Multiple-year marine connectivity modeling in the Florida Coral Reef Tract to assess Acropora Cervicornis recovery

The massive decline in coral cover quantity and quality over the last decades reminds us the urgent necessity to assess coral reef resilience to threats affecting them. This study focuses on the resilience of Acropora Cervicornis in the Florida Coral Reef Tract. Despite being among the most productive corals world-wide, this species has faced a severe decline since the 1980s, so that it was listed as ’threatened’ under the U.S. Endangered Species Act in 2006. This study intends to provide guidance on the selection of the most adequate locations for coral outplants as well as reef restoration and protection in the FCRT, by identifying connectivity patterns. A high-resolution ocean model of the FCRT’s water circulation, constructed with the multiscale ocean model SLIM, is used to simulate the hydrodynamic over the studied area and periods. The hydrodynamic outputs, together with biological parameters (i.e. the rates of competence acquisition and loss and the mortality rate) are then used as inputs for a Lagrangian particle tracker which simulates larval dispersal. This allows to generate a connectivity matrix (CM) giving information about the number of connections between all reef pairs of the network. This methodology is applied here to four different years: 2007, 2008, 2009 and 2010. Graph theory tools and inter-annual variability study are used to highlight connection patterns and to point out most relevant reefs regarding coral reef management. The strongest candidate for protection measures is a spot to the south of the Marquesas Keys. More generally, protection is needed on reefs upstream of the Florida Current, seeding larvae to all reefs downstream. Reefs worth restoring are mainly located in the inner shelf of the Lower and Middle Keys. In parallel, a metapopulation model using the CM and biological parameters (e.g. clonal growth, egg production) is developed, allowing to compare the recovery times of the reefs and this for different years. For most of the reefs, the variability of the environmental conditions, inducing biological variability, is much greater than the inter-annual hydrodynamic variability. Finally this tool is used to asses the recovery of the FCRT after the major threat that was hurricane Irma.