Employing ecosystem models and geographic information systems (GIS) to investigate the response of changing marsh edge on historical biomass of estuarine nekton in Barataria Bay, Louisiana, USA

Abstract

Louisiana's coastal ecosystem has a long historical record of productive fisheries. Even in light of the multiple perturbations experienced in this region, fish and shellfish landings have remained stable or increasing. These disturbances have resulted in many unforeseen ecological consequences; one such consequence is the loss of marsh vegetation in southern Louisiana (LA). Marsh habitats are thought to function as nursery habitats for post-larval and juvenile fishes, providing both refuge from predation and increased foraging opportunities. As the loss of marsh appeared to have a null effect on fish and shellfish yields, there evolved a hypothesis that described a positive effect on nekton production; increasing marsh edge distance during marsh degradation provides a potential short-term increase in marsh access for organisms. Here we used Geographic Information System (GIS) data to determine the patterns of marsh loss over a 10 year period and to create marsh edge maps for further analysis in an ecosystem model. We used the ecosystem model Ecopath with Ecosim and Ecospace (EwE) to determine if a suitable response mechanism between estuarine organisms and marsh edge distance could be developed. The scenario analysis of multiple theoretical response functions showed Ecospace's ability to model changing habitat and environmental variables over time and space. More specifically, while the results of this modeling effort revealed species-specific responses to marsh edge, the association between nekton and marsh edge may not be as tightly coupled as once thought in coastal LA.