The ecology of giant kelp forests in California - USGS National ...

occupation of breeding areas in Baja
California, Mexico (Rice and Wolman 1971;
Oliver et al. 1983). However, there is
now evidence that gray whales, while
migrating, feed on dense swarms of mysid
shrimp within or along the outer edges of
kelp beds and forests (Wellington and
Anderson 1978, Poole in press, Murison et
al. in press). It may be advantageous for
a gray whale cow with a dependent calf to
supplement her stored reserves by feeding
upon the abundant mysid resource
associated with kel p (Poole in press).
Ki 1 ler whale (Orcinus orca). The
status and distribution of the Cal ifornia
population of killer whales are not known
(Morejohn 1977). Killer whales feed in
small groups i n nearshore regions,
particularly near areas of high marine
mama1 concentrations (e.g., pinniped
rookeries; Rice 1968). Pods of killer
whales have been sighted traveling along
the edge of kelp forests (Daugherty and
Schuyler 1979).
4.6.2.4 Pinnipeds. Harbor seal
(Phoca vitulus). Harbor seals are yearround
residents of embayments, sloughs,
and rivers along the California coast,
with an estimated population of 20,000
individuals (Miller pers. comm. ). Jones
(1981) describes the diet of harbor seals
as consisting of shallow-bottom fishes
that 1 ive near rock habitat, but they also
feed on pelagic fishes in many areas
(Estes pers. comm. ). Green1 i ngs and surfperch,
two common groups of kelp forest
fishes (see Section 4.5), were included by
Jones as major prey items. Daugherty and
Schuyler (1979) pointed out that harbor
seals resting in thick beds of kelp with
their heads protruding above the surface
are often mistaken for sea otters.
Although we could locate no specific
reference to the harbor seal's association
with kel p beds, individual s are commonly
observed while diving in kelp and probably
forage extensively in kelp forests when
these habitats are close to seal haul-out
areas. Jameson (pers. corn.) has even
observed a harbor seal partially
hauled-out on a dense, floating canopy of
Nereocystis luetkeana.
California sea 1 ion (Zalophus californianus).
The California sea 1 ion
breeds on the Channel Islands of southern
California, along the coast of Baja
California, Mexico, and in the Gulf of
California during June and July. During
the remainder of the year, some 75,000 sea
lions (Bonnell pers. corn.) inhabit the
entire coastal region of California.
Groups of sea lions are sometimes seen
passing through kelp forests or foraging
along the kelp forest fringe. Sea lions
show a preference for pelagic prey items
(Jones 1981). It is probable that the
association of sea lions with kelp forests
is 1 imited to transitory foraging,
a1 though these animal s are commonly
observed in kelp forests by divers.
4.6.2.5 Steller'sseacow(Hydrodamalis
gigas). Giant kelp forests were,
in the oast. orobablv also inhabited bv
the now-'extinct ~tellir's sea cow. hi;
huge (6,000 kg, over 7 m long; Domning
1978) herbivorous mammal is believed to
have inhabited nearshore areas from Baja
California, Mexico, to Russia. Probably
as a result of hunting by aboriginal man,
only an estimated 2,000 animals remained
in the remote portions of the western
Aleutian Islands and eastern Ru,ssia by
1741, and the last animal is be1 ieved to
have been killed in 1768 (Domning 1978).
Hydrodamalis gigas apparently did not
com~letelv submerse, and fed on various
seaweeds -and sea grasses in very shallow
(probably 1-2 m) water (Domning 1978).
Its shallow subtidal habitat, lack of
diving, and slow movements made this
sirenian easy prey for hunters. Dayton
(1975) suggested that sea cow grazing may
have been important in the evolution of
algal assemblages in kelp forests.
However, given what is known of the sea
cow's habitat and method of feeding, this
is arguable. A1 though apparently never
observed, sea cows could have fed on
surface canopies in deeper water.
4.7 DISEASES
4.7.1 Introduction
A variety of pathogens and parasites
infect macro-organisms in giant kelp
forests, but except for a limited number
of cases reviewed below, little is known
of their effects on host populations.