Conservation of Natural Wilderness Values in the Port Davey Marine and Estuarine Protected Area, South-Western Tasmania

Home , Bathurst Channel, Davey River, Kelly Basin, Maugean skate, Munday Island, Port Davey

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) Published online 3 December 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/aqc.1079

Conservation of natural wilderness values in the Port Davey marine and estuarine protected area, south-western Tasmania

GRAHAM J. EDGARa,b,Ã, PETER R. LASTc, NEVILLE S. BARRETTb, KAREN GOWLETT-HOLMESc, MICHAEL DRIESSENd and PETER MOONEYe aAquenal Pty Ltd, GPO Box 828, Hobart, Tasmania, Australia 7001 bTasmanian Aquaculture and Fisheries Institute, University of Tasmania, GPO Box 252-49, Hobart, Tasmania, Australia 7001 cCSIRO Divison of Marine and Atmospheric Research, Castray Esplanade, Hobart, Tasmania, Australia 7000 dDepartment of Primary Industries and Water, Hobart, Tasmania, Australia 7000 eParks and Wildlife Service, Hobart, Tasmania, Australia 7000

ABSTRACT 1. Port Davey and associated Bathurst Harbour in south-western Tasmania represent one of the world’s most anomalous estuarine systems owing to an unusual combination of environmental factors. These include: (i) large uninhabited catchment protected as a National Park; (ii) ria geomorphology but with fjord characteristics that include a shallow entrance and deep 12-km long channel connecting an almost land-locked harbour to the sea; (iii) high rainfall and riverine input that generate strongly-stratified estuarine conditions, with a low-salinity surface layer and marine bottom water; (iv) a deeply tannin-stained surface layer that blocks light penetration to depth; (v) very low levels of nutrients and low aquatic productivity; (vi) weak tidal influences; (vii) marine bottom water with stable temperature throughout the year; (viii) numerous endemic species; (ix) strongly depth-stratified benthic assemblages exhibiting high compositional variability over small spatial scales; (x) deepsea species present at anomalously shallow depths; (xi) no conspicuous introduced taxa; (xii) a predominance of fragile sessile invertebrates, including slow-growing fenestrate bryozoans; and (xiii) sponge spicule- and bryozoan-based sediments that are more characteristic of deep sea and polar environments than those inshore. 2. Although this region has historically been protected by its isolation, seven major anthropogenic stressors now threaten its natural integrity: boating, fishing, dive tourism, nutrient enrichment, introduced species, onshore development, and global climate change. These threats are not randomly distributed but disproportionately affect particular habitat types. 3. For management of environmental risk, the Port Davey–Bathurst Harbour region is subdivided into six biophysical zones, each with different ecological characteristics, values, and types and levels of potential threat. In response to the various threats, the Tasmanian Government has enacted an adaptive management regime that includes a multi-zoned marine protected area and the largest ‘no-take’ estuarine protected area in Australia. Copyright r 2009 John Wiley & Sons, Ltd.

Received 4 February 2009; Revised 20 August 2009; Accepted 25 August 2009

KEY WORDS: benthic invertebrates; climate change; diver impacts; ﬁshes; introduced marine pests; World Heritage Area

INTRODUCTION (Roberts and Hawkins, 1999; Jackson et al., 2001; Dulvy et al., 2003; Boyd et al., 2008). Nevertheless, a few remote regions, As a consequence of increasing global pressures on ecosystems, including much of the oceanic, deepsea, polar and subpolar including ﬁshing, dispersal of air- and water-borne pollutants, biomes, approach this condition (Halpern et al., 2008). translocation of invasive species, and climate change, no Within temperate regions, where coastlines are generally marine region is now appropriately regarded as ‘pristine’ heavily-populated and developed, the Port Davey–Bathurst

*Correspondence to: G. J. Edgar, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, GPO Box 252-49, Hobart, Tasmania 7001, Australia. E-mail: [email protected]

Harbour estuarine system ranks as near pristine. It also for stripping of blubber and rendering of oil until the late arguably comprises the world’s most unusual estuary in both a 1890s, when stocks of that species had also become physical and ecological sense. commercially extinct (Luckman and Davies, 1978; Port Davey and Bathurst Harbour, two connected Kostoglou, 1995). embayments located on the south-western coast of Tasmania Towards the end of the 19th century, commercial fishing (Figure 1), form the only large estuarine system in southern developed in the region. The primary resource was native Australia without significant human impact. No roads or river oysters, which were harvested in tens of tonnes from James impoundments are present within the 2000 km2 catchment Kelly Basin and transported to Hobart. Because of area. Vegetation remains uncleared within the catchment other overharvesting and perhaps also disease, stocks of oysters than c.1 km2 of alluvial tin mine workings at Melaleuca, south collapsed around 1890 to negligible levels today. The most of Bathurst Harbour (Figure 1), and small abandoned important fishery resources exploited during the 20th century settlements for timber workers and bay whalers developed in have been abalone and rock lobsters taken by visiting boats the early 19th century, with associated selective logging of and one resident fisher, with minor quantities of finfish also huon pine stands along rivers at that time. The resident captured (Edgar, 1984; Resource Planning & Development population within the catchment during the past century has Commission, 2003). not exceeded 20 persons, and presently comprises two retired Other than minor tourism visits, the only commercial tin miners, supplemented by seasonally-varying numbers of activity additional to fishing undertaken during the past fishers and increasing numbers of tourists, scientists and century has been small-scale mining on claims generally managers. operated by one or two men. The largest mining field in the Because of the unusual nature of the Port Davey region and region, now abandoned, was located just outside the increasing tourism in wild areas, the maintenance of natural catchment of Bathurst Harbour on the southern Tasmanian environmental values constitutes an urgent priority for coast. An associated tin deposit beside Melaleuca Lagoon, a management as well as comprising a major administrative tributary of Bathurst Harbour, was first developed in 1935. challenge. The aims of the present paper are to: (i) summarize Initial operations at this lease involved a team of 19 men but results of unpublished ecological studies that were undertaken activity quickly dwindled, with only one to three miners to improve management in the region; (ii) integrate these working near Melaleuca Lagoon from 1941 to 2007. results with published studies to describe regional biophysical characteristics; (iii) assess threats to the biotic integrity of the History of natural resource management region; (iv) outline current management responses; and (v) provide additional recommendations to safeguard natural Following initial proclamation of a Foreshore Scenic Reserve values. in 1951 and the addition of extra lands in 1962 and 1974, the 925 km2 Port Davey catchment and 1050 km2 Bathurst Harbour catchment were fully included within a national History of natural resource exploitation in the Port Davey 2 region park with one exclusion (Edgar et al., 1999a). A small 18 km corridor permits regulated mining activity within the Bathurst Coastal south-western Tasmania, including the Port Davey Harbour catchment south of Melaleuca Lagoon. The region, has a long history of Aboriginal occupation that Southwest National Park, which includes the two large extends back at least 30 000 years. Aboriginal inhabitants catchments, is recognized as a UNESCO Biosphere Reserve modified the coastal landscape by establishing foot tracks and under the ‘Man and the Biosphere Program’, and was formally by frequent firing of vegetation to maintain moorlands. recognized by UNESCO in 1982 as a core component of the Because of relatively low plant productivity in hinterlands, Tasmanian Wilderness World Heritage Area. With south- much of the Aboriginal diet consisted of marine animals, western New Zealand and southern South America, it forms including periwinkles, abalone, fur seals, rock lobsters, one of only three major temperate wilderness areas in the limpets, oysters, cockles and shearwaters, but apparently not Southern Hemisphere. finfish (Luckman and Davies, 1978). Although the Southwest National Park included marine European history in the region commenced in 1642 with the waters inland from a line drawn across the heads of Port discovery by Abel Tasman of the southern and western Davey (Resource Planning & Development Commission, Tasmanian coastlines. Although several French and English 2003), marine and estuarine organisms were not protected expeditions passed nearby in the late 18th century, Port Davey from fishing or other exploitative activities within this national was not discovered and named until 1815. In that year a boat park until January 2005, when a zoned marine (and estuarine) visited the area in search of stands of huon pine for protected area (MPA) was gazetted. Fishing is now prohibited shipbuilding. Abundant huon pine was found, inaugurating a within Bathurst Channel, Bathurst Harbour, James Kelly timber industry that persisted intermittently in the region for Basin, Hannant Inlet, Inner Saddle Bight, and northern Port the next 65 years. At the peak of activity, a short-lived Davey. Limited fishing by hook and line, and rock lobster and settlement with over 50 inhabitants was established at the abalone capture, are permitted in central and southern Port mouth of the Davey River (Luckman and Davies, 1978). Davey, which is classed as a Habitat Protection Zone (see For about 40 years from the early 1830s, small ‘bay Figure 1). whaling’ settlements of up to 10 workers were also established Management actions within the region follow two statutory in Port Davey. These settlements were primarily developed for management plans: the Tasmanian Wilderness World Heritage the capture of inshore southern right whales, but local Area Management Plan 1999, which has precedence, and the populations of this species quickly declined. Sperm whales Melaleuca-Port Davey Area Plan 2003 (Parks and Wildlife captured further offshore were then brought into Port Davey Service, 2004). A Key Desired Outcome recognized in the

