and their prey form two distinct food webs, one involving resident, demersal fishes, and the other involving generally larger migratory and pelagic fishes. The trophic pathway for resident, demersal species is from periphyton and detritus to mobile epifaunal invertebrate grazers to small demersal fishes to larger fishes. This food chain is similar for both vegetated and unvegetated habitats (Robertson 1978). The trophic pathway for pelagic fishes is from holoplanktonic organisms to small planktivorous fishes to larger pelagic fishes (Edgar & Shaw 1995b). There is little coupling between these two trophic systems, although the strongest links are attributed to trevally (Pseudocaranx dentex), the six spined leatheljacket (Meuschenia freycinelz) and pipefish (Stigmatopora spp.) (Edgar & Shaw 1995b).

Table 10.1 Common fish assemblages in Western Port (compiledfrom literature listed in this reView)

Assemblage Family Common name Scientific name Seagrass Moridae rock cod Pseudophycus bachus Atherinidae hardy heads Kestratherina brevirosrrls Syngnathidae pipe fishes Stigmatopora nigra Stigmatopora argus Mitotichthys semisrriatis Vanacampus phillip! Urocampus carinirosrris Scorpaenidae soldierfish Gymnapistes marmoratus Platycephalidae rock flathead (adult) Platycephalus laevlgatus Apogonidae woods siphon fish Siphaem!a cephalotes Enoplosidae old wife Enoplosus armatus Odacidae blue rock whiting Haletta semifasciata Clinidae weedfish Cristieeps ausrralis Heteroclinus adelaldel Heteroclinus perspicillatus Gobiidae gobies Arenigobius frenatus Gobiopterus semivestitus Monacanthidae six spined Meuschenia freycineti leatheIjacket bridled leatherjacket Acanthaluteres spilomelanurus toothbrush Acanthaluteres vi/tiger leatherjacket pygmy leatheIjacket Brachaluteres j acksonianus

j I

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Table 10.1 (continued) Common fish assemblages in Western Port (compiledfrom literature listed in this review)

Assemblage Family Common name Scientific name Diodontidae globefish Diodon nicthemerus Unvegetated Elasmobranchs sharks and rays various (mostly mudflat undocumented) Clupeidae sandy sprat Hyperlophus vittatus Platycephalidae sand flathead Platycephalus bassiensis rock flathead Platycephalus laevigatus (juvenile) SiUaginidae King George whiting Sillaginodes punctatus Gobiidae goby F avonigobius lateralis F avonigobius tamarensis Arenigobius frenatus Pseudogobius olorum Pleuronectidae greenback flounder Rhombosolea tapirina long snouted Ammotretis rostratus flounder Tetraodontidae smooth toadfish Tetractenos glaber

Drainage channels Uroloplridae banded stingaree Urolophus cruciatus Scorpaenidae gurnard perch Neosebastes scorpaenoides Platycephalidae sand flalhead Platycephalus bassiensis Gobiidae goby Favonigobius lateralis

Mobile/pelagic Carcharinidae school shark Galeorhinus gale us gummy shark Mustelus antarcticus Callorhjl1chidae elephant fish Callorhynchus milii Rajiformes rays various (mostly undocumented) Clupeidae sandy sprat Hyper/ophus vitlatus pilchard Sardinops neopilchardus Engraulidae Australian anchovy Engraulis australis Hemiramphidae southern sea garfish Hyporhamphus melanochir Pomatomidae tailor Pomatomus saltatrix Carangidae silver trevally Pseudocaranx dentex jack mackeral Trachurus declivis Mobile Arripidae Australian salmon Arripis truttacea Sparidae snapper Chrysophrys auratus Mugilidae yellow eyed mullet AidrichettaJorsteri Gempylidae barracouta Thyrsites atun

Beach Atherinidae hardy heads Leptatherima presbyteroides Atherinosoma microstoma Platycephalidae sand flathead Platycephalus bassiensis MugiJidae yellow eyed mullet AldrichettaJorsteri Pleuronectidae greenback flounder Rhombosolea tapirina long snouted Ammotretis rostratus flounder Tetraodontidae smooth toadfish Tetractinos

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The production of small fishes, less than 109 weight, is much greater at seagrass sites than other habitats, and accounts for most of the overall fish production in seagrass. Most of the fish production in unvegetated mudflats is by fishes of intermediate size (IO-IOOg weight), while most of the production in channel habitats is by fishes> I OOg (Edgar and Shaw I995a). The differences in production of small fishes between habitats does not appear to influence the production of the predatory (ichthyivorous) fishes.

