Download Oregon Tidepools - Fort Hays State University

Marine
Ecosystems
Sunset Bay SP Tidepools
Oregon
Department of Biological Sciences, Fort Hays State University
Instructor: Mark Eberle
Course Homepage
One coastal ecosystem we visit in Oregon is the rocky tidepool. We camp at Sunset Bay
State Park, located near Coos Bay on the Cape Arago Highway, so named because it
terminates at Cape Arago.
Exploring the Tidepools at Cape Arago State Park, Oregon
(with Mary Schmidt, Niki Lambrecht, and Mark Eberle)
Photograph by William Cook, August 2000
Within the tidepools at Cape Arago and Sunset Bay, we see several species of green algae
(Chlorophyta), brown algae (Phaeophyta), and red algae (Rhodophyta). We also see
individuals from several phyla of marine animals, including sponges (Porifera); sea anemones
(Cnidaria); mussels, limpets, snails, and chitons (Mollusca); barnacles, crabs, and shrimps
(Arthropoda); sea stars, sea urchins, and sea cucumbers (Echinodermata); and tunicates and
sculpins (Chordata). Several are included in the photographs on the next page.
Marine Algae and Animals, Sunset Bay Tidepools, Oregon
Can you identify any?
Photographs by Jennifer Matiasek, August 1997 (top left) and Curtis Wolf, July 2005
Many intertidal organisms attach to the firm, rock substrate to hold themselves in place
when exposed to waves and currents. Because they are sessile, attached organisms depend on
these same currents to bring them food in the form of small organisms that swim or drift in
the water. Others, such as chitons, limpets, and sea urchins, are grazers on the various types of
algae attached to the rock surfaces. For protection against predators, many of these organisms
have hard protective shells or plates. Carnivores, such as sea stars and whelks, have developed
interesting methods to overcome the protective shells of the mussels and barnacles that they
eat. Sea stars pull the shells of the mussel apart and invert their stomach inside the bivalve to
digest the soft tissues (photograph next page). Whelks (gastropods) use an enzyme and their
rasp-like radula to bore holes through the shells. In addition to protection from predators,
shells of mollusks and barnacles also help them limit desiccation while the tide is out and they
are exposed to the sun and wind.
Ochre Sea Star Wrapped around Mussel, Cape Arago SP, Oregon
Photograph by Mark Eberle, July 2002
As in the mountains, communities of rocky tidal areas exhibit vertical zonation. In this
case, the zones are related to the height of the tides rather than precipitation and temperature
gradients. Generally, tolerance to desiccation sets the upper limits of species distributions, and
lower limits are set by competition and predation (summary by Schultz, 1990:108‒115).
These zones are easiest to discern on sloping rock faces (notice the different bands across the
photograph below); however, some mixing of species from different zones occurs around
cavities that retain water during low tides—the tidepools.
North Cove Tidepool Area, Cape Arago State Park, Oregon
Photograph by Mark Eberle, August 2000
The high intertidal zone is covered only during the highest tides. Animals commonly
inhabiting this zone include the Acorn Barnacle (Balarus glandula) and limpets that are well
adapted to tolerate desiccation. The mid intertidal zone is regularly covered and uncovered
by the tides, usually twice each day. The upper portion of this zone often can be recognized
by the presence of beds of the California Mussel (Mytilus californianus) and Goose Barnacle
(Pollicipes plymerus) (dark band in the photograph above). Ochre Sea Stars (Pisaster
ochraceus) and Green Sea Anemones (Anthopleura anthogrammica) are common in the lower
portion of the mid intertidal zone (central pinkish band in the photograph above). The
presence of the Ochre Sea Star in the lower portion of the mid intertidal zone is a primary
reason that mussels are generally restricted to the upper portion of this zone. Sea stars,
whelks, and other predators susceptible to desiccation have difficulty feeding during the
limited time high tides inundate the upper portion of the mid intertidal zone. The low
intertidal zone is only exposed during the lowest tides (dark band closest to the water in the
photograph on the previous page). It is the home to the Purple Sea Urchin (Strongylocentrotus
purpuratus), which grazes on macrophytic algae. Because the low intertidal zone is covered
by water most of the time, it has the greatest diversity of organisms in the tidal area.
Simpson Reef (photograph below) extends north from Cape Arago. Even though the reef
can be reached at low tide from the tidepools at the North Cove of Cape Arago, it is part of
the Oregon Islands National Wildlife Refuge and is closed to all public use. However, a
viewing area along the Cape Arago Highway provides a good vantage point from which to
watch marine mammals and birds with binoculars or a spotting scope. We have regularly
observed the Harbor Seal (Phoca vitulina), Elephant Seal (Mirounga angustirostris),
California Sea Lion (Zalophus californianus), Stellar (Northern) Sea Lion (Eumatopias
jubatus), Pigeon Guillemot (Cepphus columba), and Black Oystercatcher (Haematopus
bachmani) on our trips (photographs below).
Simpson Reef (Shell Island in the center), Cape Arago State Park, Oregon
Photograph by Mark Eberle, July 2005
Shell Island, Simpson Reef, Cape Arago State Park, Oregon
Photograph by Eric Hoch, July 2002
In addition to organisms among the rocky tidepools, there are animals that make their
homes on or within the sandy beaches of the coast. Among the more brightly colored animals
is the Ghost Shrimp (Neotrypaea californiensis), which can live 10 years in a U-shaped
burrow that is also home to several other species (Sept, 1999:112).
Ghost Shrimp, Sunset Bay State Park, Oregon
Photograph by Eric Hoch, July 2002
Sunset Bay is the mid-point of our trip, and we spend 2 nights camping here. Although
our mornings are filled with class activities, we spend the afternoon and evenings enjoying the
scenery, revisiting tidepools, dining on seafood, and doing laundry.
Sunset Bay, Oregon (10-minute walk from our campsite in the coastal forest)
Photograph by Mark Eberle, August 2000
Included in this “down time” is an afternoon visit to Shore Acres State Park, located
between Sunset Bay and Cape Arago. Shore Acres is a botanical garden situated on rocky
bluffs above the ocean. It features English and Japanese gardens, as well as colorful beds of
award-winning hybrid roses. Rough-skinned Newts (Taricha granulosa) live in the pond in
the Japanese garden. During the early 1900s, Louis Simpson, West Coast lumberman and
shipbuilder, had a mansion and gardens on this spot. During the Great Depression and World
War II, the tracts of land that now comprise Sunset Bay, Cape Arago, and Shore Acres state
parks were given or sold to the state of Oregon.
Bluffs and Japanese Garden Pond, Shore Acres State Park, Oregon
Photographs by Mark Eberle, August 1998
Literature Cited
Schultz, S. T. 1990. The Northwest Coast: A Natural History. Timber Press, Portland, Oregon.
Sept, J. D. 1999. The Beachcomber’s Guide to Seashore Life in the Pacific Northwest. Harbour
Publishing, Madeira Park, British Columbia, Canada.
Next Stop: South Slough Estuary | Species Checklists | Return to Trip Summary Homepage