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The area and condition of marine and coastal habitats by type. Marine and coastal habitat types include salt marshes, sandy beaches, rocky shores, intertidal mudflats, seagrass beds, soft-sediment bottoms, sponge 'gardens', algal beds, subtidal reefs, offshore islands and seamounts. Please note: Because of the way the environmental information is structured and the arbitrary nature of the boundaries in reality, there is considerable overlap between this indicator and the very closely related Extent and Condition of Estuarine Habitats indicator. Therefore, seagrass beds, soft-sediment bottoms, algal beds and subtidal reefs that occur in estuaries cannot be separated out from the rest of the coastal and marine areas and a consolidated report can be found in this indicator. Conversely, all saltmarsh data, whether estuarine or not, are reported in the related indicator. Biological diversity, or biodiversity, is a fundamental measure of aquatic environmental health. Biodiversity can be measured at a range of levels - from the molecular and genetic to ecosystem and landscape (Saunders et al. 1998). In Tasmania, there is no complete Statewide assessment of marine biodiversity at any level; instead, it is necessary to rely on surrogates and partial assessments. For this indicator the extent and condition of marine, coastal, and estuarine habitats by type is used as a surrogate. Different habitat types reflect different ecological and environmental conditions and, therefore, different components of biological diversity. Indicator reliability comment: There is no systematic collection of data to support this indicator at present, and so we have no comparative data and little certainty about either condition or trends.
Mapping of the extent of marine, coastal, and estuarine habitats is patchy, athough since the 1996 Tasmanian State of the Environment Report, a detailed Statewide seabed mapping program called SeaMap Tasmania has begun (see below). Some data are available for the extent of broad aquatic habitat types, particularly in depths less than 40 m. The extent of the intertidal habitats is based on Statewide Topographic Digital map layers (The LIST 2001). The Tasmanian Aquaculture and Fisheries Institute (TAFI) Seamap Tasmania program produces maps showing the seabed in up to 14 categories of habitat type with supporting images and video. So far, the program has covered over 1,800 km including the entire Bruny IMCRA Bioregion, the Tasmanian portion of the Twofold IMCRA Bioregion and part of the Freycinet IMCRA Bioregion (Barrett et al. 2001; Jordan et al. 2001; Jordan et al. 2002; Jordan et al. 2002). Some limited mapping has also been conducted within the Davey IMCRA Bioregion. The mapping work is unprecedented and the seabed habitats are revealed in readily accessible, detailed and accurate maps for the first time. This information is assisting with a wide range of coastal research and planning issues including Marine Protected Area development, environmental impact modelling and assessment, fisheries assessments, habitat monitoring, marine farm planning and localised coastal developments. While the maps can only provide a snapshot for this time - and therefore cannot show historical trends - they are the basis for detecting changes in the future. The following are examples of habitat maps for the Bruny Bioregion:
Habitat condition is much more difficult to assess as either the methods for condition assessment are not developed or there are very few monitoring programs in place. One exception is a Statewide study into the condition of estuaries (Edgar et al. 1999). The condition of most marine areas is poorly known, although there is a long term study into the condition of marine reef biota in Marine Protected Areas and adjacent regions which provides insights into ecological change and recovery following removal of fishing pressure (Edgar & Barrett 1999). Some estuaries have monitoring programs in place-for example, the Derwent River (Coughanowr 2000)-though they do not monitor the biological component of the ecology. Statewide intertidal zone habitat studies are very limited in number, although Richardson et. al. (1996, 1997) provided valuable information about the biodiversity of intertidal rock platforms and beaches. The lack of Statewide information on extent and condition for even one time frame means that trends through time are very difficult to perceive. The purpose of indicators is to report on trends through time, ideally using the time of European settlement as a 'baseline' or reference date and preferably reporting repeated measurements at a time scale relevant to the management of the environmental issue (Saunders et al. 1998). In the absence of such information there are considerable uncertainties, and