Researchers with NOAA’s National Centers for Coastal Ocean Science (NCCOS) are developing a scalable approach to assess the impact of shellfish mariculture on Alaskan wildlife. Oyster farming has been expanding in Alaska, although these shellfish are not native to the state. Oysters are filter-feeders, removing algae, organic matter and nutrients from the water column as they grow. However, community groups in Alaska have expressed concern that oyster mariculture could be removing excessive plankton from surface waters and limiting food resources for wild filter feeders like native mussels.
Scientists recently completed a pilot project in Jakolof Bay as a first step in addressing this concern. In this study, NCCOS scientists compared the total estimated filtration rates of wild mussels to farmed oysters. With support from two students in NOAA’s College-Supported Internship Program, they visited 10 field sites in an intensively-farmed area of Kachemak Bay to measure wild mussel density and size, using these calculations to estimate how much water these organisms filter. They then made similar calculations using counts from local oyster farmers. When they scaled filtration rates to the larger area, it was clear that total filtration by the non-native oysters was only a small fraction of the water filtered by the wild mussels. In addition, they calculated the rate at which tidal waters enter the bay to be 100-times larger than the filtration rates for both the oyster and wild mussel populations combined. This suggests there is likely more than enough food for both farmed and wild bivalves, assuming that the seawater contains sufficient plankton.
NCCOS researchers will next expand this methodology by adding three more sites in Kachemak Bay to their assessments. This will help develop a more complete picture of the impact commercial shellfish harvesting can have on wildlife by considering differing habitat types, mussel location in the tidal zone, and the presence of other filter feeders like clams and larval fishes. Future work will also aim to elucidate plankton filtration dynamics by Alaskan shellfish in greater detail.
Mariculture in Alaska can provide a sustainable food source and increase economic opportunities for communities. To date, commercial mariculture activities have been relatively small-scale and have involved Pacific oysters and seaweed. Understanding how increasing oyster mariculture would affect ecosystems is critical when developing the Alaskan Blue Economy.