Effect of high temperature on gametogenesis of the sea urchin Strongylocentrotus intermedius in the Sea of Japan, northern Hokkaido, Japan

Abstract

A long-term (1987 to 2011) monitoring survey of recruitment of Strongylocentrotus intermedius juveniles in the Rebun Island in the Sea of Japan of northern Hokkaido revealed a significant negative correlation between juvenile density and water temperature, at times of the year when adults have growing and mature gonads. It is possible that high temperature has a negative impact on gametogenesis of S. intermedius. We investigated digestion, somatic and gonad growth, and gonad development of adult S. intermedius from the Rebun Island from June to September 2011. Experimental temperature treatments were: monthly average (CT, 11.2–19.9 °C), high (HT, 13.4–22.7 °C), and low (LT, 10.5–18.2 °C). These temperatures represent the temperature range of the last 30 years in the island. At the highest temperature in late August, digested kelp dry matter in HT was lower than in LT. Body weight in CT and LT increased significantly during the experiment. Testicular development in CT and LT progressed to the spent stage in late September, but remained at the partly spawned stage in HT. Ovaries in CT and LT developed to the premature, partly spawned, or the spent stage, from early to late September, a time when ovarian development in HT progressed from the premature to the partly spawned stages, although some ovaries retained the growing stage, indicating that oogenesis was suppressed. In CT and LT, oocyte area increased significantly from early to late August, when ovaries developed from the growing to the premature stages, due to initiation of oogenesis. In contrast, in late July, oocyte area in HT was significantly larger in CT and LT, which might be due to increased digested kelp dry matter and digestibility, which enable resources to accumulate for gametogenesis at <20 °C. Oocyte area in HT was significantly smaller in late August and in early September, reflecting delayed ovarian development, but it rapidly increased from early to late September, when kelp digestibility increased, possibly due to decreased temperature, which enables animals to compensate for delayed oocyte growth leading to oogenesis. Low gonad growth in HT, and delayed maturation and spawning would be the causal factor of decreased juvenile recruitment.