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

apparent darnazje. IUllzomes and roots do
not appear to be uai.ldj~4 in any case. The
best docu~nei~ted case study is that of den
Hartoq drld Jdc~bs (19od) a£ ter the tanker
~lnocd Cadiz was stranded on thz i3rlttany
coast, krdr~ce, uls~hdrqlng L~u,wC)W tuns
(13u1363,G30 kg) ok crude uil and 4,dW
tons l~,o36,3oJ kg) of bunker fuel. The
eelgrass re,naitled alr~~ost unaffected.
,*ilmal yroups were selectively df fectzd:
gastropods dere not ~ftected, and
eclllnocierms r ecovererl. i'lle ~uphlpods,
~sopods, and plychaetcs were seriously
dan~acjed and had not recovered durlng the
year followirq the spill.
The most sensitive areas containing
eelgrass nlay be in stleltered locations
elat are poorly flusllecl (Beak Consultalts
1975). These areas will tend to retain
oil for Long periods. If spi 11s occur in
late sulntner or winter when leaf sloughing
is at a peak, mats of iirlft blades will
tend to cdpture and retain oil for later
rernobllizdtiori in the intertidal zone.
'l'he authors also warn that oiling of
blades may make them unpalatable to
mtural grazers such as waterfowl. It is
also psslble that a spill 111 spring could
interrupt the production and/or viability
of young flowers and pollen. Kesearcli
should be done on the effects of oil on
the bacterial urcomposition of dead
eelyrass blades into detrltus before it
enters the food web. It is kmwn that the
eelgrass habitat car1 retain and release
oil slowly over long prlods, resulting it1
dlronic contamination.
Ueak Consultants (1975) documented the
possible impacts of an oil spill in
northern Puget Sound for a number of
&imals that use the eelgrass system. For
the waterfowl arld stloreblrds, the loss of
food or consumption of tainteci fwd, are
the greatest impacts. For the fishes the
greatest impacts are to the bottom
dwellers; i.e., narcotization followed by
suffocation or increased predation by the
less sensitive crabs. Flatfishes may
develop tumors on their ventral surfaces
in contact with polluted sediments. For
the shoreline and open-water fishes, the
movement away from the eelgrass meadow
increases the chance of predation and the
loss of food. Crabs appear to be highly
resistant to oil, but the smaller
crustaceans are more severely and qulckly
affected. Mollusks appear to be entirely
unaffected by oil ~o~ta~nination of low
aromatic content, but highly aromatic
crudes and refined products can cause
paralysis and death. qhe same was found
for anne 1 ids .
On a ranking for physical impact, the
eelgrass bed was second only to the salt
marsh: for toxicity impact the eelgrass
bed was midway between the mixed-coarse
habitat and open water habitat (~eak
Consultants 1975).
Oil spill& on the surfgrass, Phyllos~dix
scouleri, in the pacific Northwest had
similar effects. Little damage was. done
to the plants (leaves turned brown, but
were replaced; no damage to rhizomes and
roots), but some yroups of animals
received long-term damage (Foster et al.
1971; Clark et al. 1978).
Documentation of oiL spills on the
tropical seagrass Thalassia is more
extensive (cf. Zieman 1982 for a thorough
review). The results are approximately
the same; the plants are little affected
by the oil, but associated fauna can be
severely damaged. The moat severe effect
was noted when oil was spilled on
Thalassia near Guanica, Puerto Rico. In
less than 1 wk, 3,0@0 m3 of sand washed
out, owing to the mixing of the oil with
the sediments, making them buoyant and
easier to wash out. Mass mortalities of
animals occurred following the spill.
Zieman (1982) thoroughly reviewed the
research done on the toxicity levels of
crude oil and the refined fractions. Ml
work shows that refined bunker C and No. 2
fuel oil were more toxic to all animal
forms than crude oils. Changes in
temperature and salinity enhanced the
toxic effects. The greatest danger to
aquatic organisms appears to be the
aromatic hydrocarbons as Opposed to the
paraffins or alkanes. The bicyclic and
polycyclic aromatics, especially
napthalene, are the major source of the
observed mortalities. The best indicator
of an oil's toxicity ia probably its
aromatic hydrocarbon content.
In recent years humans have dumped
increasing amounts of heavy metals and
synthetic products, including chlorinated