therefore risks, associated with management decisions affecting habitats and ecosystem diversity in Tasmanian marine and coastal waters. There is also the problem of the 'sliding baseline syndrome' where changes that occur over generations are not noticed and the new environmental conditions are thought of as 'normal' (Dayton et al. 1998). Firstly, the full extent of the marine waters for which Tasmania is responsible is defined and then available information about the extent and condition of habitats in the marine and coastal environments is presented. Total Extent of Tasmanian Coastal Waters and Coastline Tasmanian marine, coastal and estuarine waters make up just over one quarter of the area of Tasmania with the area of land being approximately 68,000 km2 and the area of State Coastal Waters being approximately 23,500 km2 (AUSLIG 2000; The LIST 2001; AAD 2000). For State of the Environment reporting purposes the State Coastal Waters are grouped into meso-scale bioregions which reflect similarities in the biological communities and physical conditions (Edgar et. al. 2000). Extent of Tasmanian Coastal Waters by IMCRA Bioregions IMCRA Bioregion Extent (square kilometres) Otway 1,316 Central Bass Strait
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n/a Twofold 291 Flinders 4,664 Boags 4,470 Freycinet 3,197 Bruny 4,110 Davey 2,223 Franklin 2,474 Macquarie 815 Total 23,560 1.The Central Bass Strait Bioregion does not overlap with Tasmania's State Coastal Waters. 2.Please note that the IMCRA Bioregions usually extend out to the 200 metre isobath (depth contour) which approximates the edge of the continental shelf. For Tasmanian State of the Environment reporting purposes the outer boundary is taken to be the outer limit of Tasmanian State jurisdiction - that is, the State Coastal Waters. Tasmania's coastline is particularly convoluted with large peninsulas, islands and bays and at the 1:25,000 map scale is 8,150 km long (The LIST 2001). At the less detailed map scale of 1:100,000 it measures 4, 882 km and is longer than Victoria and New South Wales' coastlines combined (AUSLIG 1993). Note: It is to be expected that when the scale of mapping is finer the length of the mapped coastline dramatically increases. This is mostly because at the finer scale there are more indentations and islets mapped. The main island of Tasmania is surrounded with about 370 islands greater than 1 hectare and over 6,000 islets smaller than a hectare (The LIST 2001). Seagrass bed in clear, shallow sunlit waters Source: Richard Mount, March 2002 Subtidal Marine and Coastal Habitat - extent The main types of marine and coastal habitats reported are defined as rocky reef, or consolidated substrates-which may be dominated by either seaweeds (algae) or a wide variety of sponges and other invertebrate filter feeders-and unconsolidated substrates (including vegetated and unvegetated bottoms). Reef habitat includes the hard, rocky substrates of high, low and medium profile reef as well as patchy reef. Unconsolidated substrates include hard shelly sand, sand, silty sand and silt - either covered with vegetation, such as seagrass or Caulerpa, or unvegetated. Unconsolidated substrates may host light sponge habitats with small sponges and other filter feeders growing on dead shells. Filter feeders are typically animals fixed to the bottom (sessile). The extent of the marine habitats in each of the IMCRA bioregions is shown in the table below. Please note that there are two sources for the data with clear differences in accuracy. The quality of the data for most bioregions is low because of poor definition of habitat boundaries deeper than 10 m (Edyvane K. et al. 2000). Therefore, only approximate estimates of habitat area within the shallowest 10 m are possible and none of the estimates should be used for trend or change analysis through time. The other source is the TAFI Seamap Tasmania program. While the extent of habitats for the Bruny and Twofold bioregions derived from the SeaMap program are the most accurate of all the data, the Bruny bioregion data is limited to the waters shallower than 40 metres deep and does not include some of the major estuaries (Barrett et al. 2001; Jordan et al. 2001; Jordan et al. 2002; Jordan et al. 2002). Additional estuary maps are presented for the Derwent Estuary in Jordan et. al. (2001) and Upper Pitt Water on the Seamap Tasmania web site. The table details the extent of known shallow marine habitats within Tasmanian Coastal Waters. While no seamounts occur within Tasmanian State Coastal Waters there are about 70 around Tasmania, including on and around the South Tasman Rise, which lies between 50 and 100 km south of Tasmania. This habitat type is a very distinctive deep-sea marine environment rising up from depths of between 1000 and 2000 metres (DPIWE 2000b).
