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Oysters,Crassostrea virginica, are economically and ecologically valuable but have severely declined, and restoration is needed. As with the restoration and aquaculture of many shellfish species, restored oyster reefs are often impeded by predation losses, reducing restoration success and restricting locations where restored reefs are viable. Like many organisms, shellfish can modify their morphology to reduce predation risk by detecting and responding to chemical signals emanating from predators and injured prey. Oysters grow heavier, stronger shells in response to predation risk cues, which improves their survival. We tested if using predator cues to trigger shell hardening in oysters could be performed over a scale suitable for oyster reef restoration and improve oyster survival long‐term. We constructed an intertidal oyster reef using oysters grown in a nursery for 4 weeks while exposed to either exudates from Blue crab (Callinectes sapidus) predators or grown in controls without predator cues. Oysters grown with predators were 65% harder than those grown in controls, and after 1 year in the field, had a 60% increase in survival. Predation losses on the restored reef were significant, and the benefit of predator induction for survival was highest at intermediate tidal elevations, presumably due to intermediate levels of predation and abiotic stress. Our results suggest that manipulating the morphology of cultivated or restored species can be an effective tool to improve survival in habitats where consumers impede restoration success. 

Abstract Climate change is causing rapid, unexpected changes to ecosystems through alteration to environmental regimes, modification of species interactions, and increased frequency and magnitude of disturbances. Yet, how the type of disturbance affects food webs remains ambiguous. Long‐term studies capturing ecosystem responses to extreme events are necessary to understand climate effects on species interactions and ecosystem resilience but remain rare. In the Gulf of Mexico, our 8‐year study captured two disturbances that had contrasting effects on predator abundance and cascading effects on estuarine food webs. In 2017, Hurricane Harvey destroyed fishing infrastructure, fishing activity declined, and sportfish populations increased ~40% while intermediate trophic levels that sportfish prey upon declined ~50%. Then, in 2021, a fish kill caused by freezing temperatures during Winter Storm Uri reduced sportfish populations by ~60% and intermediate trophic levels increased by over 250%. Sportfish abundance affected the abundance and size of oyster reef mesopredators. Excluding fish predators significantly altered oyster reef community structure. These results demonstrate how extreme events shape communities and influence their resilience based on their effects on top predators. Moreover, top‐down forces from sportfish are important in estuaries, persist through disturbances, and influence community resilience, highlighting the necessity of proper recreational fisheries management through extreme events. 

Predator–prey interactions are a key feature of ecosystems and often chemically mediated, whereby individuals detect molecules in their environment that inform whether they should attack or defend. These molecules are largely unidentified, and their discovery is important for determining their ecological role in complex trophic systems. Homarine and trigonelline are two previously identified blue crab (Callinectes sapidus) urinary metabolites that cause mud crabs (Panopeus herbstii) to seek refuge, but it was unknown whether these molecules influence other species within this oyster reef system. In the current study, homarine, trigonelline, and blue crab urine were tested on juvenile oysters (Crassostrea virginica) to ascertain if the same molecules known to alter mud crab behavior also affect juvenile oyster morphology, thus mediating interactions between a generalist predator, a mesopredator, and a basal prey species. Oyster juveniles strengthened their shells in response to blue crab urine and when exposed to homarine and trigonelline in combination, especially at higher concentrations. This study builds upon previous work to pinpoint specific molecules from a generalist predator’s urine that induce defensive responses in two marine prey from different taxa and trophic levels, supporting the hypothesis that common fear molecules exist in ecological systems. 

Abstract The capacity of an apex predator to produce nonconsumptive effects (NCEs) in multiple prey trophic levels can create considerable complexity in nonconsumptive cascading interactions, but these effects are poorly studied. We examined such effects in a model food web where the apex predator (blue crabs) releases chemical cues in urine that affect both the intermediate consumer (mud crabs seek shelter) and the basal prey (oysters are induced to grow stronger shells). Shelter availability and predator presence were manipulated in a laboratory experiment to identify patterns in species interactions. Then, experimentally induced and uninduced oysters were planted across high‐quality and low‐quality habitats with varying levels of shelter availability and habitat heterogeneity to determine the consistency of these patterns in the field. Oyster shell thickening in response to blue crab chemical cues generally protected oysters from mud crab predation in both the laboratory and in field environments that differed in predation intensity, structural complexity, habitat heterogeneity, and predator composition. However, NCEs on the intermediate predator (greater use of refugia) opposed the NCEs on oyster prey in the interior of oyster reefs while still providing survival advantages to basal prey on reef edges and bare substrates. Thus, the combined effects of changing movement patterns of intermediate predators and morphological defenses of basal prey create complex, but predictable, patterns of NCEs across landscapes and ecotones that vary in structural complexity. Generalist predators that feed on multiple trophic levels are ubiquitous, and their potential effects on NCEs propagating simultaneously to different trophic levels must be quantified to understand the role of NCEs in food webs.