Eastern oysters (Crassostrea virginica) are pivotal members of estuarine ecosystems and support productive aquaculture markets. Extreme precipitation events (drought and flood) driven by climate change are altering estuarine salinity. Increased estuarine salinity reduces oyster feeding rates while increasing energy expenditure, but also increases colonization of oyster predators that are limited by lower salinity. In high predation environments, juvenile oysters induce morphological shell defenses (i.e., thicker, stronger shells) that confer greater predation resistance. However, morphological defenses require increased allocation of energy for shell development, which may reduce growth rates or allocation for the development of somatic tissue. Energy acquisition through filter feeding is reduced at suboptimal salinity, and predator-exposed oysters may feed less than non-exposed oysters (Figure 1). Simultaneous exposure to suboptimal salinity and greater predation risk may drive tradeoffs in energy allocation for shell defenses and somatic tissue. If oysters reduce feeding rates due to salinity stress or predation risk, they may grow slower or produce less body tissue relative to shell tissue (condition index). Alternatively, salinity-induced reductions in feeding may leave predator-exposed oysters unable to devote adequate energy to morphological defenses, which may increase their susceptibility to predation in suboptimal salinity regimes.
Here, I exposed juvenile oysters to three salinity regimes in the presence or absence of predatory cues from the carnivorous gastropod Melongena corona. I quantified oyster feeding rates on microalgae (Tisochrysis lutea), oyster growth, and survival over eight weeks and measured tissue weight, shell weight, and shell thickness of predator-exposed and non-exposed oysters. I hypothesized that oysters grown in suboptimal salinity regimes will grow slower and have lower condition index (ratio of tissue mass to shell mass) than oysters grown in favorable conditions, and that predation risk will further reduce condition index by signaling predator-exposed oysters to produce heavier, thicker shells than non-exposed oysters. My results will benefit aquaculture by providing an example of how the presence of predators and suboptimal abiotic conditions can interact to alter the allocation strategies and development of a common aquaculture species, which can ultimately influence its growth, survival, and contribution to desired aquaculture outcomes.