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Harmless manatee grass no cause for concern on islands

By Staff | Jun 10, 2009

Late last month, a strange visitor washed up on the beaches of Sanibel and Captiva. And although this visitor hadn’t been seen on the islands before, according to marine scientists, it’s a fairly common neighbor of our undersea friends.

As of last week, piles of manatee grass (Syringodium filiforum) were still drifting ashore along beaches from Sarasota to the north and Naples to the south. Some say the dead shoots look like spaghetti, while others liken their appearance to bean sprouts.

“It looks like spaghetti,” said Jeremy Harris, 8, on vacation with his family from Longview, Texas. “I’ve never seen anything like it before.”

Dr. Rick Bartleson, a Research Scientist with the Sanibel-Captiva Conservation Foundation (SCCF), explained that unlike red drift algae, which washed up on local beaches on 2007 and poses a health hazard to humans, manatee grass is harmless.

“The manatee grass washing up does not pose a nutrient issue because the loss of nitrogen and other organic content already occurred when it decomposed in the Gulf,” he explained on the SCCF Web site. “The live shoots are green, but after they die and float to the surface in the Gulf, they bleach out and become clear-to-white.”

Under the summer sun, the manatee grass that is now on Sanibel and Captiva beaches will dry out and flatten, and look like straw wrappers. Once dry, it is very light and will probably be blown away by the wind, or washed back out into the Gulf on a high tide.

When the manatee grass first appeared, SCCF began working in cooperation with the City of Sanibel, the Town of Fort Myers Beach and Mote Marine Laboratory to determine if the substance poses any threat to the local ecology. As of late last week, thick piles of the grasses were still being found at Bowman’s Beach and floating offshore from Tarpon Bay Beach to the Clam Bayou area. There have been no fresh accumulations on Captiva.

“Mote Marine reported that it was very abundant on Casperson Beach and on beaches north of Venice, but there had been no reports of large amounts of fresh material coming onshore there,” Dr. Bartleson added.

Unlike most seagrasses, manatee grass is unique because the shoots are cylindrical rather than flat. The cylindrical shape of the blades and the internal cells probably help keep the blades from completely breaking up as other seagrass blades probably do. Manatee grass usually grows in association with other seagrasses, and its leaves can grow to about 20 inches long.

“While the manatee grass is harmless on the beach, anytime that seagrasses in this volume wash up, it’s a concern and SCCF will be working with colleagues up and down the coast to look at potential causes,” said Dr. Bartleson.

One potential problem posed by the appearance of the manatee grass on area beaches relates to sea turtle nesting season, which began on May 1. Since raking beaches is prohibited throughout the loggerhead nesting period, which doesn’t end until October, the manatee grass must be left alone to decompose naturally.

However, that should not pose any immediate risk to hatchlings, which typically don’t hatch until July.

On Monday, beach-goers at Tarpon Bay Road seemed to be taking the appearance of the manatee grass in stride.

“They say it isn’t harmful, which is good,” said Vicki Strassberg of Fort Myers. “I’d rather see this stuff wash up than the red algae that was here a few years ago. That stuff was nasty… ugly… smelly.”

Representatives from the People United to Restore our Rivers and Estuaries (PURRE) were also quick to respond to the appearance of the grasses on Sanibel’s shoreline.

“PURRE has found no indication that the white grass that washed up on Sanibel and Fort Myers beaches recently is evidence of a harmful algal bloom,” Dan Wexler, Public Policy Director for PURRE, wrote in an e-mail to coalition supporters last week. “Nevertheless, it’s here and hard to ignore.”

For more information on manatee grass or other seagrass species, visit www.sccf.org or call SCCF’s Marine Lab at 395-4617.