Local heterogeneity of coral reef diversity and environmental stress provides opportunities for small-scale conservation

Aim: Strong social-ecological trade-offs between resource extraction and protection have created challenges for large, protected area management in natural resource-dependent countries. Therefore, local governments and community conservation activities are becoming common and information about low environmental exposure and high biodiversity can provide for planning localized conservation activities.Location: The western Indian Ocean.Methods: Coral reef sites were evaluated for local-scale environmental and species richness to elucidate local patterns in spatial heterogeneity. Local coral and fish taxonomic richness and coral community susceptibility to stress were normalized to partially account for common and heterogenous disturbances to coral cover and fish biomass. Residuals of these three response variables were evaluated for local geographic patterns and specific relationships with 21 environmental variables using machine learning methods.Results: Richness was highly variable at local geographies and had a double-peaked shape with latitudes. Thirteen of the 21 examined variables were selected and indicated complex, spatially heterogeneous and weak cumulative predictive relationships with specific environmental and human influences. For example, each selected variable contributed 7% to 25% of the variance but with different relationships for the three responses. Coral fish richness and coral community susceptibility correlations were positive but weak and therefore produced different local spatial patterns. Nevertheless, these spatial patterns exhibited some coarse-scale similarities indicating locations with shared positive community attributes and potential climate refugia. Shared richness variables included depth and wave energy, temperature variables of SST skewness, excess heat and rate of rise. Human influences of distance to shore, human populations and cities were also selected for richness and community susceptibility responses.Main Conclusions: Planning to include local stress and richness patterns variability could contribute to species persistence. From these specific data, sites in the Pemba Channel between the Tanzanian mainland and Pemba Island, and northern Mozambique and Madagascar fit refugia characteristics.