Black "Blob" in Florida Waters Has Scientists Perplexed

Brian Handwerk
for National Geographic News
April 10, 2002
A large mass of blackish-green water floating off the Florida coast has
scientists and researchers scratching their heads.

Described as
"sewage-colored" and containing material that is slimy and gelatinous,
the mysterious formation was first spotted in January between Naples and
Key West. Research to determine its origin is underway.

Fishermen first reported the phenomenon in January, after having observed for several weeks a dark patch of water that seemed devoid of living organisms.

"We had people who spend a lot of time out on the water contacting us to say that they had never seen anything like this," said Beverly Roberts of the Florida Marine Research Institute. Satellite images confirmed the existence of the formation and showed that it was hundreds of square miles in size.

Roberts and her colleagues took the lead in coordinating a study of the problem by the state's top marine scientists. Leading experts from state and private laboratories have joined the effort to determine the origin of the unusual water-mass and determine its possible impacts on the ecology of the coast.

Roberts said the key clues will come from analyzing samples of the "dark water," which must be collected from boats.

But collecting the samples has not been easy. "Once people get us a report we try to get out there and get samples, but they can be very hard to collect," she said. Moreover, "samples only a few nautical miles apart or several hours apart can be very different," she said, and "sporadic, nonstandard sampling may result in quite varied results and interpretations."

Rich Pierce of Mote Marine Laboratory enjoys the challenge of solving the mystery. "It's exciting. We think that we understand coastal processes well, and then something like this comes along and we have only hypotheses and no clear answer about what's happening."

Not a "Dead Zone"

After their extensive preliminary research, the scientists think they have a basic understanding of the phenomenon, although they don't yet know why it formed. Pierce said the evidence so far—obtained from satellite imagery, nutrient analysis, and organic matter—suggests that the formation is a very unusual phytoplankton bloom.

Phytoplankton, consisting of tiny organisms that serve an essential purpose as the first link in the marine food chain, are common in seawater. The type of phytoplankton found in the dark Florida water "is typical of this region, so it's normally in the area and does normally bloom," said Pierce. "But what we're seeing," he added, "is a relatively normal event on a very abnormal scale."

As the scientists work to understand the causes, they are concerned about whether the phenomenon is damaging the marine ecosystem, and if so, how. Some observations have included reports of dying sponges, coral, and starfish.

For the most part, however, there has been little evidence of such effects, said Pierce. FMRI officials say early reports that characterized the area as a "dead zone" are not accurate because a variety of plants and animals have been found in the strange water.

Gil McRae of FMRI said the dark water is not only not a dead zone, but it teems with an "overabundance" of life. "There's a lot of productivity in a small space," he said.

That's cause for concern. While normal concentrations of phytoplankton are essential, large concentrations can mean problems for other organisms in the area. During the day, phytoplankton undergo photosynthesis and produce oxygen as well as consuming it. At night, however, the process stops and the huge masses of organisms can consume all the oxygen in an area, leading to oxygen depletion.

At the same time, the abundant "blooms" eventually die out and settle on the bottom of the sea.

Both of these processes threaten bottom-dwelling organisms such as coral, crabs, and sponges.

Lingering Mystery

Although the scientists may have figured out the nature of the mysterious blob, the cause or causes remain unknown. Pierce said the scientists will "use our data to go back in time and determine what might have caused this."

One hypothesis currently under examination points to a water circulation pattern known as upwelling. The process brings nutrient-rich deep oceanic water up the continental slope and into the surface waters of coastal areas, where it fuels the growth of phytoplankton and can cause explosive growth—though not usually on the scale of the Florida incident.

Runoff from rivers near the Everglades may be contributing to the problem by providing nutrients and dissolved organic matter that feed the phytoplankton explosion.

Also under consideration is a correlation with "red tide," which has been prevalent in the area since last August. Red tide is another type of algae bloom that is toxic and directly harmful to marine life.

McRae speculated that "the red tide event might have run its course, degraded, and then provided a nutrient source for the beginning of the current black-water bloom."

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