MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(HOR-1117-817005) Temporal Changes of Species Composition and Biomass of Benthic Community in Tokyo Bay, Japan.

Horiguchi, T.¹, Ochiai, S.², Yamaguchi, A.², Kume, G.¹, Kodama, K.¹, Shibata, Y.¹, Shiraishi, H.¹, Morita, M.¹, Shimizu, M.³, ¹ National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan² Nagasaki University, Nagasaki, Nagasaki, Japan³ The University of Tokyo, Bunkyo-ku, Tokyo, Japan

ABSTRACT- In the chain of the study to analyze the relationship between environmental pollution and qualitative/quantitative changes in biological community, temporal changes of species composition and biomass of benthic community were investigated in Tokyo Bay, Japan, from December 2002 to October 2004. Specimens (fishes, crustaceans and mollusks) were quarterly collected by 10-minute trawling at 20 stations in Tokyo Bay. Catch per unit effort (CPUE: the number of individuals and the weight per a trawl) was calculated for each species, and compared with the similar data of benthic community in Tokyo Bay from 1977 to 1995. Cluster analyses were applied using the weight CPUE data. Totally, 156 species (78 fish, 44 crustacean, 9 cephalopod and 25 bivalve/gastropod species) were collected between December 2002 and October 2004. The total number of individuals collected in the period was 28,159: 8,794 fish (31.2 %), 12,346 crustaceans (43.8 %), 854 cephalopods (3.0 %) and 6,165 bivalves/gastropods (22.0 %). There were 5 elasmobranches among 10 predominant species in the trawling surveys between December 2002 and October 2004. Although the total number of elasmobranch individuals collected in the previous surveys from 1977 to 1995 was 337, corresponding to only 0.3 % of the total number of fish (103,548 individuals), 671 elasmobranch individuals (7.6 % of total fish individuals) were collected from December 2002 to October 2004. The marked increase of elasmobranch in benthic community seemed to have recently occurred in Tokyo Bay. Results on cluster analyses showed 4 groups of duration: 1977-83, 1984-88, 1989-95 and 2003-2004 as phases I to IV, respectively. Both individual and weight CPUE increased from phases I to II, and reached at maximum in 1987 of phase II. Both individual and weight CPUE, however, decreased from phases II to III. Although the individual CPUE has remained low level in phase IV, the weight CPUE has markedly increased due to the increase of elasmobranch species as well as the Japanese sea bass. Previous predominant species, such as the mantis shrimp and the marbled sole, have markedly decreased in Tokyo Bay.

Key words: species composition, biomass, benthic community, Tokyo Bay