Partitioning scleractinian coral diversity across reef sites and regions in the Western Indian Ocean

Understanding how diversity is organized is essential for inference about appropriate scales for natural resource research and management. In this study, we investigated variation in scleractinian coral taxonomic richness and community diversity in the Western Indian Ocean (WIO) at different spatial scales. We sampled corals in 331 sites across nine countries. Sites were pooled into 11 distinct subregions based on previous investigations on coral community structure and between closures and reefs open to fishing for five regions with sufficient closure replication. We analyzed similarities in coral communities and compared differences in mean richness and Shannon diversity. Significant differences in alpha and beta components of diversity were tested at multiple spatial scales and between management types against a random distribution null model. Rarefaction was used to investigate significant difference in total taxonomic richness among regions. Coral communities were mainly structured along Acropora and massive Porites dominance lines. Highest dissimilarity among coral communities was found at the regional level and within- and between-subregion variations accounted for most of the coral diversity. Beta components were responsible for higher proportions of taxonomic richness of which a large part was explained by the site-region interaction. Alpha diversity contributed most to Shannon diversity and site level richness and Shannon diversity had similar relationships with latitude, peaking at about 10 degrees S. Alpha diversity also showed significant relationship with water temperature variability, peaking at a sea surface temperature standard deviation of about 1.4 degrees C, corresponding to the same 10 degrees S latitude. Relatively higher alpha and beta components contributed to high richness and Shannon diversity in three regions: southern Kenya-northern Tanzania, southern Tanzania-northern Mozambique and northwestern Madagascar-Mayotte. Consequently, the findings support the proposal for delineating these locations as a regional priority for biodiversity conservation.