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Primary Production based on Eddy of the Kuroshio Front - influence of the Kuroshio flow for cathes of yellowtail and juvenile of sardine -


　Disturbance by low pressure based on front wave occurs in area of the Kuroshio front (Figure 1). This phenomenon provides high density of nutrients for phytoplankton from below the photic zone, and rise the productivity of phyto and zooplanktons significantly. On the other hand, the offshore of the Kuroshio is one of the low productivity areas, which are not good for fish larvae survival. Then, how they manage these disadvantage condition? We consider spawning behavior of adults and larvae behavior to illuminate how they gain required energy.

　Numerical simulation and observation of Enshu-Nada gave the sestimate of amount of the primary production of an eddy, 4x104tons. Considering the eddy influence to whole coastal area of Enshu-Nada, the primary production would be 40gCm-2y-1 (Figure 2). The value matches to the estimates of the Gulf stream in Atlantic ocean. Thus, western boundary currents of Pacific and Atlantic would bring the biological production of similar scale. On the other hand, estimates form past resaerches indicate its 1/3 of the primary production in Enshu-Nada was brough by the eddy. To consider primary production in coastal area, the eddy influences is not negligible.

　In the eddy area, vertical mixing occurs soon after its emergence and concentration of nitrate nitrogen became uniform at 30m and 50m depth. As time goes by, the nitrate nitrogen concentration drops and chrolophyl concentration increases. Following the phenomenon, density of copepod nauplii increases, and eggs and larva of japanese anchovi distribute where the maximus density of copepod nauplii (Figure 3). Thus, eddy emergence have an influence not only primary production, but also to secondary production. Promary production as food source of larvae and juvenile and their survival depends on vertical transfer of nutirients in the Kuroshio front area, and adults actively choose the spawning grounds for better survival of larvae and juvenile.


Figure 1. Ocean Color Image of Eddy by Satelite
Figure 2. Path of Biological Production at the Kuroshio Front Figure 3. Production of Lower Trophic Level at Eddy and Distribution of Eggs and Larvae


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