Will Floating Seaweed Be Another Oil Casualty?

Florida beachgoers sometimes mistake the ugly brown mats for trash, but sargassum, a floating seaweed, plays an important role in the Gulf of Mexico ecosystem, harboring fish larvae, young turtles, and other creatures. What's more, there's increasing evidence that the Gulf of Mexico is the source for sargassum habitats in the Atlantic Ocean.

Sean Powers, a marine scientist at the University of South Alabama in Mobile and Dauphin Island Sea Lab on Dauphin Island, Alabama, tracks sargassum spread out across the gulf by airplane. He studies how reducing the size of algae mats in a specific area, which can occur for reasons including exposure to pollutants and changes in temperature, affects the surrounding marine life. Now Powers has received a National Science Foundation RAPID grant to study how sargassum fares in oiled waters. ScienceInsider spoke with Powers about his research.

Q: What role does sargassum play in the ecosystem?
S.P.:
It represents the only natural surface structure in the ocean. It's a great place for all fish to hang out. Little fish hide from predators in it; big fish come to find the little fish in it. It's also a prime habitat for five species of sea turtles when they're small (up to about 25 cm); it provides them coverage from predators. It's a neat system we don't know a tremendous amount about.

Q: How could oil impact the sargassum?
S.P.:
Maybe the oil actually poisons the plant and the plant dies, or maybe it's just the physical encounter between sargassum and the crude oil that causes the algae to sink and be decomposed by bacteria. It's a very delicate balance that the algae has. It needs to float to live. It [crude oil] makes it physically get heavier or changes the buoyancy and causes it to sink.

Q: Have you seen any immediate impacts of oil on the sargassum?
S.P.:
About 2 years ago when we started researching, we frequently encountered vast mats of sargassum. We'd find two or three algae patches in any given 60-mile stretch of water in the region east of the Mississippi to the panhandle of Florida. We're not seeing a lot of sargassum anymore. We are seeing a lot of oil. We're at the point now where it's hard for us to find sargassum for our study… Because there are no apparent changes in gulf currents or temperature, the disappearance of algae could be due to the oil spill.

Q: What organisms could be affected by the sargassum disappearing?
S.P.:
The populations that we're worried about are some of the larger game fish that people want like mahi mahi, amberjack, tuna, and they use this in their larval stages. We're not going to pick that up for a few years. ... Same things with turtles. It might be 7 to 10 years and then someone will notice that they don't see new turtles on beachfronts. ... We could see [if] the densities [of animals] are lower in oiled patches versus unoiled patches. My guess is yes.

There's another species of algae [of the same genus] that attaches to rocks. The loss of it resulted in a loss of habitat in Prince William Sound after the Exxon Valdez oil spill… Once it was lost, it triggered the loss of many mollusks and invertebrates and facilitated the growth of a type of barnacle that further inhibited recovery of the algae.

Q: Is anything being done to protect the sargassum?
S.P.:
There are no efforts, because it's beyond our capability right now to boom it off or something like that. It's a vast resource spread out over the water.

Posted in Climate, Environment Gulf Oil Spill, marine life