This pilot project was funded by NOAA’s Marine Debris Program.
A key habitat in coastal and open Gulf of Mexico (GOM) waters is the floating Sargassum (Sargassum natans and S. fluitans) complex. The pelagic brown algae represents an oasis of structure in the open ocean and supports a large and diverse assemblage of marine fish and invertebrates, including many early life history stages. Fish larvae and juveniles presumably utilize these pelagic habitats as protection from predators, but Sargassum may also provide enhanced feeding opportunities and serve to concentrate organisms with flotsam-seeking behaviors. Sargassum, therefore, serves as pelagic “nursery habitats” for many important fisheries species, including grey triggerfish, tripletail, and mahi mahi, as well as ecologically important forage fish species, such as butterfishes and flying fishes. For these reasons, Sargassum has been designated as Essential Fish Habitat in the South Atlantic, but currently it is not afforded the same protection in the GOM.
Sargassum is a near-surface habitat, and as such, it is subject to oceanographic processes (e.g., Langmuir cells, frontal zones) that aggregate floating objects, including marine debris, and in the case of the Deepwater Horizon event, surface oil, dispersant and related compounds. Relatively little is known regarding the impacts of marine plastics (which often brakes down into “microplastics”) within valuable Sargassum nursery areas. Research associated with marine debris in the Pacific gyre suggests microplastics can be consumed by fishes, but to date, this has not been documented in the GOM. Microplastics, if consumed by fishes, may serve as a vector for toxic compounds that adhere to their surfaces.
A first step in examining if this issue warrants further study is to determine whether or not microplastics are being consumed by Sargassum-associated juvenile fishes. The goals of this pilot research effort are to: 1) quantify and characterize juvenile fish assemblages and co-occurring debris collected in Sargassum mats and/or weedlines; 2) determine the microplastic frequency of occurrence in the guts of Sargassum-associated fishes; and 3) determine the “natural” diet composition in the guts of Sargassum-associated fishes.