Eastern oysters use predation risk cues in larval settlement decisions and juvenile inducible morphological defenses

摘要

Predation is an important factor affecting the recruitment of marine benthic populations. Larvae can reduce their risk of predation by avoiding settlement near predators, whereas juveniles can resist predation through induced morphological defenses. We performed a 2 mo field study to understand the nature of the predation risk cues used by settling eastern oyster larvae and developing juveniles to decrease predation threat during recruitment. We found that oyster recruitment was highest on caged tiles near juvenile oysters, but lowest on tiles near active mud crab predators that produce a combination of predator metabolites and crushed conspecific alarm cues. Chemical cues from crushed conspecifics alone did not affect recruitment in the field, yet oyster larvae avoided either mud crab cues or crushed conspecific cues when presented separately in lab behavior experiments. Comparing the field to lab results suggests alarm cues may be unreliable under natural environmental conditions or were not present at high enough concentrations in the relatively high turbulent flow environment of our field site to convey the predation threat necessary to deter oyster settlement. Oyster spat grew most quickly when exposed to crushed conspecifics and may employ different strategies in response to unique risk cues or predation risk levels by avoiding settlement near actively feeding future predators but growing quickly to reach a size refuge in the presence of alarm cues. These non-consumptive predator effects at different life stages may have important demographic consequences for oyster populations that need to be considered in conjunction with predator consumptive effects.