Olympic Coast National Marine Sanctuary embraces one of the last relatively undeveloped coastlines
in the United States. Within this coastline's intertidal zone-- the narrow belt lying between the
highest and lowest of twice-daily tides-- are some of the biologically richest areas in North
America. Here, scientists have identified over 300 resident species of aquatic plants, invertebrates
(animals without backbones) and fish. It's thought that this number may be but a fraction of the
species that actually inhabit this stretch of coast. This wealth of intertidal life can be
Contact for page content: Robert Steelquist
A Gentle Climate
Although the Olympic Coast is legendary for its ample rainfall and dramatic winter squalls, overall
the region's climate can be characterized as uniformly hospitable. Water temperatures vary little
with the seasons, while air temperatures seldom dip below freezing or rise above 80 degrees. As
such, conditions are nurturing for sea life year-round.
The Energy of the Sea
Forces of wind, wave and current batter the Olympic Coast, creating a dynamic environment for
organisms of the shore. Intertidal habitats are constantly being disturbed, and plants and animals
that can adapt to the extreme conditions are the ones that remain. There is a paradox of survival
here: richness and diversity of intertidal life depends on the constant changes brought by the
Plenty of Food
Many large rivers originate deep within the Olympic Peninsula's forests and empty into the sea,
carrying nutrients from the soil into the intertidal zone. Nutrients are also washed into the
intertidal zone by ocean currents, which carry cold, nutrient-rich waters from the ocean depths.
Both sources feed billions of small floating plants and animals (known as plankton), which, in turn,
become food for larger animals such as jellyfish, clams, mussels, anemones, sea cucumbers, and
fish. Many of these animals are food for even larger organisms - sea birds, marine mammals, other
fish, and humans.
An Array of Habitats
Along the Sanctuary's 135-mile-long coastline are exposed rocky headlands, more protected rocky
shores, boulder and cobble areas, and sandy beaches. This diversity of dwelling places offer
niches for nearly every kind of coast-dweller. Some intertidal animals and plants are specially
adapted to withstand the action of crashing waves. Many others can claim spots, however short-lived,
on tumbling boulders and rocks. Others are well suited to a life in the sand, whose seasonal
movements up and down a beach can cover and uncover areas, exposing or smothering many organisms
in the process.
An Intertidal Who's Who
Most intertidal plants and animals have elaborate life cycles that usually include a free-floating,
planktonic phase. At some point in this cycle, they settle down, adhering to the rock or burrowing
into the sand within the intertidal zone. Some intertidal inhabitants are surprisingly long-lived:
the rock scallop (Hinnites giganteus), for instance, can live for more than a century.
Predator and Prey
Some intertidal animals actively hunt and capture prey. Among the most impressive of these is the
ochre seastar (Pisaster ochraceus)-- a bright purple or orange creature that moves slowly into
shallow water to feed on California mussels (Mytilus californicus) and other stationary
invertebrates at high tide.
Protector and Protected
Others draw strength from their neighbors. This is especially evident within beds of mussels, whose
numerous nooks and crannies are known to provide shelter for over 200 species of small organisms.
A similar function is served by the various red algae (such as Iridaea spp.) that grow in dense
mats, under which many animals hide from predators, wave action or stressful conditions at low tide.
Many species have entered into curious partnerships with other life forms. The giant green anemone
is one of these: its bright hues are the product of microscopic green algae, which grow in the
anemone's digestive tract. Some scientists think that the compounds produced by the algae may be
feeding the anemone.
Be sure to read our page on tidepool ettiquette before you explore
this rich habitat.