GREAT BARRIER REEF
// Outlook Report 2014
There are more than 400 species of hard coral138,139 and at least 150 species of soft corals, sea fans and sea pens140 in the Region. Coral diversity contributes strongly to the outstanding universal value of the Great Barrier Reef World Heritage Area23. Recent studies indicate deeper, mesophotic reefs have a higher coral diversity than previously thought.88,92 In addition to the decline in hard coral cover described in Section 2.3.5, there is also evidence of changes in species composition on reefs. Evidence from Pelorus Island (in the Palm Island group, north of Townsville) indicates that the community composition of inshore coral reefs changed over the last century.76 Historically, the reefs were dominated by Acropora corals, thought to be characteristic of less polluted waters.76 However, between 1920 and 1955, the coral composition changed and either shifted to corals typical of more turbid, muddy waters or had little live coral.76 More recently, chronic impacts of poor water quality and outbreaks of disease have resulted in a loss of sensitive species in affected inshore areas and therefore reduced species diversity.78 Soft coral cover in inshore areas has been generally stable over the period 2005 to 2010 with some decline in 2011 in the central area caused by physical destruction of colonies by cyclone Yasi.83 Record flooding of the Fitzroy River in 2011 also killed almost all shallow-water soft corals (at or above two metres deep) on reefs inshore of Great Keppel Island and caused declines in deeper water.83
The community composition of inshore coral reefs changed over the last century.
2.4.6 Other invertebrates
There are thousands of species of invertebrates (animals without backbones) in the Region. This biodiversity is nationally and internationally significant (including as part of the Reef’s world heritage listing). An estimated 30 per cent of Australia’s sponge species and more than 10 per cent of the world’s echinoderms (starfish, sea urchins and sea cucumbers) are found within the Region.141 Some groups, such as prawns, crabs and sea cucumbers, are important in fisheries. Fishing activities have reduced abundances of a number of invertebrate species, although no invertebrate species are currently assessed as ‘overfished’ in fisheries stock status reports.142 The black teatfish fishery was closed in 1999 following concerns for the long-term viability of the harvested stock and has not been reopened (see Section 8.3.3). There are some concerns about the sustainability of the sea cucumber fishery.143,144 Little is known about the condition and trends of most species. Some invertebrate species have been protected (for example tridacnid clams, helmet shell, triton shell). It is likely that deteriorating water quality and the changing condition of southern inshore habitats in the southern two-thirds of the Region has affected dependent invertebrates. Outbreaks of crown-of-thorns starfish continue to occur on the Great Barrier Reef (Section 3.6.2). There is strong evidence to support a connection between human-related impacts (in particular, nutrients from land-based run-off) and outbreaks of crown-of-thorns starfish.145,146
Invertebrates are likely to be affected by changing environmental conditions and fishing activities.
These commensal shrimp are one of the Region’s thousands of species of invertebrates
2.4.7 Plankton and microbes
Although plankton and microbes play a vital role in the Great Barrier Reef ecosystem as the foundation of the food web and in many ecological processes, there remains little known about their condition and trend.147,148 Changes in water temperature and quality are likely to be altering plankton communities which, in turn, will be affecting higher trophic levels.147,148,149 For example, there is growing evidence that increases in nutrients cause shifts in phytoplankton populations, providing favourable conditions for the development of crown-of-thorns starfish larvae.146