The ecology of eelgrass meadows in the Pacific Northwest: A ...

cuots, and surf scoters prey on herring
eggs deposited on eelgrass. Bird use of
eelgrass meadows is heavy in terms of
abundance and species richness. Thls is
possible, owing to the shallow nature of
muck of the eelgrass. At low tide
numerous shorebirds, including the great
blue heron, pick animals from the beds.
The niches of the waterfowl also appear to
be divided. Diving ducks eat animals,
while the dabblers eat eelgrass blades.
Once I did observe, however, a diving
scaup come up with an entire eelgrass
plant in its bill. The bird fauna
associated with the eelgrass beds in the
Pacific Northwest is Listed in Table 13.
Also included in the list of waterfowl
which eat eelgrass in the Pacific
Northwest are ring-necked ducks,
buff lehead ducks, and ruddy ducks.
These birds obviously take a great
quantity of energy from the eelgrass
system. In Alaska, McRoy (1x6) estimated
that each black brant consumed 180 g dry
wt eelgrass/bird/day (about 4% of the
standing stock). The total amount
consumed by the other grazing birds is as
yet undetermined, as is the amount of food
taken by the epiphyte scrapers (Steller's
eiders) and animal feeders.
The waterfowl and shorebirds also add a
great but as yet undetermined amount of
nutrients to the eelgrass meadows. At low
tides one can observe numerous large white
patches of excrement dumped by gulls onto
the eelgrass, while the water fowl add
theirs directly to the water colunn.
Owing to the economic value of the black
brant on the Pacific coast from sport
hunting, the populations of this species
have been traced for years. Brant appear
to eat primarily eelgrass leaves; however,
some populations in the mid-1940's were
observed consuming rhizome-root sect ions
(Witherby et al. 1943: Cottam et al.
1944). The eastern brant depended on
eelgrass for over 85% of its diet in the
north, while in North Carolina where the
blades were shorter, Ruppia maritima
averaged up to 12% of the winter food.
Algae, mostly Ulvaceae of very low
nutritional value, only constituted 1% of
the food used. Following the wasting
disease of the 1930's, eelgrass only
constituted 9% of the food consumed;
Ruppia increased to 16%, while the
Ulvaceae increased to 36%. Most of the
birds diverted their migration route and
went inland to feed on winter wheat and
rye. Some brant from New Jersey to North
Carolina are even now raiding home lawns
for Kentucky bluegrass (Reiger 1982). On
the Pacific coast there were minor
declines of eelgrass in 1938. The black
brant there also used Ulvaceae as an
alternative diet (Moffit and attam 1941).
Black brant populations seem to be
dramatically declining in the Pacific
Northwest, correlated with the draining of
coastal marshes, conversion of bays to
boat marinas, and a general increase in
water use by people (~eiger 1982).
Proctor et al. (1980b) stated that the
major concentration areas of black brant
in the Pacific Northwest are Grays Harbor,
Willapa Bay, the Columbia River, Coos Bay,
and Humboldt Bay. The important hunted
waterfowl include American wigeon,
mallard, pintail, canvasback, Canada
geese, and the black brant. In 1976 a
total of 101,420 ducks and 3,770 geese
were harvested from five counties in
southwestern Washington. In 1972 a total
of 121,570 ducks and 2,450 geese were
taken from seven coastal counties in
Oregon (proctor et al. 1980b).
The Washington State Department of Game
(pers. comm., 1982) related that there are
two principal wintering areas for black
brant in Washington: Padilla Bay and
Willapa Bay. A few brant feed on eelgrass
throughout Puget Sound; however, there are
also two segments of the brant population:
those that winter in Washington and those
that winter in Baja California but return
to Washington in April to feed in eelgrass
during daytime low tides. Brant arrive in
Washington in mid-November and the winter
population peaks in January. An increase
is noted in April before the entire
population leaves in May.
Lane (1980) reprted that 60,000 to 70,000
black brant stop by to feed on eelgrass in
Padilla Bay in the spring migration. A
report made for Padilla Bay (NOAA 1980)
listed 239 species of birds and also
stated that an average of 5,000 brant
winter on the bay (5,000-8,000 on Padilla
Bay and Samish Bay, winter 1981-82;