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Juvenile fish and crustacean numbers steady in Alabama waters after Deepwater Horizon Oil Spill

March 13, 2013

The 2010 BP Deepwater Horizon (DWH) spill threatened numerous habitats across the Northern Gulf of Mexico. Of concern were the many commercially-harvested species, including blue crabs and shrimp, which spend time in offshore surface waters as eggs and larvae before settling into salt-marsh nurseries as juveniles.  In a recent paper in PLOS ONE, Dr. Ryan Moody of the Dauphin Island Sea Lab (DISL) found that abundances of young fish and crustaceans that spent their early days in oiled waters did not differ from pre-spill levels.

The study monitored multiple generations of young fish and crustaceans in a salt marsh located near Bayou la Batre, AL before and after the DWH spill. Surprisingly, the only observed declines were in a handful of species known to complete their entire life cycles within the estuary. The decline continued following the arrival of an oil pulse near the study site, but numbers of animals quickly rebounded to pre-spill levels by early 2011.

The most severe coastal oiling was limited to Louisiana's wetlands and much of the weathered material that made it to the shores of Mississippi, Alabama and Florida was intercepted by outer barrier islands and sandy beaches, thereby largely missing critical salt-marsh habitats. Although wetlands to the east of Louisiana escaped the brunt of the oil spill, young fish and crustaceans that spent their early first weeks of life in offshore waters would have been hard-pressed to avoid oil even if they were spawned some distance from the well site.

"It is unlikely that the majority of eggs and larvae drifting in the currents of offshore waters of the Northern Gulf were able to avoid contact with oil. Fortunately, it appears as though the blue crabs, shrimp, and numerous fish species we sampled were able to handle any strain imposed by the spill and make their way back to nursery habitats in sufficient numbers," said Moody.

"In the months following the spill, we did see a decline in the abundances of some species that spend their entire lives in salt marshes, but they began to decline in abundance before oil was ever detected at the site. It can be a difficult task to separate the effects of oil from other environmental stressors," he continued.

Moody emphasized, "Our study focused solely on juvenile fish and crustaceans and, although the crabs and shrimp we love to eat appeared to escape contamination, we are unsure what the more subtle negative effects of oil might be in terms of their future reproductive success. This study was about these species in their very early lives, not their adult eventualities.”

Dr. Just Cebrian, co-author of the study, added, "Analyzing all the information collected from this accident will allow us to determine what has or has not been affected in the Northern Gulf of Mexico. When we put the DWH spill in context with oil spills elsewhere in the world, it should improve our ability to manage more effectively the negative consequences of such accidents."

Moody, Ryan, Just Cebrian and Kenneth L. Heck, Jr. Intrannual Recruitment Dynamics for Resident and Transient Marsh Species: Evidence for a Lack of Impact by the Macondo Oil Spill. PLOS ONE, PONE-D-12-30273R1. Paper available at http://dx.plos.org/10.1371/journal.pone.0058376 upon publication


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