Ugly 'sea sawdust' floats ashore Holmes Beach

toconnor@bradenton.comMay 23, 2013 

HOLMES BEACH -- Mote Marine Laboratory scientists say the funky-looking muck floating ashore this week in Holmes Beach and elsewhere along Southwest Florida is nothing to worry about.

It is, however, an alarmingly ugly water element that usually stays far offshore, a Mote Marine Lab scientist said.

The foreign substance is likely a cyanobacteria called trichodesmium, staff scientist Vince Lovko told Nadine Slimak, director of communications at Mote Marine Laboratory and Aquarium.

"He said it's impossible to say for certain what the water discoloration is without water samples, but he thinks it's likely to be trichodesmium, given that the state has been able to verify it in wa

ter samples taken from other locations," said Slimak. "Trichodesmium is a cyanobacteria -- that's a blue-green algae -- that's found in the Gulf. It's not harmful to humans or animals like Florida's red tide, but it can discolor the water."

Sailors sometimes refer to trichodesmium as sea sawdust because it forms colonies visible to the naked eye. Small blooms resemble sawdust floating on the water surface, while larger blooms can look like oil slicks on the surface or slightly foamy pollution.

The last documented bloom in this area was May 2000 at St. Pete Beach.

"It's not harmful to humans or animals, but some people find it makes the water less attractive than they're used to," Slimak said.

Lovko made his observations with the help of aerial photography from owner Troy Morgan of Photos From The Air in Bradenton.

"This does not look like the substance we had last year," e-mailed Morgan, who maintains a gallery of Southwest Florida water phenomenon at PhotosFromTheAir.com.

Trichodesmium marine cyanobacteria occurs in surface waters of tropical and subtropical oceans globally, including the Gulf of Mexico. Larger blooms can be seen from the space shuttle.

The amount of trichodesmium on the surface varies with the time of day as the species can migrate up and down in the water column. Trichodesmium blooms every year in the Gulf, but generally far offshore. Only occasionally do blooms reach nearshore areas after currents and winds push an established offshore bloom to shore.

Trichodesmium blooms are not related to coastal nutrient sources as red tide is. High biomass trichodesmium blooms in the Gulf of Mexico tend to occur in the May-September period.

It's a global-cycle phenomenon. Most of the iron it takes up is derived from Saharan dust blown into the atmosphere by Africa storms, transported across the Atlantic Ocean and deposited in the Gulf of Mexico.

In general, trichodesmium is not a good food source for zooplankton or fish and is actively grazed on by a few specialized zooplankton species.

Trichodesmium has a unique "sweet" smell when it decays and large blooms can turn the water red or pink when stressed cells leaks water-soluble pigments.

Terry O'Connor, night metro editor, can be reached at 941-745-7040.

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