The recent calm days on the ocean might be good for diving and boating, but they are beginning to take their toll on the coral reef.
Many corals off the Florida Keys have begun to show signs of bleaching and paling, scientists and divers said.
The major bleaching currently only seems to be happening in the smaller finger corals and lettuce corals, biologists said. Some of the tips of the staghorn corals have begun to bleach, but most of the larger elkhorn and boulder corals are still healthy and not affected.
"We are getting to a real critical stage," said coral biologist Ken Nedimyer, who founded the Coral Restoration Foundation in Tavernier. "As nice as it has been for the dive community, it's taking its toll. Wind and rain is really what we need."
Nedimyer remained optimistic, stating that the days are becoming shorter, which would mean less heat stress for corals.
Cory Walter, a Mote Marine Laboratory coral biologist who oversees the Bleach Watch program in the Keys, said some areas of the Florida Keys National Sanctuary waters are under bleaching watch and warnings, which means the thermal stress is starting to occur.
"Many of the inshore patch reefs are starting to show signs of stress," Walter said.
She is asking the public's help in reporting bleaching. Divers can report what they are seeing at Mote's website at www.mote.org/bleachwatch.
Extremely warm water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae, called zooxanthellae, living in their tissues, causing the coral to turn completely white. Corals can survive a bleaching, but they are under more stress and are subject to mortality and disease.
However, not all bleaching is tied to warm-water events. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching that resulted in some coral death.
The bleaching also comes at a time when divers are reporting a strange temperature inversion in which the water at the bottom is considerably hotter than at the surface, and it is also a "thick green color," Lower Keys spear fisherman Don DeMaria said.
DeMaria was diving the reef off Summerland Key earlier this month when he witnessed the temperature inversion. During a 90-foot dive, the water on the surface was fairly clear and not too terribly hot. But as he descended, the water temperature became much warmer and visibility dropped to about eight feet on the bottom.
During his second dive in Hawks Channel, in about 40 feet, the water was somewhat clear on the surface and not too terribly warm, but it got warmer as he descended, he said. The water was 88 degrees on the bottom, "uncomfortably warm, poor visibility and greenish," he said.
Hawks Channel runs between the reef and the entire islands of the Florida Keys from Key Largo to Key West.
"There was a lot of bleached coral in Hawks Channel," DeMaria said. "Even the inshore more hardy corals are bleaching now. The water is just still and hot."
The temperature inversion occurs when water coming out of the Everglades and into Florida Bay has high concentrations of salinity, because the fresh water is evaporating at a rate much faster than usual. This occurs because of the lack of rain and fresh water flowing out of the Everglades and into Florida Bay and the Keys.
The heavier salty water sinks to the bottom as it travels through Florida Bay and the Keys, making the water at the bottom much hotter and greener than water at the surface, Nedimyer and Florida Fish and Wildlife Institute scientist Luke McEachron said.