Copyright r 2009 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) CONSERVATION OF NATURAL WILDERNESS VALUES IN A MPA 299

Davey River Southwest National Park

Payne James Bay Spring Kelly River Basin

Bramble Joe Saddle Cove Page Bight Breaksea Bay Old Island River Bathurst Port Davey Harbour Bathurst Channel Celery Top Islands Hannant Horseshoe Inlet Inlet Melaleuca Inlet Melaleuca Lagoon

Figure 1. Map of Port Davey–Bathurst Harbour marine and estuarine protected area. latter document is that ‘the marine and estuarine ecosystems of following a series of studies primarily commissioned to assist Port Davey–Bathurst Harbour are maintained and protected’. management of the region (see online supplementary material; Appendix 1). These included quantitative descriptions of aquatic biodiversity and baseline assessments of MPA zones History of aquatic research (Last and Edgar, 1994; Barrett et al., 1998; Richardson et al., Other than very limited observations, nothing was known 1998; Edgar et al., 1999a,b), habitat mapping (Barrett et al., about the underwater character of the Port Davey region until 2004), introduced marine pest surveys (Aquenal, 2003; Sutton 1979. In that year a diving expedition to Bathurst Channel — et al., 2006; Hirst et al., 2007), and assessment of potential the narrow 12 km long passage-way connecting Port Davey to impacts of cruise ship visits (Ellis et al., 2005). Bathurst Harbour — was organized in conjunction with statewide investigations of beach-seined and rotenone- The physical and hydrological environment collected fishes (Last, 1983). Participants of this expedition immediately recognized the unusual nature of the Bathurst Port Davey, Bathurst Channel and Bathurst Harbour Channel ecosystem. One new fish species collected on that trip comprise a drowned river ‘ria’ system, which includes, as (a species of cusk-eel belonging to the genus Microbrotula) still Bathurst Harbour, a large plain that was flooded about 10 000 represents the sole record of that species. years ago following sea-level rise. Although not of glacial Following recognition that the Bathurst Channel ecosystem origin, Bathurst Channel possesses many characteristics of was different to elsewhere in Tasmania, the National Parks fjords, including a shallow (o8 m depth) constricted sill at the and Wildlife Service (NPWS) commissioned a study of fishes, western entrance, deeper waters within, and a narrow central invertebrates and macroalgae that again highlighted the channel, which is generally about 300 m wide and 20–45 m unusual nature of benthic communities. The major physical deep mid-channel. cause was suggested to be a lack of light passing through dark Reef habitats are limited in distribution within Bathurst tannin-stained surface waters, which allowed a community of Channel, with most reef substrata located off headlands where sessile invertebrates to thrive in unusually shallow depths strong currents prevent sediment from settling (Barrett et al., (Edgar, 1984). 2004). Soft sediments carpet most of the estuarine system but In 1988, NPWS commissioned further surveys of the because different dominant species are responsible for hydrology and ecology of the Port Davey–Bathurst Harbour bioturbation, marked differences exist in the appearance of estuarine system (Edgar, 1991a,b; Edgar and Cresswell, 1991). the sediment surface in different depths and along the axial Surface waters in Bathurst Harbour were found anomalously cline. The most common substratum categories in order of depauperate in nitrates, and the plankton community included frequency of occurrence are silt, silty sand, hard sand and few taxa. The Bathurst Harbour fish assemblage was also rubble (Barrett et al., 2004). shown to be unusual in being dominated by sharks and skates Within the open coastal embayment of Port Davey, water rather than bony fishes. The fish fauna included a remarkable driven by waves and currents through the heads and previously unknown, estuarine-dependent species of skate predominantly moves clockwise. Wave action mixes marine with closest living relatives in New Zealand and South water with riverine water from the Davey River to the north America (Last and Yearsley, 2002; Last and Gledhill, 2007). and brackish surface waters entering from Bathurst Channel to Knowledge about the Port Davey, Bathurst Channel and the east. Sea water in western Port Davey is little affected Bathurst Harbour ecosystems advanced rapidly after 1992 by freshwater runoff as a consequence of this circulation