Subtidal Marine and Coastal Habitat - Condition Reef Habitat The only Statewide work measuring marine and coastal biodiversity is the survey of fishes, invertebrates and plants of reef habitats by Edgar et. al. (1997). The number of species recorded from over 156 sites, mostly at the 5 m depth contour, is presented in the following table. The number of species listed is not exhaustive, especially for the invertebrates, and the figures give a relative measure of diversity. Species richness is highest around Maria Island and Bruny Island - in the Freycinet and Bruny Bioregions respectively - particularly in fishes and plants. Invertebrate species richness is consistently high around the eastern and northern coasts, and the Tasmanian portion of the Twofold Bioregion has an unusually high number of fish species. (See the Statewide subtidal reef species diversity map.) While any changes in habitat condition through time are currently unknown for Tasmania as a whole or at a bioregional level, Edgar and Barrett (1999) found a change in reef condition for some specific Marine Protected Areas. The measured changes provide a glimpse into the complexity of rocky reef ecosystems. Significant differences were found in diversity, abundance and size between species outside the reserves at scientific control sites compared to those inside - particularly in largest of the reserves, the Maria Island National Park marine extension. For example, over a period of 10 years starting from the date of reserve declaration: These results strongly suggest that fishing significantly impacts the ecology of many of the Tasmanian marine reef environments outside of the Marine Protected Areas. It is important to note that significant ecological changes are likely to continue over longer time frames inside Marine Protected Areas. In New Zealand some changes only began to occur after 10 to 15 years - such as a decrease in urchin barrens (Shears & Babcock 2003). Ford (2001) considered that, in the case of the rock lobster fishery, biodiversity is now different compared to when there was no harvesting of rock lobster, 150 years ago. A recent report on the Tasmanian giant crab fishery raised concerns about potential damage to giant crab spawning grounds, fish stocks, habitat and ecosystems. Vessels associated with the Commonwealth southeast demersal trawl fishery have historically fished in waters deeper than 400m, but have recently begun demersal fishing in waters as shallow as 120m (Levitt 2002). Unconsolidated Substrate A Statewide assessment of inshore subtidal unconsolidated substrate habitats of mud, silt, sand and seagrass for finfish revealed that the densest seagrass beds hosted the richest assortment of fish species, which is similar to findings in other places (Jordan et al. 1998). In addition, the study showed that for Tasmania: While the study was not directly assessing the condition of marine and coastal unconsolidated habitats, it provides some specific measurements of relative biodiversity that could be developed into a useful indicator in the future. Seagrasses are subtidal and intertidal plants found mainly in shallow waters of protected estuaries and bays. They are highly productive habitats with production rates similar to the most productive grasslands and dense kelp beds: about 2 kg of plant material produced per square metres per year (Edgar 2001). They are particularly important in maintaining sediment stability because the seagrass acts to stabilise the underlying sediment. They are also important in maintaining water quality by using nutrients and trapping sediments in shallow water. Five species of seagrass are commonly found within Tasmania: Another species of strapweed, Posidonia angustifolia, has also recently been identified on the western shore of Flinders Island (Jordan et al. 1998). Broad-scale mapping of seagrass beds in Tasmania indicates that while P. australis and A. antarctica are the dominant species in the north of the State, H. tasmanica is the most common species in estuaries and coastal embayments in the south and east (Rees 1993, Barrett. et al. 2001). The southern extents of P. australis and A. antarctica are around Little Musselroe Bay and Maria Island, respectively. A number of human activities are known