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1. Description of Australia's marine environment and its status - continued

Status of major Marine Habitats and Ecosystems - continued

Coastal saltmarshes: undervalued and locally threatened

Coastal saltmarshes, the intertidal plant communities dominated by herbs and low shrubs, are often associated with estuaries. Saltmarshes are highly productive, key habitats which support many other organisms. They are a critical habitat for many migratory species and for rare species such as the orange bellied parrot in Victoria.(7)

It is estimated that Australia has 13,595 square kilometres of saltmarshes (Queensland 5,322; New South Wales 57; Victoria 125; Tasmania 37; South Australia 84; Western Australia 2,965; and Northern Territory 5,005 square kilometres).(7)

A major threat to saltmarshes in developed areas is land reclamation and extensive areas have been filled for ports, marinas, canal estates and urban and industrial sites. Other threats include degradation by rubbish dumps, off-road vehicles, invasion by weeds (particularly by introduced cord grass, pampas grass, para grass, and rushes), periodic surges associated with low pressure systems and drainage for mosquito and sandfly control. Although the total loss of saltmarshes has not been great in Australia, most has been concentrated in the south-east where the initial area was small, and where biodiversity and endemism is highest. Losses are therefore considered to be significant both regionally and nationally. A sea level rise resulting from an enhanced greenhouse effect could cause significant contractions in saltmarshes.(7),(84)

Mangroves: vital coastal ecosystems

Mangroves are tree and shrub species which are adapted to the periodically inundated and salty conditions between the tides. Mangrove forests are very productive ecosystems and are of major ecological and economic importance. They provide habitats and nurseries for many fish, form a buffer for estuaries from sediments and for coastlines from storm waves, are natural nutrient filters, and are critical habitats for many birds and other wildlife. Australia has the third largest area of mangroves in the world, and has some of the most diverse communities.(8)

Overall losses of mangroves in Australia are small compared with those from other countries. However, locally significant losses have occurred around Australian coastal cities and towns, for example 20% has been cleared in Moreton Bay near Brisbane(8),(51), and there has been significant die-back of mangroves near Adelaide(55). Major threats are continued local clearing and development and effects of catchment alterations. Only 8% of Australia's mangrove communities are in protected areas(8).

Seagrass beds: major declines in temperate areas

Seagrass beds are also ecologically important because of their high productivity, their ability to trap and stabilise sediments, their importance as fisheries habitats, and as the habitat for important species such as dugongs and turtles(10),(18). Australia has the highest biodiversity of seagrasses in the world, the largest areas of temperate seagrass and one of the largest areas of tropical seagrass(10).

Australia's unique temperate seagrass beds appear to be under particular threat. Increased sedimentation and nutrients from catchments have been linked with massive die-back of seagrasses in many areas. New South Wales has lost half of the Zostera seagrass in its estuaries(10),(52). In Victoria around 85% of the total biomass of seagrass in Western Port has been lost(10). In Tasmania there have also been declines in the Hobart and D'Entrecasteaux region, Triabunna and St. Helens on the east coast, and Tamar, Port Sorell and Duck Bay on the north-west(54). In South Australia's Gulf St Vincent around 5,000 hectares of seagrasses has been lost(10),(55). In Western Australia around 97% of seagrass in Cockburn Sound have been lost(10),(56). A serious loss of tropical seagrasses has occurred in Hervey Bay in Queensland, causing major mortality of dugongs(10),(18).

Once lost, seagrasses do not readily recover(10). The decline in temperate seagrass is one of the most serious issues in Australia's marine environment.

Temperate reefs: unique, poorly known and under-protected

While the submerged rocky reefs in temperate Australia may lack the glamour and accessibility of their tropical equivalents, they do have a very high species diversity and a high proportion of endemic species(5),(11). Australia's southern coastline has the world's highest diversity of red and brown algae (around 1,155 species), bryozoans (lace corals), crustaceans and ascidians (sea squirts). Long isolated in geological time and by climatic barriers, this region has a distinctive fauna and flora, with around 80% to 90% of species in most groups being endemic(11). Temperate reefs are also important for commercial and recreational fisheries such as abalone, rock lobster, snapper(11),(31), and for recreational diving(28).

Despite their high conservation and economic values, Australia's temperate reefs are inadequately studied scientifically(11), and relatively few are protected(67). Very little is known of the effects of human activities on temperate reefs but it is assumed that outside metropolitan and industrial areas, they are relatively unaffected(11).

Coral reefs: under global threat

Coral reefs are among the most productive, diverse and complex ecosystems in the world. They are also under global threat. It has been estimated that around 70% of all the world's coral reefs are degraded in some way, and there are fears that the survival of coral reefs in some areas is threatened(12).

Australia has the largest area of coral reefs of any nation and the largest coral reef complex, the Great Barrier Reef. Major areas of coral reefs are also present in Torres Strait, the Coral Sea Territories, and central and northern Western Australia. The Tasman Sea reefs (Elizabeth and Middleton Reefs and Lord Howe Island fringing reef) are the highest in latitude in the world, and thrive in conditions otherwise marginal for coral growth.(12)

General issues affecting Australia's coral reefs include effects of sediments and nutrients(42), effects of fishing and tourism(69), and the threats of oil spills(39). Specific threats include elevated nutrients in the inner Great Barrier Reef(69); outbreaks of crown-of-thorns starfish in the outer central and northern Great Barrier Reef and Tasman reefs(49),(69); damage from the passage of tropical cyclones; and outbreaks of coral-eating Drupella snails in Ningaloo Reef, Western Australia(50),(70).

Coral reefs are relatively well represented in marine protected areas in Australia(12),(67). Significant areas are protected in all of the places where reefs are found, although management is often constrained by their great size and remoteness, and by lack of financial resources. Australia's coral reefs are relatively unaffected by human activities due to low to moderate levels of use and their remoteness, but elevated nutrients and sediments resulting from inland soil erosion are a threat in non-arid regions(42),(69). Because of the general decline in many of the world's coral reefs, the conservation and tourism values of Australia's reefs are of growing importance(12).