Shell Infestation of the Farmed Pacific Oyster Magallana gigas by the Endolith Bivalve Rocellaria dubia

Oyster shells are substratum for different epibiontic and endobiontic organisms, including pests and parasites. Rocellaria dubia is endolithic and facultative tube-dwelling bivalve, boring in different calcareous substrates, including the shells of bivalves. In 2020, R. dubia was found as endolithic in the shells of the Pacific oyster Magalana gigas, from an oyster farm off the Sacca di Goro lagoon (Emilia-Romagna region, Northern Adriatic Sea, Italy). The purpose of this study was to describe this newly recorded association. Altogether, 136 specimens of R. dubia were found in 15 oysters, photographed under a stereoscope, and their length was measured. Heavily infested oysters hosted tens of R. dubia borers, which were perforating the whole thickness of the oyster valves. The flesh of these oysters was heavily damaged, suggesting parasitic association. R. dubia specimens were categorized into three age classes (0–1, 1–2, and 2–3 years old). M. gigas/R. dubia might be a widespread association, overlooked due to the very scarce research on macrofauna associated with M. gigas. Considering the negative effects of R. dubia endobiosis on oyster fitness, and possible impacts on oyster aquaculture, further research should be conducted in order to elucidate the distribution and ecological characteristics of this parasitic association.

The practice of everyday oystering: aquaculture as resistance

As members of complex social-ecological systems (SES),fishermen navigate and respond to system changes to maintain their livelihoods. These changes often involve dynamic power relationships. In Maryland (United States), commercial fishermen or watermen demonstrate a history of responding to SES changes, including power relationships in which they often feel restricted. We describe how watermen have historically employed tactics, as conceived by de Certeau (1984), to resist and succeed within a constraining system. We considerinvolvement in oyster aquaculture as a recent tactic, and compare data from interviews with watermen and non-watermen involved in aquaculture to understand power relationships and adaptations within this SES. Interviews suggest that, while both watermen and non-watermen aquaculturists perceive similar power relations within the system, only watermen begin work in oyster aquaculture as a tactic in response to these relations (P<0.001). Results illustrate diverse perceptions of power as well as ongoing changes within the SES. More broadly, we introduce the idea of SES adaptations as tactics of resistance and emphasize the need for a more integrative understanding of SES and power.

Benthic Community Assessment of Commercial Oyster (Crassostrea virginica) Gear in Delaware Inland Bays

Oyster aquaculture is one of several methods for the restoration of Delaware Inland Bays; however, little is known about its potential impacts on the benthic community of the bays. In this study, water quality parameters were measured and polychaetes were collected from 24 sampling locations at Rehoboth, Indian River, and Little Assawoman Bays from July to October 2016 and 2017. We aimed to assess the impact of Eastern oyster farming under different stocking densities (50 and 250 oysters/gear) and distances away from the sites where the off-bottom gears are implemented (under gears, one meter, and five meters away). No significant impact was detected on polychaetes’ abundance and richness in regard to the presence of oyster gears. The number of polychaetes and species richness was significantly higher in Little Assawoman Bay in comparison to the Indian River and Rehoboth Bays. Results showed that the Ulva lactuca bloom that happened in 2016 could negatively impact the low abundance and richness observed in the polychaetes community. Similarly, the values of polychaetes abundance and species richness did not change significantly in samples that were taken far from the oyster gears. Dominant polychaetes families were Capitellidae and Glyceridae contributing to more than 70% of polychaetes’ number of individuals. Our results help to understand the role of oyster aquaculture in restoring the viability in the natural habitat of the Delaware Inland Bays.

Comparison of Oyster Aquaculture Methods and Their Potential to Enhance Microbial Nitrogen Removal From Coastal Ecosystems

Coastal ecosystems are impacted by excessive nutrient inputs that cause degradation of water quality and impairments of ecosystem functioning. Regulatory and management efforts to enhance nutrient export from coastal ecosystems include sustainable oyster aquaculture that removes nitrogen in the form of oyster biomass and increases particulate export to underlying sediments where increased organic material may enhance microbial denitrification. To better understand the impacts of oyster aquaculture on nitrogen removal, we examined bacterial processes in sediments underlying three of the most common aquaculture methods that vary in the proximity of oysters to the sediments. Sediment samples underlying sites managed with these different aquaculture methods were examined using the 16S rRNA gene to assess microbial community structure, gene expression analyses to examine nitrogen and sulfur cycling genes, and nitrogen gas flux measurements. All sites were located in the same hydrodynamic setting within Waquoit Bay, MA during 2018 and 2019. Although sediments under the different oyster farming practices showed similar communities, ordination analysis revealed discrete community groups formed along the sampling season. Measured N2 fluxes and expression of key genes involved in denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) increased during mid-summer and into fall in both years primarily under bottom cages. While all three oyster growing methods enhanced nitrogen removal relative to the control site, gene expression data indicate that the nitrogen retaining process of DNRA is particularly enhanced after end of July under bottom cages, and to a lesser extent, under suspended and floating bags. The choice of gear can also potentially increase processes that induce nitrogen retention in the form of ammonia in the underlying sediments over time, thus causing deviations from predicted nitrogen removal. If nitrogen removal is a primary objective, monitoring for these shifts is essential for making decisions about siting and size of aquaculture sites from year to year.