The production of small, demersal fishes in Western Port is highly correlated with both macroepifaunal production and macrocrustacean production (Edgar & Shaw I 995a). Edgar and Shaw (1995a) hypothesised that these factors were causally linked. This is based on obselVations that: seagrass beds support more crustaeeans than unvegetated habitat and the production of small fishes is much greater in seagrass habitat; most production of crustaceans> I mm sieve size is consumed by fish; and small fish populations rapidly decline during seasons of low crustacean production (Edgar and Shaw 1995a, 1995b). In addition to seagrass biomass and invertebrate production, demersal fish production is also correlated with the proportion of silt to clay content of sediment, and temperature, and negatively correlated to fetch.

Edgar and Shaw (I995a) found no major changes in the small fish community structures when comparing with Robertson's (1978) sUIVeys, after correcting for differences in sampling techniques (Robertson 1978; Edgar & Shaw 1995a). However, the pipefish fauna has changed over the last 15 years. The wide bodied pipefish (Stigmatopora nigra) and spotted pipefish (S. argus) increased from low and unrecorded abundances, respectively, to relatively common abundances (Howard & Koehn 1985; Edgar & Shaw 1995a).

The fish assemblages and fish production of seagrass and sediment habitats of Western Port have been directly compared with similar habitats at 13 other locations around southern Australia; from Rottnest Island (W.A-) to JelVis Bay (N.S.W.). The fish assemblages and ecological relationships were similar at all locations (Edgar & Shaw J995c). Although it was shown that fish communities ofWestern Port were not unique, Edgar et aI. (1994) concluded that all seagrass habitats, and their fauna, are important components of coastal ecosystems due to their high production rates. The higher biodiversity of fishes within and near seagrass habitats also makes these areas of ecological significance.

The fish assemblages of beaches, rocky reefs and mangroves in Western Port have not been well documented. However, species known to inhabit the beaches of northern Phillip Island include juvenile yellow eye mullet (Aldrichetta forster!), atherinids (Atherinidae), anchovies and pilchards (Clupeidae), smooth toadfish, sand flathead and flounder (Shaw pers comm.).

Western Port also supports a group of highly mobile, generally pelagic species, which are distributed independently of the habitats described above. These species include Australian salmon (Arripis spp.), yellow eye mullet, pilchards and anchovies, snapper (Pagrus aura/us), barracouta (Thyrsites atun) and various sharks and rays (Robertson 1982; Edgar & Shaw 1995a). Most of these species are migratory, and at least part of their life histories occurs outside Western Port

In addition to the ecological value of the fish species in Western Port, some are also of considerable commercial and recreational value. Some fish are also of indirect value to the tourism industry, panicuJarly as a food source for seals and penguins.

92 Environment Protection Authorit)' The Western Port Marine Environment

COMMERCIAL AND RECREATIONAL FISHERIES IN WESTERN PORT

Various aspects of the fisheries in Western Port have been examined, particularly with regard to the effects of seagrass loss, and the commercial and recreational value of the fisheries (Beinssen 1978; MacDonald 1992; Jenkins et al. 1993).

Western Port has supported a commercial nct fishery for over 100 years. The principal species harvested are King George whiting (Si/laginOlies punctatus), rock flathead (Platycephalus laevigatus), southern sea garfish (Hyporhamphus melanochir), Australian salmon and yellow eye mullet (MacDonald 1992). Western Port is also a popular recreational fishing area, for both local residents, vacationers and tourists. The principal species targeted by recreational fishers are King George whiting and snapper. Other species, taken both commercially and recreationally include sand flathead, blue rock or grass whiting (Haletta semifasciata), flounder, leatherjackets, sharks, calamari and elephant fish (Table 10.2).

Table 10.2 Species recardedfrom commercial and recreational catches in Western Port (compiled from literature listed in this review)

Family Common name . Scientific name Carcharinidae school shark Galeorhinus galeus gummy shark Mustelus antarctic us Callorhynchidae elephant fish Caliorhynchus milii Clupeidae pilchard Sardinops neopilchardus Engraulidae Australian anchovy Engraulis australis Hemirarnphidae southern sea garfish Hyporhamphus melanochir Platycephalidae sand flathead Platycephalus bassiensis rock flathead (juvenile) Platycephalus laevigatus Sillaginidae King George whiting Sillaginodes punctatus Pomatomidae tailor Pomatomus saltatrix Carangidae silver !revally Ps€udocaranx dentex jack mackeral Trachurus declivis Arripidae Australian salmon Arripis spp. Sparidae snapper Chrysophrys auratus :\1ugilidae yellow eyed mullet Aldrichetta jorsteri Odacidae blue rock whiting Haletta semifasciata GempyJidae barracouta Thyrsites atun Plcuronectidae greenback flounder Rhombosolea tapirina long snouted flounder . Ammotretis rostratus Monacanthidae : leatherjackets : various

The commercial fish catches of Western Port have fluctuated considerably from year to year since eatch records began in 1914, but were steadily increasing up to 1970. The interannual variability has been largely attributed to changes in fishing effort and natural variation in recruitment (:\1acDonald 1992; Jenkins et al. 1993). However, a large decline in total commercial catch occurred between 1970 and 1984. The catch dropped from about 260 tonnes per year to 150 tonnes per year, with a further decline to about 110 tonnes per year in the. early 1990s (Figure 10.2). The 1974-1985 decline 2 coincided with a significant reduction in the area of seagrass habitat, a loss of approximately 180 km •

93 Environment Protectwn A.uthority The Western Port Marine Environment

Loss of seagrass (and therefore fish production) is thought to be the most likely explanation for the obselVed catch declines (MacDonald 1992, and unpublished data).

