Biology This is how the moon synchronises the reproduction of corals
In order for the egg and sperm cells of corals from different colonies to mix, all animals of one species must spawn at the same time. And the moon plays a crucial role in synchronising this process.
Corals are modular creatures whose colonies are often spaced several hundred metres apart. In order to maintain the genetic diversity and reef health, it’s vital that the egg and sperm cells of different colonies mix with each other during sexual reproduction. This requires that they spawn simultaneously at a certain point in time. Together with students and teachers from the local university, marine biologist Dr. Mareike Huhn from the Department of General Zoology and Neurobiology at Ruhr University Bochum, Germany, is researching how corals synchronise on the Banda Islands in the Indonesian Indo-Pacific.
To this end, the researchers match the time of spawning with various environmental factors. What is the tide like on the day in question? What are the mean water temperatures and the length of the day? When does the moon rise and set on that day? Is it full moon or new moon?
Several factors come into play
“There must be several triggers,” as Mareike Huhn sums up her observations. “Before a coral can spawn, the eggs have to mature in it for several weeks. The onset of this maturation process must also be triggered somehow – and this must happen for all corals of a species at the same time. And then the timing of the actual spawning must be triggered synchronously,” elaborates Huhn.
The researchers’ records provided answers to these riddles: according to them, environmental factor number one that triggers egg maturation is the water temperature. It always rose exactly one month before spawning. The relative increase in the surface temperature of the water, which must rise by 0.5 to one degree Celsius within four weeks, and the total temperature, which must be between 28 and 30 degrees, both play a role.
The full moon calls the shots
But how do the corals, some of which are spaced several hundred metres apart, synchronise the exact night of spawning? “The moon plays a major role in this process, as the animals perceive its light via light receptors on the surface of their bodies,” explains Mareike Huhn. “Corals here always spawn five, six or seven days after the full moon. The exact number of days depends on the type of coral.”
The findings so far help the researchers gain a better understanding of the corals’ lives. This is essential because coral reefs play a major role in maintaining a healthy environment. They, for example, provide a habitat for countless sea creatures, and the algae that live in them produce a considerable percentage of the oxygen that makes life on Earth possible.