The Ocean and the Full Moon

Lunacy and the madness associated around the moon, particularly the full moon, is a theme in many cultures’ folklore. However, they had a good reason to be a bit creeped out by the cycle of the moon. Why? Well, it did and continues to affect animals in strange ways. In particular, the moon seems to have a distinct pull among the creatures of the ocean.

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Marine animals during the full moon seem to have a certain drive towards the unexplored and perhaps even the uncomfortable. For example, during full moons, grey reef sharks are more likely to stay submerged in deeper and deeper water but during new moons, they are brought back towards the surface. The greatest depths swum by these sharks, over a three year period, usually aligned with the full moon. Perhaps it is because of a weekly change in where the shark’s food is going...but perhaps they are pulled by something other than prey. If it isn’t prey...then what could it be?

It also seems that the full moon brings forth a particular kind of lunacy in animals looking to mate. Although it only happens once a year the mass coral spawning on Australia’s Great Barrier Reef seems intrinsically tied to the full moon. In a synchronized fashion, usually aligning with a full moon, the corals spawn and this mass spawning increases the odds that the free-floating eggs and sperm will come into contact. Interestingly enough, researchers have found that if the sky is cloudy and the moon is obscured the corals will not spawn when regularly schedule and may even wait until the next full moon. How do they know when that is? Well, corals have light-sensitive neurons that are aware of the wavelengths of light that the moon shines. This ability matched with genes that sync their activity levels with the waxing and waning moon.

Crabs also seem to feel the need to mate under a full moon. It is believed that Christmas Island Crabs are pulled from the forest to the sea to mate and lay their eggs under a full moon. Seasarma crabs from Japan also head towards sea-flowing rivers where they release their eggs and sperm in alignment with the moon’s cycles. Even the strange, ancient-looking horseshoe crabs are not impervious to the full moon and come ashore only on certain nights to mate.

National Geographic recently covered french researchers that monitored the opening and closing of oysters over a 3.5-month period. It was discovered that two types of oysters in the Arcahon Bay closed significantly when the moon was full and opened up quite a bit more during a new moon. It also appeared as if “the oysters could tell the difference between the first quarter moon and the third quarter moon, and were significantly more open (by nearly 20 percent) at the latter.”

Why do they do this? Researchers aren’t quite sure and there doesn’t seem to be an easy answer. Like the sharks swimming deeper, it could have to do with prey patterns. But, it could just as easily be something else that we don’t quite know (or understand) yet.

It is fascinating to me the power of the moon. The moon does not produce light or heat of its own. It cannot sustain the earth. However, without it, it seems that the patterns of the earth would almost certainly crumble. Just through looking through the moon’s power is all-powerful and irreplaceable when it comes to the lives in our seas.

Coral by night, North Horn, Coral Sea Great Barrier Reef, Australia by Cory Doctorow. Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0)