Between a Rock
         and a Hard Place

A rocky, hard surface is best for many marine invertebrates, fish, and algae.


Story and photos by Joanne Huemoeller

T
he oregon coast may not be known for the coral reefs that grace many tropical dive locations. But our rocky reefs and other natural and man-made “hard surfaces” often rival their tropical counterparts in richness and diversity of life. Between our rocks and hard places, the Oregon Coast offers a wealth of specialized habitats for countless marine invertebrates, fish, and algae, all of which contribute greatly to the beauty of our temperate ocean waters.

It all starts with prime ocean real estate, specifically any hard surface. For many invertebrates, attaching permanently to such a surface is a way of life, the only way of life. When a free-swimming barnacle larva feels the urge to settle out, it selects a hard surface and permanently glues its head to that rock, piling, or shell. The barnacle has a lot of company in its sessile lifestyle. Other invertebrates — mussels, sponges, bryozoans, hydrocorals, tubeworms, and gorgorians — also live permanently attached to a hard surface. Should some misguided barnacle attempt to glue its head to a sand or mud bottom, the end result would be a disastrous dead-end trip up onto the beach. Attaching to a hard surface is the only option for these animals.

Other rocky reef denizens do not attach permanently, but nonetheless limit their activity to the confines of the reef.

The Giant Pacific Octopus  is found along rocky shores and at  depths up to 1650 feet.

Above: The Giant Pacific Octopus is found along rocky shores and at depths up to 1650 feet.
Below: The Rosy Rockfish lives near offshore rocky reefs.
Bottom: The Giant Spined Star roams rocky and sandy bottoms.

Rosy RockfishWhile some sea anemones can “swim,” the white-plumed sea anemone moves about more deliberately by simply extending its foot. Ribbed limpets are homing, always returning to a precise spot after grazing. That spot is the scar their shell has left on the rock. Sea cucumbers browse on detritus as they use their suction-cupped tube feet to hold the hard surface. Sea stars and crab roam the reef freely looking for prey or scavenging what has been left behind. These animals keep to the reef because they, too, need to get a grip.

Fish take a different approach to life near a hard surface. They hover on or near a reef, a shipwreck, or pilings below a dock. In each of these locations, water motion is defused much like the wind is calmed in a forest. Fish that prefer this habitat take advantage of the shelter and the abundance of food it offers. Some fish, the wolf eel for example, actually hide within the reef’s crevices and caves when not feeding.

Although an octopus is an invertebrate rather than a fish, its behavior Spined Starfishmirrors that of a wolf eel. Fully capable of jetting about when threatened or searching for food, it does not need to be attached to the reef. It prefers life on or near a hard surface because that is where it finds most of its food, and because cracks, caves, and other openings in the reef offer a variety of den sites.

Fish and invertebrates are not alone in their need for a hard surface. Rootless kelp is only found where there are rocks or hard surfaces to which it can anchor—think about the algae you see growing on pilings and the underside of floating docks. But not any hard surface will do. Spores must settle on a surface that is big enough to support the plant’s eventual weight and size. After the next big storm, look for kelp on the beach that has a small rock still attached to its holdfast—evidence of spores that settled on rocks too small to support the weight of the plant and resist the battering of waves.

For animals and plants preferring to be between a rock and a hard place, the Oregon Coast offers all they need. Rocky shores, wharfs with their pilings, and even an occasional shipwreck provide a place to hide, a place to anchor, and a place rich with food. So, you see, it’s not so much that they are caught between a rock and a hard place—for these animals, the choice is only between a rock and a hard place.

Oregon Coast July/August 2007

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