Modeling Reef Slope Coral Connectivity

While it is well documented that shallow coral reefs are threatened around the world, a ‘deep reef refugia’ hypothesis has gained popularity in recent years. Indeed, mesophotic coral ecosystems (MCEs) are found on the deeper reef slope between 30 -150m depth and may be less impacted by the synergistic effects of coastal and global stressors such as rising sea surface temperatures, acidification and coastal pollution. However, due to depth and distance from shore, little is known about the health, ecology and distribution of these environments. Based on tissue collections and histological analyses, preliminary findings suggest Montastraea faveolata corals at 34 meters are fully gravid on the same oogenic schedule as their shallow counterparts, and mature eggs have been detected from corals as deep as 44 meters. These results suggest MCE coral larval output may be substantial, and that depth may provide a reproductive refuge for imperiled shallow corals. In order to gauge the potential of MCEs in the US Virgin Islands to contribute to processes of recovery in degraded shallow environments, measurements of the effects of depth on coral reproductive biology, egg buoyancy, larval settlement and adult population density are used to parameterize the dispersion of planula larvae in a coupled biophysical Connectivity Modeling System (CMS). The CMS consists of a biological module coding for larval behavior, growth and survival, a GIS-based module depicting habitat, adult production, and proximal settlement cues, and a hydrographic module that configures the output variables (i.e., velocity fields, temperature, salinity) from a series of nested ocean circulation models. These modules are coupled to a Lagrangian stochastic particle model that tracks the movement of individual larvae in three dimensions to estimate larval transport and connectivity pathways over multiple scales.  Here we present the results of initial modeling efforts estimating the strength of connectivity pathways between deep and shallow environments in the Caribbean.