Rhythmic patterns of abundance in small sublittoral crustaceans: variety in the synchrony with day/night and tidal cycles |
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Authors: | K Oishi M Saigusa |
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Institution: | (1) Department of Biology, Faculty of Science, Okayama University, Tsushima 2-1-1 (General Education Buildings), Okayama 700, Japan, JP |
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Abstract: | Temporal fluctuations of abundance (or emergence) in small benthic and planktonic crustaceans were studied in shallow subtidal
waters (1.5 to 3.5 m in tide height). The abundances were more or less rhythmic, and showed wide diversity ranging from very
clear nocturnal patterns to patterns in sychrony with the tidal cycle alone. These abundance patterns were classified into
categories relating to the degree of synchrony with day/night and tidal cycles. Nocturnal patterns were especially strong
in benthic crustaceans, which would be inactive during the daytime, being attached to algae and stones or disappearing into
rock crevices, and actively swim in the water at night. Mysis larvae also showed a clear nocturnal pattern. Their lifestyle
might be similar to that of many benthic animals. Other planktonic crustaceans drifting in the water showed weak nocturnal
patterns. In some planktonic crustaceans (e.g., Calanoida), the ratio of abundance in the surface and bottom samples was reversed
between day and night. Their pattern might be a manifestation of weak diel vertical movement between day and night. Furthermore,
most patterns of zooplankton and benthos were modified in synchrony with tides to various degrees. Small crustaceans may respond
to changes of hydrologic variables fluctuating with the tides, which may exogenously produce a weak tidal component in their
emergence patterns.
Received: 12 January 1998 / Accepted: 29 August 1998 |
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