Abstract
The distribution of growth-inhibiting bacteria (GIB) against the toxic dinoflagellate Alexandrium catenella (Group I) was investigated targeting seagrass leaves and surface waters at the seagrass bed of Akkeshi-ko Estuary and surface waters of nearshore and offshore points of Akkeshi Bay, Japan. Weekly samplings were conducted from April to June in 2011. GIBs were detected from surface of leaves of the seagrass Zostera marina in Akkeshi-ko Estuary (7.5 × 105–4.7 × 106 colony-forming units: CFU g−1 wet leaf) and seawater at the stations in Akkeshi Bay (6.7 × 100–1.1 × 103 CFU mL−1). Sequence analyses revealed that the same bacterial strains with the same 16S rRNA sequences were isolated from the surface biofilm of Z. marina and the seawater in the Akkeshi Bay. We therefore strongly suggested that seagrass beds are the source of algicidal and growth-inhibiting bacteria in coastal ecosystems. Cells of A.catenella were not detected from seawaters in Akkeshi-ko Estuary and the coastal point of Akkeshi Bay, but frequently detected at the offshore point of Akkeshi Bay. It is suggested that A.catenella populations were suppressed by abundant GIBs derived from the seagrass bed, leading to the less toxin contamination of bivalves in Akkeshi-ko Estuary.
Highlights
The toxic dinoflagellate Alexandrium catenella (Miozoa, Dinophyceae) (Group I, formerly A. tamarense and toxic [1]) is known to produce strong neurotoxins similar to pufferfish (Takifugu rubripes, etc.) and cause paralytic shellfish poisoning (PSP) of edible bivalves (Patinopecten yessoensis, Crassostrea gigas, Ruditapes philippinarum, etc.) through the food chain in coastal seas
We investigated the reasons why shellfish poisoning has rarely occurred in the Akkeshiwere set the central part of Akkeshi-ko Estuary (Stn. 1, mean depth of 1 m, at the center koat of the seagrass field), at the inner part of the Akkeshi Bay (Stn. 2, mean depth of 5.8 m), Methods and at 2
The occurrences of harmful algal blooms spread widely due to the eutrophication in coastal areas [58,59], the introduction of causative organisms by human activities such as ballast water and juvenile transfer [60,61], and climate change [62]
Summary
The toxic dinoflagellate Alexandrium catenella (Miozoa, Dinophyceae) (Group I, formerly A. tamarense and toxic [1]) is known to produce strong neurotoxins similar to pufferfish (Takifugu rubripes, etc.) and cause paralytic shellfish poisoning (PSP) of edible bivalves (Patinopecten yessoensis, Crassostrea gigas, Ruditapes philippinarum, etc.) through the food chain in coastal seas. Occurrences of shellfish poisoning and the resultant harvesting closures have been reported in the farming of bivalves such as oysters and scallops. Hokkaido Island provides the largest production of scallops in Japan, and the incidents of paralytic shellfish poisonings in Hokkaido are frequent and have a long history [4]. Akkeshi-ko Estuary (area, 32.31 km2 ) is located in the eastern part of Hokkaido, and paralytic shellfish toxins in bivalves have only rarely been confirmed in the estuary during the monitoring by the local government of Hokkaido Prefecture. The most notable property of Akkeshi-ko Estuary is the existence of a large-scale seagrass bed that covers approximately 11–25 km of the area (Nakaoka, personal communication)
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