Another place, another timer: Marine species and the rhythms of life

Abstract

The marine ecosystem is governed by a multitude of environmental cycles, all of which are linked to the periodical recurrence of the sun or the moon. In accordance with these cycles, marine species exhibit a variety of biological rhythms, ranging from circadian and circatidal rhythms to circalunar and seasonal rhythms. However, our current molecular understanding of biological rhythms and clocks is largely restricted to solar-controlled circadian and seasonal rhythms in land model species. Here, we discuss the first molecular data emerging for circalunar and circatidal rhythms and present selected species suitable for further molecular analyses. We argue that a re-focus on marine species will be crucial to understand the principles, interactions and evolution of rhythms that govern a broad range of eukaryotes, including ourselves.

Figure 1

Common biological rhythms under solar and lunar influence. The overview lists a given biological rhythm (left), along with the corresponding environmental cycle (middle) and the periodicity of this environmental cycle (right). For simplicity, no distinction is made between the synodic (29.5 days) and the sidereal (27.3 days) lunar period. For additional terminology, see Box 1.

Figure 2

Lunar-controlled rhythms are widespread and of fundamental importance for marine organisms. Simplified phylogeny of metazoan groups with representatives exhibiting moon-controlled rhythms. In most mentioned cases evidence for a free-running lunar clock mechanism exist. Note that it is likely that all the mentioned species also possess a circadian clock and many also exhibit seasonality. All mentioned groups represent marine species. Lunar-controlled rhythms have also been described outside metazoans in green and brown algae (bottom) , –, , , , .

Figure 3

Habitat and rhythms of S. roscoffensis. A-B: Shallow coastal areas in Roscoff (France) during high and low tide periods, either covering or exposing the natural habitat of S. roscoffensis. C: During normal tide fluctuations over 24-hour periods (blue line), S. roscoffensis migrate to the surface of the sand or stay burrowed during low and high tides, respectively (red line). This process is dependent on the presence of sunlight (yellow line). D: In summer months, when long days overlap two low tide periods, S. roscoffensis migrate twice a day to expose themselves to sunlight. (C, D: after 88).