The eastern oyster (Crassostrea virginica) is a reef-forming bivalve found naturally along the western Atlantic coast from Canada to Venezuela, including the Gulf of Mexico. The eastern oyster provides habitat structure, filters water, protects environments from degradation and erosion, and is a lucrative seafood product. Despite being essential for the environment and economy, oyster populations have been declining due to natural and anthropogenic events such as overharvesting, disease, and climate change, including potentially excess CO2 absorption into the ocean.
As oceanic CO2 levels increase, carbonate saturation state decreases and impedes the synthesis of oyster shell. The estuarine ecosystem is especially vulnerable to changing carbonate chemistry conditions that result from ocean acidification due to its generally low alkalinity and low buffering capacity. Oyster hatcheries, typically located in estuaries, are vulnerable to the negative effects from ocean acidification. A relatively new concept in oyster hatcheries is the utilization of closed recirculating aquaculture systems (RAS) with artificial seawater (ASW) to mimic optimum water chemistry. The use of RAS and ASW can reduce the risk of poor outcomes by providing control over water quality parameters, but little is known about the combined effects of suboptimal aragonite saturation, low pH, alkalinity, CO2, and salinity on larval growth and survival.
This project examines individual and combined effects of aragonite saturation state and salinity on survival and growth of oyster larvae. Previous research using recirculating larval rearing systems and altered pH has used large-volume systems and examined only a few parameters at a time. This project uses a low-volume, recirculating artificial seawater system to increase the number of treatments and replicates under a manageable workflow to carry out the experimental run. The system supports four salinities, three pCO2 levels, and one lower river endmember alkalinity comprising twelve 40L combinations in triplicate for a total of 36 4L tanks.
Larvae were spawned from Gulf Coast native broodstock. On day 2, larvae were stocked into the recirculating systems. On even days, a subsample of larvae was counted and measured. The trial continued until larvae were harvested or they reached 18 days of age. Water samples were taken every other day to monitor alkalinity, pH, and salinity. Aragonite saturation state was calculated. Preliminary data analysis using multifactorial ANOVAs suggest that survival is greatly affected by salinity (p<0.001) and the interactive effects of salinity and CO2 (p<0.01), whereas harvests are affected by mostly salinity (p<0.01).