to impact on the extent and overall 'health' of seagrass habitats. There is solid evidence of a strong relationship between decreased light levels and seagrass loss in many areas around the world (Walker & McComb 1992, Dennison et al. 1993). This happens because increased sediments in the water cause reduced water clarity and increased nutrient levels. The increased nutrients stimulate filamentous algae growth that shades the seagrass leaves. As there is evidence for increased sediments and nutrients in coastal waters, there is little doubt that some changes in seagrass extent and health have occurred throughout Tasmania. This is supported by the trends in the collected data which show that maximum seagrass loss occurs in areas closest to population centres where the water clarity and nutrient levels are impacting the most (Rees 1993). However, given the lack of detailed measurements on the extent of change in seagrass habitats in Tasmania over an extended time frame (decades), there is considerable uncertainty of the extent of change due to natural variability compared to human induced impacts. Some limited seagrass monitoring is under way in south-east Tasmania, including annual mapping of extents and seasonal transects recording species, percent cover (plant density), blade length and epiphyte loading. Little is known about either the extent or condition of the filter feeder, or sponge 'garden', habitats around the State. There are high levels of uncertainty and risk regarding ecological impacts from human activities, such as bottom trawling, on these habitats. A recent report from the TAFI Seamap Tasmania program indicates there may be considerable areas of light sponge habitat in Bass Strait, mostly occurring below 40 m and particularly where currents are strongest. Seamounts The condition of this offshore deep-sea marine environment is mixed. A survey by CSIRO in January 1997 found that the seamounts, which were most heavily trawl-fished for species like orange roughy and deepwater oreos had up to 83% less benthic biomass, and the number of species per sample was 59% less. Examples of such seamounts are Main Pedra and Sister. The remaining seamounts have high levels of biodiversity in global terms and are generally dominated by filter feeders such as hard and soft corals, sponges, hydroids, ophiuroids and sea stars. Many unique communities were found and between 24% and 43% of species had not been seen before (Koslow et al. 2001) Intertidal habitat - Extent Note: for saltmarsh please see the related Indicator: Extent and Condition of Estuarine Habitats This subsection presents information about the intertidal coastal habitats found between Mean High Water Mark and Mean Low Water Mark as delineated by the LIST (2001) . The habitats types are limited to the categories of Rocky Shore, Sand and Mudflat as defined by the LIST. The data is further split between estuarine and coastal areas. The tables display the information by IMCRA bioregion. Even though a recent report suggests that the IMCRA bioregions do not apply to Tasmanian estuaries (Edgar et al. 1999), in the absence of a separate estuarine bioregionalisation, the estuarine intertidal habitat extent is reported, both separately and combined with the open coastal areas, in the following tables by IMCRA. The table shows that the Boags Bioregion completely dominates all three categories of habitat type containing almost exactly half of the entire intertidal habitat in Tasmania including over three quarters of the Mudflat habitat. This is largely explained by both the much larger tidal range experienced on the shores of Bass Strait and the relatively good shelter from the prevailing south-westerly swell created by the orientation of the coastline and the islands of the north-west. Extent of intertidal habitat types - estuarine only hectares IMCRA Bioregion Rocky Shore Sand Mudflat Unknown Total Otway 1 0 1 4 6 Central Bass Strait n.a. n.a. n.a. n.a. n.a. Twofold n.a. n.a. n.a. n.a. n.a. Flinders 0 583 0 2 585 Boags 32 4,019 4,221 37 8,309 Freycinet 12 671 1,529 38 2,250 Bruny 167 3,219 830 47 4,263 Davey 129 645 155 47 976 Franklin 68 1,633 49 46 1,796 Macquarie n.a. n.a. n.a. n.a. n.a. Totals 409 10,770 6,785 221 18,185 Source: The LIST 2001 Extent of