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he reproductive cells are found on the lease to settlement lasts only a few days, but because of the shallower depths they ex-
some planulae can survive afloat for several ist at. The reefs are susceptible to damage
T mesentery membranes that radiate in- weeks. They are vulnerable to predation and by fishing, especially bottom trawling and
environmental conditions. The lucky few dredging. In typical groundfish trawling, a
ward from the layer of tissue that lines the planulae which successfully attach to sub- large net is dragged across the ocean floor,
stomach cavity. Some mature adult corals strate next confront competition for food its mouth held open by two 2-tonne doors
are hermaphroditic; others are exclusively and space. called otterboards. The siliceous skeleton of
male or female. A few species change sex as the sponges is fragile, and these organisms
they grow. O ver 4,000 species of fish inhabit coral are easily broken by physical impact. While
reefs. The vast majority occupy the Mid less harmful, hook and line fishing as well
I nternally fertilized eggs develop in the Reef zone. Healthy reefs can produce up to as crustacean trapping may also damage the
polyp for a period ranging from days to 35 tons of fish per square kilometer each reefs. When the fishing gear is hauled to the
weeks. Subsequent development produces year, but damaged reefs produce much less. surface, the lines and traps drag along the
a tiny larva, known as a planula. Externally Much attention in marine biology is focused ocean floor and have the potential to break
fertilized eggs develop during synchronized on coral reefs and the El Niño weather phe- corals and sponges. Broken sponge “stumps,”
spawning. Polyps release eggs and sperm nomenon. In 1998, coral reefs experienced as well as those with abraded sides, were
into the water en masse, simultaneously. the most severe mass bleaching events on found in regions where line and trap fish-
Eggs disperse over a large area. The timing record, when vast expanses of reefs across ing took place. Coral reef animals use many
of spawning depends on time of year, wa- the world died because sea surface tem- different forms of protection. Some hide
ter temperature, and tidal and lunar cycles. peratures rose well above normal. Some in the sand, others hide among the coral.
Spawning is most successful when there is reefs are recovering, but scientists say that Some swim into the lagoon and hide among
little variation between high and low tide. between 50% and 70% of the world’s coral the mangrove roots while others swim in
The less water movement, the better the reefs are now endangered and predict that schools along the reef face. Some eject
chance for fertilization. Ideal timing occurs global warming could exacerbate this trend. poison while others inflate themselves to a
in the Spring. Release of eggs or planula The Shallow Shore and the Mid Reef are the much larger size.
usually occurs at night, and is sometimes most susceptible to such beaching events
in phase with the lunar cycle (three to six
days after a full moon). The period from re-
