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

Abstract

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.

Characteristics and particularities of bacterial community variation in the offshore shellfish farming waters of the North Yellow Sea

“…Desulfobacterales plays important roles in nitrogen cycling and removal, and could contribute about 12% of the genes in nitrogen pathways (Nie et al, 2021). Recently, dominant sulfate reducing microorganisms (SRM) within Desulfobacterales were also reported in the sediments of coastal oyster aquaculture ecosystems (Mara et al, 2021). The proportional abundance of Actinobacteriota (1.3%) in this study was obviously lower than that in other studies, in which it was reported up to 5%-20% (He et al, 2017;Yu et al, 2018).…”

A seasonal study on the microbiomes of Diploid vs. Triploid eastern oysters and their denitrification potential

“…Moreover, in this study, the nasA , narG , and napA genes were also observed ( Figure 10 B), along with the with dominant narG gene. It is known that the NarG encodes for membrane-bound nitrate reductase, 99 which has previously been found to be high in sediments from oyster farms 100 and appears to be dominant in eastern oysters, regardless of ploidy. The higher abundances of nosZII and narG, relative to 16S genes in eastern oysters using the QMEC method are shown in Figure 10 C.…”

Study on the Treatment of Simulated Recirculating Mariculture Wastewater by Thiosulfate-Based Autotrophic Denitrification

“…As the S/N ratio decreased, the abundance of Chromatiales and Bradymonadaceae decreased. Genera and species affiliated with these two families are SOB known to utilize the accumulated sulfides, or thiosulfates using nitrate as an electron acceptor [26]. On the other hand, Trueperaceae, Alphaproteobacteria, Desulfobacteraceae, and Vibrionaceae showed significant increases.…”