Life on the Great Barrier Reef is shaped by the rhythms of the tide and the rhythms of day and night. The assortment of animals that are active on the reef at any given time reflect the dynamics of the reef itself.
Only those best adapted to take advantage of the unique opportunities available to them on the reef at any given time will survive. To begin to understand the rhythms of the reef is to begin to understand how the many lifeforms of the reef coexist, interact, and flourish.
Dawn on the Great Barrier Reef
In the early morning hours when tides are low, birds come out and hunt the exposed areas of the reef. When the tide is low, tips of corals are naked above the surface and pockets of water trap a variety of organisms in shallow water where birds such as grey reef egrets and silver gulls can capture an early morning feast of small fishes, shellfish, and invertebrates.
Underwater, nocturnal fishes and invertebrates seek the cover of dark crevases and overhangs as the dawn light seeps through the water. They stay hidden away until the daytime sun subsides and they can again come out in the cover of darkness.
In contrast, fish that are active during the day such as wrasses and goatfishes slowly emerge from their nighttime hiding spots and start their search for food.
The Midday Feast
By midday, the species active during the sunlight hours are in full force. Scores of species feast on plankton and other fishes along the coral slope. The diversity of fishes out and about during the day is astonishing, as many as 150 species can be packed into a space of just 100 square meters.
Dusk Descends on the Reef
As the afternoon sun falls low in the sky, dusk settles over the reef. Fishes such as sweetlip emperors and paddle-tail hussars venture out in the dimming light to forage. Schools of daytime fish tighten and descend, seeking cover from emerging predators.
Darkness Envelops the Underwater World
As dusk gives way to the darkness of night, sharks such as the grey reef shark and the white-tipped reef shark emerge at the reef's edge and seek their prey. Sharks are well adapted for nighttime hunting. Their eyes function well in dim light and they have sensitive skin that enables them to detect movements in the nearby water.
Sources
- 'Visitor's Guide to the Great Barrier Reef', Reader's Digest. New York, 1988.
