Page 188 - Hawaii: Diving, Surfing, Pearl Harbor, Volcanoes and More

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