Marion COUËDEL

Cryptic biodiversity of coral reefs: studies of spatial and temporal patterns of cryptobiome

Coral reefs are the most biologically diverse marine ecosystems but are being degraded worldwide by human activities and climate change. The cryptobiome, small living organisms hidden within the reef matrix, remains poorly studied, although it represents the majority of the biodiversity associated with coral reefs and an essential component of ecosystem functioning. These organisms comprise trophic groups that are essential parts of the food web as well as important food resources for fish, macro-invertebrates and more broadly for reef productivity. Numerous metazoan phyla are represented such crustaceans, polychaetes and sipunculan worms, molluscs, sponges, chordates (mainly ascidians), bryozoans, echinoderms, etc.

This thesis investigates the diversity of the coral reef cryptobiome and its spatio-temporal patterns in Mascarene Islands (Reunion, Rodrigues). Using artificial micro-reefs (Autonomous Reef Monitoring Structure ARMS) in combination with molecular taxonomy approaches through metabarcoding will allow us to investigate this cryptic reef biodiversity. Currently, only few sequences can be assigned to species level, which highlight the specificities of Mascarene’s cryptobiome and the necessity to develop a regional barcode reference database to improve ecological interpretations of metabarcoding results.