Nutrient reduction by eastern oysters exhibits low variability associated with reproduction, ploidy, and farm location.

Enhancement of shellfish populations has long been discussed as a potential nutrient reduction tool, and eastern oyster aquaculture was recently approved as a nutrient reduction best management practice (BMP) in Chesapeake Bay, USA. This study addressed BMP-identified data gaps involving variation in nutrient concentration related to ploidy, effects of reproductive development, and a paucity of phosphorus concentration data. Diploid and triploid oysters were collected from farms in Maryland and Virginia across the typical local reproductive cycle. The nutrient concentration of tissue and shell was consistent with the currently implemented BMP. Minor variation observed in nitrogen and phosphorus concentration was within the previously reported range, for farm location, ploidy, and reproductive cycle timing. Ploidy-based differences in tissue dry weight were not observed at either farm, which contrasts with current nutrient reduction estimates. These results suggest separate crediting values for diploids and triploids may need further investigation and potential re-evaluation.

Microbiota of Crassostrea virginica larvae during a hatchery crash and under normal production: Amplicon sequence data.

We present oyster larval microbiota from two feeding studies, in which wild type and low-salinity tolerant lines were either fed or starved. In one study, all larvae unexpectedly died, which was concurrent with an event in which all larvae in an adjoining oyster hatchery also died. In the other study, no crash occurred in either the study or hatchery. In both cases, larvae were collected and stored frozen, and microbial and host DNA was isolated by phenol-chloroform extraction. Both host 18 s rRNA genes and microbial 16 and 18 s rRNA genes were sequenced using universal primers. We present raw sequences, the pipeline that was used to quantify amplicon sequence variants, and our analysis pipeline that we used to describe how the overall microbial community varied between projects (crashed and non-crashed), feeding status (fed vs not), and strain (wild vs not). These data will be valuable to anyone interested in the microbiota of larval oysters, especially anyone interested in exploring hatchery crashes, effects of starvation, or strain level differences. They also contain a reproducible pipeline of amplicon analysis of host associated microbiota which may serve as a template for other studies. These data are a co-submission to a manuscript submitted to Aquaculture by Matthew grey et al. (2021) entitled Hatchery crashes among shellfish research hatcheries along the Atlantic coast of the United States: a case study at Horn Point Laboratory oyster hatchery. (Manuscript#: AQUACULTURE-D-21-01351R1).

Effects of freshwater release on oyster reef density, reproduction, and disease in a highly modified estuary.

Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for assessing the impact of altered hydrology on natural oyster reef (Crassostrea virginica) populations. The watershed has been highly modified and greatly enlarged by an artificial connection to Lake Okeechobee. Accordingly, to generate data to support water management recommendations, this study monitored various oyster biometrics over 15 years along the primary salinity gradient. Oyster reef densities were significantly affected by both prolonged high volume freshwater releases creating hyposaline conditions at upstream sites and by a lack of freshwater input creating hypersaline conditions at downstream sites. Low freshwater input led to an increase in disease caused by Perkinsus marinus and predation. Moderate (< 2000 cfs) and properly timed (winter/spring) freshets benefited oysters with increased gametogenesis, good larval mixing, and a reprieve from disease. If high volume freshets occurred in the late summer, extensive mortality occurred at the upstream site due to low salinity. These findings suggest freshwater releases in the late summer, when reproductive stress is at its peak and pelagic larvae are most vulnerable, should be limited to < 2000 cfs, but that longer freshets (1-3 weeks) in the winter and early spring (e.g., December-April) benefit oysters by reducing salinity and lessening disease intensity. Similar strategies can be employed in other managed systems, and patterns regarding the timing of high volume flows are applicable to all estuaries where the management of healthy oyster reefs is a priority.

Are bivalves susceptible to domestication selection? Using starvation tolerance to test for potential trait changes in eastern oyster larvae.

Conservation efforts are increasingly being challenged by a rapidly changing environment, and for some aquatic species the use of captive rearing or selective breeding is an attractive option. However, captivity itself can impose unintended artificial selection known as domestication selection (adaptation to culture conditions) and is relatively understudied for most marine species. To test for domestication selection in marine bivalves, we focused on a fitness-related trait (larval starvation resistance) that could be altered under artificial selection. Using larvae produced from a wild population of Crassostrea virginica and a selectively bred, disease-resistant line we measured growth and survival during starvation versus standard algal diet conditions. Larvae from both lineages showed a remarkable resilience to food limitation, possibly mediated by an ability to utilize dissolved organic matter for somatic maintenance. Water chemistry analysis showed dissolved organic carbon in filtered tank water to be at concentrations similar to natural river water. We observed that survival in larvae produced from the aquaculture line was significantly lower compared to larvae produced from wild broodstock (8 ± 3% and 21 ± 2%, respectively) near the end of a 10-day period with no food (phytoplankton). All larval cohorts had arrested growth and depressed respiration during the starvation period and took at least two days to recover once food was reintroduced before resuming growth. Respiration rate recovered rapidly and final shell length was similar between the two treatments Phenotypic differences between the wild and aquaculture lines suggest potential differences in the capacity to sustain extended food limitation, but this work requires replication with multiple selection lines and wild populations to make more general inferences about domestication selection. With this contribution we explore the potential for domestication selection in bivalves, discuss the physiological and fitness implications of reduced starvation tolerance, and aim to inspire further research on the topic.

