Spatial patterns of benthic invertebrate assemblages within atoll lagoons: importance of habitat heterogeneity and considerations for marine protected area design in French Polynesia

Abstract

We investigated spatial patterns of stony corals, molluscs and echinoderms among six habitat types within the lagoons of six atolls in the Tuamotu Archipelago (French Polynesia). Percent cover (stony corals only), abundance and richness were recorded within habitat types delineated by specific geomorphological features. Among six habitat types defined a priori, four encompassed distinct assemblages of corals and molluscs: (1) pinnacles possessed maximum richness, abundance and coverage, (2) passes showed relatively high abundance and coverage, (3) lagoon floors were marked by the commonness of a few coral genera, and minimum mollusc abundance and richness, and (4) inner reef flat stations, independent of their location in front of spillways, motu or rim zones, had low cover, abundance, and richness. While habitat associations were similar for stony corals and molluscs, echinoderms were preferentially found on the inner reef flat facing the rim. Lowest echinoderm abundances and species richness were recorded on pinnacles and in the vicinity of the pass. Such small-scale spatial heterogeneity appears to be one of the distinctive characteristics of coral communities in French Polynesian reefs. These results, along with those of the TYPATOLL program, demonstrate the importance of both local and regional factors in determining the diversity and structure of coral assemblages. Habitat fidelity was weak: many species/genera were poorly represented among habitats and restricted to a few atolls, while others were present across all lagoons and habitats. Therefore, marine protected areas design based solely on representativeness will require the protecting the vast majority of lagoon habitats.