親潮域における低次生産特性とカイアシ類日周摂食リズムに関する研究(1998年度日本海洋学会岡田賞受賞記念講演)

概要

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Variability, control factors and adaptive significance of the diel feeding rhythm (DFR) of copepods were examined in the Oyashio region. All the species examined, which were dominant copepods, showed DFR. The increase in feeding rate was observed at dusk, and the decrease was at dawn or several hours before sunrise. These showed the timing of the increase in feeding rate was triggered by light cycle but the decrease was controlled by not only light cycle but also other factors, e.g., circadian rhythm. However, the timing of the change in feeding rate was variable by species and developmental stages. Diel amplitude in feeding rate also showed variations by species and stages. DFR is thought to be available to decrease the risk of visual predation because of the inconspicuous body during the day with low gut contents. In order to examine this hypothesis, the cost of DFR was determined by a simple DFR model. The model revealed that large species, which were vulunerable to the visual predation, paid more cost on DFR than small one. The prey selectivity experiments on full- and empty-gut copepods showed consistent results on the hypothesis that fish selected more on full-gut copepods than the empty-gut one. These results show that DFR is the behavior to reduce the risk of visual predation. Variations in the DFR by species are the results of the trade-off between foraging and survival.
日本海洋学会の論文
1998-12-05