ミズクラゲの生態学的研究-I

Abstract

The patches of the common medusa, Aurelia aurita LAMARCK, have often been drawn into the intake-tunnel of thermal power stations using huge volumes of sea water for condenser cooling. This has created serious trouble in sea water intake. To obtain some basic knowledge for the planning of countermeasures, distribution of the patches was investigated three times by ship in the north-east region of Tokyo Bay, where there are several power stations on the coast. Tracks and stations of these surveys in which one was aerial observation from helicopter are shown in Fig. 1. When patches were found, their characteristics were examined: area and shape were estimated by observation, density was obtained by horizontal towing of a net with an opening 100cm in diameter and with 8.0mm mesh-openings, and biomass was calculated from density and mean diameter of the bells using the relation as shown in Fig. 5. Results of these examinations are shown in Table 2. As for the relation between oceanographic structure and distribution of Aurelia patches, chlorinity distribution presented a fine relation in each surveys as seen in Fig. 2-4. Result of the 1st survey showed that patches have surrounded a low chlorinity line, the contour of 16.00‰ (Fig. 2). Results of 2nd and 3rd surveys are shown in Fig. 3 and Fig. 4 respectively, in which patches were situated near the projecting points of high chlorinity lines. These results suggest that the patches have drifted with the off-shore current of high chlorinity. Results of two vertical towings of patches showed the change of density as seen in Fig. 6 and Fig. 7.