Copyright r 2009 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) 300 G.J. EDGAR ET AL. pattern, whereas waters in the north and east are strongly Port Davey, and bottom waters in Bathurst Harbour and estuarine-influenced. Two large, shallow sedimentary basins, Bathurst Channel, typically possess nitrate concentrations of James Kelly Basin and Hannants Inlet, connect to Port 1–3 mmol LÀ1 (Edgar and Cresswell, 1991). Davey, and support sparse beds of seagrasses and Caulerpa algae. Waters passing through Bathurst Channel from Bathurst Harbour are very strongly stratified for most of the year, with PATTERNS OF DISTRIBUTION OF MARINE a low-salinity surface zone of mixed fluvial and marine BIODIVERSITY origin overlying fully marine waters below (Thomson, 1978a,b; Edgar and Cresswell, 1991; Last and Edgar, 1994). General characteristics of the flora and fauna The depth of the halocline separating these zones varies All marine and estuarine species reported from the Port seasonally from 0 m during extended dry periods in summer to Davey–Bathurst Harbour region, including museum records c.6 m during peak winter rainfall. and descriptions in unpublished reports and journal The two water layers differ markedly in physico-chemical publications, are listed in online supplementary information. characteristics, including temperature, salinity, transparency, A total of 46 microalgal species, 119 macroalgae, one seagrass, chemical composition and density. Bottom water has a very 609 macro-invertebrates, and 102 fishes have been recorded 1 stable temperature at about 14 C throughout the year, whereas (Table 1). Compared with other regions of Tasmania, the surface temperatures in Bathurst Harbour range from 5 to invertebrate fauna is diverse, the seaweed flora moderately- 1 25 C annually (Edgar and Cresswell, 1991). diverse, and the fish fauna depauperate. Although Port Davey has a small tidal range (c.0.3 m in One notable aspect of compiled species lists for both western Bathurst Channel), strong current flows are generated invertebrates and algae is that relatively few species have been through Bathurst Channel as a consequence of the large recorded during more than one survey (Table 1). Only 21% of surface area of Bathurst Harbour and long constricted invertebrate and algal species have been recorded on at least two connection to the sea. Great quantities of water move in and occasions. This low percentage of duplicate records clearly out with tides and atmospheric changes in barometric pressure, indicates that the biota remains largely unexplored, with many which frequently affect the tide as much as lunar influences. new records for the region yet to be discovered. Fishes comprise Water currents are particularly strong off headlands associated the best studied group, with 37% of species reported only once. with constrictions in Bathurst Channel. Because of interacting Echinoderms are the next best studied group, but the majority density and tidal gradients, low-salinity surface waters at the (60%) had only been reported during one investigation. entrance to Bathurst Channel can at times flow strongly A second notable aspect of the fauna is that it includes a towards the sea while currents at depths410 m move rapidly relatively large component of undescribed species, including in the opposite direction. numerous possible endemic species that have not been Riverine water entering the estuary is darkly stained by recorded elsewhere. Further research on offshore continental tannins and other humic leachates because of a predominance shelf and upper continental slope environments is required to of peaty soils within the catchment. This ‘tannin-staining’ has properly assess the level of biotic endemism. The fauna of deep profound effects on the estuarine ecosystem, primarily because Tasmanian reefs is virtually unknown but clearly has an light is very rapidly absorbed within the surface layer, affinity with some elements of the benthic fauna in Bathurst precluding plant photosynthesis and net primary production Channel (Barrett and Edgar, in press). Several invertebrate at depths greater than 2 m for most of the year. During winter, species identified in Bathurst Channel are widespread in divers swimming within the marine bottom layer are generally unable to see any light from the sun, while another diver with a Table 1. Total number of marine species in major taxonomic groups torch at 40 m distance is readily seen in conditions of recorded from the Port Davey–Bathurst Harbour region, and number exceptional horizontal water clarity. of species recorded on only one occasion Aquatic productivity within Bathurst Harbour and Taxon Species Single records Percentage Bathurst Channel also appears to be negatively affected by single records ancient nutrient-depleted bedrock in surrounding catchments and poor local soils. Whereas estuaries worldwide typically Diatoms 21 21 100 Dinoflagellates 25 21 84 show increasing nutrient concentrations upstream (Lee et al., Macroalgae 119 86 73 2004), surface waters in Bathurst Channel and Bathurst Seagrasses 1 1 100 Harbour show the opposite trend. In a 1988/1989 Sponges 30 28 93 investigation of dissolved nitrate, surface concentrations were Cnidarians 32 28 88 found to be below detectable limits ( 0.1 mmol LÀ1) in all four Polychaetes 78 65 83 o Sipunculids 1 1 100 seasons of the year in Bathurst Harbour (Edgar and Cresswell, Echiurans 1 1 100 À1 1991) compared with c.1 mmol L near the entrance. Pycnogonids 4 3 75 Nitrate levels near detection limits were also encountered in Crustaceans 150 130 87 a second seasonal study in 1995/1996 in Melaleuca Inlet, a Kamptozoans 2 2 100 Bryozoans 61 55 90 southern tributary waterway of Bathurst Harbour (Davies and Chaetognaths 1 1 100 Driessen, 1997). That study further indicated that phosphate Molluscs 165 145 88 concentrations were almost equally low. Nitrate, nitrite and Echinoderms 30 18 60 phosphate concentrations were slightly elevated in summer Ascidians 54 51 94 2001 (Davies and Driessen, 2002), probably because of the Fishes 102 38 37 Total 877 695 79 incursion of marine water. Marine waters in the vicinity of

Copyright r 2009 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) CONSERVATION OF NATURAL WILDERNESS VALUES IN A MPA 301 offshore waters but have not previously been recorded in and death in predatory species including humans (Hallegraeff depths o40 m (e.g. the sea whip Primnoella grandisquamis, the et al., 1988, 1989; Hallegraeff, 1992). gorgonian Pteronisis plumacea, the kamptozoan Pedicellinopsis fructicosa, and the ascidian Ascidia challengeri) (Kott, 1985; Alderslade, 1998). Soft-sediment communities The presence of one endemic fish species (the cusk-eel, Microbrotula sp.) is notable. Port Davey is the only Australian The sediments in Bathurst Channel are unusual for inshore estuary with a fish species not recorded elsewhere. The ecosystems. They possess a high proportion of silicious sponge presence of the near endemic Maugean skate Zearaja spicules and calcareous bryozoan fragments, and thus show maugeana is also highly unusual (Last and Gledhill, 2007). considerable similarity to sediments generated at some deepsea Although this large fish has now been recorded from one other and polar locations (Reid et al., 2008). Bathurst Channel has estuary in western Tasmania (Macquarie Harbour), very few been regarded as a unique location for studying sediment elasmobranch species worldwide occur primarily in temperate formation because processes that normally occur in depths estuaries and no other skates are known to be restricted to 460 m can potentially be investigated in diveable depths (Last estuaries. This skate has interesting phylogenetic relationships and Edgar, 1994). with its nearest relatives in New Zealand and Chile, indicating In contrast to the biogenically-formed sediments in a Gondwanan connection (Last and Stevens, 1994; Last and Bathurst Channel, wave-sorted sands predominate through Yearsley, 2002; Last and Gledhill, 2007). much of Port Davey, and silts and muds comprise the predominant benthic habitat type in Bathurst Harbour. Sparse beds of seagrasses (most notably Zostera capricorni in Planktonic communities the low intertidal) are distributed around the margins of sheltered bays, while an unusual form of green alga (Caulerpa The little that is known about plankton in the Port Davey cf. trifaria) extends as a large bed within central James Kelly region is derived from a single one-year study in 1988/1989 Basin. (Edgar and Cresswell, 1991). Bathurst Harbour possessed a The soft sediment fauna and flora of the Port Davey region very low richness of phytoplankton and zooplankton taxa, remains poorly studied. Beach-seined fishes are generally particularly in comparison with a rich coastal and oceanic depauperate compared with other sites sampled around plankton biota in Port Davey; however, densities of planktonic Tasmania (Last, 1983; Edgar, 1991b; Edgar et al., 1999b). organisms in near-surface water showed a very pronounced The isolation of Port Davey, particularly the absence of gradient upstream with extremely high densities in Bathurst comparable sheltered habitats and seagrass beds for tens of Harbour. kilometres in both directions along the Tasmanian coast, The plankton flora in Bathurst Harbour consisted almost presumably contribute to the relative paucity of species. exclusively of blooms of a single dinoflagellate species Some information on subtidal fish assemblages on soft (Dinophysis acuminata) during the cooler months, but with sediments has been collected using gillnets set in Bathurst two other dinoflagellates (Gyrodinium cf. uncatenum and Channel and Bathurst Harbour (Edgar, 1991b). The fish fauna Potoperidinium cf. bipes) becoming almost as abundant as of the upper estuary (i.e. Bathurst Harbour) was remarkable in D. acuminata in summer (Edgar and Cresswell, 1991). The its predominance of sharks and rays, including gummy shark fauna was dominated by the calanoid copepod Gladioferens (Mustelus antarcticus), elephant shark (Callorhinchus milii), inermis, the cyclopoid copepod Oithona australis and the thornback skate (Dentiraja lemprieri), spotted dogfish (Squalus appendicularian Oikopleura sp., while larval bivalves and acanthias) and the Port Davey skate (Zearaja maugeana). The gastropods were also conspicuous in summer plankton latter two species are listed as threatened on the IUCN Red samples. List (IUCN, 2006), the spotted dogfish as Vulnerable and the Mixing between estuarine and oceanic assemblage types Port Davey skate as Endangered. The majority of species occurred in Bathurst Channel, with coastal species penetrating recorded in Bathurst Harbour notably possess distributions into Bathurst Harbour during the dry 1989 summer, and the that extend well beyond the coastal zone to at least the outer estuarine assemblage extending as a dominant component of continental shelf (Barrett and Edgar, in press). the plankton to the western limits of Bathurst Channel in Knowledge of benthic invertebrates associated with soft winter and spring. Diatoms were much more abundant than sediments is based on: (i) an analysis of 197 macroinvertebrate dinoflagellates in the marine waters of Port Davey (Edgar and species collected in grab samples at 70 subtidal locations Cresswell, 1991). distributed throughout the wider Port Davey–Bathurst Additional studies are needed to confirm whether seasonal Harbour system (Hirst et al., 2007); (ii) a study of intertidal patterns identified in 1988 and 1989 persist to the present. estuarine species collected in cores taken in James Kelly Basin A major recent concern is the presence in surface sediments and the mouth of the Old River (Edgar et al., 2000); (iii) studied in 2003 of cysts of the introduced toxic dinoflagellate subtidal cores collected during surveys of introduced marine Gymnodinium catenatum (Aquenal, 2003). This species, which pests (Aquenal, 2003); and (iv) minor collections of beach- was introduced into Australia about 1980, was not found in washed shells (Thomson, 1978a; Sullivan and Brain, 2003). samples collected in Bathurst Harbour in 1987 (Bolch and These studies indicate a soft-sediment invertebrate fauna that Hallegraeff, 1990), although recorded at that time on the varies with sediment type. The sandy sediments in Port Davey eastern Tasmanian coast (McMinn et al., 1997). Toxins are primarily dominated by crustaceans, while the muddier produced by blooms of Gymnodinium catenatum are sediments in Bathurst Channel and Bathurst Harbour are concentrated within the tissues of filter feeding bivalves such dominated by deposit-feeding polychaete worms. Species as mussels, potentially causing paralytic shellfish poisoning richness of infaunal macrobenthos is higher in Bathurst

