Coasts and oceans
Trevor J Ward, Greenward Consulting, Perth, Western Australia
Alan Butler, CSIRO Marine and Atmospheric Research, Brisbane, Queensland
prepared for the 2006 Australian State of the Environment Committee, 2006
Australia has oceanic ecosystem features of great international interest and of great importance for fisheries, biodiversity and control of our climate, such as the East Australia Current and the Leeuwin Current. For example, one of Australia’s most prominent and predictable upwelling systems occurs along the Bonney Coast (Robe in South Australia to Portland in Victoria), between November–December and March–April each year. The waters are highly productive as a result, producing a discrete sediment type, with a distinctive colder-water flora and rich assemblages of sessile filter feeders such as sponges, bryozoans and corals. It is also a productive fishing ground, in particular for rock lobster, sustaining a relatively large fishing industry. It is one of the 12 global feeding areas where Blue Whales aggregate in relatively high numbers (Butler et al. 2002) (Figure 1).
The patterns of variability in Australia’s upwellings, and their relationship with large-scale climate features, such as currents and wind patterns, are unclear. It is likely that changes in climate and ocean currents will affect the location, extent and duration of upwellings, and this has direct implications for biodiversity conservation and fisheries production in Australian waters.
Figure 1: Sea surface temperature satellite image from March 1995, showing strong cold water upwelling along the Bonney Coast, and cool water near Eyre Peninsula, Kangaroo Island, and eastern Victoria
Source: CSIRO Marine Laboratories Remote Sensing Facility ; (a related image, slightly further west, is published in Griffin et al. 1997)
The world’s climate is coupled to the oceans at three important spatial levels: ocean basins, regional areas (such as the eastern coast of Australia), and the local shores, estuaries and bays. Changes in the coupling of the global ocean–climate systems are already having substantial and important ramifications for the world’s coasts and oceans (Hays et al. 2005). Increases in the acidity of seawater as the ocean absorbs carbon dioxide from the atmosphere will make it more difficult for coral and other calcareous organisms in the sea to build new skeletons (The Royal Society 2005). In Australian waters, perhaps the most visible impact of changes in climate is the bleaching of coral reefs as a result of increased water temperatures. Changes in the oceanic water column—in the plankton—may have more far-reaching effects (Hays et al. 2005) and there are many other changes that are related to changes in the climate, and they are becoming more evident in Australian marine ecosystems.
The sea level is rising around the Australian coastline at about 1.2 millimetres per year (Sea Level Survey 2003; Church et al. 2004). The Intergovernmental Panel on Climate Change (IPCC) concluded that sea level has risen globally by between 0.1 and 0.2 metres during the twentieth century. The IPCC predicts, for the period 1990 to 2100, a further rise of between 0.09 and 0.88 metres globally, an increase in the frequency of extreme sea-level events, and a resulting significant increase in storm damage.
These changes in climate are likely to have negative effects on Australia’s coral reefs, seagrasses, reef systems and other nearshore marine habitats, and cause complex readjustments in the physical structure of beaches, estuaries and sheltered foreshores. Benthic species that are able to colonise new territory may be able to adjust, but those that cannot might become locally eliminated or even extinct. For example, increased sea level is likely to reduce the species diversity of corals because of from the indirect effect of water depth on coastal erosion, nutrients and suspended solids (Wilkinson 1999).
In south-eastern Tasmania, there are changes in the distribution of kelps, changes in the distribution of sea urchins, and problems with the salmon culture industry that can be related to climate change and, potentially, to other human influences (Edgar et al. 2005, Pittock 2003). These may be associated with the warm East Australia Current moving further south more frequently (Thresher et al. 2004). For example, the dominant mainland sea urchin (Centrostephanus rodgersii) has extended its range southward along the east coast of Tasmania. Concomitantly, macro-algal (kelp) communities have declined.
The aquaculture industry is also at risk. Water temperature shifts of just a few degrees may mean the difference between successful and unsuccessful aquaculture of a number of species. For example, warmer waters (and higher rainfall leading to reduced salinity) can increase the incidence of amoebic gill disease in Atlantic Salmon (Salmo salar) (Clark and Nowak 1999).
Responses so far to the issues of climate change in coastal and ocean ecosystems have been very limited, such as the National Biodiversity and Climate Change Action Plan 2004–2007 (Natural Resource Management Ministerial Council 2004). Few marine industries have established precautionary climate change adaptation strategies, and there is no specific set of national responses that are designed to ensure that biodiversity issues driven by climate change are properly identified, or to provide a suitable planning base to respond to the pressures created by climate change. If management and conservation strategies do not urgently begin to take climate-driven variability and the likely long-term shifts into account, it may be difficult to effectively mitigate or manage impacts.
