Growth in the VA oyster industry over the past decade has been due in large part to the increased use of hatchery-produced oyster seed. In 2014, oyster larvae at a VA hatchery began exhibiting poor food digestion and eventual mortality coincident with a potential source of zinc contamination in the adjacent water body. Hatcheries support the extant VA oyster industry and programs coordinated through VMRC to encourage new culturists as well as oyster restoration efforts, and long-term mortality events in hatcheries are a major concern to the industry.
It has long been established that oyster and other bivalve larvae are highly sensitive to some metals, which can cause reduced growth and mortality. In addition, exposure to and/or ingestion of harmful dinoflagellates present in the water can result in mortality or alterations in shellfish feeding patterns. The purpose of this project is to determine the potential impact of zinc contamination and coincident exposure to harmful algae on larval oysters in coastal VA waters.
Bioassays are used to test the toxicity of dissolved zinc and harmful algal species to healthy oyster larvae. Retention and dispersion of metals within the water body by the affected hatchery are being addressed through 3D hydrodynamic modeling. The project is designed to determine minimum zinc concentrations for larval mortality and growth retardation, potential reduction of toxicity due to physical transport and mixing, and synergistic toxicity of dissolved zinc and naturally-occurring harmful algae. Results of the project will provide VA oyster hatcheries with guidance on early detection of such toxicity and potential ways to reduce adverse impacts on hatchery productivity.