Acoustic indices' 3D maps of benthic biophony reflect the health status of coral reefs: demonstration in the Philippines through a coupling with photogrammetry

It has been proven that coral reefs are suffering from global warming, from the proliferation of plastic, but also from fishing techniques such as dynamite or cyanide fishing, as it is the case in the Philippines. Ecological restoration solutions can be implemented to boost these ecosystems. However, the coral reef is home to a whole ecosystem including benthic invertebrates and fishes that feed, reproduce or protect themselves in the reef. So it is essential to assess not only the health status of the coral but also whether these ecosystems’ functionalities are being achieved on site. This information could help implementing the ideal ecological restoration solution.

Ecoacoustics makes it possible to efficiently evaluate, through acoustic indicators of diversity, abundance and richness, the biodiversity of a site and the achievement of some of these vital functions.

In the Pangatalan Island Marine Protected Area in the Philippines, using ecoacoustic indicators that we developed, we assessed the biodiversity of several sites with known and graduated health status. This ground truth on coral health status has been elaborated thank to the photogrammetry which makes it possible to evaluate a habitat complexity index, and photos, which make it possible to evaluate a biodiversity index. Through hydrophone networks, we have demonstrated that acoustic hot spots are spatially correlated with reef biodiversity hotspots on a 50m*20m coral reef slope. The use of a hydrophone network enables to provide maps of acoustic biodiversity indices with a resolution of 4m². The elaboration of these maps and their coupling with the structural complexity index given by photogrammetry constitute the two innovative parts of this work.