What does a long-term coral recruitment study tell us about reef recovery
E. Turak
Australian Institute of Marine Science
PMB 3, Townsville MC, Townsville, Qld 4810
Australia
In recent years coral reefs worldwide have suffered from some severe and widespread impacts. Today, their current status and capacity to recover is one of the most contentious issues confronting reef scientists and managers of reef resources. Recovery of a coral community will in the first instance depend on recruitment at two levels; regeneration of remnants of damaged colonies and supply of propagules derived locally or from outside. However these alone will not ensure successful recovery if the local environment is not suitable for recovery.
Rates of coral settlement and recruitment were assessed in a variety of disturbed and undisturbed sites on the Great Barrier Reef in Australia. Settlement was assessed with settlement plates and the densities and fates of recruits were recorded by mapping of quadrates. Settlement and recruitment patterns were variable and not predictable over the short term (1-2 years). However in the long-term (5-7 years) patterns began to emerge in trends of settlement at particular positions on reefs, depths and geographical locations. Over all, settlement numbers showed a gradual decline over the seven years. However most sites had both good and bad years for settlement numbers, only the low density sites showing more constant numbers. At individual sites, it was generally not possible to correlate rate of recovery with rate of recruitment. While there was no big difference in settlement densities between shallow and deep sites, shallow sites recovered better. However at the level of larger groupings (depth, reef position, geographic location) the long term influence of recruitment may be seen. This indicates that the role of recruitment in the recovery process is not predictable over short term or in a limited range of sites. However a long-term recruitment study with a larger number of varied sites, coupled with studies on other demographic processes and observance of local scale phenomena (eg. predation, bioerosion, bleaching, sedimentation) can give us this predictive capacity.
