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2015 Puget Sound Factbook Book | v3.0
terrestrial sources. Beach wrack available to beach detritivores is composed of ~60% marine
algae, 24% terrestrial plant materials, and 13% eelgrass.
8. Shoreline armoring reduces talitrid (beach hopper) abundance (Sobocinski et al., 2010),
which is an important food source for shore crabs (Hemigrapsus nudus) (Lewis et al., 2007),
birds and other animals (Toweil, 1974; Vermeer, 1982).
9. There are many types of detritivores in estuarine and marine ecosystems. Suspension
feeders, such as mussels, littleneck clams, barnacles and oysters, filter food suspended in the
water as it passes by. By contrast, benthic-deposit feeders engulf sediments, digesting the
bioavailable portions. Benthic-deposit feeders include several types of clams, polychaete
worms, gastropods, sea cucumbers, crabs and sand dollars. Grazers also depend on benthicassociated
food production, but are not classified as detritivores. Grazers consume (as a
group) a combination of fresh macroalgae, epiphytic algae, and fresh detritus. Grazers
include such organisms as snails, limpits, sea urchins, and chitons (Encyclopedia of Puget
Sound, Herbivores and detritiores in Puget Sound).
10. The benthic and nearshore communities of Puget Sound rely strongly on detritus for food
web support, especially near river mouths, tidal marshes, eelgrass and kelp beds.
Suspension-feeding mussels, for example, obtain between 11-88% of their nutrition from
detrital sources, depending on the season (Hoffnagle et al., 1979; Tallis, 2009; Howe &
Simenstad, 2014), and a variety of estuarine and nearshore invertebrates ultimately derive
their nutrition from sources other than phytoplankton (Simenstad & Wissmar, 1985).
The Salish Sea’s intertidal food webs echo those studied across the world. From
Amchitka, AK (Duggins et al., 1989), San Francisco Bay, CA (Howe & Simenstad 2011,
2011), and the tip of South Africa (Bustamante et al., 1995), strongly relying on detritus
to fuel community metabolism.
11. Detrital food webs support keystone predators, such as the Ochre seastar (Pisaster
ochraceus) which plays a key role in regulating community diversity in Puget Sound’s rocky
intertidal habitats (Paine, 1980). P. ochraceus feeds preferentially on barnacles (proportion
of diet = 10-54%) and mussels (~20%). Detritus comprises 11-88% of the diet of both prey
species (Tallis, 2009).
Pisaster ochraceus populations have dramatically declined in Puget Sound as a result of
seastar wasting disease. The cause of the disease has yet to be unequivocally identified,
but emerging research points to a viral infection of densovirus (Hewson et al., 2014),
perhaps augmented by higher than normal water temperatures (Bates et al., 2009). The
loss of this keystone predatory species indicates that nearshore food webs are dynamic in
space and time, and we expect extensive restructuring of rocky intertidal communities as
a result its removal via densovirus (Paine, 1980).
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