Lunar Reproductive Cycles of Benthic‐Brooding Reef Fishes: Reflections of Larval Biology or Adult Biology?

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Abstract
Lunar reproductive cycles are common among marine animals. Most hypotheses concerning the adaptive nature of such cycles consider the effects of the tidal regime or moonlight on the dispersal of planktonic eggs or hatchlings away from adult habitats. We determined the reproductive periodicity of 17 paternal—brooding reef fishes at three neotropical sites with different tidal regimes. We used these and published data to assess the explanatory potential of hatchling—dispersal hypotheses, and of other larval—biology and adult—biology hypotheses. Among the 17 species (15 damselfishes and two blennies), two of which we studied at two sites, we found 14 with lunar and semilunar spawning cycles, one sporadically synchronized spawner, two acyclically variable spawners, and one continuous spawner. In 16 species individual nests experienced frequent alternation of short brood—care and rest periods (brood cycling). Simple hatchling—biology hypotheses are unable to account readily for the range of variation in the types, precision, and lunar timing of spawning cycles among species within and between depth zones at the same site, or for intra— and interspecific variation in spawning patterns in relation to seasonal and geographic differences in tidal regimes. The hypothesis that lunar spawning cycles have evolved to maximize the availability of relatively uniform—age larvae that settle during preferred lunar settlement times is supported by some but not all data. Adult—biology hypotheses can account for the higher frequency of lunar spawning cycles among brooders than nonbrooders, and can accommodate various patterns of reproductive cyclicism and synchronization in brooders. Synchronized activity may be favored in some brooders because colonial spawning provides enhanced defense against egg predators. Further, the cost of brood care may result in reduced egg survivorship, and both brood cycling and the temporal concentration of spawning may reduce egg losses by allowing males to recuperate and increasing benefits to brood—care for them. Adult—biology constraints may produce variability in spawning patterns. Differences in social systems may determine the ability to form nesting colonies, and to strongly synchronize spawning independently of lunar cues. Changes in short—term food availability may influence the regularity of spawning. Adult—biology hypotheses represent generally underemphasized alternatives that have at least as much explanatory potential as larval—biology hypotheses. If hatchling biology is of general importance to paternal brooders, there must be considerably more interspecific variability in hatchling ecology than is generally assumed.