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Deep Sea Habitats
 A
fortunate combination of characteristics make seas of the
Glacier Bay region immensely productive. The waters of the
adjacent Pacific Ocean warm and enrich the waters locally,
which are then further fertilized by nutrient runoff from
the land. Complicated shoreline and bottom topography combine
with exceptionally high tidal energies to produce strong currents
that stir nutrients to the surface making it more available.
Two other factors are necessary to translate nutrients into
productivity: enough light for plant plankton to photosynthesize
rapidly, and enough water column stability to allow these
tiny organisms to stay in the zone of light near the surface.
All these factors come together in spring and early summer.
Then,
for a few weeks, the concentrations of plant plankton reach
astronomical proportions. Many animal plankton
(e.g., krill, copepods) and bottom-dwelling invertebrates
(e.g., starfish, sea urchins, worms, and clams) time their
reproduction to coincide with this brief time of plenty. Vast
shoals of small fishes such as herring, capelin and sand lance
in turn feed upon this animal plankton. Salmon, sea
lions, porpoises, cormorants, and murrelets forage
on the fishes, while humpback whales come
from Hawaii and Baja California to harvest small fish and
the plankton by the ton.
Seaweed
and salt-marsh vegetation also begins to grow in early spring.
They support an abundance of grazers, from deer and geese
(at low tide) to snails (at high). When this vegetation decomposes,
it produces detritus for bottom-dwellers like worms and sand
fleas.
 Summer
in the upper waters is a brief but exuberant season. Hordes
of migrants arrive to join the winter holdouts in harvesting
the bounty. Most marine birds and mammals raise their young
and then put on fat while the good times last. Fishes exhibit
a variety of reproductive strategies. Herring and cod release
eggs that hatch into larvae which fend for themselves in the
rich plankton soup. Skates produce large yolk-rich eggs produced
from stored energy from the previous season. Ling cod males
use stored energy reserves to defend their brood of eggs from
predation.
As
the snows and gales of winter come, and the sun moves ever
lower in the sky, much of the marine world goes "on hold."
Many species leave for the south or the warmer temperatures
of the open sea. Most of the rest curtail their activity.
Salmon eggs rest in creek gravels. Herring and rockfish school
in a rocky deep to await the coming of spring when the drama
will be replayed.
 But
the marine ecosystem does not grind to a halt over winter.
A portion of the living matter from upper waters makes its
way to the bottom in the form of detritus, where it is eaten
by filter feeders such as barnacles, anemones
and clams. What they miss is incorporated into bottom sediments
to be eaten through the year by tiny crustaceans and worms.
These in turn feed flounders, crabs, cod and diving birds
such as scoters. Seals, sea otters
and flounders provide the next link in this benthic food chain,
which fluctuates much less through the seasons than that of
the open waters, and thus becomes disproportionately important
during winter.
Marine
productivity comes ashore in numerous ways. Salmon carry it
to the far corners of the region when they spawn. The young
of some species remain in ponds and streams, where they are
important food for mergansers and kingfishers. Eagles, otters
and mink hunt at sea and carry their catch to land.
Most
important, shores provide hundreds of miles of interface between
land and sea. They provide thoroughfares and den sites; carcasses
wash up on them; and they grow lush intertidal communities
that are dry land when the tide is out. A large array of predators
and scavengers from bears to shrews and ravens patrol the
beaches, eating flotsam and some of the intertidal invertebrates.
Herbivores like deer, moose, mountain goat, porcupine and
voles graze on plants of the upper intertidal zone or eat
kelp for salt.
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