SPATIAL VARIATION IN FISH SPECIES RICHNESS ON CORAL-REEFS - HABITAT FRAGMENTATION AND STOCHASTIC STRUCTURING PROCESSES

Most studies of coral reef fish communities have been restricted to si te-attached species on small. isolated patches of habitat. Few have in vestigated spatial variation in fish species richness in relation to p redictions based on stochastic or deterministic processes of community organisation. Our aims were to. (1) compare species richness on conti guous and fragmented reef habitats, and (2) investigate the mechanisms underlying spatial variation in species richness. Quantitative compar ison of species area curves for contiguous and patchy coral reef indic ated that patch reefs support more species than equivalent areas of co ntiguous reef. However, Monte-Carlo simulated rarefaction curves indic ated little difference in the species-individuals relationship for bot h habitats. Rarefaction was employed to eliminate variation in species richness among sites due to differences in sample size (number of fis h present). After removal of sample-size effects, multiple regression models explained 30% and 25% of total variability in species richness on contiguous and patchy coral reef based on variation in habitat stru cture (e.g., depth, shelter availability, substratum characteristics). To investigate the likely importance of stochastic processes in deter mining spatial variation in species richness, we compared the species- individuals relationship from contiguous reef sites with the relations hips derived from null models involving the random reallocation of fis h among sites. Comparisons of the observed data with the outcomes of t he null models indicated that spatial variation in species richness wa s not wholly attributable to stochastic processes. We suggest that the observed patterns of species richness may reflect species interaction s (e.g., competition and predation) within fish communities.