Macrobenthic fauna of Gokasho bay [Mie prefecture, Japan]: Comparison of 1993 and 1941 surveys
1996
Yokoyama, H. (National Research Inst. of Aquaculture, Tamaki, Mie (Japan)) | Toda, S. | Abo, K. | Yamamoto, S.
To evaluate the influence of fish farms on the macrobenthos in Gokasho Bay, quantitative information including the density, biomass and number of species of the macrobenthos, and the distribution of the main constituent species were obtained by a Bay-wide survey in April and August 1993. Three distribution types were found, i.e., species found in the mouth of the Bay, those found in the central part, and those found in the innermost part. This differentiation seems to be dependent on the grain size gradient associated chemical factors of the sediment along the main axis of the Bay. Three species (the polychaetes, Pseudopolydora paucibranchiata and Capitella sp., and the amphipod Protomima imitatrix) occurred at the stations close to the fish farms in April; at that time, low oxygen concentrations (58-64% saturation) were found in the bottom water. In August, however, these species disappeared together with the other constituent species, and a near azoic situation was found. This fluctuation may have been caused by the rich food source originating in the organic wastes from the fish farms (food pellets and fish excreta) leading to the serious oxygen depletion. Comparison of this survey with the previous survey conducted in 1941 indicates a change of the species distribution in the Bay; the bivalve Theora fragilis has expanded its distributional range from the innermost part to the central part of the Bay; the spatangina Schizaster lacunosus has disappeared and the three species occur in close association with the fish farms. These changes suggest the influence of eutrophication and fish farming on the bottom of the Bay
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