THE BENTHIC FAUNA OF THE TUGGERAH LAKES B. J. Powis This thesis is submitted for the Degree of Master of Science at University of New South Wales JULY, 1975. UNIVERSITY CF N.3.W.,, 55701 1 3. JAN. 7 6 LIBRARY This is to certify that this thesis has not been submitted for a higher degree to any other university or institution. ACKNOWLEDGEMENTS I would like to thank Dr. R.J. MacIntyre for his continued guidance and advice throughout this project. This study was financed by the Electricity Commission of N.S.W. and the Wyong Council. I would like to thank them for this assistance. I would also like to thank the Electricity Commission for their cooperation and assistance in the collection of field material. I am grateful to the following people for their assistance in the identification of the various taxonomic groups: Dr. Pat Hutchings (polychaetes), Cathy Drummond (crustaceans) and Dr. Winston Ponder (molluscs). I am also very grateful to Leon Collett who has given a great deal of assistance in many areas of this study, especially with the computer analysis. With regard to the use of computer programs I would like to thank Alan Collins who has given a great deal of assistance with the computer analysis. Thanks are also due to Professor Stephenson for his advice on statistical procedures. Considerable assistance has been given in the collection of samples by Bill Jefferson, Stephen Sparkes, Gary Bebbington, Bruce Hodgson and Ray Wallis. For proof reading and grammatical correction of the text I would like to thank Helen Stoddart, Charles Pregenzer, Harry Booth and Paul Kloedon. I would also like to thank Judi for her expert drawings and Mrs. Hutton for her typing. SUMMARY Qualitative and quantitative studies were conducted on the benthos of Tuggerah Lakes. Fifty-eight sites were sampled in the qualitative study using a diver-held corer. Information analysis was used to delineate the major faunal groups. Four groups were found and all were related to the substrate type. The substrates were; mud, sand, weed in mud, and weed in muddy sand. Nineteen sites were sampled in the quantitative surveys. These were sampled both in winter and summer. Within any substrate the fauna throughout the three lakes was homogeneous and seasonally stable. The most diverse communities were those associated with the weed Zostera capricorni. Assessment of the effects upon the benthos of Munmorah Power Station and of weed clearing operations were made. The Power Station discharge changed the community structure in weed beds. Only in weed near the discharge were found large numbers of the gastropod Velacumantis australis. A "before and after" study of a weed clearing operation showed that it greatly reduced the numbers of both species and individuals living in the test plot. The effects upon the benthos of a very severe flood were shown to be rather variable. The mud and Halophila fauna was greatly euffected with a reduction of species and of individuals. However, no other weed areas were affected. CONTENTS PAGE LIST OF FIGURES i LIST OF PLATES CHAPTER 1 INTRODUCTION 1 CHAPTER 2 AREA STUDIED 3 2.1 TUGGERAH LAKES 3 2.2 LAKE MACQUARIE 5 CHAPTER 3 PRELIMINARY SURVEY 9 3.1 INTRODUCTION 9 3.2 METHODS 9 3.3 RESULTS 15 3.4 DISCUSSION 30 CHAPTER 4 QUANTITATIVE SURVEY 31 4.1 INTRODUCTION 31 4.2 METHODS 31 4.3 RESULTS AND DISCUSSION 35 4.31 Faunal Similarity 35 4.32 Community Structure of Site 43 Groups 4.33 Comparisons with Fauna of Lake 56 Macquarie CHAPTER 5 THE EFFECT OF A SEVERE FLOOD UPON THE 63 BENTHOS 5.1 GENERAL EFFECTS 63 5.2 THE HALOPHILA COMMUNITY 64 5.3 FAUNA OUTSIDE OURIMBAH CREEK 68 CHAPTER 6 THE EFFECT OF WEED CLEARING OPERATIONS UPON 72 THE BENTHOS 6.1 INTRODUCTION 72 6.2 METHODS 74 6.3 RESULTS AND DISCUSSION 74 CHAPTER 7 THE EFFECT OF POWER STATION DISCHARGES UPON 77 SHALLOW WATER BENTHOS 7.1 INTRODUCTION 77 7.2 SCUBA OBSERVATIONS 79 7.3 BEHAVIOURAL EXPERIMENTS 79 7.4 POWER STATION DISCHARGES AND BENTHOS: 83 AN OVERVIEW CHAPTER 8 GENERAL CONCLUSION 84 REFERENCES 85 APPENDIX A SITE/SPECIES DATA FOR PRELIMINARY SURVEY 87 APPENDIX B CLASSIFICATION TECHNIQUES 95 APPENDIX C SITE/SPECIES DATA FOR QUANTITATIVE SURVEYS 108 APPENDIX D HYDROLOGICAL DATA 113 APPENDIX E DESCRIPTION OF SPECIES 117 LIST OF FIGURES PAGE Tuggerah Lakes 2 2 Sediment of Tuggerah Lakes 4 3 Circulation in Budgewoi/Munmorah Lakes g 4 Lake Macquarie 7 5 Sampling Sites in Munmorah Lake 10 6 Sampling Sites in Budgewoi Lake 11 7 Sampling Sites in Tuggerah Lake 12 8 Distribution of Nassarius fonasi 17 9 Distribution of Xenostrobus securis 18 10 Distribution of Owenia fusiformis 19 11 Distribution of Nereis (Hediste) diversicolor 20 12 Distribution of Macoma deltoidalis 21 13 Distribution of Family Capitellidae 22 14 