The perfect storm: match-mismatch of bio-physical events drives larval reef fish connectivity between Pulley Ridge and the Florida Keys

Mesophotic reefs have been hypothesized to act as a refugia, by exporting larvae to more vulnerable shallow water reefs and potentially aiding the replenishment of disturbed populations. Despite the fundamental role of mesophotic reef for the recovery and conservation of shallow water reef ecosystems, the spatio-temporal extent of such connections is currently unresolved. Here we aim to explore the underlaying mechanisms of the connections between a mesophotic reef, the Pulley Ridge, and the shallow water Florida Keys reefs, by simulating the dispersal of the bicolor damselfish, Stegastes partitus. We use the Connectivity Modeling System (CMS) of the University of Miami, an open-source individual-based model, and present new biophysical modeling code to allow a realistic representation of 3-dimensional discreet coral reef habitats and investigate vertical connectivity. Virtual larvae are released and tracked within a fine resolution (~900m) hydrodynamic model until their settlement. S. partitus biological traits such as spawning periodicity, mortality and vertical migration are also incorporated on the model. Probabilistic simulations indicate mesophotic-shallow connections, with larvae spawned at Pulley Ridge reaching the Florida Keys settlement grounds during sporadic settlement pulses. These “perfect storm” settlement events are modulated by the co-occurence of larval traits with physical processes, particularly by the interaction of ontogenetic vertical migration and the Florida Current fronts and cyclonic eddies. This demonstrates that mesophotic coral reef ecosystems can also serve as a refugia for coral reef fish and suggests that they could increase the resilience of their shallow counterpart.