Page 204 - Mexico Diving From the Caribbean to Pacific Isles

he reproductive cells are found on the survive afloat for several weeks. They are ble to damage by fishing, especially bottom
vulnerable to predation and environmental trawling and dredging. In typical ground-
T mesentery membranes that radiate in- fish trawling, a large net is dragged across
ward from the layer of tissue that lines the conditions. The lucky few planulae which the ocean floor, its mouth held open by
two 2-tonne doors called otterboards. The
stomach cavity. Some mature adult corals successfully attach to substrate next con- siliceous skeleton of the sponges is fragile,
and these organisms are easily broken by
are hermaphroditic; others are exclusively front competition for food and space. physical impact. While less harmful, hook
and line fishing as well as crustacean trap-
male or female. A few species change sex as O ver 4,000 species of fish inhabit coral ping may also damage the reefs. When the
they grow. Internally fertilized eggs devel- reefs. The vast majority occupy the fishing gear is hauled to the surface, the
op in the polyp for a period ranging from lines and traps drag along the ocean floor
and have the potential to break corals and
days to weeks. Subsequent development Mid Reef zone. Healthy reefs can produce sponges. Broken sponge “stumps,” as well
as those with abraded sides, were found
produces a tiny larva, known as a planula. up to 35 tons of fish per square kilometer in regions where line and trap fishing took
place.
Externally fertilized eggs develop during each year, but damaged reefs produce
C oral reef animals use many different
synchronized spawning. Polyps release much less. Much attention in marine biolo- forms of protection. Some hide in the
sand, others hide among the coral. Some
eggs and sperm into the water en masse, gy is focused on coral reefs and the El Niño swim into the lagoon and hide among
the mangrove roots while others swim in
simultaneously. Eggs disperse over a large weather phenomenon. In 1998, coral reefs schools along the reef face. Some eject
poison while others inflate themselves to a
area. The timing of spawning depends on experienced the most severe mass bleach- much larger size.

time of year, water temperature, and tidal ing events on record, when vast expanses

and lunar cycles. Spawning is most success- of reefs across the world died because sea

ful when there is little variation between surface temperatures rose well above nor-

high and low tide. The less water move- mal. Some reefs are recovering, but scien-

ment, the better the chance for fertilization. tists say that between 50% and 70% of the

Ideal timing occurs in the Spring. Release world’s coral reefs are now endangered and

of eggs or planula usually occurs at night, predict that global warming could exacer-

and is sometimes in phase with the lunar bate this trend. The Shallow Shore and the

cycle (three to six days after a full moon). Mid Reef are the most susceptible to such

The period from release to settlement lasts beaching events because of the shallower

only a few days, but some planulae can depths they exist at. The reefs are suscepti-