ABSTRACT Distribution of the sea urchin Hemicentrotus pulcherrimus was monitored monthly or bimonthly from April 1998 to May 1999 at a 100 [m.sup.2] permanent site in intertidal to subtidal zones at depths of up to 2.8 m in Onagawa Bay, northern Honshu, Japan. Factors causing seasonal demographic changes were analyzed from vertical algal vegetation, sea urchin size, gonad development, and gut content. The highest density of H. pulcherrimus was found on algal turf on boulders at the ...
<0.0026). There was no statistical difference in the gonad indices at algal turf from May to September 1998, when those ranging from 11.9-13.8 were in the recovering stage (P><0.05) and remained at that value until May. The gonad indices on crustose corallines ranged from 5.0-11.2 from May 1998 to January 1999, and no seasonal difference in the indices was found (P>