| Research Abstract |
1. Feeding interactions between inshore marine copepods Pseudodiaptomus marinus and Acartia omorii, and 15 red-tide flagellates from Japanese coastal waters were studied by examining egestion rate, mortality and egg production rate of the copepods offered a suspension of each phytoplankton species. Among flagellates, a dinoflagellate Gymnodinium nagasakiense, and four raphidophytes Olisthodiscus luteus, Heterosigma akashiwo, Chattonella marina and Fibrocapsa japonica were almost entirely rejected by the copepods. It was found that the deterrent chemical compounds which inhibit feeding of copepods were intracellularly present. These compounds were ephemeral, being deactivated within 12 h at 20ﾟC. Chemically-mediated rejection by copepods is an important factor in the development of monospecific red tides.
2. Behavior of a copepod Calanus sinicus feeding on red-tide flagellates was examined using a video system. This species tended to ingest the flagellates which were rejected by the former two copepods, indicating the degree of rejection varies with grazer species.
3. Gut content of field-collected calanoid copepods was examined in detail, and showed a variety of phytoplankters were ingested by them. However, it was noted certain phytoplankton groups were not ingested by some copepods, indicating feeding rejection occurs in nature.
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