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he reproductive cells are found on the several weeks. They are vulnerable to pre- by fishing, especially bottom trawling and

T mesentery membranes that radiate in- dation and environmental conditions. The dredging. In typical groundfish trawling, a
ward from the layer of tissue that lines the lucky few planulae which successfully attach large net is dragged across the ocean floor,

stomach cavity. Some mature adult corals to substrate next confront competition for its mouth held open by two 2-tonne doors

are hermaphroditic; others are exclusively food and space. called otterboards. The siliceous skeleton of

male or female. A few species change sex O ver 4,000 species of fish inhabit coral the sponges is fragile, and these organisms
as they grow. Internally fertilized eggs de- reefs. The vast majority occupy the Mid are easily broken by physical impact. While
velop in the polyp for a period ranging from less harmful, hook and line fishing as well

days to weeks. Subsequent development Reef zone. Healthy reefs can produce up to as crustacean trapping may also damage the

produces a tiny larva, known as a planula. 35 tons of fish per square kilometer each reefs. When the fishing gear is hauled to the

Externally fertilized eggs develop during year, but damaged reefs produce much less. surface, the lines and traps drag along the

synchronized spawning. Polyps release eggs Much attention in marine biology is focused ocean floor and have the potential to break

and sperm into the water en masse, simul- on coral reefs and the El Niño weather phe- corals and sponges. Broken sponge “stumps,”

taneously. Eggs disperse over a large area. nomenon. In 1998, coral reefs experienced as well as those with abraded sides, were

The timing of spawning depends on time the most severe mass bleaching events on found in regions where line and trap fishing

of year, water temperature, and tidal and record, when vast expanses of reefs across took place.

lunar cycles. Spawning is most successful the world died because sea surface tem- C oral reef animals use many different
when there is little variation between high peratures rose well above normal. Some forms of protection. Some hide in the
and low tide. The less water movement, the reefs are recovering, but scientists say that

better the chance for fertilization. Ideal tim- between 50% and 70% of the world’s coral sand, others hide among the coral. Some

ing occurs in the Spring. Release of eggs or reefs are now endangered and predict that swim into the lagoon and hide among the

planula usually occurs at night, and is some- global warming could exacerbate this trend. mangrove roots while others swim in schools

times in phase with the lunar cycle (three to The Shallow Shore and the Mid Reef are the along the reef face. Some eject poison while

six days after a full moon). The period from most susceptible to such beaching events others inflate themselves to a much larger

release to settlement lasts only a few days, because of the shallower depths they ex- size.

but some planulae can survive afloat for ist at. The reefs are susceptible to damage