Several oyster species are cultured globally, and the Pacific oyster, Crassostrea gigas, is a widely cultured species in both the USA and Japan. In Japan, aquaculture production of the Pacific oyster is decreasing slightly for multiple reasons including large die-offs of adults during and after the reproductive season due to a delay in the reproductive season and poor post-spawning recovery, poor wild spat collection, and a labor shortage for both operation of aquaculture and post-harvest processing. These problems may be aggravated by environmental changes such as global warming and oligotrophication around Japan’s coastal areas. The Japan Fisheries Research and Education Agency is investigating the causes of the die-off during the reproductive season and attempting to establish countermeasures. The Pacific oyster is native to Japan and was introduced to the USA for aquaculture in the early 1900’s. Nonetheless, there are large differences in the culture system, habitats and environmental conditions between the two countries. A comparative study was initiated to evaluate oyster reproduction in the two countries in order to understand the effects of habitat and the environment on future success of aquaculture given predicted environmental changes. Oyster culture experiments were conducted in intertidal and subtidal zones inside and outside of seagrass habitat in Hiroshima Bay in Japan and Willapa Bay in USA during the reproductive season (March to June 2019 and February to July 2019, respectively). We focused on elucidating the effects of habitat and the environment on the energy allocation of the oyster between reproduction and somatic growth.
Hasegawa et al. (Mon,) studied this question.