Page 17 - AlertDiver_Spring2013
Basic HTML Version
The algae is even an important part of coastal ecosystems.
Wind blows it onto beaches, where it helps anchor sand and
contributes nutrients. While other seaweeds reproduce and begin
life on the seafloor, sargassum floats and grows vegetatively,
with new mats produced from parts of the parent organism
rather than from seeds or spores. “That makes the Sargasso Sea
essentially one enormous super-organism,” Witheringon said.
According to a 2008 study, most new growth in the
Sargasso Sea occurs in the northwest Gulf of Mexico, where
sargassum grows rapidly in the spring. It then travels via the
Loop Current into the Atlantic, where it accumulates in the
gyre. The Gulf produces about a million tons of sargassum
a year, McKinney said, and at any given time between 4.5
and 12 million tons of it bob in the Gulf and Atlantic. An
individual mat lives about a year or possibly two, starting out
bright orange and gradually becoming brown as it ages. It
eventually loses its buoyancy and sinks.
Sargassum’s abundance waxes and wanes and can be hard to
measure; storms sink it, currents break it up and move it, and
nutrients make it grow. Some worry that it is in decline, but
McKinney said there is little scientific evidence of that. A recent
study analyzed images from the Medium Resolution Imaging
Spectrometer (MERIS), a satellite launched by the European
Space Agency, to measure abundance of sargassum from 2002
to 2008. The images showed an increased abundance in 2008
compared to 2002 and a maximum abundance in 2005.
That could change, however. As recently as the late 1990s,
tons of sargassum were harvested for use in animal feed and
as fertilizer. Given its importance as habitat, the U.S. South
Atlantic Fishery Management Council set a commercial
annual catch limit of 5,000 pounds and prohibited harvesting
within 100 miles of shore, effectively halting commercial
harvesting. However, the council’s authority only covers U.S.
waters off North and South Carolina, Georgia and eastern
Florida. Elsewhere in the U.S. and on the high seas, where
most sargassum is found, the algae has no protection. The
Sargasso Sea Alliance, a collaboration led by the government
of Bermuda and including the World Wildlife Fund, Sylvia
Earle’s Mission Blue and the Marine Conservation Institute,
is working on a mechanism to protect and manage what it
calls “the golden floating rainforest.” New potential uses for
sargassum, including pharmaceuticals and biofuel, make the
need to protect it more urgent, as do increasing threats such
as climate change, ship traffic and pollution.
Those who have been diving around mats of sargassum
say they make excellent dive sites because of the many
critters living in them and the predators that hang out
around them. “Diving under sargassum is like diving in
another world,” said Billy Causey, Southeast Regional
Director for NOAA’s Office of Marine Sanctuaries. “If you
can’t get out on a reef, it’s just as good.”
— Melissa Gaskill
|
15
Most new growth
of sargassum
occurs in the Gulf
of Mexico. From
there the seaweed
rides currents into
the north Atlantic
where, after a
year or two of life,
it sinks into the
depths.
Fish Species Found in Sargassum
(Transient and Resident)
jacks (rainbow runners, almaco jacks, banded rudderfish, greater and
lesser amberjack, round scad, bar jack, hardtail, jack crevalle and
Atlantic bumper), white mullet, flying fish, tripletail, cobia, dolphinfish,
vermilion snappers, swordfish, pipefish, scrawled filefish, gray trig-
gerfish, sargassumfish, barracudas, mackerels, tunas and billfishes
1 4
/ S i g n i f i c a n t S a r g a s s u m
1 6
/ M i s s i o n : U S S H a t t e r a s
1 8
/ A q u a r i u s L i v e s O n
2 0
/ C o n f r o n t i n g C a r d i o v a s c u l a r
H a z a r d s
2 2
/ d a n m e m b e r p r o f i l e
2 6
/ o c e a n c l a s s r o o m s
2 7
/ d a n c a l e n d a r o f e v e n t s
/ d a n o n l i n e v i d e o s e r i e s
/ d a n e d u c a t i o n s p o t l i g h t
NED DELOACH
MASA USHIODA
MASA USHIODA
