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

days; at the other site, only 10% remained
after 51 days (based on dry weight).
In the laboratory Harrison and Mann
(1975a) found that dead eelgrass leaves
lost 35% of the original dry weight in 100
days at 20O C. Whole leaves lost 0.5% of
the organic content per day; particles
smaller than 1 mn lost l%/day. Since most
leaves of Thalassia and Zostera remain
attached to the plant during senescence
and death (McRoy 1966; Zieman 1968;
Harrison and Mann 1975a), the data
indicate that the loss of organic matter
from attached leaves is slow during the
remainder of processing. Godshalk and
Wetzel (1978) described three phases in
eelgrass leaf decomposition based on
changes in decay rates in time: (1)
increasing weight loss from leaching and
production of DOM; i.e., initial leaching
and maximum weight loss/unit time (may
last from a few minutes to several days);
(2) decay rates decreased; during phase 2,
the microbial flora on the decomposing
leaves enriched the material with ATP and
nitrogen (may occur in a few days to a few
months); (3) rate of breakdown of residual
refractory material closely approaches
zero, but can be accelerated by changes in
physical conditions or nutrient
replenishment to stimulate microbial
growth (may last from several months to
several years).
Thus, the mechanisms that give rise to
detached plants and to leaf decay and
detritus are apparent. What are lacking
are the studies that define seasonality
and ab-ance of the fractions of eelgrass
material (DOM, particulate matter, whole
leaves) which are retained within the
system and are exported to adjacent
systems, and their contributions to these
adjacent systems.