17 May 2001

The very low tides next week will tempt many people to visit our rocky coast.

Many visitors and school groups, as well as local residents, trek down to the rocky beach to take advantage of the life exposed by the tide.  Tides vary quite a bit, and very low tides expose communities of plants and animals that are seldom uncovered.

The exotic, jewel-toned animals and plants are the first to draw us, but the big stories can be even more tantalizing. Experienced tidepoolers look closely and watch carefully to get the most from their limited visit before the tide returns.

The life exposed by the ebbing tide are marine plants and animals that can withstand various amounts of exposure to the non-marine environment.  Air, sun, wind, rain, snow and hail, as well as land animals, are serious threats to sea life.  Drying, heating, freezing, becoming too fresh or too salty, and being crushed or eaten by land animals are critical challenges for intertidal life that their deep-water cousins do not face.

Shells that seal tightly and tissues that hold water are common adaptations that keep animals from drying out.  Animals that can move seek shade and moisture by hiding in crevasses, seeking cover under and between mussels and plants, sharing pits and holes with sea urchins and piddocks, or clamping down on the rocks or each other.  And while free-floating youngsters of attached adults may settle broadly, those that attach to a too-exposed location die young.

The ability of a given marine organism to survive the rigors of non-marine exposure is a primary factor in where it can be found.  The horizontal patterns of communities, called "zones," are chiefly determined by the physical limits of the organism, as well as by the limits of its enemies and competition.  For example, the upper limit of the mussel bed is primarily determined by the young mussels' tolerance for exposure; the lower limit of the mussel bed is primarily determined by the upper limits of a major predator's–the seastars'–tolerance for exposure.

Even with these significant challenges to survival, animals and plants are often tightly packed beside and atop each other as they compete for space.  Of course, the highest competition is for the most protected spots: in cracks and under other animals and plants.  Even an apparently empty shell will likely harbor a hermit crab, tiny snails, minute tube worms, small barnacles, and a variety of plants.

Although very low tides are targeted by many tidepoolers seeking more glamorous animals and plants, the bright colors, strange shapes, and exciting stories are available with any tide below +1 feet.

Adapted to withstand the rigors of limited stranding from their marine environment, the plants and animals of the rocky intertidal aren't well adapted to withstand the rigors of people.  Human visitors should step carefully and touch gently.  Moving kelp and rocks to explore beneath brings whole worlds to our view–and to their danger:  the kelp and rocks must be returned to the position found to protect the animals sheltered there.  Many loose animals can be gently picked up to examine, but those attached should be left attached.  Pulling a seastar off it's rock, for example, will rip off many of the tube feet that it needs to move and to stay attached when the surf returns.

And, most easily accessible, rich rocky beaches on the Oregon Coast are protected by law to preserve these remarkable places.  We visitors should take the memories of our delightful discoveries with us, but leave the plants, animals, and shells in their homes.

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Visit our pages on related topics:  

tides

low tides for 2002 (on the southern Oregon Coast)

tideflat denizens