Channel than Bathurst Harbour or Port Davey (Hirst et al., location, a transect line was extended from the shore down 2007). to the depth at which the habitat type stabilized, usually on Diving observations indicate that sediments in Bathurst mud at about 15 m depth. Divers recorded the biota present Harbour are far from homogeneous, with different regions under each transect line using video for permanent reference, affected by different bioturbator species (G. Edgar, personal and they also recorded on waterproof paper the depth at which observations). Callianassid shrimps, heart urchins, changes in major habitat types occurred. The results of these polychaetes, tube anemones, and holothurians each dominate surveys are described here. particular areas and presumably influence faunal community A total of six major biophysical zones were identified (see structure, with many associated species unidentified and Figure 2), four with geographic breaks that correspond with probably undescribed. major changes in Bathurst Channel communities (Barrett and Edgar, in press). Each geographic zone is subject to a different Rocky reef communities combination of anthropogenic threats. Plant and animal communities associated with reefs in Port Bramble Cove Zone Davey differ greatly from those found in Bathurst Channel and Bathurst Harbour, with few species in common (Edgar This zone extends from the western entrance of Bathurst and Barrett, in press). Within Port Davey, the fish fauna is Channel to Turnbull Island, including Bramble Cove (Figure 2). characterized by the virtual absence of some species that are It is characterized by brown and green algae distributed down to abundant elsewhere around the Tasmanian coast. The rocky about 5 m depth, with red algae occurring at 4–6 m. Below the reef fauna is even more depauperate in Bathurst Channel, algal zone, cup sponges are abundant down to at least 20 m, while less than ten species are known to be associated with together with sea whips, octocorals and solitary corals. In rocky reefs in Bathurst Harbour. deeper water, reef habitat grades into sand or mud substrata By contrast, mobile macrofaunal invertebrates, including with tube anemones common. mollusc, polychaetes and crustaceans, are rich and abundant in The sessile invertebrate assemblage in this zone is greatly western Bathurst Channel and eastern Port Davey (Edgar, restricted in distribution to steep subtidal walls fringing 1991a). The macroalgal flora is extremely rich in the same area, Bathurst Channel. This assemblage off Turnbull Island with numerous red algal species. Species numbers decline includes many delicate and fragile bryozoan, sea whip, rapidly along the estuarine cline towards Bathurst Harbour sponge, hydroid and ascidian species (Figure 3(A),(B)), hence (Barrett and Edgar, in press). is highly sensitive to mechanical damage from divers or by nets In general, the benthic rocky reef community in Bathurst and anchors. By contrast, Bramble Cove itself has a sandy Channel comprises an extremely anomalous ecological feature seabed and shallow algal-covered reefs, so possesses a high when compared with coastal and estuarine reefs elsewhere, resistance to physical damage. including Port Davey and Bathurst Harbour (Barrett and Edgar, (in press); Edgar and Barrett, in press). The sessile reef Bathurst Channel Sea Pen Zone biota varies along the estuarine cline, with foliose algae This zone extends from Turnbull Island along the channel to, reaching 20 m depth in Port Davey, 5 m depth at the western and including, Munday Island (Figure 2). It primarily differs entrance of Bathurst Channel, but not penetrating below 1 m from the Bramble Cove Zone in possessing the fucoid alga depth in eastern Bathurst Channel. Delicate sessile Hormosira banksii and green alga Ulva sp. on low intertidal invertebrates predominate below the macroalgal zone, and shores rather than the ‘bullkelp’ Durvillaea potatorum. Brown are most abundant below 5 m depth in western, and 2 m depth and green algae occur to a depth of 3 m with red algae in eastern, Bathurst Channel. extending down to 5 m. A rich and diverse band of plate and Darkly tannin-stained surface waters severely restrict light encrusting sponges, bryozoans, solitary ascidians, soft corals penetration, thereby regulating the maximum depth at which and other sessile invertebrates occurs from 3 to 7 m. Sea pens algal species survive in Bathurst Channel and Bathurst are most common at 6–9 m depth (Figure 3(C)), particularly Harbour. The lack of fast-growing algal competitors below along a wide sandy shelf located along the western half of the the first few metres depth presumably allows sessile southern Bathurst Channel shore, but can extend to 15 m. invertebrates to dominate space on rock surfaces. Sessile Distinctive bands of sea whips and other cnidarians are animals colonize much shallower habitats than elsewhere patchily distributed on reef between 7 and 12 m (Figure 3(D)). along the Tasmanian coast (Edgar and Barrett, in press). Silt substrata with tube anemones and tubeworms occur below Characteristic benthic invertebrate species within Bathurst the sea pens. Channel include filter-feeding bryozoans, sponges, anemones, This zone is extremely sensitive to physical damage because sea pens, soft corals, hard corals, seawhips and other rock surfaces covered with fragile sessile invertebrates occur octocorals, tubeworms, and ascidians. Many undescribed from the shallows to the depths of the channel. Soft sediments invertebrate species are also present in this system, as well as are frequently colonized by meadows of sea pens. species only recorded elsewhere in deep offshore waters (Last and Edgar, 1994). Bathurst Channel Tube Worm Zone

Biophysical zones This zone extends east of Munday Island to Joan and Farrell Points, excluding much of Joe Page Bay and Horseshoe Inlet Benthic communities in the Bathurst Channel and Bathurst (Figure 2). It differs from the Bathurst Channel Sea Pen Zone Harbour estuary were mapped in 1995 using video and in commonly possessing the octocoral Clavularia sp., the jewel photographic images at over 50 dive locations. At each anemone Corynactis sp. (Figure 3(E)) and the bivalve Barbatia

