Abundance and Size of Gulf Shrimp in Louisiana's Coastal Estuaries following the Deepwater Horizon Oil Spill

Abstract

The Deepwater Horizon oil spill impacted Louisiana's coastal estuaries physically, chemically, and biologically. To better understand the ecological consequences of this oil spill on Louisiana estuaries, we compared the abundance and size of two Gulf shrimp species (Farfantepeneus aztecus and Litopeneus setiferus) in heavily affected and relatively unaffected estuaries, before and after the oil spill. Two datasets were used to conduct this study: data on shrimp abundance and size before the spill were available from Louisiana Department of Wildlife and Fisheries (LDWF). Data on shrimp abundance and size from after the spill were independently collected by the authors and by LDWF. Using a Before-After-Control-Impact with Paired sampling (BACIP) design with monthly samples of two selected basins, we found brown shrimp to become more abundant and the mean size of white shrimp to become smaller. Using a BACIP with data on successive shrimp year-classes of multiple basins, we found both species to become more abundant in basins that were affected by the spill, while mean shrimp size either not change after the spill, or increased in both affected and unaffected basins. We conclude that following the oil spill abundances of both species increased within affected estuaries, whereas mean size may have been unaffected. We propose two factors that may have caused these results: 1) exposure to polycyclic aromatic hydrocarbons (PAHs) may have reduced the growth rate of shrimp, resulting in a delayed movement of shrimp to offshore habitats, and an increase of within-estuary shrimp abundance, and 2) fishing closures established immediately after the spill, may have resulted in decreased fishing effort and an increase in shrimp abundance. This study accentuates the complexities in determining ecological effects of oil spills, and the need of studies on the organismal level to reveal cause-and-effect relationships of such events.

Change and recovery of coastal mesozooplankton community structure during the Deepwater Horizon oil spill

“…For example, numerous exposure studies on small coastal fishes (primarily Fundulus grandis) suggest negative impacts on an individual level [43,44,45], however field observations from coastal habitats suggest fish population abundances were stable, or in some instances greater, after the oil spill [42,46]. There is also evidence to suggest that commercially important shrimp species (Farfantepeneus aztecus and Litopeneus setiferus) from impacted areas increased in abundance after the spill, and mean size of shrimp was unchanged, even though previous lab studies suggest decapods are negatively impacted by contaminants present in oil [47]. Compensatory processes and complex interactions in marine ecosystems may lessen the overall impact of large disturbances at a population level [42], however as in the case of Pacific herring following the Exxon Valdez spill, latent effects may exist within populations, therefore continued biological monitoring in northern Gulf of Mexico ecosystem is advisable.…”

Marine Oil Spills

“…This study shows that the concentrations of oil released and dispersant used during the DWH event could have negatively affected penaeid shrimp in the GOM, whether through altered behavioral responses, delayed development, or mortality. Even though the spill occurred during the spring spawning season and likely affected shrimp larvae at select locations, GOM shrimp populations as a whole do not appear to have been affected long term, perhaps in part due to fishery closures that were put in place following the spill [69].…”

Effects of Exposure of Pink Shrimp, Farfantepenaeus duorarum, Larvae to Macondo Canyon 252 Crude Oil and the Corexit Dispersant

“…Even though the spill occurred during the spring spawning season and likely affected shrimp larvae at select locations, GOM shrimp populations as a whole do not appear to have been affected long term, perhaps in part due to fishery closures that were put in place following the spill [69].…”