MEPS 329:179-189 (2007)  -  doi:10.3354/meps329179

Long-term study of gamete release in a broadcast-spawning holothurian: predictable lunar and diel periodicities

Annie Mercier1,*, Roberto H. Ycaza2, Jean-François Hamel1,3

1Ocean Sciences Centre (OSC), Memorial University of Newfoundland, St. John’s, Newfoundland A1C 5S7, Canada
2Investigaciones Especies Acuaticas (IEA), Klm 1012 Via San Pablo, Santa Elena, Ecuador
3Society for the Exploration and Valuing of the Environment (SEVE), 21 Phils Hill Road, Portugal Cove-St. Philips, Newfoundland A1M 2B7, Canada

ABSTRACT: Annual and monthly patterns of gamete release by the sea cucumber Isostichopus fuscus on the coast of Ecuador were studied to determine the proximal spawning cue and variations in reproductive output throughout the year. Several hundred newly collected individuals were monitored nearly every month for 4 yr. I. fuscus displayed a lunar spawning periodicity: 0.7 to 34.9% of individuals consistently spawned 1 to 4 d after the new moon. Spawning mostly occurred within one evening; however, some gamete release was often recorded over 2 to 4 consecutive evenings. Individuals maintained in captivity for several months retained their spawning periodicity and timing with the lunar cycle. Conversely, newly caught individuals that were shaded from the moonlight did not spawn, thus demonstrating the apparent lack of endogenous rhythms and prevalence of lunar luminance over other cues (i.e. tidal cycle, fluctuations in barometric pressure). On a spawning night, males typically initiated gamete release around sunset; females spawned just after the peak male broadcast. The percentage of spawning individuals was higher and a greater overlap between male and female peak spawning activity was observed during clear conditions compared with overcast conditions. The gonads of individuals that did not spawn in a given month showed a variety of maturity levels, including post-spawning, growth and mature gametogenic stages. Hence, the individual reproductive cycle is apparently longer than the monthly spawning periodicity observed at the population level, enabling I. fuscus populations to be reproductive year round.

KEY WORDS: Spawning · Periodicity · Lunar cycle · Reproductive synchrony · Holothurian · Echinoderm · Isostichopus fuscus

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