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Key Dive Sites 1 Breaksea Island 2 Milner Head 3 South Channel Head Bathurst 4 Turnbull Island Joe Page 5 Waterfall Bay Harbour Port Bay 6 Munday Island Davey 2 Bramble 7 Forrester Point 1 8 Farrell Point Cove 3 4 9 Joan Point 8 5 6 7 9 Bathurst Channel Horseshoe Inlet

Bramble Cove Zone Bathurst Channel Sea Pen Zone Bathurst Channel Tube Worm Zone Bathurst Narrows Lace Coral Zone Shallow Embayment Zone Port Davey Zone

Figure 2. Distribution of major ecological zone types in Bathurst Channel, and location of Key Dive Sites.

pistachia on patches of rock at depths below 10 m, and Shallow Embayment Zone with numerous soft corals at 5 m depth (Barrett and Edgar, This zone occurs throughout Bathurst Harbour and all the in press). A shallow red and green algal zone is generally major bays along Bathurst Channel. The main feature of this present in the upper 3 m depth. Below this, tube worms, zone is a ﬂat substratum of deep ﬁne sediments. Tube B. pistachia, soft corals and lace bryozoans are typically anemones are patchily distributed, as are holothurians present on a shelly bottom down to about 9 m, after which the (Figure 3(H)), heart urchins and polychaetes. Algae on sea bed has little hard substrata and is generally mud with tube shores rarely extend below 1 m depth. anemones. Habitats in this zone are the least sensitive to physical This zone is not as sensitive as others in Bathurst Channel disturbance. Shallow reef surfaces are adapted to extreme to physical impacts. Sessile assemblages are relatively poorly variation in hydrological conditions, while deeper areas developed on the shallow reefs, and sea pens have not been comprise soft sediment that is dominated by infaunal species. recorded. An exception is the southern shore of Little Woody The occasional rock surface exposed in depths43 m appears Island, which possesses a well-developed bryozoan band largely devoid of macroscopic plants or animals. between 3 and 7 m depth (Last and Edgar, 1994).

Port Davey Zone Bathurst Narrows Lace Coral Zone The Port Davey Zone includes coastal reefs and soft sediment This zone extends along Bathurst Narrows from Joan and habitats that more closely reflect conditions found along the Farrell Points to the western entrance of Bathurst Harbour. It open south-western Tasmanian coast than in Bathurst differs from the Bathurst Channel Tube Worm Zone primarily Channel; they are less affected by tannin-stained surface due to the presence in the low-salinity surface band of Mytilus water and more exposed to direct or diffracted oceanic swell galloprovincialis rather than the fucoid alga Carpoglossum (Edgar and Barrett, in press). Nevertheless, much regional confluens or the laminarian kelp Ecklonia radiata. The algal variation is evident within this zone, particularly between the and mussel band extends down to about 3 m depth, after which western seaward shore and eastern shore where light a narrow encrusting sponge layer is present. Fragile bryozoan penetration is affected by tannins following periods of heavy colonies (Figure 3(F)), soft corals (Figure 3(G)) or a serpulid rainfall. tubeworm band generally dominate reef substrata from 4 m to 8 m depth. Deep (48 m) current-scoured sections of the main channel are dominated by solitary stony corals (Barrett and Edgar, in press). THREATS TO AQUATIC BIODIVERSITY As in western Bothurst Channel zones, reef surfaces fringing the central channel possess complex assemblages of The major threats to biodiversity values of the Port Davey fragile bryozoans and other invertebrates. These are highly region can be categorized as: (1) boating impacts; (2) fishing susceptible to diver and anchor damage because they have impacts; (3) recreational diver impacts; (4) effluent impacts; (5) developed in areas with strong laminar currents but little water introduced species; (6) onshore activities; and (7) climate turbulence, and are crushed or dislodged if brushed by divers change. Current risks associated with these threats vary greatly positioning near the sea bed to avoid currents. between the major biophysical zones (Table 2).

Figure 3. Sessile invertebrates of Bathurst Channel. The gorgonian Pteronisis plumacea (A) and the ascidian Ascidia challengeri (B) inhabit the Bramble Cove Zone and also outer continental shelf waters. Common species in the Bathurst Channel Sea Pen Zone include seawhips (Primnoella australasia) with basket stars (Conocladus australis) (C), and sea pens (Sarcoptilus grandis) (D). The corallimorph Corynactis sp. (E) commonly frequents open rock surfaces in the Bathurst Channel Tube Worm Zone. Bands of bryozoans (F) and soft corals (Drifa sp.) (G) typify the Bathurst Channel Lace Coral Zone. Sediments in the Shallow Embayment Zone are heavily bioturbated by invertebrates including holothurians (H). Photos G. Edgar.

Boating impacts Anchors and anchor chains can cause significant damage to invertebrate communities, either by live-aboard vessels Embayments in the Port Davey region are regularly used by anchoring for extended periods or from dinghies used by fishers and increasingly by private yacht and tourist boat divers to access interesting dive sites. Fortunately, with the operators, particularly over summer months. Local ecosystems exception of sandy sea beds colonized by dense aggregations of are potentially susceptible to boating impacts associated with sea pens, the most heavily-used anchorages are not located in (1) mechanical damage to habitats from anchors, propellers sensitive habitats. Damage from dive dinghies carries and vessel wakes, (2) disturbance to the halocline, (3) oil spills, potentially higher risk given that the major dive sites are (4) effluent and waste disposal, and (5) introduced marine small reef areas in Bathurst Channel where delicate colonies of pests. sessile invertebrates carpet rock walls.

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Table 2. Risk matrices for major biophysical zones, showing likelihood of different threats, impact if those threats manifest, and overall risk Habitat type Boating Fishing Diving Efﬂuent Introduced species Onshore activities Climate change

Likelihood Port Davey 2 2 1 1 2 1 3 Bramble Cove 2 1 3 1 3 1 3 Bathurst Channel Sea Pen 2 1 3 2 3 1 3 Bathurst Channel Tube Worm 1 1 2 1 2 1 3 Bathurst Narrows Lace Coral 2 1 3 1 2 1 3 Shallow Embayments 2 1 1 2 2 1 3 Impact Port Davey 1 2 1 1 2 1 2 Bramble Cove 2 1 3 2 3 1 3 Bathurst Channel Sea Pen 3 1 3 2 3 1 3 Bathurst Channel Tube Worm 3 1 2 2 3 1 3 Bathurst Narrows Lace Coral 3 1 3 2 3 1 3 Shallow Embayments 1 1 1 2 3 2 3 Risk Port Davey 2 4 1 1 4 1 6 Bramble Cove 4 1 9 2 9 1 9 Bathurst Channel Sea Pen 6 1 9 4 9 1 9 Bathurst Channel Tube Worm 3 1 4 2 6 1 9 Bathurst Narrows Lace Coral 6 1 9 2 6 1 9 Shallow Embayments 2 1 1 4 6 2 9 Likelihood and impact are ranked: 1 low, 2 moderate, 3 high. Risk rankings are calculated as the product of likelihood and impact ranks: 1 very low, 2 low, 3–4 moderate, 6 high, 9 extremely high.

