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

CHAPTER 3
THE EELGRASS SYSTEM
3.1 E'UNCI'IONS OF THE EET-GRASS SYSTEM 2. Food and feeding pathways
All seagrasses perform a number of
functions in their environments.
Depending on the size and growth form of
the plant, the seagrass species can modify
the physical and biological environment t6
some degree. In the tropics, early
success~onal genera, ~aio~hila an;
Halcdule, and temperate species such as &
japnica and - Z. noltii, have shallow root 3.
systems and small blades and produce
little litter. As ecological succession
in multispecies systems proceeds to climax
species with their large dimensions, high
litter production, and deep penetrating
roots, the environment can be modified in
more dramatic ways. Except for surfgrass,
Phyllospadix, which grows on rocky 4.
substrates, seagrasses occur on
unconsolidated substrates, mostly of
uniform relief. Owing to their presence
on and penetration into their substrates,
seagrasses create a diversity of habitats
and substrates, providing a structured
habitat from a structureless one (Phillips
1972, 1978).
Zieman (1982) recently revised a list of
seagrass functions that were originally
enmerated by Wxd et al. ( 1969 : 5.
1. High prduction and growth
The ability of seagrasses to exert a
major influence on the marine
seascape is due in large part to
their extremely rapid growth and high
net productivity (leaves typically
grow 5 rnm/day but can attain 18
4-1
Seagrass material may follow two
energy pathways: direct grazing on
the living plant material or
utilization of detritus from decaying
seagrass material, prirnar ily leaves.
Both living and detrital material may
be exprted £ran its original source.
Shelter
Seagrass beds serve as a nursery
ground for food and shelter for
juveniles of 3 variety of finfish and
shellfish of commercial and
recreational importance.
Habitat stabilization
Seagrass stabilizes sediments in two
ways: a. leaves slow and retard
current flow, reducing water velocity
near the sediment-water interface,
which promotes sedimentation of
particles and inhibits resuspension
of organic and inorganic material; b.
rhizomes and roots form an
interlocking matrix, which bonds
sediment and retards erosion.
Nutrient effects
Detrital production and sedimentation
provide organic matter for sediments
and maintain an active environment
for nutrientrecycling. Seagrasses
and epiphytic algae can fix nitrogen,
adding to the nutrient pool.
Seagrass absorbs nutrients from the
sediments and releases them into the
water from the leaves, acting as a
nutrient pt~np for the sediment.