A new synthetic index to evaluate reef coral condition

Coral reefs are threatened worldwide by climatic change and increasing anthropogenic pressures. Standardized and simple metrics assessing their status and their potential to recover are urgently needed to achieve large scale homogeneous information. Here we propose a synthetic Coral Condition Index (CCI) based on the proportional abundance of coral colonies belonging to six ordinal categories which represent their condition: recently dead, bleached, smothered, upturned, broken, and healthy. CCI ranges from 0 (100% of dead corals) to 1 (100% of healthy corals) with low values suggesting large scale disturbances (e.g., climate impacts), and high values suggesting disturbances acting on a small scale that can be averted by local management actions. We tested the performance of this index in Maldives, which suffered from coral mass mortality following bleaching in 1998 and mechanical damage due to the tsunami of 2004. In our evaluation CCI was applied on the most represented species, i.e., tabular Acropora and Pocillopora, which were counted from 2005 to 2010 using replicated belt transects at several depths and across different habitats. CCI did not show correlated to the number of total coral colonies suggesting the possibility to employ the index under different levels of coral abundance. CCI detected high levels of coral damage, which is likely due to the documented slow recovery of Maldivian reefs after the two major disturbance events. Further tests in other tropical regions with different coral species might promote CCI as an additional parameter for coral reef monitoring and restoration programs.