A new ecological index for assessing benthic invertebrate assemblages in tropical coral reef ecosystems

Benthic invertebrate assemblages are often assessed in coral reef monitoring owing to their ecological and economic importance, yet a biotic index for assessing the ecological health of these assemblages has not yet been developed. This index is useful for stakeholders to help design management actions, including conservation and restoration of target taxa. In this study, we developed a new biotic index to assess the ecological health of benthic invertebrates on the basis of coral reef monitoring data from 38 locations (8–19 sites per location) across Indonesia (n = 464 sites). At each site, a belt transect of 2 m × 70 m was performed to collect invertebrate data (Holothuroidea, Tridacninae, Palinuridae, Trochidae, Acanthaster planci, Diadema, Drupella, and Linckia laevigata) and benthic habitat data. The index was constructed on the basis of the ecological quality ratio concept (the ratio between observed and reference values) using 11 metrics from training data (n = 389 sites) and validated by that on the basis of testing data (n = 75 sites). The index was also validated by evaluating the linear regression between the index and anthropogenic pressures, and ranged between 0 (very poor) and 1 (very good). The index ecological quality ratio of invertebrates (EQRinv) decreased with declining water quality and increasing fishing pressure but increased with habitat heterogeneity (p < 0.05). This suggests that the EQRinv could indicate the presence of poor water quality, overfishing, and habitat modification in coral reef ecosystems. Based on our index, the ecological health of benthic invertebrate assemblages in Indonesian coral reef ecosystems was fair, with a mean EQRinv of 0.47. The EQRinv can improve the assessment of coral reef health in Indonesia and can also be applied across the tropical Indo-Pacific to support coral reef conservation and management.