Predation risk management of sea stars ( Asterias amurensis and Distolasterias nipon ) by adjusting the density and size of seeded scallops ( Mizuhopecten yessoensis ): an improvement to local mariculture

Optimizing the release density and size of juvenile commercial species for local ecosystems is a critical issue that should be considered when countering predation impacts. To ascertain whether mariculture production of the Japanese scallop ( Mizuhopecten yessoensis ) could be enhanced by modifying releasing practices, we experimentally investigated the effects of density and size of scallop seeds on their survival in the presence of two sea star species, Asterias amurensis and Distolasterias nipon , with different predation capacities. Under current mariculture practices, the juveniles are briefly exposed to air just before release; therefore, we also examined how air exposure stress increased the predation risk. Scallop survival in the presence of both sea stars increased by > 20% by increasing scallop size from 30 to 50 mm. Increasing scallop density (range: 5 to 30 scallops m −2 ) increased each individual’s survival in the presence of A. amurensis but had no significant effect on predation by D. nipon . Therefore, the release of smaller quantities of large-sized scallops rather than larger quantities of small scallops is recommended to reduce D. nipon predation. In the presence of sea stars, especially by D. nipon , the predation impact on small scallops increased after just a few hours of air exposure, indicating that air exposure of juvenile scallops should be minimized. Our results will mitigate the economic cost of mariculture by facilitating the determination of optimal release conditions for juvenile scallops.