Mussel Watch team collecting oyster samples from Tampa Bay, Florida. Credit: NOAA.

The Mussel Watch Program has monitored the nation’s coastal waters for chemical contaminants since 1986 and in recent decades has expanded its monitoring to include trace metals, legacy contaminants, and contaminants of emerging concern (CECs). In 2023, the program collected sediment and oyster (Crassostrea virginica) samples from a network of 65 sites in the Gulf of Mexico. Results from this study will support a better understanding of the sources, fate, and transport of contaminants in the region and will fill important data gaps for local stakeholders.

Why We Care
The physiography, climate, and hydrology in the Gulf of Mexico provide natural conditions that support a rich and abundant diversity of plant and animal communities in the basin. The Gulf of Mexico region also supports highly productive fishing/shrimping, petrochemical, energy, tourism, aerospace, biomedical research, and agricultural industries. Thousands of chemical contaminants from many land-based point and nonpoint sources accumulate in the Gulf of Mexico every day, compromising water quality and, consequently, threatening human and ecosystem health.

Previous studies in the region have investigated legacy contaminants, such as trace elements and persistent organic pollutants (e.g., polychlorinated biphenyls (PCBs), organochlorine pesticides, chlordane, and polycyclic aromatic hydrocarbons (PAHs)). These research and monitoring efforts have helped managers limit the impact that legacy contaminants have on coastal ecosystems, but such efforts are lacking for the increasing number of new and unregulated compounds known as contaminants of emerging concern (CECs), many of which are known to be harmful to people, animals, and the environment. n response to resource managers’ concerns about the extent and impact of these chemical stressors, the Mussel Watch Program conducted a basin-wide survey in 2023 to assess the magnitude and distribution of a suite of CECs, metals, and legacy contaminants in the Gulf of Mexico.

What We Are Doing
The Mussel Watch Program uses an ecosystem-based approach to monitoring, which entails measuring the concentration of chemical contaminants in sediments and the tissues of indigenous bivalves, such as oysters and mussels, as a way to evaluate local environmental quality. Bivalves are used as indicator organisms for chemical pollution because they tend to bioaccumulate contaminants from the large amounts of water they filter, they have limited mobility, and they are found throughout the U.S. coastal zone.

The program currently analyzes sediment and bivalves for both legacy contaminants and CECs. Legacy contaminants, monitored by Mussel Watch since 1986, include compounds such as chlordanes, chlorobenzenes, dichlorodiphenyltrichloroethane (DDT), dieldrins, endosulfans, hexachlorocyclohexanes (HCHs), butyltins, PAHs, and PCBs. The monitoring of CECs began in 2009 and includes contaminants such as alkylphenols, alternative flame retardants, current-use pesticides, (per- and polyfluoroalkyl substances (PFASs), polybrominated diphenyl ether (PBDEs), polybrominated biphenyls (PBBs), and pharmaceuticals and personal care products. In general, CECs are minimally regulated, not commonly monitored, but potentially toxic chemicals that are finding their way into the environment.

In 2023, Mussel Watch analyzed sediment and oyster (Crassostrea virginica) samples from a network of 95 sites in the Gulf of Mexico for metals, legacy contaminants, and CECs. In this survey, 65 samples of Crassostrea virginica and 35 of sediment were collected across the coastlines of the five Gulf states (FL, AL, MS, LA, TX) following standard Mussel Watch Program protocols. These sites were selected from long-term Mussel Watch Program monitoring sites. Although 95 sites from the region were identified to be sampled, only 65 sites yielded enough oysters for laboratory analyses due to site accessibility and oyster abundance at historic locations.

The national Mussel Watch Program designed the 2023 Gulf of Mexico chemical stressors survey in collaboration with the Southeast Fisheries Science Center (Galveston, Baton Rouge, Pascagoula, and Panama City), the U.S. Fish and Wildlife Service (Cedar Key), the Florida Fish and Wildlife Conservation Commission (Tampa Bay), the City of Naples Public Works Department, and the Rookery Bay National Estuarine Research Reserve.

Benefits of Our Work
This study supplies much-needed data to the national Mussel Watch Program and local stakeholders and managers in the Gulf of Mexico region and informs water quality data used by coastal resource managers to develop effective, long-term policies to protect ecosystem services provided by the Gulf of Mexico.

Map of sites sampled in the Gulf of Mexico in 2023 as part of the NOAA Mussel Watch Program. Credit: Lauren Swam, NOAA.