,.,

T 0 ". :,..,• , } Total ro commercial catch • 1$10, "" "3' " ... '''' ,,'" 14'" ... , 6IJ -

T 45 0 • ,. King George • whiting , commercial catch " • ,.,. 191. '''' ",. '''' .... "'" "'., "'" "! "t :301 Rock flathead :" 1 commercial catch 1 "" '960 7.171 "'" ,:1

~ ,,1 Grass whiting " , (stranger) 1 commercial catch ,,., ,..., ,,.. 7D111 '910 "" ,'" " .. "'"'" -

Figure 10.2 Commercial fISh catches in Western Port (Published and unpublished data provided by Dr. CAl MacDonald)

94 Environment Protection Authority The Western Port Marine Environmeut

The species for which commercial catches most noticeably declined were King George whiting, rock flathead, blue rock or grass whiting and several leatherjacket species. All of these, except King George whiting, are directly associated with seagrass habitats. It is likely however that juvenile King George Whiting are indirectly dependent on food items derived from seagrass systems (Jenkinset ai. 1993; Edgar & Shaw 1995a). Although it is possible that increased fishing pressure could have contributed to dcclines in some species, the decline of non-targeted, bycatch species such as the leatherjackets and blue rock whiting suggest that fishing pressure was not the sole Or even the primary cause. The fact that catches of King George whiting in Port Phillip Bay did not decline over this period, despite probable increases in catch and fishing pressure (MacDonald 1992) is additional evidence for this hypothesis. Catches of other commercial spccies, such as yellow eye mullet, Australian salmon and sea garfish have been generally unaffected, but the total commercial catch has remained low since the 1980s.

In addition to the commercial catch records, there is considerable anecdotal evidence of declines in both the commercial and recreational fishing in Western Port (Town and Country 20 September 1983; South Gippsland Sentinel l1mes 17 January 1984; Fishing World April 1984; Cranbourne Sun 13 June 1993). Evidence suggests there was an increase in recreational and commercial fishing in the mid 1960s, and decline in fish catches in the late 19605. The decline in fish catches, and the number of commercial fishers, is reported to have continued to the present, corresponding with massive habitat changes, particularly near Lang Lang (Ridgeway,pers camm.)

Despite a significant decline in fishery catches, most of the fish production loss due to seagrass denudation would have been amongst the small non-commercial species, notably syngnathids, clinids and scorpaenids. The loss of small fish production was estimated by Edgar & Shaw (1995a) to be significant.

95 Environment Protection Authority The Western Port Marine Environment

BIBLIOGRAPHY

The bibligraphy listed below includes all references used in the text of this document. Other publications found during the course of the investigation and relevant to various aspects the Western Port environment are also included.

AGC Woodward-Clyde Pty Limited. 1993. Victorian case study: coastal management and decision making processes in the Westernport region prepared for Victorian Department of Premier and Cabinet and Resource Assessment Commission Coastal Zone Inquiry.

Ahsanullah M. 1976. Acute toxicity of cadmium and zinc to seven invertebrate species from Western Port, Victoria. Australian Journal ofMarine and Freshwater Research 27: 187-196.

Ahsanullah M. Negilski D.S. and Tawfik F. 1980. Heavy metal content of Callianassa Spp. in Western Port. Australian Journal ofMarine and Freshwater Research 31:847-850.

Andrew D.L. 1981. Sites of zoological significance in the Westernport region (W04-903) interim report: planning policy area one and French Island. Victorian National Museum.

Andrew D.L., Lumsden L.F. and Dixon J.M. 1984. Sites of zoological significance in the Westernport region. National Museum of Victoria for the Environmental Studies Division. Ministry for Conservation. Victoria.

Amott G.H. 1974. An ecological study of the zooplankton of Westernport and adjacent Bass Strait waters. Report 4.4.2 to the Westernport Bay Errvironmental Study (1973-1974). Ministry for Conservation. Victoria.

Ashton D. 1972. Mangroves in Victoria. Victoria's Resources 13:27-30.

