Littoral biodiversity across scales in the Seychelles, Indian Ocean

The 16 Marine Protected Areas in the Seychelles Archipelago (Western Indian Ocean) are monitored by a wide range of scientific and conservation organizations, but these mainly focus on coral or fish. We have investigated variability in littoral biodiversity (with emphasis on molluscs, anomuran and brachyuran crustaceans, echinoderms and polyclad flatworms) across four spatial scales, including the largest, and previously unsurveyed, Silhouette Marine National Park. We recorded all fauna >4 mm within 1-m2 quadrats replicated at three tidal heights across transects and sites on the central granitic islands of Mahe and Silhouette and the outer Desroches coral cay. We sampled 438 quadrats and recorded 292 species of our study taxa, but accumulation curves did not reach asymptote. Most species were rare and encountered only once, although a few key species were highly abundant. Biodiversity was dominated by gastropod molluscs, which non-metric multidimensional scaling analyses showed to be a reasonable surrogate for overall faunal patterns. Non-metric multidimensional scaling showed that the fauna of each island were quite dissimilar, and after island, site explained the most variance in our generalised linear mixed models. The two least rich sites were adjacent to the only established hotel on Desroches but we cannot establish causality due to lack of a-priori data. However major enlargening of a hotel adjacent to one site on Silhouette should enable future scrutiny of tourism influences.