抄録
Composition of benthos in Mutsu Bay is as follows: polychaetous annelids 57.8%, molluscs 25.2%, echinoderms 6.7%, crustaceans 2.8% and others 7.5%. According to MOTOMURA (1935), the correlation coefficient between the composition of benthic animals of a station and that of others was calculated one by one and thus the reciprocal relation between each station was represented by twenty four series of correlation coefficients (Fig. 1). Here, the correlations between the stations 15, 13 and 21 ; 24 and 8 ; 20 and 17 are statistically insignificant. Thus four groups are distinguished in these coefficient series, viz. four benthic communities in Mutsu Bay (Fig. 2a). In order to clarify the forms of four communities the application of the law of geometrical progression (MOTOMURA, 1932), logy+ax=b, where y is the number of individuals of one species, x is the rank in number of it and value of u means degree of complexity of community, was tested. The law is applicable with 95% reliability (Fig. 3). Of the whole bay the numerical and gravimetric population is 330per square meter, and 175.1g. per square meter respectively in the spring to summer of 1947 (Table). In the next same season 368per square meter and 113.8g. per square meter respectively. Judging from the composition of benthos, and the numerical and gravimetric population, the bay seems to be one of the oligotrophic bay in high latitude. The configuration of distribution of benthic communities seems to depend upon the isohaline curves showing the mixed conditions of oceanic and coast waters (Fig. 2b).