intertidal habitat types - coastal only hectares IMCRA Bioregion Rocky Shore Sand Mudflat Unknown Total Otway 812 490 1 0 1,303 Central Bass Strait n.a. n.a. n.a. n.a. n.a. Twofold n.a. n.a. n.a. n.a. n.a. Flinders 1,693 2,670 0 0 4,363 Boags 2,157 9,392 5,244 0 16,793 Freycinet 443 1,041 88 0 1,572 Bruny 987 3,766 191 0 4,944 Davey 582 373 127 0 1082 Franklin 1,924 1,698 0 0 3,640 Macquarie n.a. n.a. n.a. n.a. n.a. Totals 8,598 19,430 5,651 0 33,679 Source: The LIST 2001 Intertidal Habitat - Condition The intertidal zone of the eastern half of Tasmania's shoreline has recently been assessed for biodiversity. The sandy beaches were assessed for invertebrate faunal biodiversity and the rocky shores for faunal invertebrate and floral biodiversity (Richardson et al. 1996, Richardson et al. 1997a). Sandy Beaches Sandy beaches are a particularly harsh environment because of a continuously shifting abrasive substrate, high levels of salinity, episodic inundation and huge temperature ranges. Virtually no multi-cellular plants live in the zone and vegetation cast up by the sea forms the often abundant, but unpredictable, food supply. The animal species are almost entirely arthropods including crabs, sandhoppers, isopods and insects. Vertebrates include birds, scavenging mammals and reptiles. A survey by Richardson et. al. (1996) of 120 beaches on the east coast of Tasmania found 108 Recognised Taxonomic Units (RTUs), or 'species', of which 3 occurred at over half the sites while 30 occurred at a single site only. The average number of 'species' at each site was 15.5 (± 4.26 Standard Deviation). 'Species' richness was higher at the top of the beach compared to the bottom. Geographically, the sites with the richest species diversity were related to the complexity of the coastline rather than wave exposure. For example, the Great Oyster Bay and Storm Bay/Frederick Henry Bay areas have relatively diverse faunas while the more open coastlines between Orford and Little Swanport and between Freycinet Peninsula and St. Georges Bay show generally low diversities. Rocky Shores It is notable that the ancestors of the species on rocky shores-unlike beaches or saltmarshes-have their origins in the marine environment. The majority of the fauna is made up of molluscs, crustaceans and annelid worms while algae and lichens dominate the flora. A recent broad-scale survey of rock platform diversity showed there are consistently high levels around the eastern half of the State from Catamaran in the south to Port Sorell in the mid-north coast with 30 to 40 species found at most sites. Ten species occurred at 90% of the sites - including a tube worm, a chiton, a barnacle, some limpets, some winkles and some bivalves- and about half the species were found at 5 sites or fewer (Richardson et al. 1997a). There are few clear geographic trends in rocky shore species diversity although some species have northern, or southern, limits to their distributions. There are, however, some trends through time that have been noticed. Richardson et. al. (1997a) identify several previous studies of rocky shores, including: various papers by Guiler (1950-1960), Bennett and Pope (1960), Dartnall (1974) and Edgar (1984), although Bennett and Pope conducted the only other broad-scale survey. It is clear that over the last 40 years there have been significant shifts in the distribution of several species including some of the barnacles. For example, Austromegabalanus nigrescens is now found as far south as Cape Queen Elizabeth. The changes seem to be related to an increase in water temperatures (Edgar 1984, Edgar et al. 1997). These noted temporal changes, however, only apply to a few species and, overall, the descriptions of the rocky intertidal zone by Bennett and Pope are still accurate today. Also, while there was obvious evidence of trampling and bait collecting at many sites, there appeared to be no impact on species diversity. Saltmarsh Note: for saltmarsh please see the related Indicator: Extent and Condition of Estuarine Habitats Offshore Island Habitat - Extent The number of islands counted by various sources is quite variable, which can be explained as follows. Firstly, until very recently, no comprehensive map of all of Tasmania's islands existed. The LIST