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

CHAPTER 4
COMPONENTS OF THE EELGRASS COMMUNITY-STRUCTURE AND FUNCTION
A community is characterized by its
species composition and related features
(den Hartog 1980). The community can be
described as a structural framework in
which to study plant and animal
interrelationships, while the ecosystem is
a functional framework in which the
interrelationships are viewed as processes
and in which the effects of the abiotic
environment are integrated.
animals that may crawl onto the leaves
from the sediment. Epibenthic organisms
are those that live on the surface of the
sediment, both mobile and sessile forms.
Infauna live buried in the sediments.
Some organisms, such as shrimp and some
crabs, lie partially buried during the day
and move on the sediment surface to feed.
These are treated as epibenthic organisms.
Nekton live in or above the plant canopy.
This chapter will, for the most part, be
organized along a community orientation.
Many studies have shown a great diversity
of plant and animal life associated with
eelgrass meadows, from epiphyte lists
(Davis 1913; Kita and Harada 1962; Ledoyer
1962; van den Ende and Haage 1963; den
Hartog 1970; Main and McIntire 1974;
Harlin 1980) to large lists, some of which
also analyzed the functional
interrelationships of animals associated
with eelgrass (~legvad 1914, 1916; Allee
1923; Blois et al. 1961; Ledoyer 1962,
1964a,b; Kikuchi 1966, 1968, 1974, 1980;
Nagle 1968; Orth 1973, 1977a; Adams
1976a,b; Kikuchi and Peres 1977; Simenstad
et al. 1979; Jacobs and Huisman 1982).
The animals organize conveniently into
functional groupings, largely without
concern for their taxonomic placement.
The principal groups are (1) epiphytes,
(2) e~ibenthic organisms, (3) infauna, and
(4) nekton. Birds will be treated as a
separate category. These four groupings
follow the classification set by Stauffer
(1937).
There are at least two other ways in which
to classify animals in an eelgrass meadow
by function. Kikuchi (1966, 1980)
proposed the following system reflecting
the use of Japanese eelgrass meadows. I
have attempted to classify the animals in
eelgrass systems of the Pacific Northwest
according to this system: (1) permanent
residents, (2) seasonal residents, (3)
transients, and (4) casual species.
Thayer et al. (1975b) subdivided the
infauna into deposit feeders and
suspension feeders, but this refinement
is not adopted here.
It is interesting that Nagle (1968),
working on epiphytes of eelgrass at Woods
Hole, Massachusetts, concluded that
general trophic abundances were the same
geographically everywhere. In a recent
paper, Lewis and Hollingworth (1982),
working in Thalassia meadows at Barbados,
confirmed Nagle's observation.
4.1 HORIZONTAL AND VEHTICAL STRUCTURE
Throughout the limited geographic extent
The term epiphyte means any organism of the Pacific Northwest, there appears to
living on a plant surface, plant or animal be little, if any, horizontal structure of
(Harlin 1980)- It includes both sessile the associated organisms of the eelgrass
and mobile plants and animals, as well as community. Epiphytes, benthic algae,