Research On Carbon Sequestration - July 5, 2006. From
Oceanus - Online.
Animal May Play Overlooked Role in the Ocean
by the billions, gelatinous salps transport tons of carbon to
don’t get much respect. They’ve been around for
millions of years, but hardly anyone even knows they exist.
many who have heard about these transparent, jelly-like creatures
consider them a dead-end in the ocean food web: They cruise around,
vacuuming up microscopic plants, but don’t get eaten by other
animals, making them a marine equivalent of inedible cows.
in the May issue of Deep Sea Research, scientists report that salps
may play an important and overlooked role in determining the
of the greenhouse gas carbon dioxide in the ocean. Swarming by
the billions in salp “hot spots,” they transport
tons of carbon per day from the ocean surface to the deep sea
from re-entering the atmosphere, the scientists say.
Laurence Madin of Woods Hole Oceanographic Institution and
Patricia Kremer of the University of Connecticut led researchers
Mid-Atlantic Bight region (between Cape Hatteras and Georges
Bank) in four summers
since 1975, and each time found that one species, Salpa aspera,
multiplied into dense swarms that lasted for months.
swarm covered 38,600
square miles (100,000 square kilometers) of the sea surface,
containing perhaps trillions of thumb-sized salps. The scientists
that the swarm consumed up to 74 percent of microscopic carbon-containing
plants from the surface water per day, and their sinking
fecal pellets transported up to 4,000 tons of carbon a day to deep
carbon to the depths
The oceans absorb carbon dioxide from the
including some of the carbon dioxide emitted by fossil-fuel
burning. In sunlit surface waters, tiny marine plants_phytoplankton_use
it to grow. Animals then consume phytoplankton and incorporate
but most of it dissolves back into the oceans when the
animals defecate or die. The carbon can be used again by plants,
to the air as heat-trapping carbon dioxide.
send carbon down a third path by making heavy, fast-sinking fecal
efficiently ship carbon to the deep sea, where
it is sequestered from the atmosphere.
swim, feed, and produce waste continuously,” Madin said. “They
take in small packages of carbon and make them into big packages
work, Madin and WHOI biologist Richard Harbison found that salp
fecal pellets sink as much as 3,280 feet
(1,000 meters) a day, far faster than most pellets. The scientists
also showed that when salps die, their bodies also sink fast—up
to 1,575 feet (475 meters) a day. If salps are really a
dead-end in the food web and remain uneaten on the way down,
they send even
more carbon to the deep.
migrations to the surface
Salpa aspera swims long distances down
in daylight and back up at night.
Madin and Kremer and colleagues—Peter Wiebe and Erich
Horgan of WHOI and Jennifer Purcell and David Nemazie of the
of Maryland—found that the salps stay at depths of 1,970
to 2,625 feet (600 to 800 meters) during the day, coming to
only at night. “
At the surface,” Madin said, “salps can feed on phytoplankton.
They may swim down in the day to avoid predators or damaging
sunlight. And swimming up at night allows them to aggregate to
multiply quickly when food is abundant.”
of this behavior, salps release fecal pellets in deep water, where
few animals eat
them. This enhances the transport of carbon away from the
2004 and 2006, Madin and Kremer studied salp swarms in
a different ecosystem, the Southern Ocean near Antarctica. Some
have reported larger salp populations there in warmer years
sea ice. If this proves true and if Antarctica's climate
to warm, salp swarms could have a greater effect on phytoplankton
and carbon in the Southern Ocean ecosystem.