Australia’s coral reef ecosystems are unique. The Great Barrier Reef (in Queensland) and Ningaloo Reef (in Western Australia) are Australia’s coral reef icons, but there are many other coral reef ecosystems with unique species assemblages, including deep-water corals, the low to high latitude transitional reefs in New South Wales and Western Australian waters, and coral atolls in the Indian Ocean and South Pacific Ocean. Each of these types of coral ecosystems supports a broad array of fish and invertebrates, many of which are endemic. They also support a range of species that are important for recreational, commercial and traditional fisheries.
The Australian Government, the Great Barrier Reef Marine Park Authority (GBRMPA), and the state and territory governments each have a different system for protecting and managing coral reef ecosystems. Despite the overwhelming global and national importance of these ecosystems, there is no national system for assessing or reporting on the condition of Australia’s coral ecosystems, and so, overall, the condition of Australia’s coral reef ecosystems remains unclear.
The Great Barrier Reef is managed under one of the best-developed and most effective coral reef management systems in the world. The major responses to the identified pressures on the Great Barrier Reef are the development of new fisheries management plans, a water quality protection plan to reduce the impacts of land-derived nutrients, sediments and pesticides, and a new zoning plan for GBRMPA to protect more than 30 per cent of the Great Barrier Reef within ‘no-take’ sanctuaries. Western Australia is developing management arrangements for Ningaloo Reef, but there appear to have been few initiatives developed in the Northern Territory to protect coral reef systems.
Many coral ecosystems are probably in good condition, but the limited monitoring conducted on the Great Barrier Reef and in Western Australia shows that there is considerable local damage at some places caused by cyclones, bleaching, invasive species, fishing, sedimentation and pollution. It is unlikely that there will be any major reductions in these key pressures on coral reef ecosystems in the short to medium term outside the Great Barrier Reef; therefore, despite considerable management efforts, the future for Australia’s coral reef ecosystems is uncertain.
More information is available at:
- Environmental status of corals on the Great Barrier Reef
- The state of the Great Barrier Reef online
- Ningaloo reef website
Australia has the world’s most diverse array of tropical and temperate seagrasses, including 34 species, which is more than half of the world’s 60 species, and 11 of the world’s 12 genera of seagrasses (Short and Coles 2001). Australia has about 51 000 square kilometres of seagrass meadows , with major areas in the Gulf of Carpentaria, Shark Bay (the world’s largest seagrass bed), the southern coast of Western Australia, and in Spencer Gulf and St Vincents Gulf in South Australia.
There is no systematic national assessment and reporting system for seagrasses, but where there have been studies, major seagrass losses have been documented in the past—in Queensland, Victoria, South Australia and Western Australia. These have been caused by changes in estuarine hydrology, rainfall and flooding patterns; elevated nutrients from factories, sewage and agricultural runoff; increased turbidity and siltation; and the destruction of seagrass beds by sand mining (Butler and Jernakoff 1999). For example, seagrass beds declined in St Vincent Gulf by 720 hectares between 1995 and 2002. Some of these losses are continuing (such as losses caused by sand mining in Cockburn Sound, Western Australia) although many agricultural sources of nutrients and sediments are being reduced through improved catchment management programmes.
Since replanting and transplanting of seagrasses is not a viable option for mitigating degraded seagrass beds, it is most prudent to avoid as much damage as possible, by ensuring that activities such as trawling and dredging, sand mining, and water pollution from local catchments do not have any negative effects on Australia’s remaining seagrass beds.
Many of Australia’s birds live on the coasts and islands, and depend on both coastal and inland wetlands. Monitoring of many of the wetland species indicates that their populations are generally stable, although some are highly variable. In particular, extreme storms and extended droughts and floods have major impacts on the size of bird populations (Olsen et al. 2003).
