Larval occurrence and environmental factors associated with spawning of Pacific oyster Crassostrea gigas in Matsushima Bay, Japan

Abstract

The spawning of Pacific oysters is an important phenomenon for aquaculture because the Japanese oyster culture industry has traditionally utilized natural seed collection from sea areas. The relationship between spawning and environmental factors was investigated on the spawning dates, which were estimated from larval occurrence based on the temperature-dependent growth rate from 2012 to 2020 in Matsushima Bay, a key area for oyster seedling production located in eastern Japan. The annual minimum temperature tended to increase and occur earlier during the 9 years, suggesting warming in the bay. The integrated temperature reaching 600°C, which is as an index for the onset of spawning, was limited to 9 days from late June to early July, and exhibited no trends. Larval abundance at each spawning had a significant relationship with the change of sunshine hours from the previous day, the daily mean seawater temperature, and the maximum tidal range. With relatively extreme environmental factors, mass spawning between neap and half tides was more frequent than one during other tides. A significant relationship was found between precipitation during the rainy season and the mass spawning dates. An empirical method of predicting a mass spawning date was proposed using the relationship to precipitation during the rainy season to ensure efficient seedlings and a constant nationwide supply of Pacific oysters for the aquaculture industry.