Factors regulating the breeding and foraging activity of a tropical opisthobranch |
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Authors: | Jean-François Hamel Annie Mercier |
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Institution: | (1) Ocean Sciences Centre (OSC), Memorial University of Newfoundland, St. John’s (Newfoundland), Canada, A1C 5S7;(2) Society for the Exploration and Valuing of the Environment (SEVE), 21 Phils Hill Road, Portugal Cove-St. Philips, (Newfoundland), Canada, A1M 2B7 |
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Abstract: | This study investigated the influence of environmental factors on the foraging cycle, breeding activity, settlement and growth
of the opisthobranch Hydatina
physis using laboratory trials and field observations. Results showed that H. physis follows a nocturnal circadian rhythm mediated by photic intensity and modulated by food availability. The adults foraged
between 1900 and 0530 h, with an activity peak between 2000 and 2200 h, and remained inactive and burrowed in the sand during
the day. This pattern was clearly influenced by cloud cover, rain and laboratory manipulated light:dark cycle. The reproduction
of H. physis was primarily influenced by the lunar cycle. For 4 consecutive months, hermaphroditic reciprocal copulation, preceded by
pre-copulatory courtship behaviour, occurred at night 5–7 d before the full moon. Spawning occurred 3–5 d later for up to
5 consecutive nights, the egg mass gradually decreasing in size with each spawning. An overcast sky or rain prevented or delayed
both copulation and egg release. Settlement of veligers was largely influenced by the nature of the substrate. In multiple-choice
experiments, settlement occurred predominantly on sand containing cirratulid polychaetes. The juveniles reached ca. 3.9 mm
in shell length after 5.5 months growth. |
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Keywords: | Hydatina copulation spawning settlement reproduction |
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