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

CHAPTER 5
INTERACTION WITH ADJACENT SYSTEMS
There is very Little known about the
quantitative aspects ofthe transport of
living and/or dead eelyrass material, IX)M
(dissolved organic matter), and detritus.
For that reason, the discussion in this
chapter is general.
Anyone who has walked beaches where
seagrasses occur offshore has observed
detached leaves and perhaps whole plants
washed ashore, occasionally in large
windrows. In October 1975, I observed
great piles of eelyrass leaves up to 1 rn
(3 ft) deep on the beaches and covering
the intertidal zone as far as the eye
could see in Izembek Lagaon, Alaska. The
presence of a deep compacted layer of
eelgrass peat on the beach attested to
this occurring annually. In May 1976, the
Leaf matter over the intertidal zone had
decayed completely, leaving a 15-cm (6-
inches) layer of soft jelly-like ooze.
Barsdate et al. (1974) stated that the
bre&down prcducts of eelgrass in Izembek
Lagoon supportedthe entire fisheries of
the southern Bering Sea, implying a net
transport of eelgrass decomposition
products into the adjoining pelagic
system.
It is unlikely that much eelgrass in the
Pacific Northwest becomes dislodged
through herbivore activity. Waterfowl eat
the leaves they detach. In isolated
locations sand dollars (Dendraster sp.)
wedge into intertidal and shallow subtidal
meadows and uproot considerable plant
material (Figure 23). Exclusion cages
have shown that eelgrass may recover from
this perturbation. It is possible that
Figure 23.
Sand dollars ee end raster sp.) digging up eelgrass in Puget Sound.