Hulls and propellers scraping over the sea bed can damage turbulent current flow in Bathurst Channel Narrows may intertidal and shallow subtidal mudbanks and seagrass beds. additionally inject fuel oil to depth, where it would contact This threat is highly localized, with damage currently evident sensitive invertebrate communities. as propeller scars through seagrass meadows in Melaleuca Boating threats to regional biodiversity values are presently Inlet and Melaleuca Lagoon. Shoreline erosion resulting from managed through a complex set of acts, regulations and wake generated by passing vessels is evident in, and presently guidelines, which vary between tourism operators, commercial confined to, Melaleuca Inlet. fishing operators, and recreational visitors. In order to A broader-scale impact of propellers is water turbulence minimize mechanical damage, wake-induced bank erosion, that pushes brackish water to depth, potentially disrupting the and pollution in the event of a motorboat accident, access halocline and resuspending fine sediments. Marine organisms prohibitions or speed limits apply to all vessels operating in living in Bathurst Channel at depths 46 m are not adapted to sheltered inlets, particularly shorebird habitat and shallow low-salinity water, and may suffer mortality if exposed to it. mudflat areas. Motorized boating is not permitted upstream of This potential problem is most significant in winter and during the mouths of most major river systems (Parks and Wildlife periods following heavy rainfall, when the water column in Service, 1999), while a speed limit of 5 knots applies in inlets Bathurst Channel is highly stratified and surface waters and rivers where small boat access is permitted (Marine and possess low salinity. This threat relates primarily to cruise Safety Authority Act, 1995). Operators of vessels with planing ships with drafts 43 m when manoeuvring near channel walls hulls are encouraged to minimize wake impact on shorelines by (Parks and Wildlife Service, 2004). keeping their keel parallel to the water surface and by avoiding All types of vessels pose a risk of oil spill within the region. travel close to shore (Parks and Wildlife Service, 2003). This risk is exacerbated in Bathurst Channel by strong surface All commercial vessels other than fishing boats require a currents, submerged rocks obscured in the tannin-stained licence to operate in the region (National Parks and Reserves waters, and narrow channels restricting boat manoeuvrability. Management Act, 2002). Commercial vessels are additionally Given the difficult conditions and number of visiting vessels, restricted with respect to maximum draft, maximum length, and the likelihood of an oil spill from a small vessel is high. The number of vessels permitted at any one time. Large vessels environmental impact associated with an oil spill in the region require a pilot. Published Guidelines for the Preparation of varies from low to moderate for a small spill (o1 tonne) to Licences for Commercial Tourism Vessel Operations in Port high for a spill from a large vessel (4100 tonnes). Davey-Bathurst Harbour 2004 specifically attempt to protect While highly toxic, diesel fuel released from small vessels sensitive environmental zones from mechanical damage and should evaporate and be flushed from the system relatively disruption to the halocline. To minimize turbulence impacts, a quickly (1–4 days). The less-toxic higher viscosity oils used by statistical regression relationship (Propeller Flow Turbulence large boats may persist for years with little weathering, Prediction Model) is used to calculate the maximum speed that particularly when buried on gravel beaches (Hayes and a vessel of given length may operate in water of particular Michel, 1999). Intertidal plants and invertebrates, and depth. Commercial vessels are further prohibited from associated bird communities, face the greatest risk of impact operating in waters with depths less than twice the operational because most fuel spilt in confined conditions ends up draft of the vessel, and are required to anchor in approved deposited in the high intertidal zone (Lee and Page, 1997), as anchorages, other than in cases of emergency. Private vessels would be the case in the confines of Bathurst Harbour or and fishing vessels are also encouraged to anchor in these Bathurst Channel. In the event of a large spill and strong tides, anchorages, although these guidelines are not mandatory.

Environmental risks associated with the presence of private experienced divers and filmmakers who have visited Bathurst vessels poses an increasing threat to the region, particularly Channel rank it among the most interesting and unusual dive given that many activities associated with private boats are not locations on earth. controlled. Environmentally detrimental actions of private Diving in Bathurst Channel requires a high level of boat owners (e.g. anchoring in sensitive zones, transportation competence due to poor surface visibility, lack of light, of potential pest species, and discharge of waste water) often strong currents, cold water, vertical walls, and remoteness. reflect poor awareness of environmental risks to marine flora Underwater lights are necessary on most dives because the and fauna. dark tannin-stained waters reduce light penetration to the In order to combat ignorance about the values, subsurface marine layer. Operating from small boats can also environmental risks and legal regulations associated with be hazardous due to strong winds and currents. visiting the region, a Users Guide and Map for boat operators Unless regulated, growing numbers of divers visiting the and vessel-based visitors has been produced. This Guide is region will increasingly cause physical damage to seabed distributed to commercial and private vessel operators visiting habitats through mechanical impact from divers’ fins, hands Port Davey. It includes background information on the unique and gauges, or divers resting or kneeling on the sea bed biota, legal regulations, threats to biodiversity, quarantine (Tratalos and Austin, 2001). The most interesting dive sites in protocols to reduce risk of transfer of introduced species, the region — the Key Dive Sites indicated in Figure 2 — are safety issues, and locations of no-anchoring zones. also the most susceptible to diver impact. Most of these sites are highly localized, with diverse faunal assemblages confined Fishing impacts to headlands with strong currents, and extensive intervening areas with little macroscopic life. Although considered a near pristine environment, marine The sensitivity of sites in Bathurst Channel tends to ecosystems in the Port Davey region have historically been increase from west to east because declining wave exposure affected by fishing. In particular, large native oyster beds and water turbulence allow bryozoans and other sessile existed within James Kelly Basin until overexploitation in the invertebrates to develop structures of increasing fragility in late 19th century. This fishery closed when stocks collapsed that direction. The likelihood of impact is lower in the around 1890 and no mature native oyster has been recorded Bathurst Channel Tube Worm, Shallow Embayment, and Port from the Port Davey region during recent scientific research Davey zones compared with elsewhere because of a paucity of trips. The loss of oyster reefs presumably caused huge changes visited dive sites (Table 2). to the local marine ecosystem, particularly in terms of filtration capacity, nutrient recycling, and loss of habitat structure Effluent, waste disposal, and nutrient impacts (Rothschild et al., 1994; Jackson, 2001). Following proclamation of the zoned MPA in 2005 and An additional threat that requires precautionary management through earlier regulations, threats associated with is the discharge of effluent and waste, either from vessels or aquaculture, gillnets, bottom trawls and dredges — the from land-based facilities. Clearly, the release of toxic fishing techniques with greatest potential impacts — have materials or plastics into coastal environments is undesirable been removed. Fishing methods permitted in the MPA in any circumstance, and thus is explicitly banned under the Habitat Protection Zone are generally selective for target MARPOL Convention; however, the Bathurst Harbour– species, hence produce little bycatch, a threat to biodiversity Bathurst Channel ecosystem is additionally susceptible to associated with fisheries elsewhere (Edgar et al., 2005b). The nutrient enrichment including release of effluent. only current physical impact of fishing, a minor one, is damage An integral and characteristic feature of this estuarine to habitats caused by rock lobster pot deployment and ecosystem is low levels of dissolved plant nutrients in surface retrieval within Port Davey. waters (Edgar and Cresswell, 1991), hence a relatively minor The most substantive current threat associated with release of effluent could potentially affect nutrient dynamics ongoing fishing in the Port Davey region, other than indirect and lead to unnatural phytoplankton blooms. At present all ones such as translocation of introduced marine pests, anchor vessels are legally obliged to comply with the Tasmanian damage and oil spills, is the cascading change to the food web Pollution of Waters by Oil and Noxious Substances Act, 1987, that accompanies removal of large keystone species targeted by which prohibits discharge of waste within 12 nautical miles of fishers (Pauly et al., 1998; Edgar et al., 2009). Extant reef the coast. Commercial vessels are additionally obliged to ecosystems in Port Davey probably differ substantively from contain sewage and other wastes in holding tanks while in the ecosystems that would exist if large predatory rock lobsters region. However, sewage effluent continues to be discharged and herbivorous abalone were not removed by fishing (Tegner from private vessels and fishing boats on a regular basis. and Dayton, 1999; Edgar et al., 2009; Edgar and Stuart-Smith, Management guidelines ‘encourage all vessel users to reduce or 2009). Very few rock lobster or abalone are protected from eliminate their effluent discharge in the area’ (Parks and fishing in the Port Davey MPA because sanctuary zones are Wildlife Service, 2003). either too estuarine for survival of these resource species or encompass little reef habitat (Edgar and Barrett, in press). Introduced species