map layers now depict the physical islands, which, for SoE reporting purposes, consist of all of the land above high water mark. According to this method, the main island of Tasmania is surrounded with about 370 islands greater than 1 hectare and over 6,000 islets smaller than a hectare (The LIST 2001). Secondly, an island may be defined by name and there are 257 officially named islands in the DPIWE nomenclature database (13 March 2003) but that number does not include rocks, pyramids, stacks, towers and islets. In summary, the number of islands depends on the definition used. It is reasonable to state that over 300 islands and many thousands of islets surround the main island of Tasmania. At February 2000, the DPIWE published a map of Tasmanian Offshore Islands indicating land tenure status. A summary of the map is given in the following table: Summary of separate land tenure categories for 287 Tasmanian islands Land Tenure Number of Islands Percentage Nature Reserve 38 13.24 National Park 69 24.04 Non-allocated Crown Land 88 30.66 State Recreation Area 1 0.35 Conservation Area/Wildlife Sanctuary 32 11.15 Multiple Land Use 18 6.27 State Reserve 2 0.70 Coastal Reserve 3 1.05 Muttonbird Reserve 3 1.05 Game Reserve 10 3.48 Historic Site 6 2.09 Private property 17 5.92 Total 287 100.00 Source: DPIWE 2000 Offshore Island Habitat - Condition Many of the islands off the coast of Tasmania have largely been protected by a combination of their remoteness and inaccessibility. Being discrete ecosystems predominantly free from human interference, they may provide baseline information on evolutionary processes and harbour unique flora-for example, Maatsuyker Island's Westringia and Blandfordia species-and fauna such as the Pedra Branca skink. Several islands such as De Witt Island and Actaeon Island are nationally significant geoheritage sites. Others harbour unique ecological diversity including Ile du Golfe and Maatsuyker Island. The islands also offer shelter to species that may be threatened by feral predators on the larger islands. For example, the potential threat created by the introduction of foxes to Tasmania increases the value of the offshore islands as sanctuaries for some native species. Moriarty Rocks, Tenth Island, Judgement Rocks, West Moncoeur Island and Reid Rocks Nature Reserves are important as they provide approximately 50% of the global Australian fur seal (Arctocephalus pusillus) breeding habitat, the other 50% being provided by Victorian administered colonies in Bass Strait and Port Phillip Bay (Shaughnessy 1999). Foster Islands, Low Islets and Penguin Islet Nature Reserves are important as they are the only known breeding sites of the Australian pelican (Pelecanus conspicillatus) in Tasmanian waters, and are the most southerly known Pelican breeding sites in the world, apart from one possible site in New Zealand. Black Pyramid Rock Nature Reserve is the sole currently successful breeding site for the Australasian gannet (Sula serrator) in Bass Strait and is the largest of approximately 35 known global sites. Cat Island Conservation Area was significant as the largest gannet colony in Australian waters before it was depleted by fishermen using the gannet meat as bait and then destroyed by fire in 1984. It is still considered important for its potential to be recolonised (Brothers et al. 2001). It also serves as a reminder and educational example of what can happen to a 'protected' species, if protection strategies are not adequately implemented. Albatross Island Nature Reserve is important as one of only three shy albatross (Thalassarche cauta) breeding sites, worldwide. The shy albatross is listed as Vulnerable globally under IUCN category D2 because its population is restricted to less than 5 sites. Albatross Island is also significant because it is the most northerly breeding colony of shy albatross and as such, differs in various ways from the other colonies on Pedra Branca and Mewstone off southern Tasmania (Gales 1993). Rodondo Island Nature Reserve is important because it supports ecological climax communities of Eucalyptus globulus, and Melaleuca armillaris, which have evolved without the interference of fire (Kirkpatrick et al. 1971). |
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