COLLECTING THE MARINE INVERTEBRATES OF OREGON’S ROCKY INTERTIDAL AREAS

Oregon’s rocky marine intertidal areas are often an easy opportunity for the casual observer to view a sampling of our coastline’s teeming underwater wilderness up close. Though seemingly hostile in appearance, the habitat created by the shallow, pounding surf and cold, nutrient rich waters provides a unique home to a vast array of diverse and interesting aquatic denizens. However unique it may be, one can attempt to bring a small piece of this beautiful creation into their own home aquarium for study and appreciation. But, beforehand, careful research and preparation is vital before such an undertaking can be successfully accomplished.

Idealistically, the marine intertidal fauna of Oregon’s coast are very much suited for life in their own challenging and narrow habitat. For many of us, however, driving several hours to see these animals is simply not enough: we must attempt to bring them home. It is a lawful prospect in many areas, and careful explanation of the laws can be described in the list of Oregon Department of Fish and Wildlife regulations, updated annually and easily obtained through many bait and tackle stores statewide. Though best suited for a refrigerated marine aquarium, many of the animals from tidepools will survive if kept in a purposely understocked marine aquarium placed in a cool basement or room at room temperature during the cooler times of the year. Most animals thrive at 50 to 55 degrees Fahrenheit, though they can tolerate temperatures up to 75 degrees for limited periods of time as the tidepools they often occupy may warm up significantly after several hours of direct, summer sunshine. Any extra aeration or water movement in such a setup will only increase the oxygenation and, hence, the animals’ survival.

When choosing a collecting site, one should be careful to observe the law. Special rules and regulations often apply to certain areas of the coast which have found to be under a great deal of potential risk. Haystack Rock at Cannon Beach, for example, is now closed to the taking of all intertidal animals due to its extensive intertidal habitat that is easily accessible to beachcombers. Another similar area lies adjacent to Cape Foulweather on the Central Oregon Coast. This area lies immediately below the town of Otter Rock and is known as "Marine Gardens" on some maps. It is also closed, chiefly due to the size of extensive marine intertidal area, boasting a hugely diverse ecosystem that even includes marine mammals and shore birds. While both sites are closed to the taking of animals for personal use, they are still quite open to those who wish to come and observe, and only "capture" on film. These noteworthy sites aside, there are numerous smaller intertidal areas all along the coast which allow the taking of up to ten (10) nonfood intertidal invertebrates in one day by any one person. Such a haul would most certainly be enough to establish and populate almost any size of a native marine aquarium in no time at all.

The habitats within Oregon’s intertidal areas can be easily divided up into three basic zones: high, middle, and low. Each respective area contains lifeforms well-suited for survival in their unique habitat. The zoning of the intertidal region obviously reflects the fact that areas closer to the ocean will be more frequently covered and inundated with sea water than those areas which are higher and further away from the water. The tides vary in height and reach as well, rather than predicatably covering the same spot along the beach twice a day. This difference in fluctuating tides proves advantageous to some animals and disadvantageous to others. For example, colonies of California Mussels can exist in higher intertidal areas than that of the Ochre Sea Star (Pisaster ochraerus), its chief enemy, because the mussel has a hard bivalve shell to keep water inside, whereas the sea star does not and must remain under rocks or further down in the intertidal area to avoid prolonged exposure to the air and surface predators, like birds. Therefore, the sea star can only advance a certain point up into the mussels’ territory.

Due to how certain animals exist and co-habitate in the intertidal ecosystem, the demarcations between zones can become very clear. Higher intertidal zones usually consist of exposed rock covered with a thin film of algae. Acorn barnacles exist in great numbers here, as they can readily withstand being exposed to sunlight and air for great lengths of time without drying out. Small periwinkle snails and limpets also exist here, feeding off the thin film of algae at high tide and hiding in cracks or under rocks when the water level has dropped. The middel intertidal zone is an area typically populated with dense colonies of mussels and various species of small macroalgae, like sea lettuce (Ulva sp.) and rockweed. The mussel beds are great hiding places and habitats within themselves, providing a dense, labrynthine home for all sorts of marine organisms, from barnacles and porcelain crabs to sea cucumbers and even small fishes, who wait there for the returning tide. Often lining the tidepools of the middle intertidal area are large numbers of the delicately-colored Aggregating Sea Anemone, Anthopleura elegantissma. The lower intertidal zone is an area predominated by larger kelps and coralline algae. The most obvious inhabitant of this area is probably the Giant Green Sea Anemone, Anthopleura xanthogrammica, and, in certain cases, the Purple Sea Urchin, Stronglyocentrotus purpuratus. The lower intertidal zone contains the most diversity of life forms when compared to the other two zones of the intertidal region.

