Status of the Coral Reefs at the Cocos (Keeling) Islands, Indian Ocean
A report on the status of the marine community at Cocos (Keeling) Islands, East Indian Ocean, 1997-2005
Commonwealth of Australia, 2005
About the Report
The Cocos (Keeling) Islands are a remote coral reef atoll located in the eastern Indian Ocean . The marine community comprises largely Indo-West Pacific species, with little endemism. A range of disturbances have impacted on the Cocos marine community including subsistence fishing, cyclones, coral bleaching, crown-of-thorns starfish outbreaks, and mass die-off events. Disturbances such as these on remote islands have the potential to cause drastic changes in the marine community. To determine the status of coral reefs at Cocos and document changes in community composition and species abundances, Parks Australia has developed an extensive monitoring program using internationally recognised Reefcheck survey methods. Underwater censuses were conducted by Parks staff at 11 representative sites from 1997 to 2005. Data were collected on important indicator, keystone and harvested marine fish and invertebrate species as well as on habitat composition.
Evidence from the underwater surveys at 11 sites from 1997 to 2005 indicates that the coral reef community at Cocos (Keeling) Islands is very healthy and in a stable period with little impact from anthropogenic activities. Live coral cover is high and there is minimal impact from coral damage, bleaching, and disease although some coral cancers are present. Crown-of-thorns starfish were found at high densities at some sites and further monitoring is required to determine the impact of these starfish on the coral community. Overall, fish and invertebrate abundances were found to be relatively constant throughout the survey period at all sites. A small number of significant changes occurred in the abundance of some study taxa, but these changes were usually the exception, involving only short-term fluctuations. Densities of fish and invertebrates calculated in this study were comparable with previous studies at Cocos (Keeling) Islands and similar to other coral reef locations. Two notable exceptions were the very high densities of small sea cucumbers and relatively low densities of snappers. Further monitoring will determine whether these levels are typical for Cocos (Keeling) Islands or just short-term phenomena observed during the 1997-2005 survey period.
With the exception of the presence of crown-of-thorns starfish, disturbance events that have been reported previously for Cocos were generally lacking during the study period. Given that isolated islands generally have high extinction rates and low recovery rates, and given the history of disturbance events that have occurred at Cocos, it is of utmost importance that monitoring be continued. Disturbance events are likely to occur in the near future and assessing their impact on the reef community and its subsequent recovery, and identifying susceptible species, is fundamental to effective management. Expansion of the monitoring program into the southern lagoon, where mass die-off events have been reported previously, would be beneficial to determining adverse impacts on the reef community.
For more information
More information on the Cocos (Keeling) Islands conservancy is available at www.environment.gov.au/parks/cocos.
This report is available from the Department's Community Information Unit, phone 1800 803 772.