How the moon affects marine animals – S.E.A. Aquarium, Dolphin Island blog

There are many legends associated with the moon, from werewolves to a lady named Chang Er who flew to the moon after consuming an elixir. While these are likely the result of our fascination with the supernatural, here’s something factual: ocean tides are caused by the gravitational pull of the moon. Twice each month at full moon and new moon, the sun, Earth and moon are lined up, producing higher than normal tides.

Now that we know the oceans are affected by the moon, what about its inhabitants? Here are 4 ways the moon affects marine animal behaviour:

Corals spawn

Mass coral spawning is an annual phenomenon that usually occurs over several days to just over a week after a full moon. Depending on location, it happens at different times of year. For example, coral spawning in Curaçao, Netherlands Antilles, normally occurs in September and October. Whereas the same happens at Australia’s Great Barrier Reef in Spring.

Such synchronised spawning help the corals increase the odds that free-floating sperm will contact and fertilise eggs. But this only occurs at night, after rising water temperatures have stimulated the maturation of gametes (the egg and sperm) within the polyps. According to a recent paper by Dr. Howells of the New York University branch in Abu Dhabi, the rising warmth coincided with the northward movement of the seasonal rite. Here’s a video of the corals’ rite of reproduction by Natalia V. Osipova:

Sharks swim deeper

Research by the University of Western Australia’s Ocean’s Institute and the Australian Institute of Marine Science has shown that sharks tend to stay submerged in deep water during a full moon but surface to the shallows with the new moon.

The team tagged 39 grey reef sharks off the coast of Palau, east of the Philippines, and used acoustic telemetry to track their movements for almost three years. Data collected showed that grey reef sharks tend to swim at greater depths through the lunar cycle, with the greatest depths usually coinciding with the full moon. It seems likely that the use of deeper waters during the full moon could be a response to equivalent changes in distribution patterns of their prey.

Fiddler crabs have stronger claw power

Despite their (lack of) size, male sand fiddler crabs have a big powerful claw used for attracting females and for battling rivals over the best burrows.

Findings by US scientists revealed that these oversized claws have greater snapping force around new and full moons. Researchers suggested that such enhanced snapping performance could be driven by the abundance of females searching for a mate. Female numbers peak at these times so that their babies would emerge at the next new or full moon when greater tidal flux could transport them away safely.

Zooplankton migrate

Researchers also found a mass of zooplankton from the surface waters sinking to 50m every 29.5 days during winter, which coincides with the full moon, which is likely an attempt to avert predator hunting by moonlight.

Watch this video on the lunar influence on Artic zooplankton in the polar nights.