Collection of a Bacterial Community Reconstructed from Marine Metagenomes Derived from Jinhae Bay, South Korea

Marine bacteria are known to play significant roles in marine biogeochemical cycles regarding the decomposition of organic matter. Despite the increasing attention paid to the study of marine bacteria, research has been too limited to fully elucidate the complex interaction between marine bacterial communities and environmental variables. Jinhae Bay, the study area in this work, is the most anthropogenically eutrophied coastal bay in South Korea, and while its physical and biogeochemical characteristics are well described, less is known about the associated changes in microbial communities. In the present study, we reconstructed a metagenomics data based on the 16S rRNA gene to investigate temporal and vertical changes in microbial communities at three depths (surface, middle, and bottom) during a seven-month period from June to December 2016 at one sampling site (J1) in Jinhae Bay. Of all the bacterial data, Proteobacteria, Bacteroidetes, and Cyanobacteria were predominant from June to November, whereas Firmicutes were predominant in December, especially at the middle and bottom depths. These results show that the composition of the microbial community is strongly associated with temporal changes. Furthermore, the community compositions were markedly different between the surface, middle, and bottom depths in summer, when water column stratification and bottom water hypoxia (low dissolved oxygen level) were strongly developed. Metagenomics data contribute to improving our understanding of important relationships between environmental characteristics and microbial community change in eutrophication-induced and deoxygenated coastal areas.

Small-Scale Spatiotemporal Pattern in the Spawning of Pacific Herring (Clupea pallasii) in the Jinhae Bay, Korea, Estimated Using Hydroacoustic Survey

Acoustic surveys were used to locate coastal Pacific herring (Clupea pallasii) spawning grounds, and the spatial and temporal patterns of their spawning in Jinhae Bay, Korea were examined. We deployed mooring with a newly designed autonomous echosounder for ~70 days during the Pacific herring spawning season in Jinhae Bay, from January to April 2018. At the same time, ship-based acoustic surveys were conducted to identify the spatial distribution twice, at 38 and 120 kHz, onboard the fishing vessel in January and April 2018 in the bay. Fish school signals, including those from adult Pacific herring, are often detected through ship-based acoustic surveys in January, from outside the bay. In the spring, weak scattering signals from fish larvae and zooplankton were continuously detected inside the bay. Backscatter at the mooring in the center of Jinhae Bay was low from mid-January to early March, gradually increasing to higher levels until the end of March. The backscatter observed from the mooring correlated well with ship-based acoustic surveys in the center of the bay. This study proposes that the mooring type acoustic echosounder is a valuable tool for temporal abundance information and other aspects of fish behavior.