Subtropical climate is marked by a wet season during which intense precipitations have significant consequences on the ecological equilibrium of the land-sea continuum. River run-off effect after a cyclonic rainy event was studied in a coastal oligotrophic lagoon of New Caledonia (SW Pacific). Using environmental DNA (eDNA) metabarcoding, the short-term dynamic of water surface coastal microbiome (protist and bacterial communities) was studied both during a dry season, used as a baseline ecological condition, and after the cyclone passage. Community composition was mainly influenced by temperature, organic matter and hydrodynamic processes. During the dry season a coastal-off-shore microbial diversity and biogeochemical gradient was highlighted. This spatial pattern was destructured by the river plume which extended about 20 km, reaching the coral barrier reef of the lagoon. The first day after the cyclone, coastal microbiome decreased in diversity and eDNA microbiological signatures of terrestrial and riverine origins were identified, expecially in coincidence with an increase in terrigenous matter concentration. After the run-off disturbance, particulate matter indicators and community composition were not reestablished to baseline ecological conditions during the 6 days of following monitoring. This study suggests that subtropical lagoons require longer resilience time after an intense run-off impact and that the potential increase in extreme rainy events due to the on-going climate deregulation might cause long-term coastal ecological disequilibrium.

Primary Presenter: Mathisse Meyneng, Ifremer (mathisse.meyneng@ifremer.fr)

Authors:

Hugues Lemonnier, Ifremer  (hugues.lemonnier@ifremer.fr)

Romain Le Gendre, Ifremer  (romain.le.gendre@ifremer.fr)

Gwen Plougoulen, Ifremer  (gwen.plougoulen@gmail.com)

Florence Antypas, Ifremer  (florence.antypas@ifremer.fr)

Dominique Ansquer, Ifremer  (dominique.ansquer@ifremer.fr)

Raffaele Siano, Ifremer  (raffaele.siano@ifremer.fr)