Abstract

Abstract. Synchronised reproduction offers clear benefits to planktonic foraminifera – an important group of marine calcifiers – as it increases the chances of successful gamete fusion. Such synchrony requires tuning to an internal or external clock. Evidence exists for lunar reproductive cycles in some species, but its recognition in shell flux time series has proven difficult, raising questions about reproductive strategies. Using spectral analysis of a 4-year time series (mostly at weekly resolution) from the northern Gulf of Mexico, we show that the shell flux of Globorotalia menardii, Globigerinella siphonifera, Orbulina universa, Globigerinoides sacculifer, Globigerinoides ruber (both pink and white varieties), Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globigerinella calida and Globigerinita glutinata is characterised by lunar periodicity. However, the lunar rhythm is not present in all size fractions of each species and tends to be more dominant in the flux of larger shells, consistent with reproduction being more prevalent in larger specimens. Lunar periodicity is superimposed on longer term/seasonal changes in the shell fluxes, but accounts for a significant part of the variance in the fluxes. The amplitude of the lunar cycle increases roughly proportional with the magnitude of the flux, demonstrating that most of the population is indeed affected by lunar-phased synchronisation. In most species peak fluxes occur predominantly around, or just after, full moon. Only G. siphonifera and G. calida show a contrasting pattern with peaks concentrated around new moon. Although the exact cause of the synchronisation remains elusive, our data considerably increase the number of species for which lunar synchronised reproduction is reported and suggest that such reproductive behaviour is common in many species of planktonic foraminifera.

Highlights

  • Planktonic foraminifera reproduce by releasing large amounts of gametes (Bé et al, 1977; Spindler et al, 1978)

  • This is clearest in the shell flux of Globorotalia menardii, which peaks around full moon and G. siphonifera, which seems to peak preferentially around new moon (Fig. 1)

  • In almost all species peaks in the shell flux occur around full moon and/or in the week following full moon, suggesting that reproduction occurs in response to the same trigger

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Summary

Introduction

Planktonic foraminifera reproduce by releasing large amounts of gametes (Bé et al, 1977; Spindler et al, 1978). Reproductive synchrony requires the existence of an internal biological clock or an external trigger for reproduction. In their seminal work, Spindler at al. Gamete release in Hastigerina pelagica in laboratory culture occurs with lunar periodicity approximately 5 days after each full moon (Spindler et al, 1979). Synchronised gamete release was not observed in other species kept in the same laboratories (Hemleben et al, 1989). Lunar and semi-lunar periodicity was subsequently observed in nature in the abundance and test size of several species.

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