Diver impacts One of the most unusual characteristics of Port Davey in a regional sense is the paucity of introduced species other than Although dark cold environments are unattractive to most cryptic fouling taxa (Hirst et al., 2007). A diverse range of divers, dive tourism in the Port Davey area is increasing as its introduced species increasingly dominates Tasmanian estuaries fascinating biota becomes more widely known. Most and sheltered bays (Edgar et al., 2005b), with recent broad-scale

Copyright r 2009 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) CONSERVATION OF NATURAL WILDERNESS VALUES IN A MPA 307 surveys indicating that introduced taxa now comprise about are illegally taken for consumption. Assays of shellfish collected 45% of total benthic biomass associated with soft substrata in from south-eastern Tasmania during G. catenatum blooms south-eastern Tasmania (Edgar et al., 2005a). regularly reveal tissues sufficiently toxic to cause human death Introduced marine taxa that are now abundant and through paralytic shellfish poisoning if mussels or oysters are conspicuous in south-eastern Tasmania include the bivalves consumed. Corbula gibba, Crassostrea gigas, Theora lubrica and Raeta The second notable exotic species recently introduced to Port pulchella, the mollusc Chiton glaucus, the ascidian Ascidiella Davey is the New Zealand screw shell Maoricolpus roseus.Three aspersa, the seastars Asterias amurensis and Patiriella regularis, live specimens of this mollusc were discovered in western the porcellanid crab Petrolistes elongatus, and the crab Bathurst Channel in 2003 (K. Gowlett-Holmes, pers. obs.). Carcinus maenas (Edgar et al., 2005b). None of these species Subsequent targeted searches on three separate occasions have been recorded at Port Davey (Aquenal, 2003), but their revealed six additional living individuals, and slightly more establishment could cause major declines in populations of dead shells. Based on current information, it is uncertain whether native species. Only one alga and six invertebrates regarded as M. roseus spread to Port Davey via natural dispersal from other introduced have been recorded from the region (Table 3), and parts of the Tasmanian coast, or has been translocated via a further three algae and ten invertebrates are considered vessels, or even whether a large deepwater population exist off cryptogenic (i.e. possibly introduced but with such widespread the southern Tasmanian coast (Aquenal, 2003). distribution that their native range is uncertain). This screw shell poses a high potential risk to benthic Two species recently introduced to Port Davey are of assemblages in the region. Populations of M. roseus elsewhere considerable environmental concern. Recent surveys revealed in Tasmania dominate the sea bed (Edgar et al., 2005b), greatly that the toxic dinoflagellate Gymnodinium catenatum now changing benthic habitats and presumably altering the food dominates the dinoflagellate community at some sites, at least web (Bax and Williams, 2001; Bax et al., 2003). In sheltered in terms of numbers of cysts produced (Aquenal, 2003). This south-eastern Tasmanian waters, M. roseus now contributes phytoplankton species — the only organism in Port Davey E82% of total mollusc biomass within the 5–50 m depth range regarded by national authorities as a Target Pest (Aquenal, (Edgar et al., 2005b). 2003) — was not found in Bathurst Harbour samples analysed The current population of M. roseus in Bathurst Channel for cysts in 1987 (Bolch and Hallegraeff, 1990), nor during appears to be small and localized within an area spanning 3 km plankton surveys in 1988/1989 (Edgar, 1990). The species in western Bathurst Channel. All individuals so far observed probably arrived in Tasmania between two and three decades have been juveniles with thin shells, and the number of recently ago, and is now common in south-eastern Tasmania (McMinn dead shells has exceeded the number of living animals. Thus, et al., 1997). Natural dispersal from that region, or conditions in Bathurst Channel may be marginal for survival translocation via boat traffic, provide equally plausible of M. roseus, although it survives well in New Zealand fjords explanations for the occurrence of G. catenatum at Port within its native range (K. Gowlett-Holmes, pers. obs.). Davey (Aquenal, 2003). The threat of introduced pests is currently managed The consequences of the recent establishment of primarily through prohibitions on dumping of ballast water G. catenatum at Port Davey are threefold. First, its apparent within Port Davey (Parks and Wildlife Service, 2004). dominance of the phytoplankton assemblage has negative Guidelines for the Preparation of Licences for Commercial implications for other local plankton species in terms of Tourism Vessel Operations in Port Davey-Bathurst Harbour competition for nutrients and resources. Second, the bio- recommend that all visiting operators check anchors and accumulation and bio-magnification of toxins produced by fishing gear for introduced marine pests prior to arrival, and G. catenatum up the food web could cause poisoning of animals regularly clean and anti-foul exposed hull surfaces. at all trophic levels, from filter-feeding sessile invertebrates such as mussels that directly capture dinoflagellates to higher Onshore activities predatory fishes such as gummy shark (Mustelus antarcticus). Third, the presence of G. catenatum poses a risk to human Onshore infrastructure facilities present in the Bathurst health if shellfish from the Bathurst Channel Sanctuary Zone Harbour catchment that may potentially affect the estuarine environment are limited to a summer tourist camp, park service buildings, mine workings and associated private residences, bushwalkers huts, and an airstrip, all within the Table 3. Introduced (i) and cryptogenic (c) species recorded from Port Melaleuca Inlet region. These and future onshore Davey and Bathurst Channel developments are subjected to detailed management Algae Mollusca strategies through the Tasmanian Wilderness World Heritage Gymnodinium catenatumi Maoricolpus roseusi Area Management Plan (Parks and Wildlife Service, 1999) and c Cladostephus spongiosus Bryozoa Melaleuca–Port Davey Area Plan (Parks and Wildlife Service, Medeiothamnion lyallic Aetea anguinac Ulva stenophyllac Bowerbankia gracilisi 2003). For commercial operators, restrictions include access Cnidaria Bugula stoloniferai prohibitions to sensitive areas, and maximum party size and/or Bougainvillia muscusc Celleporella hyalinac obligatory presence of guide for the most popular sites. Clytia cf johnstonic Conopeum seuratic c c The greatest risk of onshore developments affecting the Obelia dichotoma Membranipora membranacea aquatic ecosystem is through runoff, with released effluent and Phialella quadratac Echinodermata Turritopsis nutriculac Astrostole scabrai waste potentially impacting plants and animals through heavy Crustacea Chordata metal, organic and hydrocarbon pollutants, increased Cancer novaezelandiaei Botrylloides leachiic turbidity, and increased nutrients. This risk appears to be i Halicarcinus innominatus highly localized.

