Sargassumon Sanibel Beaches
July 8, 2009
(http://www.magneticnewsletter.com/members.aspx?Task=OO&SI=3315373&E=&S=42)
There have been recent accumulations of brown algae on Sanibel beaches
(it has also been reported in Boca Grande). SCCF’s Marine Lab and the City
of Sanibel have identified it as Sargassum; it is not red drift algae.
Sargassum moves in floating mats on the ocean’s surface.
The City of Sanibel surveyed the beach from Lighthouse Beach to Bowman’s
this past weekend, noting the presence of Sargassum both in the water and
on the beach. Both the Sargassum and this past June’s accumulation of
manatee grass on Southwest Florida beaches may be related to storm events and
larger regional issues.
What is Sargassum?
The floating mats of Sargassum weed that recently made landfall on island
beaches traveled by ocean currents until winds blew them ashore. Most
Sargassum weed originates in the Sargasso Sea of the North Atlantic Ocean.
Pushed by four different currents including the Gulf Stream, the plants float
with the help of small, air-filled structures. Along the way, waves break
this algae apart, the parts multiply asexually, and the Gulf’s warm waters
encourage rapid growth. As the beached weed gets pushed further up into the
shoreline it is covered by sand.
Sargassum weed is like a floating hotel and nursery to a myriad of other
organisms. Small sea turtles swim near the seaweed looking for cover and an
easy meal of the shrimp and crabs that live there. The loggerhead turtles
now hatching on island beaches swim thousands of miles to the Sargasso Sea
spending as many as 11 years feeding on jellyfish, snails, crabs, and
shrimps protected from predators in the Sargassum weed. It is breakfast, lunch,
dinner, and home to them.
Acareful examination of the beached Sargassum may also reveal a
nudibranch still in residence. Sea Hares live attached to floating Sargassum weed,
feeding on small plant-like animals called hydroids that grow there. Many
of the animals that live in this goldish green seaweed have evolved into
shapes and colors resembling their host. If you visit the touch tank at SCCF
youwill find the spider and hermit crabs hiding in and munching on the
floating Sargassumweed.