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.
Highlights
As result of the Deepwater Horizon oil spill in April 2010, a large amount of spilled oil was introduced in the coastal estuaries of eastern Louisiana
A consistent pattern emerges from our two analyses: the abundance of both brown and white shrimp was significantly higher after the spill occurred
Even though this trend is clearly present for both shrimp species in the 2011 year-class, it is absent in most basins in the 2012 year-class
Summary
As result of the Deepwater Horizon oil spill in April 2010 (referred to as the spill hereinafter), a large amount of spilled oil was introduced in the coastal estuaries of eastern Louisiana. The two species enter estuaries as postlarvae during different periods of the year: brown shrimp typically from February to April, white shrimp from May to November. Shrimp of both species initiate their migration offshore when they reach a threshold size [10]. Exposure to PAHs can result in increased mortality rates in crustaceans [15,16] and affect various other physiological and behavioral aspects of crustacean biology [17,18,19] Such contamination may have been the cause for the immediate decrease in crab burrows following the spill as described by McCall and Pennings [6]. For this and others reasons, shrimp populations have been predicted not to suffer dramatic effects as result of the spill [20]
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