Subject: Productivity, Whales

Mike Williamson (pita@www1.wheelock.edu)
Mon, 20 Apr 1998 10:56:24 -0400 (EDT)

Subject: Why these waters teem with lif

Why these waters teem with life

By LIDIA WASOWICZ
 UPI Science Writer
   SAN FRANCISCO, April 17 (UPI) -- A researcher has uncovered the
secret of whatmakes the Southern Ocean teem with life, a finding that
may prove useful in the recovery of whale populations in areas where
they've been depleted.
   The Southern Ocean -- a huge water mass surrounding the Antarctic
continent that comprises one-tenth of the world's oceans -- supports
one of the most productive marine ecosystems on Earth.
   The research shows the southernmost reaches of the strongest ocean
current, called the Antarctic Circumpolar Current, or ACC, is of key
importance to the ocean's complex and predictable food web.
   The study found the distributions of blue, fin and humpback whales
coincide with the penetration of the deep, nutrient-rich water. The
configuration of this water mass marks the current's Southern Boundary
and corresponds to areas where phytoplankton blooms, krill and whales
abound.
   Cynthia Tynan ofthe National Marine Mammal Laboratory at the
National Oceanic and Atmospheric Administration in Seattle tells UPI,
"The circumpolar association of phytoplankton, krill and whales with
the Southern Boundary of the ACC suggests it provides productive
foraging for many species and is of critical importance to the function
of the Southern Ocean ecosystem."
   Her research helps explain why, prior to the invasion by commercial
whalers, the waters around Antarctica harbored more whales than any
other place on the planet.
   Says Tynan, "This feature is of continued importance to the recovery
of whale populations in the Southern Hemisphere."
   During the past century, whalers decimated sperm, blue, fin, right,
humpback and sei whales. Only the minke escaped rampant slaughter.
   Says Tynant, "This loss altered the composition and structure of the
Southern Ocean ecosystem. Most of these species were so severely
depleted, that their recovery remains exceedingly slow."
   Scientists estimate thereare only 460 or so blue whales left in the
Southern Hemisphere. In response, the International Whaling Commission
in 1993 created the Southern Ocean Sanctuary to protect these species
from commercial whaling and to support research on the effects of
environmental change on these populations.
   Most species of baleen and male sperm whales in the Southern
Hemisphere migrate between low latitude breeding grounds in winter and
highly productive Antarctic feeding grounds in summer. During their
southward journey, baleen whales -- such as blue, fin and humpback --
feast on the rich bounty of their principal prey, krill, at the
current's Southern Boundary. Sperm whales, which favor cephalopods, or
squid, at deeper depths also congregate there.
   Says Tynan, "The presence of balaenopterids and sperm whales at the
Southern Boundary suggests the availability of both krill and
cephalopods is enhanced at this feature. This oceanic feature is a
subsurface water mass boundary where a defining water mass of the ACC --
Upper Circumpolar Deep Water -- reaches its southernmost extent."
   Tynan found a thick layer of warm, saline, nutrient-rich water
permeating the current. At the Southern Boundary, this mass reaches its
shallowest depth, 200-500 meters, where wind-whipped waters bring high
concentrations of nutrients -- phosphate, nitrate and silicate -- to
the surface.
   The ample nutrient supply breeds phytoplankton and krill (an
estimated 100 million tons a year), which, in turn, attract baleen
whales, pinniped species, such as crabeater seals, leopard seals, fur
seals, and birds, such as petrels and penguins.
   Says Tynan: "The food web of the Southern Ocean is more complex than
was represented in a traditional short food chain: phytoplankton
(diatoms), krill, whales. We now recognize that although the transfer
of carbon from diatoms to apex predators appears short, there are other
components, such as the 'microbial loop,' that are important in the
cycling of organic carbon in the system."
   Because of the area's prominent place in the world's food web,
environmental factors, such as climate change, that could affect it are
of great signficance.
   Says Tynan, "Sufficient climate-induced alteration in the
circulation patterns and water mass structure of the Southern Ocean
would be expected to have large ecological consequences. Therefore,
global warming is a very important scientific issue in the Antarctic."
   "Oceanographers are still discovering how biological, chemical and
physical processes in oceanic and coastal regions interact to make some
regions, such as frontal zones and water mass boundaries, particularly
productive," she concludes. "Whales, seabirds and other species which
occupy the highest trophic levels, are key integrators of the
productivity and prey densities of their environment."