Current environmental status of the oyster farms on Lake Kamo in Japan; viral control of the harmful bloom of Heterocapsa circularisquama

Natsuko Nakayama; Saho Kitatsuji; Masami Hamaguchi

doi:10.7717/peerj.14813

Current environmental status of the oyster farms on Lake Kamo in Japan; viral control of the harmful bloom of Heterocapsa circularisquama

PeerJ. 2023 May 11:11:e14813. doi: 10.7717/peerj.14813. eCollection 2023.

Authors

Natsuko Nakayama¹, Saho Kitatsuji¹, Masami Hamaguchi²

Affiliations

¹ Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Hatsukaichi, Hiroshima, Japan.
² Faculty of Marine Science and Technology, Research Center for Marine Bioresources, Fukui Prefectural University, Obama, Fukui, Japan.

Abstract

Lake Kamo is an enclosed, low-inflow estuary connected to the open sea that is famous for oyster farming in Japan. In the fall of 2009, this lake experienced its first bloom of the dinoflagellate Heterocapsa circularisquama, which selectively kills bivalve mollusks. This species has been detected exclusively in southwestern Japan. The completely unexpected outbreak of H. circularisquama in the northern region is believed to have been caused by the contamination of purchased seedlings with this species. The water quality and nutrient data collected by our group from July through October over the past 10 years revealed that the environment of Lake Kamo has not changed significantly. However, in the open water around Sado Island, where Lake Kamo is located, the water temperature has increased by 1.80 °C in the last 100 years, which is equivalent to 2-3-fold the world average. This has resulted in a rise in the sea level, which is expected to further deteriorate the water exchange between Lake Kamo and the open sea and low dissolved oxygen in the bottom layer of the Lake and the associated dissolution of nutrients from the bottom sediment. Therefore, seawater exchange has become insufficient and the lake has become nutrient rich, making it prone to the establishment of microorganisms, such as H. circularisquama, once they have been introduced. We developed a method to mitigate the damage caused by the bloom by spraying sediments containing the H. circularisquama RNA virus (HcRNAV), which infects H. circularisquama. After ∼10 years of performing various verification tests, including field trials, this method was used at the Lake in 2019. During the 2019 H. circularisquama growth season, a small amount of sediment containing HcRNAV was sprayed on the lake three times, which resulted in a decrease in H. circularisquama and an increase in HcRNAV, indicating that this method is effective in diminishing the bloom.

Keywords: Enclosed; HcRNAV; Heterocapsa circularisquama bloom; Lake Kamo; Low inflow; Viral control.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Aquaculture
Dinoflagellida*
Japan / epidemiology
Lakes
Ostreidae*
RNA Viruses* / genetics

Grants and funding

This research was supported by a Grant-in-Aid from the Fisheries Agency of Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.