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Atlantic sea scallops, Placopecten magellanicus, are the most economically important marine bivalves along the northeastern coast of North America. Wild harvest landings generate hundreds of millions of dollars, and wild-caught adults and juvenile spat are increasingly being cultured in aquaculture facilities and coastal farms. However, the last two weeks of the larval maturation phase in hatcheries are often plagued by large mortality events. Research into other scallop- and aquacultured-species point to bacterial infections or altered functionality of microbial communities which associate with the host. Despite intense filtering and sterilization of seawater, and changing tank water every 48 h, harmful microbes can still persist in biofilms and mortality is still high. There are no previous studies of the bacterial communities associated with the biofilms growing in scallop hatchery tanks, nor studies with wild or hatchery sea scallops. We characterized the bacterial communities in veliger-stage wild or hatchery larvae, and tank biofilms using the 16 S rRNA gene V3-V4 region sequenced on the Illumina MiSeq platform. Hatchery larvae had lower bacterial richness (number of bacteria taxa present) than the wild larvae and tank biofilms, and hatchery larvae had a similar bacterial community (which taxa were present) to both wild larvae and tank biofilms. Bacterial richness and community similarity between tank samples fluctuated over the trial in repeated patterns of rise and fall, which showed some correlation to lunar cycle that may be a proxy for the effects of spring tides and trends in seawater bacteria and phages which are propagated into hatchery tanks. These results along with future work, will inform hatcheries on methods that will increase larval survival in these facilities, for example, implementing additional filtering or avoiding seawater collection during spring tides, to reduce bacterial taxa of concern or promote a more diverse microbial community which would compete against pathogens.

Despite the profitability of the wild Atlantic Sea Scallop, Placopecten magellanicus, fishery, the U.S. still imports more than 26,000 tonnes of various scallop products annually. Atlantic Sea Scallop (hereafter referred to as scallop) aquaculture is one method of mitigating this imbalance. We examined scallop growth at three sites across the mouth of Penobscot Bay, Maine to determine the coupled effects of lantern net stocking density and temperature on growth and mortality. Scallops were held in high and low (20 and 10 individuals tier−1, respectively) density treatments, and shell height measurements were recorded monthly for one year. We divided the growth rate analysis into three periods: winter - spring, summer, and fall. During summer across all sites, growth rates were 75 % higher in low-density nets than in high-density nets. We observed significant nonlinear relationships between shell height growth rate, temperature, and stocking density. Optimal growth occurred within a window of 10–15 °C. Above this threshold, there was a distinct negative relationship between temperature and growth. Our results highlight the importance of maintaining low densities within nets, particularly during periods of high temperature and growth. However, handling in summer and early fall may lead to mortality. Therefore, we recommend that growers stock nets at low densities in the spring, ensuring that they will not require thinning during peak temperatures. Similarly, finding sites that maximize time within a thermal envelope of 10–15 °C will be critical, which in the case of the Gulf of Maine will most likely warrant leasing sites at the mouths of estuaries and bays. These locations offer a combination of sufficient depth and space for sparsely stocked nets, adequate food levels, and optimal salinity and temperature.