Decadal response of marine food-chain to bottom-up and top-down controls
2003
Isoda, Y. (Hokkaido Univ., Sapporo (Japan))
Abstract Using a simple four-level food-chain model (nutrient, phytoplankton, zooplankton and fish), the phase relationships in a decadal time scale were investigated under a periodical nutrient supply, i.e. bottom-up control, and under a periodical flow-parameter from zooplankton to fish, i.e. top-down control. This model expressed seasonal changes imitating the spring bloom and assumed the possibility that the predation of fish could positively affect zooplankton productivity. In the model results, the bottom-up control revealed that decadal variation of annual mean zooplankton stock (Z) was stabilized and furthermore that the maximum of Z led to 90 deg from that of the annual mean fish stock (F). On the other hand, the top-down control amplified the decadal variation of Z and showed that the phase relation between Z and F was out of phase. The results were then applied to a diagnosis for the present marine ecosystem in the western Pacific.
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