1Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido 085-0802, 2Hokkaido Kushiro Fisheries Experimental Station, Kushiro, Hokkaido 085-0024, Japan
The spatial distribution and population structure of the benthic isopod crustacean Tecticeps glaber were surveyed in the sandy beach area of Hamanaka Bay, eastern Hokkaido, Japan. T. glaber densities were higher in the more turbulent area than in the more sheltered area with seagrass bed. Annual mean T. glaber density in the turbulent area was 893 per m2 , and the density in the turbulent area peaked at 2,060 per m2 in September. Seasonal changes in frequency distributions of T. glaber population suggest the presence of 3 year groups: 0 + group, 1 + group, and 2 + group. The newly recruited individuals, mancas, were observed from September to December. Two peaks, a major peak in September and a minor peak in November and December, were observed in the recruitment. It was supposed that the recruitment of this population was mainly produced by reproduction of the 2 + group.