Relative influence of habitat fragmentation and inundation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico salt marshes

We used a spatially explicit individual-based model to investigate the relative influences of inundation and habitat fragmentation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico (NGOM) salt marshes. The model simulates the mortality, growth, and movement of a population of brown shrimp from their arrival in Spartina salt marsh as post-larvae in spring to their emigration as sub-adults in summer and fall. We quantified production in terms of sub-adult export, growth production (a measure of total shrimp growth), and trophic transfer (total shrimp mortality). We utilized a factorial design to simulate shrimp on all combinations of 4 maps that represented an idealized progression of habitat fragmentation and 4 inundation regimes from each of 2 locations in the NGOM (Louisiana and Texas). We also quantified the configuration of the marsh landscape to determine if specific metrics could be utilized as a proxy for shrimp production within a single inundation regime. Our results indicate that inundation is more important than habitat fragmentation for determining sub-adult export, growth production, and trophic transfer, but that marsh configuration has a strong influence on shrimp production within a single inundation regime. Inundation affected all 3 measures of shrimp production, primarily due to decreased mortality incurred when shrimp have access to vegetation through marsh flooding. We conclude that simple metrics of marsh configuration are capable of adequate predictions of shrimp production in static landscapes, but future research must consider the dynamic relationship between inundation and marsh fragmentation to fully assess how these forces affect shrimp production.