Model estimation of eastern oyster larval performance from food quantity and quality measures in western Mississippi Sound

ABSTRACT: Oyster Crassostrea virginica population recovery is critical in degraded estuarine systems, such as Mississippi Sound, USA, where repeated mass mortality events have depleted local oyster stocks. Owing to multiple recent die-offs, the western Mississippi Sound oyster population is recruitment-limited; population growth is constrained by the entry of new individuals into the extant population. Therefore, oyster recovery requires an adequate supply of larvae capable of timely development, growth, and successful metamorphosis. Larval performance and settlement potential are influenced by ambient temperature, salinity, and food supply. Food quantity is important to larvae, but so is food quality, as larvae require a balanced diet of lipids, proteins, and carbohydrates to develop and survive through metamorphosis. In this study, in situ environmental and food conditions during the 2021 and 2022 spawning seasons from 7 oyster reefs in western Mississippi Sound were integrated into an established biochemically based larval performance model to estimate periods facilitative of successful metamorphosis. In 2021, model-estimated larval survivorship was suppressed through much of the spawning season by prolonged, extremely low salinity (<5 ppt) and inadequately balanced food supply. Higher seasonal salinity and more balanced food composition increased model-estimated larval survivorship in 2022, despite lower total food content, suggesting larval performance was primarily governed by the quality of available food. Model-estimated settlement windows were compared to settlement windows derived from concomitant field observations of recruitment. Strong agreement between model-estimated and observed settlement windows validates the effectiveness of the model and informs on the underlying causes of recruitment limitation in western Mississippi Sound.