Study on the Japanese horseshoe crab as an keystone species for conservation of the coastal ecosystem

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Activity rhythms of the Japanese horseshoe crab in the coastal environment were investigated using bio-telemetry and bio-logging techniques developed in this study. The activity in short-term (up to 40 days) was monitored using acceleration loggers and ultrasonic transmitters. For the long-term (up to 500 days) analysis, depth-temperature loggers were used in this study.The results showed that the horseshoe crab has complex activity rhythms as circatidal (0.5 day) or circadian (1 day) rhythms synchronized with tidal and day-night cycles nested in ultra-circadian rhythms (14 days and 365 days) synchronized with lunar and annual cycles. We concluded that such marine animals have complex activity rhythms adapted to complex environmental fluctuations in the coastal environment.