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

Abstract

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