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

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Figure 12. Oxic and anoxic detrital decomyx,sition and the cycle of sulfur in seagrass
Ms (after Fenchel 1977).
proximate constitutents of eelgrass
( Boysen-Jensen 1914; Candussio 1960;
Einarsen 1965; Burkholder and Doheny 1968;
Park 1979; Stahlheber 1982; Felyer and
Moeer 1973, 1976; Table 9). No studies
have been made on 5 japonica, a large
staple of the black brant geese in the
Pacific Northwest.
Protein contents of eelgrass Leaves range
from a low of 8.1% of dry weight to 20.3%.
The value for the rhizomes ranges from
2.8% to 6,143. Unfortunately, no seasonal
comparisons have been conducted for
eelgrass, as have been done for the
tropical seagrasses (cf, Zieman 1982 for a
summary). This area needs a lot of work.
Lipid amtents of all plant para are low
(0.84% of the dry weight to 2.29% in
leaves; 0.91% for rhizomes; 1.0% for
seeds). Fiber contents are relatively
high in leaves and rhizomes (a low of
5.45% of dry weight in one analysis to
61.7%). Ash contents range from a low of
8&% of dry weight to 32.6%. Carkrhydrate
contents are highly variable (1.3% of dry
weight to 44.6% in leaves to 50.9% in
seeds). There have been so few studies
made and no systematic analyses either
seasonally or regionally that it is
difficult to draw any conclusions from the
few results reported.
McRoy (1970a) collected data on the
elemental composition of eelgrass as
compared to the ocean (28 elements;
Table 10). It is apparent that eelgrass
is actively accumulating great quantities
of many minerals.
Caution must be used in assuming that the
nitrogen content of eelgrass vegetation is
a good indicator of food value. Harrison
and Mann (1975b) have shown that up to
two-thirds of the nitrogen content of
young green leaves may represent lowmolecular-weight
soluble compounds
(nonprotein nitrogen). Actual protein
content should be determined for foodvalue
analyses.
Recent studies show that eelgrass contains
phenolic acids, suggested to be among the
primary allelopathic agents of land plants
(cf, Zapata and McMillan 1979 for a
review). In a following study, McMillan
et al. (1980) demonstrated that eelgrass
and 2. japonica contain flavone sulphates.
he^-suggested that if these seagrasses