THE RESILIENCE OF CORAL REEF ECOSYSTEMS THROUGH TIME

Refugia are sanctuaries to which organisms migrate during times of environmental stress. Ecologists have begun to use resilience, the capacity of an ecosystem to respond to perturbations, as a way to predict ecosystems that may act as refugia during severe stress. The resilience of an ecosystem is evaluated using functional diversity and functional redundancy. However, since environmental conditions have not yet reached magnitudes exhibited by past extinction events, it is difficult to evaluate whether resilience is an appropriate indicator of potential refugia. Therefore, it is important to asses this approach using the fossil record. The overall aim of this study is to test whether the resilience of modern coral reef ecosystems is measurable in the fossil record. 19 transects were studied across coral reefs found around San Salvador Island, Bahamas. Organisms found along transects were identified to species level, counted and placed into a functional group (combining motility level, trophic habit, and tiering). In addition, a value was assigned to each organism reflecting its preservation potential (0= will not preserve; 1= unlikely to be preserved, 2= will preserve). Transects were partitioned into samples representing five metre intervals, each covering a 10 m² area. Organism abundance and beta diversity observed in the modern record (using both preservable and non-preservable organisms) were compared with the simulated “fossil record” (assembled using only data from preservable organisms). Bray-Curtis dissimilarity was used to analyse data, a method that calculates the mean difference in beta diversity between samples derived from the same reef. Results show that differences in beta diversity are adequately preserved within the simulated fossil record. In addition, Bray-Curtis similarity was used, a method that compares similarity in beta diversity amongst samples from different reefs. Again, results show that these similarities between reefs are also preserved in the simulated fossil record. From these data, it appears that the beta diversity observed in modern reefs will be detectable in the fossil record. These findings are important as they suggest that the study of ancient coral ecosystems during extinction events can help to predict the fate of modern coral reef ecosystems.