An estimated two million migratory waders from 69 species enter Australia each year. There is no systematic national monitoring of waders, but data from the Coorong in South Australia—one of the most important Australian sites for waders—show there has been a steady decline in wader abundance. In the 1980s there were 50 000 to 60 000 waders using this wetland system, but in the last five or so years there have been consistently only about 5000 to 15 000 waders. Curlew sandpipers (Calidris ferruginea) and fairy terns (Sterna nereis) seem to be in continuing decline in the Coorong, while numbers of some of the other species (red-necked stint (Calidris ruficollis), sharp-tailed sandpiper (Calidris acuminata), red-capped plover (Charadrius ruficapillus) appear to have stabilised . The populations of many waders have declined over the past few decades, and, because many of the threats occur in overseas countries, a number of international agreements (such as Japan–Australia Migratory Bird Agreement, JAMBA) have been developed to attempt to prevent the decline in these highly migratory species and promote their recovery.
Of the 142 species of seabird that occur in Australian waters, 76 breed and spend their lives in the region, and 34 are regular or occasional visitors. Several species are threatened by incidental capture during fishing operations. The Wandering Albatross (Diomedea exulans) came close to extinction in the 1980s as a result of longline fisheries bycatch, but with the introduction of mitigation measures in 1994, the population has remained stable at the very low level of about 19 breeding pairs. Considerable reductions in the fisheries bycatch of many other seabirds has apparently been achieved in the last five years, but tuna fisheries may still pose a serious threat so some bird species, particularly the Flesh-footed Shearwater (Olsen et al. 2003, page 19).
The main pressures on shorebirds and migratory waders are loss of habitat, disturbance of feeding, nesting and roosting areas, predation, especially by introduced pests, and droughts and floods. Also, the once rich feeding grounds of many urban estuaries have been degraded by pollution and the increasing mobility of tourists now places many formerly secluded bird feeding and roosting areas within easy reach, increasing levels of stress on individuals and populations.
Australia hosts eight (62 per cent) of the world’s 13 cetacean families, 27 (68 per cent) of the 40 genera, and 43 (54 per cent) of the 80 or so currently recognised species of cetacean. This includes about 29 species of whales , 13 dolphins and one porpoise.
All cetaceans are fully protected in Australia, and from acts by Australian citizens globally, under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). Even so, cetaceans everywhere are subject to a number of significant pressures from both human activities and from long-term climate change. The main issues in Australian waters are boat-strike, entanglement in fishing gear (nets, ropes) or shark protection nets, marine debris (plastics, ropes), oil spills, acoustic survey impacts, tourism and whale-watching activities, and viruses and diseases from terrestrial mammals. For example, a recent university study in Shark Bay found that the mean abundance and reproductive output of dolphins was lower in an area subject to commercial tourism interactions than that of dolphins in a control area (Bejder 2005).
The ingestion of foreign matter such as plastic bags can lead to serious gastrointestinal blockages in cetaceans, potentially causing the animal to starve. In 2000, a Bryde’s whale with almost six square metres of ingested supermarket bags, food packaging, two-metre long plastic sheets and fragments of garbage bags was found stranded on a beach in Cairns.
There are also many global-scale pressures on cetacean populations. These include hunting and commercial fishing (practiced by a number of countries), the impacts of changing ocean currents and production, the depletion of krill (an important whale food) by commercial fisheries, climate change factors, and the accumulation of persistent organic pesticides and other long-lived chemicals.
Australia has declared a Whale Sanctuary over all Commonwealth-managed waters for all whales, dolphins and porpoises. All the states and territories also protect these species in their waters. Five whale species are currently listed as nationally threatened under the EPBC Act, and recovery plans have been developed for each species (DEH 2005).
The Dugong (Dugong dugon) is the only herbivorous mammal that is strictly marine, and in Australia, ranges from the New South Wales – Queensland border to Shark Bay in Western Australia. Torres Strait and the northern waters of the Great Barrier Reef support the largest known populations of Dugong in the world. The largely undisturbed population of Dugong in Shark Bay is the largest intact population of Dugong in the Indian Ocean. In all parts of their range, Dugong populations are under pressure, and in some places they have already been eliminated.
There are no national surveys of Dugong in Australia’s waters, but the populations in waters off Western Australia, the Northern Territory and the Torres Strait are thought to be reasonably stable despite a number of pressures, including impacts on seagrass habitats and hunting. In contrast, south of Cooktown on the Queensland coast, surveys and catches of Dugong in beach protection shark nets indicate that there has been a major reduction in Dugong population in this region since the 1960s. In response to this, 16 Dugong Protection Areas were declared in 1997.
