Study: Creatures in Ala. Coastal Marshes Mostly Unaffected by BP Spill

By: al.com
By: al.com

A three-year study of an Alabama marsh suggests the 2010 BP spill had little effect on the number of juvenile fish, shrimp and crabs living there before and after the disaster.

There was a drop in the number of daggerblade shrimp, the most common resident of the marsh, during the year of the spill, but their numbers returned to pre-spill levels the following year. The spill did not appear to affect the abundance of other animals using the marsh, including blue crabs, brown and white shrimp, mullet, and various snapper species, according to the study. The study was titled, “Interannual Recruitment Dynamics for Resident and Transient Marsh Species: Evidence for a Lack of Impact by the Macondo Oil Spill," and conducted by researchers from the Dauphin Island Sea Lab.
Mangroves, specks and pipes
Enlarge Ben Raines | braines@al.com This mess of tiny mangrove snapper, speckled trout and pipefish were caught in a single trawl around Horn Island. The trout and snapper were all smaller than two inches long and perfect replicas of their parents. (Press-Register/Ben Raines) Baby fish show up in big numbers despite spill gallery (15 photos)

Chain pipefish
White perch and sea lice
Stargazer
Baby burrfish
Tiny speck

“In a nutshell, we sampled the organisms that use the marsh when they are juveniles. We were able to split the organisms we sampled into two main groups: Animals that spent their entire lifecycle in the estuary, and animals that use the marsh as juveniles before moving offshore,” said Ryan Moody, one of the study’s authors. “The one thing I want to be very clear on, our work is limited to these juveniles. We are optimistic about the number of babies that came to the marsh, but we do not have information on the harvestable size shrimp and crabs that fishermen would have been after.”
Alabama’s Point aux Pins marsh experienced light oiling during the summer and fall of 2010, mostly in the form of small tarballs and occasional sheens that washed ashore. The marsh is located along the north shore of the Mississippi Sound, and is protected from the open waters of the Gulf by a string of barrier islands, including Dauphin Island and Petit Bois Island.

The islands, and the fact that the marsh was 100 miles away from the Deepwater Horizon well head, meant the area escaped the disastrous oiling seen in Louisiana marshes.

But, many of the larval and juvenile creatures that settle in the marsh each summer were exposed to oil during the portion of their life cycle spent in the Gulf in 2010.

Blue crabs, white and brown shrimp and other species spawn out around the barrier islands, which received large amounts of oil throughout the spill. Mullet, snapper, and other species caught during the study also spawn far offshore in waters where oil was present for months. The larval stages of those creatures would have been exposed to oil before they arrived in the marsh, Moody said.

Baby fish show up in big numbers despite spill
Baby fish show up in big numbers despite spill Baby snapper are everywhere. So are baby trout, grouper and grunt. Early results from an annual count of juvenile fish in grass beds scattered around the northern Gulf of Mexico suggest that the larvae of some species survived the oil spill in large numbers, according to the scientists involved. Press-Register reporter Ben Raines encounters many species during a recent outing that took him to Grand Bay and Horn Island. Watch video

“Our results, therefore, provide little evidence for severe acute or persistent oil-induced impacts on organisms that complete their life cycle within the estuary and those that spent portions of their life history in potentially contaminated offshore surface waters,” reads the conclusion of the study. The research suggests, “the most severe oil impacts were relegated to coastal Louisiana and the deep sea.”

The marsh work bolsters research conducted in the grass beds of the Mississippi Sound by Ken Heck, who is one of the coauthors of this study, and Joel Fodrie, a University of North Carolina researcher. They conduct trawl surveys of seagrass meadows along the Gulf Coast. Recruitment of snapper, speckled trout, cobia and other offshore species appeared to be about normal during the year of the BP spill, according to that work.

“There is a sense of optimism because you do have juveniles returning, but we don’t know what happened to the adults. That’s an important qualifier for this study,” Moody said. “The overall abundances, we did not see a statistically significant difference between years. The blue crabs, the shrimp and other species, they did not seem to be affected by the oil.”

The study was published in the scientific journal Plos One.


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