The brown unsightly material washed ashore recently on Anna Maria Island beaches is partly non-toxic algae known as Trichodesmium. At the same time, brown seaweed also is drifting ashore, scientists say, and combined, the two substances may appear to some people as the result of an oil spill or dumping in the Gulf of Mexico. Islander Photo: Rick Catlin
That brown-looking scum that some Island beach-walkers recently reported seeing washed up along the shoreline is not from an oil spill, as some think, but is an alga common in the Gulf of Mexico that has mixed with ordinary reddish-brown seaweed.
Hayley Rutger of Mote Marine Laboratory on City Island in Sarasota, said scientists at the laboratory have identified the algae as Trichodesmium. Although it is generally found farther out in the Gulf of Mexico, Rutger said its appearance is not unusual.
“Although for many years we don’t see any along the beach,” she said.
At the same time as the brown Trichodesmium algae is washing ashore, so is common reddish-brown seaweed. When the two combine on the shore, it appears much like that from an oil spill, she said.
The algae is not considered harmful to humans, but Mote scientists are studying samples from several beaches along Florida’s west coast to ensure there is no harmful bacteria or red tide algae hidden in the substance.
When Trichodesmium washes ashore with ordinary seaweed, Rutger said, it can give off a “rotten odor” as it decomposes.
Rutger said red-brown seaweed is common along area beaches this time of year, but Trichodesmium usually stays further out in the Gulf — unless currents carry it to shore.
Manatee County Natural Resources Department director Charlie Hunsicker said Trichodesmium is “not a prelude to red tide” because of different conditions in the water.
County work crews will be cleaning the algae and seaweed from county beaches, but not from areas where private homes and businesses front the Gulf of Mexico.
He said the algae should not leave behind “large masses of decaying vegetation,” but a “fine particle residual.”
Although the Trichodesmium algae is not harmful to bathers or beach walkers, Hunsicker said it’s always possible someone might have an allergic reaction because of their own physiology. “But I’m not a medical doctor to comment on that,” he said.
Rutger said red tide usually produces sore throats and sinus issues in people who have been in or near water containing the red tide algae. Red tide, known scientifically as Karina Brevis, kills fish when it forms in the Gulf, she said.
Mote scientists will continue to monitor area Gulf waters for the next few weeks for any algae problems, including red tide, Rutger said.