Anthropogenic and natural perturbations on lower Barataria Bay, Louisiana: detecting responses of marsh-edge fishes and decapod crustaceans

Barataria Bay, Louisiana is a dynamic estuary with ongoing disturbances that is in need of restoration. Development and validation of a lower Barataria Bay index of biotic integrity (IBI) for the summer season was the focus of my research. This IBI was created using 2005 data and evaluated with 2006 and 2007 data to demonstrate the feasibility of this approach in coastal Louisiana. The IBI successfully distinguished sites with differing levels of degradation using nine fish metrics. While pursuing this effort, two serendipitous events occurred when an oil spill then a hurricane impacted the study area. This gave me opportunities to examine pulse perturbations in the area. I showed immediate effects from the 2005 oil spill using a before-after-control-impact (BACI) analysis and found that fish abundances were significantly different days after the spill. I examined the recovery path of the nekton community after Hurricane Katrina and found that by the spring the year following the storm there were differences in species composition from pre-Katrina compositions. However, by two years post-Katrina species compositions and environmental variables measurements were similar to pre-storm conditions. I examined the transformation from Spartina- to black mangrove- dominated marsh edge (a long-term or press perturbation) and its effects on the nekton community. Nekton abundances were higher in the black mangrove and transition (mixed Spartina and black mangrove) vegetation dominated marsh-edge habitat type than the Spartina dominated marsh-edge. However, a fisheries species, Farfantepenaeus aztecus (brown shrimp), was more associated with Spartina than mangrove. By creating loop models of the study area’s marsh-edge community, I explored three other press perturbations along with black mangrove encroachment. These other perturbations were freshwater diversions, shrimping pressure, and wetland loss. Models predicted that mangroves encroachment decreased grass shrimp, freshwater diversions increased the water column predators, shrimping decreased wading birds and algae, and wetland loss had a negative effect on algae. Variations to the model showed some differences among the community responses. This dissertation illustrates how resilient the fauna is in Barataria Bay, which along with the proper assessment techniques, makes this area a strong candidate for restoration and management efforts