抄録
The distribution of sea urchins (Echinodermata, Echinoidea), and changes therein over the course of a decade, were investigated around Cape Bansho, which marks the southern limit of Tanabe Bay, Japan (33°42′N, 135°20′E). Censuses were carried out once each in 2000 and 2011, using a semi-quantitative timed search technique on both occasions. Fourteen species of sea urchin were recorded in the two survey years, of which 64% were tropical Indo-Pacific species. Echinostrephus aciculatus, Anthocidaris crassispina, and Stomopneustes variolaris were more abundant in the intertidal than subtidal zone. In contrast, Echinometra sp. A, Toxopneustes pileolus, and Diadema setosum were more abundant in the subtidal zone than intertidally. The densities of Echinometra mathaei, Echinometra oblonga, and Stomopneustes variolaris were higher on more exposed shores whereas those of Echinometra sp. A and Mespilia globulus were higher on more sheltered shores. The present results concerning Echinometra species and wave exposure are consistent with previous reports from Okinawa. From 2000 to 2011 there was a contraction in the ranges of Mespilia globulus, Diadema setosum, and Stomopneustes variolaris, all of which are tropical species, but the range of the warm-temperate species Anthocidaris crassispina remained constant. Environmental and biological evidence around Tanabe Bay suggests that climatic events such as a severe winter and typhoons were responsible for the decline of the three tropical species between 2000 and 2011.
