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

masses among the eelgrass stalks. This
commonly occurs in areas where tidal
currents are aluggieh. There are no
rhizophytic benthic macrophytic algae in
the Pacific Northwest.
In the Hood Canal, Washington, Sargassum
muticum grows on shell fragments among
eelyrass, In summer these algae grow to
2-3 m (6-L0 ftf long and could possibly
shade the eelgrass. However, by October
the planta die back and overwinter as
short stubs 2-4 cm (1-15 rnct~es) long.
Qccas~~.rally, Laminaria, Alaria, Gracilar-
-- ea, ~smarestia, atxi Necxg2irdhiella occur
&tween the eelgrasa shoots.
Cbscnrations on benthic algae of elgrass
wadows of tk Pacitic Nortkst have been
made by Phill ips (1972; unpubl. research),
Davis (1981), and Procjnall (1983).
Often, Large mats of diatotns cover the
substrata between the shoots. This was
observed by Phifer (1929) and has been
corroborated many times. Recently,
W~iting (1983) anumeratal the micr-nthic
alq&o E L S L ~ ~ C L with ~ ~ U the ~ setlimeut of
euLqraea tneadows in Netarts Hay, Oregon.
Little has been done an the procluct~on
values of Ulese algae.
1975; McRoy and McMlllan 1977). Penhale
(1977) observed that eelgrdss epiphytes
can constitute up to 1~3% oE the annual
production of carbon of the eelgrass
primary production system (20Gt
mgc/m2/day). Carbon, nltroyen, and
phosphorus travel from t-lgrass blades to
epiphytes to the water and vice versa
(Harlin 1973, 1975, 19W; Wetzel ailti
Penhale 1979; Penhale atd Thayer 1980:.
In the Pacific Northwest, Keiltula (i983)
found that epiphyte biomass coultf be as
much as 2.3 tlmes that of the Leaf. she
also estimated that the net prrrnary
productlon of these epiphytes accounted
for approximately 85 of the cornbilled
eelgrass (above- and below-ground) and
epiphyte prorluction.
The epiphyte list can be enornlous and
varied urider the usage ddopted r11 th~s
report. It may include sessrle plants axl
animals, mobile epifauna and epibenthos
+A&t crawl onto the plants, bacterld, and
detritus (tlarlm 190B). Kikuchl ad Peres
(1977) also included In the rnobile
epifauna a group of swir~ning anrmals which
often rest on the eelgrass leaves. Table
11 I from Burkholder and 1)rjheriy l96U) lists
the numbers of bacterla associated with
the sediment, water, and eelgrass Ln New
York .
tlarlin I19751 listed the factors which
~nf luetlce the coexistence between host an3
c"pi#lyte r
1. Physical substrate
2. Rccwas to photic zone
3. F'tw rrlde through wing waters
4. Nutrient excharge with host
5. Oqctnic cdrborl wwcw
The epiphytic plants, bacteria, and diatom
coating on the leaf surface often form a
brownish felt. This felt shelters and
feeds members of the epifauna, as well as
inat~y grassbed predators (amphipods and at
least four species of ducks and some
Table 11. Bacteria in the eelgrass
hbitat ( ~ ter f Burkholder and IBheny
1968) .
---- ----
Ol.casion*Lly it; waters with little tidal
movument, coating of blue-green algae Station '1- of sample bcteria/g
my ba found otl the eelgrass blades (Davis
--------
or ml
1913). Blue-green algae are occasionally
found on the eelyrass in the Pacific 1 Mud 1,388,0@0
Northwest. McRy et al. (1973) found that Water 27,7W
these algae may fix a small amount oE Eelgrass 68,964,W
nitrogen. Considering the nitrogen
dsf iciency in eelgrass beds, this may be 2 Mud 2@0,L%M
an hnprtant source. Water 30,000
Young elgrass 1,600,000
Epiphyt@ biomass at times equals the Old eelgrass 28,72c3,000
biomass of the leaves (Marsh 1973; Harlin
36