wants to know what role snow plays in transferring nutrients into the
deep sea. The abundant life below the surface requires sustinence, she
says, but "we really don't know how [food] gets into the deep sea."
to researchers like Silver, though, we do know that marine snow is likely
a major food source for life in the abyssal deep.
Marine snow forms when
plant and animal detritus floating about in the ocean sticks together.
The binding substance is mucus, which ocean dwellers make a lot of. The
mucus glues together scraps of crustacean shells, remnants of plants,
and excrement of animals. The particles are all different shapes and denser
than the surrounding ocean, but have many cavities.
And while the particles
have to be at least one-half millimeter in diameter to be considered snow,
they can grow to be quite large, on the order of feet. But since the snow
is fragile, the large marine snow grows only in calm waters.
of a good snow particle requires a nucleus--a solid chunk of sticky matter
to serve as the basis for the growing particle. A common base for snow
in the open ocean is the cast-off houses of the giant larvacean, a small,
tubelike hemichordate (which is not quite an invertebrate and not quite
a vertebrate) that weaves a chambered house around itself. The chambers
collect food for the larvacean nestled within--so effectively, in fact,
that a larvacean must drop its house up to four times a day and start
again. The released houses shelter living bacteria and plankton and collect
other matter on their way downward.
Another starting point for snow--especially
common in the Monterey Bay--is a colony of diatoms. These single-celled
algae build walls of opal (a type of silica), and some species can form
long chains. When the colonies grow old and die, they "get goopy," Silver
explains. Goopy clumps are perfect for collecting dead organisms and waste.
The turbulence of the water drives the formation of snow and determines
the ultimate size of the particles. "Intermediate" turbulence favors snow
growth by bumping the particles into each other. Too much turbulence,
however, fragments the flimsy aggregates, Silver says.
Small sea creatures swimming through the snow also
influence the size of the particles. Alice Alldredge, a professor of
marine biology at the University of California, Santa Barbara, studies
how some marine organisms, such as the centimeter-long shrimp-like krill,
break up the snow into smaller particles. She wants to understand the
relationship between the turbulence caused by various krill activities--like
swimming and eating--and the size of snow particles. If krill swimming
can affect the size of snow, then perhaps other marine organisms can
as well. Ultimately, the size of the particles determines how much of
it reaches the bottom of the ocean.