This paper examined the possibility of applying the water temperature control on seedling production of urchins. The experiment was conducted from May to November 2001 in order to evaluate the effects of lowering seawater temperature in summer, on the maturity promotion of sea urchins (Strongylocentrotus intermedius). Sea urchins were collected by scuba diving on the west coast of Hokkaido, Japan. They were then grouped into control group and experimental group. Sea urchins in experimental

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... were reared in cooled sea water below 18℃, while other urchins in control group were placed in ambient sea water. The comparative analysis was conducted to evaluate the effect of water temperature control between two groups. The change of gonad index (GI) prior to spawning was almost the same among urchins in both groups. However, urchins in experimental group showed early spawning by a month as is shown for decrease in GI and appearance of urchin in the spent stage (V) in September, comparing to urchins in control group. Although the result of our experiment did not show positive effects of lowering seawater temperature on the maturity promotion, it implied that lowering water temperature in summer contributed to inhibit a delay of spawning, and stabilized seedling production process of sea urchins.