Nighttime on the Reef

Many corals feed at night and divers can lure light-sensitive plankton into the extended coral polyps with a dive light trained on one coralhead and watch the feeding process. In the water column your light will pick up the odd shapes of small jellyfish, microscopic plankton, and tiny self-propelled organisms twisting and pulsating in the light. Turn the light off and see the bioluminescent animals shining with their chemically generated light, trailing behind your sweeping arm movement.

Basket stars unfold and nocturnal crinoids, having crawled out from their daytime crevices, feed by extending their arms into the current. Sea urchins emerge from their holes and march about the reef borders, grazing on algae and creating bare pathways as they go. Brittle stars and small shrimp and crabs are often seen, as are bristleworms out eating coral polyps or munching on anemones. This is the time to look for active octopuses, lobster, giant crabs, and large annelid worms. Hermit crabs are usually everywhere, scavenging the reef in their clumsy, borrowed shells.

About an hour before dawn, a reversal of the evening transition begins. Schools of foraging goatfish, snappers, grunts, sweepers, squirrelfish, and drums reassemble from the sandy and rock bottom surrounding the reef and prepare to make their mass transit back to daytime resting valleys and crevices. Plankton eaters, some in groups and some one by one, scurry back to bed in coral recesses as the night sleepers awaken.
© 2004 Linda Gettmann

Go To Page: 1 2