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Moonrise timing is key for synchronized spawning in coral Dipsastraea speciosa - PubMed

  • ️Fri Jan 01 2021

Moonrise timing is key for synchronized spawning in coral Dipsastraea speciosa

Che-Hung Lin et al. Proc Natl Acad Sci U S A. 2021.

Abstract

Synchronized mass coral spawning typically occurs several days after a full moon once a year. It is expected that spawning day is determined by corals sensing environmental change regulated by the lunar cycle (i.e., tide or moonlight); however, the exact regulatory mechanism remains unknown. Here, we demonstrate how moonlight influences the spawning process of coral, Dipsastraea speciosa When corals in the field were shaded 1 and 3 d before the full moon or 1 d after the full moon, spawning always occurred 5 d after shading commenced. These results suggest moonlight suppresses spawning: a hypothesis supported by laboratory experiments in which we monitored the effects of experimental moonlight (night-light) on spawning day. Different night-light treatments in the laboratory showed that the presence of a dark period between day-light and night-light conditions eliminates the suppressive effect of night-light on spawning. In nature, moonrise gets progressively later during the course of the lunar cycle, shifting to after sunset following the day of the full moon. Our results indicate that this period of darkness between sunset and moonrise triggers synchronized mass spawning of D. speciosa in nature.

Keywords: coral; moonlight; reproduction; spawning mechanism; synchronized.

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Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.

Spawning day of D. speciosa in the field manipulation experiment. (A) Study location at Lyudao (Green Island), Taiwan. The white dot indicates Gonggan, where D. speciosa fragments were collected and the field observation and experiment were conducted. (B) An egg trap in a transparent plastic bag and (C) an egg trap in an aluminum foil bag. (D) Spawning in natural populations of D. speciosa (>10 colonies) at the study location and (E) spawning of D. speciosa fragments under the moonlight-blocking treatment commencing at 3 d before the full moon (panel 1), 1 d before the full moon (panel 2), and 1 d after the full moon (panel 3). Black bars indicate major spawning (>hundreds of eggs), and white bars indicate minor spawning (several eggs) in four replicate fragments. Note that “NA” indicates no observation. Different letters in the panels in E indicate significant differences between the treatments (ANOVA and Tukey HSD test; P < 0.001). For detailed results of statistical analysis, refer to

SI Appendix, Table S2

.

Fig. 2.
Fig. 2.

Spawning day of D. speciosa under different moonlight exposure days. (A) The design of one experimental unit, including four replicate tank systems for each experimental treatment. (B) D. speciosa fragments were exposed to three experimental moonlight (dim light [∼0.3 lx]) conditions with different exposure days at nighttime (18:30 to 05:00): no light treatment (panel 1), 2-d exposure treatment (panel 2), and 4-d exposure treatment (panel 3). Black bars indicate major spawning (>hundreds of eggs), and white bars indicate minor spawning (several eggs) in four replicate fragments. Different letters in the panels indicate significant differences between the treatments (ANOVA and Tukey HSD test; P ≤ 0.001). For detailed results of statistical analysis, refer to

SI Appendix, Table S2

.

Fig. 3.
Fig. 3.

Spawning of D. speciosa under different moonlight exposure hours. D. speciosa fragments were exposed to four experimental moonlight conditions (dim light [∼0.3 lx]) with different exposure hours at nighttime (18:30 to 05:00) for the first 4 d of the experiment: no light (panel 1), dim light in 18:30 to 05:00 (panel 2), dim light in 18:30 to 00:00 (panel 3), and dim light in 00:00 to 05:00 (panel 4). Black bars indicate major spawning (>hundreds of eggs), and white bars indicate minor spawning (several eggs) in four replicate fragments. Different letters in the panels indicate significant differences between the treatments (ANOVA and Tukey HSD test; P < 0.001). For detailed results of statistical analysis, refer to

SI Appendix, Table S2

.

Fig. 4.
Fig. 4.

Schematic relationship of sunset and moonrise time regulate the spawning behavior in D. speciosa. (A) Sunset and moonrise time in Lyudao during the spawning season, periods from April 4th to April 12th (4 d before full moon to 4 d after full moon), 2020, were shown as an example. Moonrise occurs prior to sunset before the full moon day (April 8th), whereas moonrise occurs following sunset after the full moon day. Note that sunset time changes from 18:11 on April 4th to 18:14 on April 12th, and moonrise time changes from 14:11 on April 4th to 22:48 on April 12th. (B) Before the full moon day, the presence of moonlight after sunset suppresses the process of spawning. (C) After the full moon day, the presence of darkness after sunset triggers the process of spawning.

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