The Eastern Oyster provides essential ecosystem and economic services. However, oyster populations have declined significantly due to various natural and anthropogenic stresses. Aquaculture can potentially meet the demand for commercial and restoration purposes, but hatcheries have yet to consistently meet demand due, in part, to water quality/chemistry problems. Salinity, temperature, pH, dissolved oxygen, and carbonate chemistry were monitored at three hatcheries along the Gulf coast during April-October from 2022-2024. Water quality was compared among the hatcheries, and associations with larval growth, percent hatch, and survival were assessed.
Data from Auburn University Shellfish Laboratory (AUSL), a flow-through hatchery, the University of Southern Mississippi (USM), a recirculating hatchery, and Bay Shellfish Company (BSC), a flow-through hatchery, showed that, on average, BSC produced larger larvae than USM and AUSL across different ploidies. USM’s percent survival in 2022 and 2023 was 34.9% and 28.4%, respectively; AUSL’s was 26.8% and 43.6%, respectively; and BSC’s was 36.1% in 2023. Individual water quality parameters influenced larval growth (MANOVA). Temperature and salinity interactions significantly impacted growth across all sites, while temperature and pH interactions were significant at all sites except AUSL. The interaction between salinity and pH was notable only at BSC, and interactions between aragonite saturation and both salinity and alkalinity were significant across all sites, suggesting variations in environmental factors have a substantial impact on larval development. The significance of interactions suggested that larval growth was influenced by the combination of environmental factors rather than individual ones. Segmented regression models initially suggested a potential positive effect on growth below the breakpoints at a temperature of 23.3°C, a pH of 7.71, a salinity of 23.19 ppt, and a calcium of 5.002 mmol/Kg; and a potential positive affect above breakpoints at an alkalinity of 1929.85 µmol/kg, and an aragonite saturation state of 0.232Ω. Further analysis is needed to clarify these findings and their implications for improving larval production.
To better assess how water quality, temperature, salinity, and pH affected larval survival, the data from all locations in 2022-2023 were combined. Linear mixed models (LMM) analysis revealed that only pH significantly influenced survival (negatively). In a LMM including interaction terms, there were no significant linear interactions among any of the factors. A generalized additive model (GAM) that looked for non-linear relationships among water quality parameters showed that interactions between pH and salinity, and interactions between temperature, pH, and salinity were significant. These results indicated that survival depended on the individual factors and their combined effects. The results from both models offered unique insights that can improve hatchery practices. Further refinement of these models is needed to determine optimal water quality parameters that enhance survival in hatchery settings.