Intellectual Merit: While an extensive literature exist of the acute affects of oil spills on marine communities in nearshore habitats, little is known about the potential responses of pelagic communities to such acute disturbances. One of the key habitats of the coastal and open oceans that will be affected by the ongoing Deepwater Horizon Oil Spill is floating Sargassum mats Sargassum natans and S. fluitans). The Gulf of Mexico region represents the second most productive Sargassum system in the world. The pelagic brown algae represent an oasis of structure in the open ocean that supports a large and diverse assemblage of marine fish and invertebrates. The loss and degradation of structurally complex brown algae (Fucus) in Prince William Sound, Alaska following the Exxon Valdez oil spill was responsible for a myriad of direct and indirect impacts on the foodweb, many of which persisted for years.

This RAPID project has four components designed to evaluate trophic interactions within this habitat at risk: 1) areal distribution of Sargassum in the north-central Gulf of Mexico; 2) ship-based neuston, ROV aand pelagic long-line surveys of the larval, juvenile and adult fish communities; 3) stable isotope analyses (C and N) of the food web and (4) mesocosm experiments to examine the role of Sargassum in modulating predator-prey interactions.

The Sargassum ecosystem is going to be significantly impacted and the need to increase our mechanistic understanding of the role Sargassum plays is important. Further, some systematic way to assess the potential consequences of changes in the distribution of the habitat will be a critical element of assessing the ecological response of the Gulf of Mexico to this disaster.

Broader Impacts: Episodic disasters such as the Deepwater Horizon Oil Spill provide an opportunity to train young scientists to be responsive and adaptive in their research careers as well as fulfill a critical service to the nation during assessment, mitigation and restoration activities. Marine education activities will be strengthened by exposing undergraduate and graduate students to the role of science in evaluating ecosystem resistance and resilience to disturbances. The project will directly involve graduate students and undergraduate interns, many of whom represent historically underrepresented groups. This RAPID project will also be highlighted in the education and outreach activities of Dauphin Island Sea Lab's Discovery Hall Program, which has an outstanding K-Gray program that educates over 5,000 students through its year long program, a public aquarium and the NSF sponsored COSEE Gulf of Mexico program. Outreach to historically underrepresented groups will be facilitated through membership of the University of South Alabama in the Alabama Alliance for Graduate Education and Professoriate. The attention the oil spill will bring to this project will greatly assist efforts in recruiting and teaching students who have an interest in environmental studies and their application to solving the pressing societal issues of the next generation.

Project Report

The pelagic brown algae Sargassum supports an oasis of biodiversity and productivity within the otherwise featureless ocean surface. The vast pool of floating oil fed by the release of over 760 million liters of oil as a result of the Deepwater Horizon explosion persistedfor 3-4 months in summer 2010 and may have severely degraded this critical ursery habitat. The neustonic nature of both Sargassum and floating oil enhance contact between the two at small and meso-scale convergence zones in the Gulf. Aerial surveys performed during and after the spill show strong evidence of loss and subsequent recovery of Sargassum. Experimental studies indicate three possible pathways for injury of Sargassum and its associated animals: (1) Sargassum accumulates floating oil on the surface exposing animals to high concentrations of contaminants along the algae’s horizontal oceanic journey; (2) application of dispersant rapidly sinks Sargassum thus removing the habitat and potentially transporting oil and dispersant vertically to mesopelagic and benthic systems; and (3) low oxygen forms around the habitat as a result of microbial degradation of oil and dispersant further stressing animal remaining on the surface and reducing their fitness. Our pathways represent sublethal and indirect effects that are rarely considered in evaluating the effect of oil spills and response procedures.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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David Garrison
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University of South Alabama
United States
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