Mesophotic coral ecosystems (MCEs), located at depths greater than 30m, are one of the last lifeboats for coral reefs worldwide. Being partly sheltered from global warming, they could fare better than shallower coral reefs in the next decades and help repopulate them through larval exchanges. The United States Virgin Islands (USVI) are home to some of World’s richest and best documented MCEs. However, these islands are highly threatened by the spread of the stony coral tissue loss disease (SCTLD). The transmission of the SCTLD is likely to be supported by the dispersal of fine sediments transported by the same ocean currents responsible for larval exchanges. As connectivity can be a double-edged sword, it is therefore particularly challenging to identify which reefs are best suited to protection/restoration efforts. Here, we aim to assess the contribution of USVI MCEs to the resilience of the entire coral ecosystem. More specifically, we simulate the dispersal of larvae and disease agents thanks to a Lagrangian transport model coupled with a three- dimensional unstructured-mesh hydrodynamic model to deal with the USVI’s deep and steep bathymetry. We then identify the best larvae exporters and weakest disease importers in the connectivity networks by deriving conservation metrics based on graph theory algorithms. We consider different species with various susceptibilities to SCTLD and various larval traits in order to account for the USVI’s coral diversity. This allows us to highlight the MCEs with the most positive impact on the entire coral ecosystem and that should therefore be protected/restored in priority. In addition, we give a quantitative estimate of MCEs’ contribution to shallow larval recruitment and inform on the potential of the SCTLD to reach mesophotic reefs and spread among them.

Primary Presenter: Colin Scherpereel, UCLouvain (colin.scherpereel@uclouvain.be)

Authors:

Daniel Holstein, Louisiana State University, Department of Oceanography and Coastal Sciences  ()

Thomas Dobbelaere, UCLouvain, Earth and Life Institute  ()

Jonathan Lambrechts, UCLouvain, Institute of Mechanics, Materials and Civil Engineering  ()

Emmanuel Hanert, UCLouvain, Earth and Life Institute  ()