Page 62 - French Polynesia

he reproductive cells are found on the some planulae can survive afloat for several ble to damage by fishing, especially bottom
weeks. They are vulnerable to predation trawling and dredging. In typical ground-
T mesentery membranes that radiate in- and environmental conditions. The lucky fish trawling, a large net is dragged across
few planulae which successfully attach to the ocean floor, its mouth held open by
ward from the layer of tissue that lines the substrate next confront competition for two 2-tonne doors called otterboards. The
stomach cavity. Some mature adult corals food and space. siliceous skeleton of the sponges is fragile,
are hermaphroditic; others are exclusively and these organisms are easily broken by
male or female. A few species change sex as O ver 4,000 species of fish inhabit coral physical impact. While less harmful, hook
they grow. reefs. The vast majority occupy the and line fishing as well as crustacean trap-
Mid Reef zone. Healthy reefs can produce ping may also damage the reefs. When the
I nternally fertilized eggs develop in the up to 35 tons of fish per square kilometer fishing gear is hauled to the surface, the
polyp for a period ranging from days to each year, but damaged reefs produce lines and traps drag along the ocean floor
weeks. Subsequent development produces much less. Much attention in marine biolo- and have the potential to break corals and
a tiny larva, known as a planula. Externally gy is focused on coral reefs and the El Niño sponges. Broken sponge “stumps,” as well
fertilized eggs develop during synchronized weather phenomenon. In 1998, coral reefs as those with abraded sides, were found
spawning. Polyps release eggs and sperm experienced the most severe mass bleach- in regions where line and trap fishing took
into the water en masse, simultaneously. ing events on record, when vast expanses place.
Eggs disperse over a large area. The timing of reefs across the world died because sea
of spawning depends on time of year, water surface temperatures rose well above nor- C oral reef animals use many different
temperature, and tidal and lunar cycles. mal. Some reefs are recovering, but scien- forms of protection. Some hide in the
Spawning is most successful when there is tists say that between 50% and 70% of the sand, others hide among the coral. Some
little variation between high and low tide. world’s coral reefs are now endangered and swim into the lagoon and hide among
The less water movement, the better the predict that global warming could exacer- the mangrove roots while others swim in
chance for fertilization. Ideal timing occurs bate this trend. The Shallow Shore and the schools along the reef face. Some eject
in the Spring. Release of eggs or planula Mid Reef are the most susceptible to such poison while others inflate themselves to a
usually occurs at night, and is sometimes in beaching events because of the shallower much larger size.
phase with the lunar cycle (three to six days depths they exist at. The reefs are suscepti-
after a full moon). The period from release
to settlement lasts only a few days, but