Effect of seawater temperature on long-term recruitment of Strongylocentrotus intermedius juveniles in northeastern Sea of Japan

To elucidate the effects of seawater temperature on long-term recruitment of juvenile Strongylocentrotus intermedius, annual changes in the juvenile density were monitored for 25 years from 1987 to 2011 off the coast of Rebun Island in the Sea of Japan off northern Hokkaido, Japan. The densities of 8-9 month and 1 year old juveniles fluctuated greatly from 0 to 47.2 ind/m2 and from 1.2 to 79.2 ind/m2, respectively. However, the recruitment occurred frequently and the densities of 1 year old juveniles exceeded 20 ind/m2 in 1987, 1989, 1992, 1997, 2004, and 2007, indicating a high level of recruitment. Significant negative correlations between the densities of 8-9 month old juveniles and the monthly average water temperature from June to September of the previous year were detected (p <0.05). In particular, the correlation was the most significant in June (p <0.01). The densities were high (>20 ind/m2) at 10-11 °C and low (<10 ind/m2) at 12-13 °C. As a previous study indicates that the gonads develop from growth to spent stage during these months in Rebun Island, no significant increased water temperature in the northeastern Sea of Japan may be concerned with gonad maturation and spawning of adult population, leading to success in juvenile recruitment.