22. Connectivity of the Gulf of Mexico Continental Shelf Fish Populations and Implications of Simulated Oil Spills

The Gulf of Mexico (GoM) marine ecosystem is experiencing acute stressors. Natural (e.g., hurricanes, harmful algal blooms) or anthropogenic (e.g., oil spills), these stressors have the potential to impact fish populations and decrease biodiversity that may be difficult to recover unless the ecosystem is resilient.

One of the most effective factors governing the resilience capacity of sensitive Gulf fish species is the degree of connectivity and network modularity among spatial sub-units of species occupying the continental shelf. This chapter is a meta-study that looks at the relationship between the Lagrangian dynamical geography of the GoM regions, the community structure of demersal fish, and the potential for larval connectivity. We use adult fish movement from tagging data, larval fish migration from biophysical modeling, and oceanographic patterns from satellite-tracked Lagrangian drifters to quantify the degree of connectivity and modularity of the GoM ecosystem. We evaluate the biophysical model output with 20+ years of data from the Southeast Area Monitoring and Assessment Program (SEAMAP) ichthyoplankton survey and use the drifter inferred dynamics provinces to access mechanisms underlying retention or exchange for each species and GoM province. The tagging analyses reveal a modular network structure consistent with the Lagrangian oceanographic provinces. While the oceanographic dynamic patterns drive self-recruitment levels and the size and location of these provinces, they do not constrain connectivity patterns between distant locations within the GoM. In contrast, larval transport and migration between the provinces and subregions drive the patterns of connectivity and community structure similarity. Ultimately, it is the combination of within-scale functional redundancy and cross-scale species connectivity that can amplify resilience and speed of recovery and minimize the potential for catastrophic regime shifts in ecological meta-communities such as in the GoM. The importance of such studies to natural resource management and oil spill preparedness outcomes is discussed.