Correction: Restoring oysters to urban estuaries: Redefining habitat quality for eastern oyster performance near New York City.

[This corrects the article DOI: 10.1371/journal.pone.0207368.].

Restoring oysters to urban estuaries: Redefining habitat quality for eastern oyster performance near New York City.

Restoring and conserving coastal resilience faces increasing challenges under current climate change predictions. Oyster restoration, in particular, faces threats from alterations in precipitation, warming water temperatures, and urbanization of coastlines that dramatically change salinity patterns, foster the proliferation and spread disease, and disrupt habitat connectivity, respectively. New York City (NYC) coastal waters, once home to a booming oyster fishery for eastern oysters (Crassostrea virginica), are now nearly devoid of live oyster reefs. Oyster restoration in urban estuaries is motivated by the synergistic ecosystem benefits this native keystone species can deliver. Recent surveys have documented substantial remnant populations of adult oysters in the upper low salinity zone of the Hudson/Raritan Estuary (HRE) near Tarrytown, NY. This study assessed fitness-related performance across the HRE salinity gradient to evaluate habitat suitability on an estuarine scale. Oysters were hatchery-produced from wild, moderate-salinity broodstock, then outplanted for measurement of growth, survival, reproduction and disease prevalence over two years. Survival was generally higher in the lower salinity river sites and in the higher salinity Jamaica Bay sites relative to mesohaline NYC harbor sites. Growth rate was highest in Jamaica Bay and had high variation among other sites. Surprisingly, the highest proportion of individuals with sex-differentiated gametes and the highest average gonad maturation index was found at a low salinity site. Consistent with the advanced gametogenesis measured in experimental animals at low salinity, annual wild recruitment was documented near the low salinity remnant population in each of five monitored years. These results suggest that the remnant HRE oyster population is a robust, self-sustaining population that can be leveraged to support restoration of subpopulations in other parts of the estuary, but further research is required to determine if the mesohaline and near-ocean reaches of the HRE can support the full oyster life cycle.

Potential impacts of blooms of the toxic dinoflagellate Karenia brevis on the growth, survival and juvenile recruitment of the non-native green mussel Perna viridis in southeastern United States.

Red tide blooms formed by Karenia brevis are frequent along the Gulf coast of Florida and it is unclear what tolerance the green mussel Perna viridis, a recently introduced species to coastal waters, has toward these events. Established populations of P. viridis were monitored along the coastal waters of Estero Bay, Florida before, during and following two consecutive red tide blooms to assess the potential effects on growth, survival and juvenile recruitment. Upon onset of the bloom, growth rates fell from 6 to 10 mm month(-1) (March 2011-November 2011) to less than 3 mm month(-1). In the succeeding years, K. brevis blooms were present, and average growth of individually tagged mussels remained below 3 mm month(-1). During growth monitoring the use of calcein as an internal marker was tested with positive staining results and no observed effect on growth or survival. In March 2012, following the first red tide bloom, a population-wide mortality event was observed. Following this event, increased mortality rates were observed with peaks during onset of the bloom in the fall of 2012 and 2013. Juvenile recruitment was also limited during years in which blooms persisted into the spring spawning period suggesting gamete and/or larval sensitivity to K. brevis. Although it cannot be conclusively determined that the cause of reduced growth and survival is due to red tide events, the parallels observed suggest that K. brevis is a factor in the observed changes in population structure.

Uptake and elimination of brevetoxin in the invasive green mussel, Perna viridis, during natural Karenia brevis blooms in southwest Florida.

Perna viridis is a recently introduced species to US coastal waters and have vigorously spread throughout the southeastern seaboard since their invasion. Little information regarding their response to local environmental factors has been reported including responses to the local HAB species, Karenia brevis. This study monitored the tissue toxin concentration of brevetoxins in P. viridis from existing populations throughout two consecutive natural K. brevis blooms. The results showed P. viridis to rapidly accumulate PbTx upon exposure to the bloom, far exceeding the peak tissue concentrations of oysters, Crassostrea virginica, sampled during the same period, 57,653 ± 15,937 and 33,462 ± 10,391 ng g(-1) PbTx-3 equivalent, respectively. Further, P. viridis retained high PbTx concentrations in their tissues post bloom remaining above the regulatory limit for human consumption for 4-5 months, significantly longer than the depuration time of 2-8 weeks for native oyster and clam species. In the second year, the bloom persisted at high cell concentrations resulting in prolonged exposure and higher PbTx tissue concentrations indicating increased bioaccumulation in green mussels. While this species is not currently harvested for human consumption, the threat for post bloom trophic transfer could pose negative impacts on other important fisheries and higher food web implications.

Cedkathryns A and B, pentanortriterpenoids from Cedrelopsis gracilis (Ptaeroxylaceae).

The stem bark of Cedrelopsis gracilis (Ptaeroxylaceae) has yielded three known prenylated coumarins, O-methylalloptaeroxylin, ptaerochromenol and umtatin and the novel pentanortriterpenoids, cedkathryn A and cedkathryn B.