Lunar rhythms in growth of larval fish

Growth and survival of larval fishes is highly variable and unpredictable.
Our limited understanding of this variation constrains our ability to
forecast population dynamics and effectively manage fisheries. Here we
show that daily growth rates of a coral reef fish (the sixbar wrasse,
Thalassoma hardwicke) are strongly lunar-periodic and predicted by the
timing of nocturnal brightness: growth was maximized when the first half
of the night was dark and the second half of the night was bright. Cloud
cover that obscured moonlight facilitated a ‘natural experiment’, and
confirmed the effect of moonlight on growth. We suggest that
lunar-periodic growth may be attributable to light-mediated suppression of
diel vertical migrations of predators and prey. Accounting for such
effects will improve our capacity to predict the future dynamics of marine
populations, especially in response to climate-driven changes in nocturnal
cloud cover and intensification of artificial light, which could lead to
population declines by reducing larval survival and growth.
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