Attiwill P.M. and Clough B.F 1974a. The effects of nutrients on productivity of marine plants - A review. Project Report to the Westernport Bay Environmental Study (1973-1974). Ministry for Conservation. Victoria.

Attiwill P.M. and Clough B.F. I 974b. The role of mangrove and seagrass communities in nutrient cycling in Westernport Bay. Project Report 4.3.7 to the Westernport Bay Environmental Study (1973- 1974). Ministry for Conservation. Victoria.

Attiwill P.M. and Clough B.F. 1978. Productivity and nutrient cycling in the mangrove and seagrass communities of Westernport Bay. Publication No. 253. Environmental Studies Series. Ministry for Conservation. Victoria.

Attiwill P.M. Clough B.F 1980. Carbon Dioxide and Water Vapour Exchange in the W'bite Mangrove. Photosynthetica 14:40-47.

Aust Government (Ed.) 1988. Noise Control Act. Aust Government. ACT.

Australian and New Zealand Environment Council. 1990. National water quality guidelines Background statement and water quality criteria.

96 Environment Protect/on Authority The Western Port Marine Environment

Australian & New Zealand Environment & Conservation Council 1992. Australian Water Quality Guidelines for Fresh and Marine Waters. National Water Quality Management Strategy.

Australian Water Supply and Sewerage Authorities. 1981. Standard Specifications for Various Forms of Pumps.

Axelrad DM. 1978. Effect of the Werribee Sewage Treatment Farm Discharge on Phytoplankton Productivity Biomass and Nutrients in Port Phillip Bay (Task No. P603). Melbourne.

Axelrad DM. 1986. Experimental addition ofthe snapping shrimp to a seagrass bed in Western Port. Internal Report. No. 144. Marine Science Laboratories. Queenscliff.

Axelr.ad D.M. and Bulthuis D.A. 1977. Phytoplankton nutrient limitation in the Gippsland Lakes. Environmental Stodies Series. Ministry for Conservation. Victoria.

Ayling G.M. 1974. Uptake of cadmium, zinc, copper, lead and chromium in the pacific oyster, Crassostera gigas, grown in the Tamar River, Tasmania. Water Research 8:729-738.

Baird D. 1995. Presentation to EPA Workshop on Western Port Marine Environment. 13 February 1995.

Baker G. 1942. Sand Stalagmites. Journal of Geology 50:662-667.

Baker G.1945. Heavy black sands on some Victorian beaches. Journal ofSedimentary Petrology 15: 11-19.

Barson M.M. 1976. Tidal salt marshes in Victoria. Victoria's Resources 18:11-14.

Barton C.M. 1975. A geotechnical facies analysis of some quarternary sediments beneath Westernport Bay. Proceedings of the Royal Society of Victoria 87: 139-147.

Bate W. and Maries F. 1974. History ofthe Western Port region. Project Report No. 3.1. to the Westernport Bay ElWironmental Study (1973-1974). Ministry for Conservation. Victoria

Bate W. and Maries F. 1978. Dilemma at Western Port: a case study in land use conflicts and the growth of the planning imperative. Sarrett Publishing. Melbourne.

Bauld 1. 1974. Role of bacteria in nutrient cycling in aquatic ecosystems. Report 4.3.8 to the Westernport Bay Environmental Study (1973-1974). Ministry for Conservation. Victoria.

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II i! Environment Protection Authority The Western Port Marine Environmelll

McKinnon A.D. and Kimmerer W.J. 1984. Description of the male of Labidocera caudataNicholls (1944) (Copepoda: Pontellidae) with remarks on the female. Proceedings of the Royal Society of Victoria 96: 169-172.

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Phillips DJ.H. 1976. Zinc, cadmium, lead and copper in Victorian waters: their incidence and effects. Msc. Thesis. University of Melbourne.

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,~; Envir()nment Protection Authority The Western Port Marine Environment

Robertson AJ. 1984. Trophic interactions between the fish fauna and macrobenthos of an eelgeass community in Western Port Victoria. Aquatic Botany 18: 135-153.

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PERSONAL COMMUNICATIONS

Dr D. Ashton (1995). Latrobe University

Mr. D. Ball (I996). Victorian Institute of Marine Sciences.

Dr K Burns (1995). Australian Institute of Marine Science

Mr. R. Cowdell (1996) Victorian Fisheries Research Institute

Professor J. Hinwood (1995) Monash University

Mr. M. Marsden (1995)

Mr. A. Murray (1995) Australian Geological Survey Organisation

Dr B. Robinson (1996) Environment Protection Authority ng Mr. B. Ridgeway (1995)

Mr. C. Shaw (1995) University of Melbourne

Dr I. Wallis (1995) Consulting Environmental Engineers

Dr J. Watson (1995) Marine Science and Ecology

of n.

123 ENVlr(ONMENT PROiECTlON AL:iHORJiY

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