Dendrogram of Site Groups in Preliminary Survey 24 15 Topographic Illustration of Site Groups 25 16 Isoplethes of the Abundance of Owenia fusiformis 29 and Nereis diversicolor 17 Sampling Sites for Quantitative Surveys 32 18 Dendrogram of Winter Site Groups 36 19 Topographic Illustration of Winter Site Groups 37 20 Dendrogram of Summer Site Groups 39 21 Topographic Illustration of Summer Site Groups 40 22 Number of Species in Mud Zone 42 23 Number of Individuals in Mud Zone 42 24 Particle Size Structure of Sediment in the Mud 44 Zone 25 Number of Species at Zostera Sites 48 26 Number of Individuals at Zostera Sites 48 ii 27 Abundance of various species at Zostera Sites 49 28 Sampling Sites in Myuna Bay 59 29 Salinity Levels at Site 3 for the Period 62 4/73-12/74 30 Total Number of Individuals Present in Mud Zone 66 before and after the Flood 31 Distribution of Dead Velacumantis Outside the 78 Discharge of Munmorah Power Station 32 Test Chamber Used in Behavioural Study of 80 Velacumantis 33 Response of Velacumantis to a Temperature 82 Gradient 34 Choices of Classification 97 35 The Dendrogram 97 36 Divisive and Agglomerative Dendrograms 100 37 Group Average Sorting 105 iii LIST OF PLATES PLATE PAGE 1 A Core being taken in Shallow Water 14 2 Owenia fusiformis 27 3 Nereis diversicolor 27 4 A Core being taken in Deep Water 46 5 Debris from Ourimbah Creek 67 6 Weed in. Budgewoi Lake 71 7 Weed Clearer in Operation 73 1 CHAPTER 1 INTRODUCTION Benthic animals live in or above the sediment. They are an integral part of the aquatic food chain. Apart from work conducted by MacIntyre (1959) there is very little knowledge regarding the ecology of benthic animals in estuarine lakes in Australia. It was the aim of this investigation to examine in detail the benthos of the Tuggerah Lakes. The Tuggerah Lakes fauna were examined in two ways. Firstly, a qualitative study was carried out to establish what species were present and where. Secondly, a quantitative seasonal study was done to examine the differences in community structure of the benthos throughout the three lakes. A comparative study was also carried out on the fauna of Myuna Bay in Lake Macquarie. The area around Tuggerah Lakes is rapidly becoming the site for large scale regional development. The effects of man's influence upon the lake system need to be minimal if the lakes are to survive unchanged. This study examined the effects upon the benthos of changes in the lakes' ecology induced by power stations and weed clearing operations. The impact of the changes must, however, be considered in relation to the effects of natural phenomena. The effects upon the benthos of a severe flood that occurred in the Tuggerah Lakes were also examined. 2 Munmorah Power Station Wallerah Creek Munmorah Wyong Creek Ourimbah Creek The Entrance Long Jetty Figure 1. - The Tuggerah Lakes. 3 CHAPTER 2 AREAS STUDIED 2.1 TUGGERAH LAKES Tuggerah Lakes consist of three interconnected lakes - Munmorah Lake, Budgewoi Lake and Tuggerah Lake (Figure 1) - located 112 kilometres north of Sydney. They have an area of 116 square kilometres. The water level in the lakes is controlled mainly by the amount of freshwater runoff, most of which is fed into the lakes by one of three creeks. These are Wallarah Creek located in Budgewoi Lake and Wyong and Ourimbah Creeks situated in Tuggerah Lake. Tidal exchange is negligible with the rate of seawater exchange being restricted by the narrow channel connecting Tuggerah Lake to the Pacific Ocean. This channel is located near the township of "The Entrance". The lakes are shallow with an average depth of only 2 metres (Higginson, 1971). They are also essentially brackish with salinities of 17°/oo to 25°/oo being most common. Tuggerah Lake, because of its connection to the Ocean, has the highest salinities of the three lakes (Harper, 1972). Three weed species exist in the lakes; Zostera oapricorni Ashers, Ruppia spiralis Dumort and Ealophila sp. Weiner (1974), working on the distribution of these weeds in Tuggerah Lakes, has shown that all three species are found in a band around the perimeter of the lakes. Roy and Peat (1974) have analysed the sediments of the three lakes. Four basic types were recognised; Sand, Muddy 4 Sandy Mud (51-99% mud) Muddy Sand (0-50% mud) Sand Figure 2. - The sediment of Tuggerah Lakes (modified after Roy and Peat 1974). 5 Sand (1-50% mud), Sandy Mud (51-99% mud) and Mud. A simplified version of their sediment map is presented in Figure 2. A feature of the Munmorah/Budgewoi Lakes is an artificial warm water current that circulates from the discharge of Munmorah Power Station, located in Budgewoi Lake, to the intake of the Power Station which is located in Munmorah Lake (Figure 3).