Dying sponges offer clues about the `blob'

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Wed, Mar. 27, 2002

Dying sponges offer clues about the `blob'

BY CURTIS MORGAN

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A zone of dying sponges and coral off Key West has suddenly elevated the

formation dubbed ''black water'' from scientific mystery to major

environmental concern.

In the first reliable underwater assessment of impact on marine life, a

commercial diver documented enough damage to raise alarms that the baffling

blob may have left a swath of unseen destruction in its wake as it slowly

drifted from the Gulf of Mexico across Florida Bay over the last few months.

''This certainly sounds like it's the effects of something very nasty going

on,'' Causey, superintendent of the Florida Keys National Marine

Sanctuary, said Tuesday.

The devastated sponges were observed over the weekend in the northwest

channel off Key West by Ken Nedimyer, a member of the sanctuary's advisory

council who collects specimens for the aquarium trade.

''The water was a creepy green at the surface and by the time I got to the

bottom, it was really creepy and dark,'' wrote Nedimyer in an e-mail sent to

the sanctuary and several of scientists studying the curious discoloration.

He noted six species of rope sponge as the hardest hit, with 50 to 75

percent wiped out, as well as a number of other sponges dead or dying. Brain

coral and starfish also seemed to be suffering. Fish in the area seemed

healthy, though curiously unhungry.

''There's a real meltdown occuring down there right now,'' Nedimyer wrote.

Before Nedimyer's report, scientists had not confirmed any toxic effects

from the black water but Nedimyer's observations were serious enough that

the sanctuary planned to dispatch its own divers to survey for more

widespread damage. While the mass described as the color of sewer water is

breaking up and shrinking, at one point it spanned several hundred miles.

While scientists were still sorting through water samples, satellite images,

weather reports and historical studies and observations, the sponge dieoff

is another strong indicator that the culprit is an explosion of some sort of

microscopic plankton, said Keller, the sanctuary's science

coordinator.

During a series of algae blooms that plagued Florida Bay in the mid-1990s,

sponges, which feed by filtering water, were among the first organisms to

go, in vast acres, followed by seagrass beds. Those blooms did not kill

fish, like red tide does, but fish do avoid the areas during outbreaks and

lose forage and shelter until the areas recover, which can take years.

''The fact that it appears to be a fairly selective mortality indicates to

me that it's not like some general toxin in the water column that would kill

everything,'' Keller said.

But Keller agreed it would take more study to issue a definitive word. A

loose-knit team of state, federal and private scientists studying the patch

plans to discuss the data and issue a list of probable causes, perhaps by

week's end.

As of now, ''it's a phenomenon about which we are uncertain,'' said Beverly

, research administrator at the Florida Marine Research Institute in

St. sburg. It could be caused by anything from pollution to some sort

of decaying plant material, perhaps flushed to sea from land.

Scientists at the institute, the Mote Marine Laboratory in the Keys and

Sarasota, and the University of South Florida were all analyzing data. Water

samples have shown medium to high levels of two types of phytoplanktons,

tiny plants so essential to the marine food chain that they're called ''the

grass of the sea,'' said.

''It's eaten by a lot of smaller stages of the fishes,'' she said. They're

normal in sea water but plankton or a variety of them can cause problems in

high concentrations.

The samples also detected low concentrations of another bottom plankton that

produces ciguatera, a toxic that can sicken people who eat fish with high

levels. But said it unlikely it played a major part.