Evaluation of the Allen Coral Atlas benthic habitat map product for New Caledonia using representative habitat observations from a multi-species fishery assessment

Several remote sensing projects have produced coral reef habitat maps globally. This includes the Allen Coral Atlas (ACA) project. The present study focuses on assessing the accuracy of the ACA 6-class benthic habitat products available for New Caledonia in the 0-10-m depth range. The assessment involves using independent control data collected through thousands of in situ photographs of the benthic environment during sea cucumber stock assessments on multiple sites around New Caledonia. The overall accuracy of the ACA benthic product ranked from 20 to 67% depending on the sites and evaluation method. These results are generally lower than those achieved by other global and local coral reef mapping and products which can be primarily explained by the lack of local ground-truth data to train the classifications. In addition, we discuss other significant misclassifications immediately detectable through historical knowledge, and the limited relevance of the classification scheme to represent the actual diversity of New Caledonia coral reef habitats, a key criteria to guide conservation with habitat maps. Overall, the study highlights the limitations of the ACA benthic product that users should be aware of and offer some recommendations and caveats for both potential users and map producers in other areas.