There are seven species of marine turtles in the world, and six of them occur in Australian waters—the Flatback (Natator depressus), Green (Chelonia mydas), Hawksbill (Eretmochelys imbricata), Leatherback (Dermochelys coriacea), Loggerhead (Caretta caretta) and Olive Ridley (Lepidochelys olivacea) turtles. The Flatback Turtle nests only on Australian beaches from Exmouth (Western Australia) to the Great Barrier Reef, and is endemic to the Australia-New Guinea continental shelf. More than two-thirds of the world population of this species breeds in Australian waters.
All the turtle species are migratory, with some travelling vast ocean distances; hunting of turtles in overseas waters is of major concern to the populations of all turtle species. Human impacts in Australian waters are also important, including boat strikes; bycatch in trawl fisheries; entanglement in lost fishing nets and ropes (see Figure 2); predation on eggs by other animals; the loss and pollution of habitats; the encroachment of vehicles, coastal development and light pollution onto nesting beaches; turtle hunting for traditional food; and ingestion of marine debris. In Queensland in 2002, 69 turtles were found stranded and dead, most after entanglement with marine debris from various sources.
Source: Limpus and Chatto (2004)
The number of female Loggerhead Turtles breeding annually on the east coast of Australia has declined by about 86 per cent from an annual nesting population of about 3500 females in the 1970s to the present level of less than 500 females breeding. This decline means the Loggerhead Turtles of the South Pacific Ocean are critically endangered. Data on trends in other marine turtle species are not available.
All six marine turtle species in Australia are listed as threatened under the EPBC Act, under CITES, and some are also protected under state and territory legislation. A recovery plan for marine turtles has been prepared in accordance with the EPBC Act to promote the recovery in the wild of all Australia’s turtle populations. Trawl fisheries are now expected to take major steps to reduce their bycatch (and the mortality) of turtles. For example, in the Northern Prawn Fishery, through the use of bycatch reduction devices, the annual bycatch of turtles has been reduced by 99 per cent since 1999. Less than 100 turtles were caught as bycatch in the Northern Prawn Fishery in 2001, and actual turtle drownings are considered to be less than 20 per year (Brewer et al. in press).
The condition of Australia’s coastal and ocean ecosystems can be understood and assessed only in the light of data and knowledge about their features and values. It is important to understand and, where necessary, mitigate pressures that might tend to degrade these ecosystems, but knowledge of pressures alone cannot provide a solid indication of the condition of the ecosystems. This is because it is not always clear how the various pressures affect the ecosystem conditions, nor how different pressures can interact with each other to create greater impacts.
There are few measurement or reporting programmes across much of Australia’s coastal and ocean ecosystems. The lack of an integrated and national analysis and reporting system creates the situation where ‘sliding baselines’ can occur without our knowledge. Here managers and scientists only assess and report on the significance of changes that are within their own personal experience, and not against a documented set of benchmark conditions that would more properly reflect historic conditions, the expectations of the community, conditions in other regions, or changes over more than a decade or two. For example, recent evidence suggests that there has been a major loss of shell (mollusc) species over the past 150 years in shallow, sheltered estuarine waters of south-eastern Tasmania (Edgar and Samson 2004). These losses were previously undetected, and this example highlights the risk of the ‘sliding baseline syndrome’, where changes that occur over generations are not noticed and the new environmental conditions become considered to be ‘normal’ (Dayton et al. 1998).
There is a broad appreciation of some of the important features and values of Australia’s coastal and ocean ecosystems (Ward et al. 1998), but there is neither nationally consistent data nor knowledge about their condition. The lack of a systematic and national approach to documenting the conditions in Australia’s ecosystems means there is very little reliable knowledge that can be assessed to report on changes in their condition.
While it is clearly expensive to design, establish and implement long-term monitoring, assessment and reporting systems, the eventual benefits are much greater than the short-term costs. Critical insights about the way in which ecosystems operate, the way in which they respond to major stresses, and patterns of natural change have all been secured through long term monitoring studies of ecological systems both in Australia and in other countries. It is only with long-term knowledge of the condition of ecosystems and how they respond to pressures that effective response strategies can be designed and tested.
Given the inevitable climate-driven changes in the oceans (Link to Indicator CO_76), and with these changes already being recognised today in marine systems, more systematic and strategic planning will be required for the coastal zone to allow for a gradual transition and systematic adaptation of regional and urban communities to new coastal and ocean conditions of the future. Without a systematic and planned transition, both biodiversity and the existing basis for wealth-generation from coastal ecosystems will be disrupted in an unpredictable way, and this will undermine the security of resources for coastal industries and the systematic protection and management of coastal biodiversity into the future.