Virtual Viewing

Inside Passage Audio Guide
Intertidal Zone


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Intertidal Zone

The tidal range in the Inside Passage is extreme. The average difference between a low and high tide is about 15 vertical feet, and is often as much as 25 feet. This creates a wide intertidal band chock-full of seaweeds and small animals. Tide pools in the zone teem with small fish, hermit crabs, anemones, marine worms and other life.

Tlingits have a saying, "When the tide is out, the table is set." The abundance of food in the intertidal zone draws foragers from both the marine and terrestrial worlds. When the tide is up, fish, otters, diving seabirds and ducks feed in the shallows; when the tide is out, mink, bears, ravens, crows and gulls tear mussels from the rocks and hunt for crabs and other edibles amid the rocks and tide pools.

In some ways the intertidal is a harsh zone that demands special adaptations from those living there. Plants and animals must be tolerant of both fresh and salt water, dehydration, baking sun and complete immersion. Wave action can batter the shoreline. But life has adapted to these conditions, and hundreds of species of vertebrate and invertebrate life inhabit this zone. Most are specialized to a certain part of the zone, and can be seen in bands across the rocks.

The upper level of the intertidal zone is home to the hardier creatures: barnacles, snails and limpets, which can withstand the longer twice-daily exposure to air. Limpets are mollusks with a single, cone-shaped shell they pull down tight against the rock when the tide is out. The familiar crusty white shell of the barnacle protects a tiny animal inside that filter-feeds when the tide is up, combing the water with a feathery appendage.

The midlevel abounds with blue bay mussels - filter feeders that siphon the water when the tide is up and close up tight when the tide is out. Chitons (small, flat mollusks with a shell of eight overlapping plates) slowly creep through the zone rasping algae off the rocks. Sea slugs and anemones find shelter in cracks and puddles.

The lower intertidal level supports the greatest variety of life. This is where brightly colored sea stars prowl, "starfish" that prey on mussels, snails and slow-moving intertidal creatures. Sea urchins, polycheates (segmented marine worms), snails, clams and mussels, and a myriad of more mobile creatures such as fish, shrimp, crabs and octopus thrive here. Kelp and other seaweeds flourish at this level as well.

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