English: Figure 1  The emergence of complex rhythms from solar and lunar cycles in marine ecosystems. (a) Earth and the moon as seen from space. Arrows highlight coordinates used in panels d–f. (b,c) Summary of weekly solar and lunar photocycles, with the perimeter indicating hours of the day and concentric circles representing consecutive days (1–7). The daily cycles of solar light cause the well-known diel light cycle of ∼24 h. The gradual shifts of moonrise and moonset cause an independent lunidian photocycle, with an average period of ∼24.8 h. Twilight is not included. (d–f) Exemplary 7-day diagrams covering one month (new moon, waxing moon, full moon, and waning moon) around the summer (top) and winter (bottom) solstices at three distinct coastal locations at different latitudes, illustrating the complexity of superimposed solar and lunar light cycles. Twilight is not included. (g) Overview of the period lengths of major natural cycles and the associated (endogenous) biological rhythms generated by the solar (top) and lunar (bottom) photocycles. (h) Period lengths of major natural cycles and associated biological rhythms generated by the lunar gravitational cycles. Tidal cycles have a basic period length of half a lunar day (∼12.4 h), while the mutual constellation of the sun, the moon, and Earth also causes a longer cycle (semilunar, ∼14.8 days, spring tides). Image in panel a created by Reto Stockli with the help of Alan Nelson, under the leadership of Fritz Hasler, and reproduced from NASA's Visible Earth catalog (https://visibleearth.nasa.gov/images/54388/earth-the-blue-marble)