Crown-of-thorns starfish
(COTS) are marine invertebrates that feed on coral and occur naturally on reefs
throughout the Indo-Pacific region. When conditions are right for COTS to
multiply, they can reach plague proportions and devastate the hard coral
population on affected reefs.
In the past
40 years, three major COTS outbreaks have had a major impact on many reefs
of the Great Barrier Reef (GBR). COTS outbreaks are responsible for a
greater decline in coral cover than any other threat to the GBR.
AIMS has implemented the most
comprehensive COTS monitoring program in the world across the GBR. This
long-term program, combined with genetic studies, has shown that COTS outbreaks
begin in the north and migrate southward on ocean currents over about a 15 year
period. These surveys also show that healthy reefs generally recover between
outbreaks, taking 10-20 years to do so. Reefs affected by additional stresses,
such as coral bleaching, cyclones or poor water quality, may take a lot longer.
Laboratory research at AIMS has shown that survival of COTS larvae increases
dramatically as phytoplankton, their food source, becomes more abundant.
Although land runoff rich in fertilisers and other pollutants can cause peaks in
phytoplankton, scientists are still unsure whether there is a link between human
activity and COTS outbreaks, given that the biggest increases in phytoplankton
production follow natural events such as cyclones and high rainfall and
outbreaks propagate effectively on mid-shelf and outer reefs in the central GBR
that are hardly ever affected by runoff.