Toward a spatialized index of the “benthic ecological state” using a new Coral Reef Rapid Assessment Method (CORRAM): case study at Reunion Island

Abstract

The development of a spatial index that can be used to represent the benthic ecological state of coral reefs is essential for guiding public conservation policies. We propose the spatialization of a new index of “benthic ecological state” using the Coral Reef Rapid Assessment Method (CORRAM). Eight benthic biodiversity indicators selected from the literature that reflect key resistance and resilience mechanisms were assessed in 786 circular plots on the Saint-Pierre reef flat of Reunion Island. The “benthic ecological state” index was constructed from the eight benthic biodiversity indicators and spatialized using ordinary kriging. To better assess functional mechanisms with respect to environmental pressures, the “benthic ecological state” index can be sub-divided into two indexes. By establishing the associations between these indexes and abiotic environmental variables, the “coral community structure” and “benthic community vitality” showed a differential response sensibility including interaction with abiotic environmental variables studied. Our large dataset enabled us to propose a “benthic ecological state” of reference based on habitat type for the Saint-Pierre reef flat in 2021. These indexes highlight areas of high socio-ecological issues and contribute to quantifying the deviation between the “reference ecological state” and the “benthic ecological state” at a given spatio-temporal point. This proof of concept provides a methodological framework that can be replicated at multiple scales (from local to global) in other reefs. Using a field-based method with spatial indexing and pressure data, it is now possible to accurately locate and quantify areas of coral reef are vulnerability and of major concern.

Keywords

• Coral reef health
• Circular plot
• RAM
• Coral reef index
• Western Indian ocean island states