November 11, 2013 at 11:00 pm #972MikeKeymaster
Warm waters bleaching reefs
The loss of color of some of Florida’s reefs, caused by weeks of hot
weather, indicates the system is under stress and in danger.
BY CURTIS MORGAN
The vibrant colors of Florida Keys reefs have begun to fade in recent
weeks, a sign scientists hope doesn’t erupt into serious coral
Bleaching, triggered by extended weeks of hot and calm weather,
doesn’t immediately kill coral but can weaken it, slowing growth and
reproduction and leaving already fragile colonies more vulnerable to
assorted diseases, pollution and even the accidental brush of a
The last widespread bleaching preceded coral die-offs that killed
about 30 percent of the reef tract, said Cheva Heck, spokeswoman for
the Florida Keys National Marine Sanctuary.
”If it does go on for too long, the coral may actually die,” she
With reef-building hard corals already reduced to a small fraction of
their historic range by near and far pressures — including sewage
seeping out of aging Keys cesspits and global warming — another
widespread loss would be devastating biologically and economically
for the Keys and North America’s largest living reef system.
Hurricane Katrina, which wreaked so much human havoc, offered a brief
respite for reefs, dumping enough rain to temporarily cool coastal
waters, said Brian Keller, science coordinator for the sanctuary.
Ocean temperatures dropped from a hot-tubbish near-90 degrees to 84
degrees, warm but not so potentially damaging.
Still, Keller cautioned, the relief may be short term, and the threat
”I’m pretty pleased that we’re getting this break in the thermal
stress,” he said,
but we still have a lot of warm months ahead.” An early warning of the threat came from a new Coral Bleaching Early Warning Network established this year. The effort, coordinated by the National Oceanic & Atmospheric Administration and Mote Marine Laboratory Branch on Summerland Key, combines both high-tech monitoring with firsthand observation. SATELLITE SYSTEM In July, the NOAA created an online satellite system that monitors ocean temperatures and automatically sends out hot-spot e-mail warnings to scientists, sanctuary managers and others who monitor 24 shallow coral reefs around the world. In the Keys, they’re being combined with ”BleachWatch” reports filed by a team of volunteer observers, including dive operators, trained to spot symptoms. There’s not a lot the network can do to reverse bleaching, but scientists hope the alerts will provide a better sense of the impact. The satellite first alerted for potential problems four weeks ago. Last week, Mote biologist Cory Walter saw enough to raise the bleaching threat to ”high.” It was lowered to ”moderate” Aug. 30. Satellites showed water temperatures as steamy as they had been since 1998, year of the last big coral loss. And 16 observers reported isolated ”paling” or partially bleached coral colonies. Seven others reported significant bleachings. Walter said the impact varies depending on the types of coral, water depths and the type of reef community. ”Right now, we’re seeing the inshore patch reefs are pretty much paling overall,” she said. Scientists say the phenomenon typically hits when water temperatures stay too high for too long. Corals begin to shed an algae called zooxanthellae, which lives in a symbiotic relationship with polyps, the living tissue within hard coral skeletons. Because the algae provides the rainbow hues of a reef, any affected corals will begin to appear duller and can turn a stark bone-white. They remain healthy for a time and can rebound if conditions change, Walter said, but die-offs are common after extended bleachings. Keller said a team on a 10-day research dive observed symptoms as far north as Carysfort Reef off North Key Largo down through Looe Key near Marathon into the Western Sambos off Key West and to the Dry Tortugas. TELLTALE SIGNS The most telltale indications were from what Keller called ”the canaries in the coal mine” — fire coral, anemones and other corals that typically are affected earliest by bleaching. Fire corals also have begun turning white as far north as the patch reefs behind Elliott Key in Biscayne National Park. Mote hopes to expand the volunteer observer network to cover the reefs off Miami- Dade County, the northernmost tip of the reef tract. ”We saw extensive what we would call coral paling, meaning the loss of some of the color, from all the major reef-building corals,” Keller said.
Anytime you see that, it shows the reef system is
under considerable stress.”’
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