Coasts and oceans: Marine biodiversity

Independent report to the Australian Government Minister for the Environment and Heritage
Beeton RJS (Bob), Buckley Kristal I, Jones Gary J, Morgan Denise, Reichelt Russell E, Trewin Dennis
(2006 Australian State of the Environment Committee), 2006

6.1 Marine biodiversity

Australia’s vast and varied coasts and oceans are largely unexplored. There is very little information about Australia’s marine biodiversity, much of which might not yet have been discovered (Ponder et al 2002). This is especially the case for species and ecosystems in more remote, deeper oceanic areas. The risk is that small, but cumulative changes might not be detected because of a lack of knowledge of these vast and varied systems. The recently discovered loss of shell (mollusc) species over the past 150 years in shallow, sheltered estuarine waters of south-eastern Tasmania is just one example (Samson and Edgar 2001).

The limited information that does exist is generally for coastal biodiversity, with some species and systems  showing mixed trends and others in apparent decline:

  • of the limited number of bird species studied in a narrow range of monitored habitats, seven species appear to be stable, seven are declining, four have declined but appear to be rising or stabilising again, and five have expanded either their population or their range in at least one location
  • mangroves are declining in some places as they are cleared for coastal development, and expanding in certain areas, especially northern Australia, but the extent to which they are expanding into other ecosystems is unclear
  • monitoring in the Great Barrier Reef and in Ningaloo Reef shows considerable local damage and changes in resident species from cyclones, bleaching, fishing, sedimentation and pollution (see‘Natural and cultural heritage’)
  • major seagrass losses have been documented in Queensland, Victoria, South Australia and Western Australia
  • giant kelp declined, both in overall area and in number of beds, in some places, until the 1990s with only slight recovery since then
  • there is very little systematic monitoring of fish populations except in the commercial fisheries and many fisheries have no biomass reference points, little reliable data and no fully independent assessment of stocks. Reports on Commonwealth commercial fisheries by the Bureau of Rural Sciences show a steady increase in the number of species considered to be overfished. As researchers have found out more about these fisheries’ resources, they have rated more species as overfished.

Further information about marine biodiversity is available through the Ocean Biogeographic Information System database at http://www.obis.org.au >.

Up to mid-2005, 18 marine species had been listed as threatened  under the EPBC Act, and the number is likely to increase. It is not yet possible to predict whether protection alone will allow some of these species to recover. An emerging issue is that some species that have apparent niche overlaps are recovering differently. For example, Australian fur seals are increasing rapidly while sea lions are not showing such a recovery. The reasons for this difference are not well understood and are at the moment only speculative.

Overall, the lack of knowledge makes it difficult to predict the impact of climate change on Australia’s oceans. Even the effects of a small change in water acidity  due to increasing carbon dioxide concentrations are not known.