Climate change No-take sanctuary zones in marine-influenced areas of Port Davey appear poorly located and of insufficient size to protect Global climate change represents the greatest long-term threat reefs from cascading trophic effects associated with rock lobster to marine and estuarine biodiversity in Tasmania (Edgar et al., and abalone capture (Edgar and Barrett, in press). Improved 2005b), including Port Davey, through rising water zone design would involve extension of the boundaries of temperature, changing seawater acidity, and changes to local sanctuary zones within Port Davey to encompass at least 5 km2 rainfall patterns (Poloczanska et al., 2007). Any reduction in of optimal reef habitat for these two commercial species. regional rainfall will cause less riverine runoff, a reduction in Such a change would protect small populations of rock the depth of the Bathurst Channel halocline, increased light lobster, abalone and finfish with adequate boundary buffer penetration through the brackish tannin-stained surface layer, zones, thereby allowing some marine reef ecosystems in Port and increased infiltration of macroalgae into the sessile Davey to develop trophic structures unaffected by fishing invertebrate zone. Thus, any major reduction in rainfall (Edgar et al., 2009). With appropriate monitoring and poses an extremely high risk to the unique Bathurst Channel policing, such reefs would generate secondary benefits in ecosystem (Table 2). terms of providing data on ecosystem impacts of rock lobster With respect to water temperature, large future rises in the and abalone fishing in southern Tasmania. Such information is region are likely given projected increases in air temperatures presently unavailable but of great importance for fishery and across Australia of 0.4–2.01C by 2030, and 1–61C by 2070 conservation management in an era of global climate change. (Pittock, 2003; Natural Resource Management Ministerial Impacts of onshore activities and effluent discharge Council, 2004). Future changes will compound with generally appear well managed in the Port Davey–Bathurst temperature rises already established over the past half- Harbour region (Table 2). Present laws and regulations also century (Poloczanska et al., 2007). adequately address most of the potential impacts of Although no data are available on historical changes to commercial vessels on estuarine plants and animals. water temperatures in the Port Davey region, sea surface Nevertheless, in order to better protect sensitive sites, temperatures have risen 1–21C off the Tasmanian east coast anchoring within the main arm of Bathurst Channel should during the past 60 years (Crawford et al., 2000), and air be prohibited to reduce anchor damage to sensitive temperatures across Tasmania have risen about 0.81C over the invertebrate assemblages on rocky reefs caused by dive same period (Harris et al., 1992). Moreover, eastern Tasmania operations. Such a change in boating regulations should not is predicted to show the greatest sea surface temperature rise in greatly affect vessel operators given that alternative the Southern Hemisphere over the next century (Cai et al., anchorages are available in nearby inlets, and that dives are 2005; Ridgway, 2007). most safely conducted with a boat crew that follows divers. A rise in minimum annual water temperature of 21Cis An alternative process to reduce risk of anchor damage is equivalent to the latitudinal difference between southern the installation of moorings (White et al., 1994; Gittings et al., Tasmania and north-eastern Victoria (Edwards, 1979). If 2003); however, this intrusive management option should not such a change occurs, as projected during the next century, be necessary given the variety of safe anchoring alternatives then many species are likely to fall outside their climatic available near sensitive areas, the high deployment and envelopes or be negatively impacted by invasive warm- maintenance costs, a loss of visual amenity, and liability temperate species. Local species most affected by such issues. Also, environmental impacts can increase at mooring changes will be those of greatest conservation importance, sites due to a concentration of diver impacts within a localized namely species with preferences for cool conditions, including area (Garrabou et al., 1998; Tratalos and Austin, 2001). taxa endemic to Port Davey and southern Tasmania. The very act of declaration of an MPA attracts attention, One notable recent arrival in the region in this context is the potentially compromising some biodiversity values if increased hollow-spined sea urchin Centrostephanus rodgersii, a single visitation rates are not foreseen and appropriately managed specimen of which was collected in western Bathurst Channel (Badalamenti et al., 2000). Coupled with prohibitions on in 2005. Increasing abundance and southward penetration of anchoring, an effective way to eliminate mechanical damage to this widespread south-eastern Australian species, first detected fragile reef assemblages is to ensure that divers maintain in Tasmania in 1978, appears directly related to rising sea appropriate buoyancy control and remain above the sea bed at temperatures (Johnson et al., 2005; Ling et al., 2008; Stuart- all times. Policies that promote mimimal impact diver behaviour, Smith et al., 2009). Centrostephanus rodgersii is an aggregating including avoidance of contact with the sea bed, similar to those and habitat-modifying urchin, capable of eliminating widely applied at coral reef dive sites (Barker and Roberts, 2004; macroalgae and sessile invertebrates from reefs (Johnson Worachananant et al., 2008) are planned for Port Davey. The et al., 2005; Ling, 2008). If a dense population establishes in responsible management agency — the Tasmanian Parks and Bathurst Channel, then ‘barrens’ areas will expand across reefs Wildlife Service — has developed a Code of Conduct for divers presently colonized by octocorals, sponges, anemones and visiting the region that includes the following elements: ascidians, potentially threatening populations of local species. Divers must not contact the sea bed on reefs in Bathurst Options to further reduce risk to biodiversity values Channel. Divers require a high level of experience before Establishment of the Port Davey MPA has greatly reduced attempting dives in Bathurst Channel. risk to biodiversity associated with fishing impacts, with risk Divers must possess a good level of buoyancy control now low for all habitats types other than in the Port Davey before attempting dives. Zone, where a moderate risk exists because of the removal of Divers must be familiar with cold, low-visibility, current- species with a potential habitat-engineering role (Table 2). swept situations before attempting dives.

Copyright r 2009 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 297–311 (2010) CONSERVATION OF NATURAL WILDERNESS VALUES IN A MPA 309

Underwater lights must be carried. level, management can potentially minimize interactive effects Safety sausages and whistles must be carried. that reduce resiliency of communities and exacerbate impacts of No discharge of effluent or other waste from boats. climate change, but only if these interactions are recognized No anchoring in Bathurst Channel. (Hughes et al., 2003; Occhipinti-Ambrogi, 2007; Poertner and Knust, 2007). Although the Port Davey estuarine system has An additional option to minimize mechanical damage to historically been protected by its isolation and paucity of benthic assemblages is to prohibit or restrict access by divers to exploitable resources, proactive and adaptive management sensitive sites. Such an option is most appropriate if faunal based on ongoing monitoring of ecological condition, and social communities are homogeneous and extend over sufficient and environmental pressures, is a necessary prerequisite for the distance for representative sections of fragile habitat to be long-term persistence of the area’s unique wilderness values. protected. However, Bathurst Channel faunal communities are highly heterogeneous, varying greatly over short horizontal and vertical distances; consequently, closure of sensitive sites to ACKNOWLEDGEMENTS divers could substantially reduce the variety of community types available for observation by divers. Also, a small number We would particularly like to thank support to the project of closed sites may not encompass the full range of biodiversity from the Tasmanian and Australian governments through the in need of protection. Regardless, limited ‘diver-free’ Wilderness Ecosystem Baseline Studies (WEBS) and conservation zones, where diving is prohibited without special associated Tasmanian Wilderness World Heritage Area scientific or filming permit, appear warranted to safeguard fauna programmes, and from the Tasmanian Aquaculture representative invertebrate assemblages and as scientific and Fisheries Institute. The Australian Research Council, reference sites for assessment of long-term diver impacts in National Heritage Trust, Fisheries Research and Development the Channel. Such conservation zones are now being Corporation, and Commonwealth Environment Research established by the Tasmanian Parks and Wildlife Service. Facilities programme provided additional funding. We thank One urgently-needed programme to reduce extremely high Miles Lawler for drafting Figure 1. risks associated with diver impacts, climate change and introduced species (Table 2) in Bathurst Channel is the development of a long-term ecological monitoring strategy based on a statistically-rigorous design. Within this REFERENCES programme, photoquadrat or video records should be made at fixed sites within diver-free conservation zones and nearby Alderslade P. 1998. Revisionary systematics in the gorgonian open-access Key Dive Sites to allow an assessment of the family Isididae, with descriptions of numerous new taxa impact of divers on growth rates, colony health, and (Coelenterata: Octocorallia). Records of the Western fragmentation of sessile invertebrate colonies. Such data are Australian Museum Suppl. 55: 1–359. needed to better define management strategies for addressing Aquenal 2003. Exotic marine pests survey. 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