Many of the common intertidal animals make good aquarium residents. Probably the hardiest of the animals include the sea anemones, Anthopleura sp.. Both the Giant Green Anemone and Aggregating Anemone can make excellent, long-lived aquarium residents after they have been carefully peeled from their rocky moorings. Bright lighting is must for all sea anemones’ survival.

Mollusks, like the ubiquitous Black Turban Snail (Tegula sp.), Shield Limpet, and Mossy Chiton, can make fine grazers of algae that grow on the rocks and panes of the aquarium. Most nudibranchs or "sea slugs" are indeed very beautiful but should not be expected to live long in the home aquarium, due to their delicate nature and particular dietary needs. One such exception is the Sea Lemon, Archidoris montereyensis, which prefers sponges but may also graze on "live rocks" from tidepools. Other nudibranchs, like the Hermissenda (Hermissenda crassicornis) are active carnivores, preying on sea anemones and even other nudibranchs.

Of the echinoderms, two species of sea urchin are known to occur in Oregon’s rocky intertidal zone, but both occur in the lower areas and thus do best in a chilled tank. Both are predominately vegetarian in nature. The Red Sea Urchin is a large animal that demands a lot of room: this is the species most commonly associated as a main threat to kelp forests, dining on the rootstalks of Giant Sea Kelp off the coasts of California and the Pacific Northwest. The Purple Sea Urchin is smaller and usually more abundant, living in dense colonies at the bottom of pools and channels in choicest habitats. The sea urchins relatives, the sea stars, are predatory in comparison. Even small species, like the Six-Rayed Star, can prey on snails, sea cucumbers, and even other sea stars. The big and abundant Ochre Sea Star is unsuitable for most aquariums but often small individuals can be found under rocky shelves or boulders and may potentially work as suitable aquarium inhabitants. The giant, ultra-carnivorous Many-Rayed Star (Pycnopodia helianthoides) is fascinating to watch, but its demands are best met in public aquariums maintained by professionals. Also related to the urchins and the stars are the sea cucumbers, which are filter feeders and detritivores. White Sea Cucumbers (Eupentacta sp.) are commonly found in mussel beds of the middle tidal zone, while Red Sea Cucumbers (Cucumaria miniata) are found in pools of the lower intertidal zone. If handled carefully and kept cool, both species may survive in marine aquariums. If they are not happy they will die immediately and generally do a good job of fouling the water if they are not immediately removed.

Various crabs can be found all throughout the intertidal region. The Hermit Crab (Pagurus sp.) and Purple Shore Crab (Hemigraspus sp.) are scavengers by nature and usually quite fun to watch. The aquarium must be carefully covered, however, to prevent the crabs from crawling out along an airline or filter attachment to "freedom." Additional shells should be added to the aquarium as it will be necessary for the Hermit Crab to change into a larger shell as it grows. Less frequently found, Decorator Crabs are interesting scavengers that decorate the backs of their carapaces with seaweed fragments and small sessile invertebrates as camoflauge. However, they must have chilled water in order to survive. Rock Crabs (Cancer sp.) can be found as attractively striped juveniles under rocks or in pools. However, these predators should not be trusted with other inhabitants: some species are also covered by shellfish regulations. Many other animals occur in the intertidal ecosystem, but are usaully best left alone unless one has a refrigerated aquarium and is willing to experiment.

REFERENCES:

McConnaughey, Banard H. & Evelyn. 1986. "The Audubon Society Nature Guides: Pacific Coast." Alfred A. Knopf, New York.

Osis, Laimons. 1975. "A Guide to Oregon’s Rocky Intertidal Areas." Oregon Department of Fish and Wildlife, Newport.

Used with permission. Article copyright retained by author.