Oregon Coast Tidepools

Within the tidepools at Cape Arago and Sunset Bay, we see several species of green algae (Chlorophyta), brown algae (Phaeophyta), and red algae (Rhodophyta or Heterokontophyta), as well as individuals representing several phyla of marine invertebrates, including sponges (Porifera); sea anemones (Cnidaria); mussels, limpets, snails, & chitons (Mollusca); barnacles, crabs, & shrimps (Arthropoda); sea stars, sea urchins, & sea cucumbers (Echinodermata); and tunicates & sculpins (Chordata).

Many intertidal organisms attach to the firm substrate to hold themselves in place in the 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 the chiton, 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 below). Whelks (gastropods) use an enzyme and their rasp-like radula to bore holes through the shells. The shells of mollusks and barnacles also help them to limit desiccation while the tide is out and they are exposed to the sun and wind.

As in the mountains, the communities of rocky tidal areas exhibit vertical zonation. In this case, the zonation is related to the height of the tides, rather than precipitation and temperature gradients. As a general rule, tolerance to desiccation sets the upper limits of the distributions of intertidal species, and the lower limits are set through competition and predation (summary by Schultz, 1990:108-115). This zonation is easiest to discern on sloping rock faces (notice the different bands across the photograph below); however, some mixing of species from different zones occurs, especially around cavities that retain water during low tides (tidepools). The high intertidal zone is covered only during the highest tides. Animals commonly found here 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). Ochre sea star (Pisaster ochraceus) and green sea anemone (Anthopleura anthogrammica) are common in the lower portion of the mid intertidal zone. The presence of the ochre sea star in the lower portion of the mid intertidal zone is a large part of the 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 amount of time that high tides inundate the upper portion of the mid intertidal zone. The low intertidal zone is only exposed during the lowest tides. This is the home of the purple sea urchin (Strongylocentrotus purpuratus), which grazes on macrophytic algae. Because it is covered by water most of the time, the low intertidal zone 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, the reef 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 in late July and early August.

In addition to the organisms among the rocky tidepools, there are also animals that make their home on or within the sandy beaches of the coast. Among the more brightly colored animals is the ghost shrimp (Neotrypaea californiensis), which can live for 10 years in a U-shaped burrow that is also home to several other species (Sept, 1999:112).

Sunset Bay is the mid-point of our trip, and we spend a couple of nights camping here. Although our mornings are filled with class activities, we spend the afternoon and evening enjoying the scenery, revisiting tidepools, dining on seafood, and doing laundry.

Included in this "down time" is a visit to Shore Acres State Park, located between Sunset Bay and Cape Arago. Shore Acres is a botanic garden situated on the rocky bluffs above the ocean. It features English and Japanese gardens, as well as a colorful planting of 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.

Literature

• 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.

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