Coral reefs are full of color easily seen during daytime. But divers who have experienced night diving would know how different and impressive the reefs are at nighttime. Many fish hunt during the day, but there are also many species of fish and critters that hunt at night. During the night, all the diurnal fish have to finds ways to hide, whereas all the nocturnal fish have to find ways to ‘see’ or sense their prey with no or little light – although the full moon does provide light to shallow reefs.
Although night fish have big eyes, they cannot see much color, so nighttime creatures are often less colorful than the daytime animals seen in a reef. For example, the squirrel fish is light red with big eyes that can be seen during the day just chilling near rocks. This fish moves to the nearby grass meadows to feed and use its big eyes to find its prey at night. All the daytime fish are at risk at night from night predators like moray eels and reef sharks. The parrot fish, once very abundant in the reefs of the Riviera Maya, hides in the reefs’ cracks and uses a mucus cover on its entire body that stops other fish from detecting it.
Coral polyps, which are the tiny animals that form the coral reefs, extend their tentacles into the dark waters to catch plankton as it passes by, as many species of plankton often move up from the bottom of the ocean towards the surface at dusk and go back down at dawn. Also, sometimes in some spots you can see the bioluminescence produced by some species of plankton that, when disturbed, produces light, creating an amazing view for those diving in it.
Often, the most fun part of the day-night event happens at dawn and dusk; these transition times are when those fish and critters that were out and about during the day, try to find shelter, and those fish that were asleep during the day, come out and start feeding. Many sharks and rays and other predators have higher activity during these times. So, nighttime is not really a sleepy time in a reef, it’s actually more similar to a big city that never sleeps!