Abstract
Abstract: Sexual and asexual reproduction of the fissiparous asteroid Coscinasterias acutispina(Stimpson)was studied in two populations(Kurosaki and Uozu)in Toyama Bay, Sea of Japan, during April 1998-March 1999(Kurosaki)and April 1998-October 1999(Uozu). A total of 96% and 87% of all starfish collected at Kurosaki and Uozu, respectively, showed signs of asexual reproduction by fission. Monthly changes in the ratio of regenerated arm length to maximum arm length revealed that starfish in these populations split most frequently in summer. There was a marked difference in the development of gonads between the two populations. In the Kurosaki population, monthly changes of gonad indices and histological observations on gonads indicated a distinct annual cycle, with a winter spawning season in both males and females. In the Uozu population, gonad indices remained low, and no starfish with mature gonads were observed during the study. An unbalanced sex ratio was observed in both populations; the Uozu population was composed entirely of males. The absence of mature gonads and the extremely biased sex ratio suggest that larval recruitment was low or absent in the Uozu population.
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