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Between Land and Sea

Tide Pools - Intertidal Zones
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Between Land and SeaSpringtime tide pools are full of lifeStory by Sue MadsenTide Pools - Intertidal ZonesThe space between sea and land is a mysterious and intriguing world called the intertidal zone. Plants and animals that live on the edge need to be either tough and highly adaptable, or fast enough to avoid being stranded on land after the tide recedes. The intertidal zone is often a flat, seemingly empty beach populated by broken shells, loose bits of seaweed and the occasional sea bird. If you know where to look, a whole new world is often revealed in the tide pools that can be found at many beaches in the Northwest.

Tide pools are pockets of seawater along rocky shorelines that are created as the water retreats after high tide. They can range from shallow depressions on the tops of rocks to deep cracks filled with abundant sea life. Tide pools contain water throughout the 5 to 6 hour low tide cycle; so marine animals can survive or even thrive over the long term. Pacific Northwest tidepool denizens include ochre stars, green anemones, mussels, barnacles, chitons, hermit crabs, sea cucumbers and various species of a hardy little fish called the sculpin.

Tidepools are usually found on any coast that has a rocky shoreline, and we are fortunate there are several nearby state or provincial parks that provide excellent sites for tide pooling. One of my favorites is Larrabee State Park near Bellingham. Check out the rocks just southwest of boat launch. Deception Pass State Park near Anacortes is also a wonderful tidepooling destination. Deception Pass actually sports a marked tidepool trail along Urchin Rocks at Rosario Beach on the northwest side of the park. I dive this area regularly and am always amazed by the abundance of orange sea cucumbers in the area. To the north, try Lighthouse Park in West Vancouver. Lighthouse Park has beach access to many small rock-rimmed coves. As an added bonus, the park also offers an abundance of hiking trails through the city’s last remaining stand of old growth Douglas fir. Lily Point in Point Roberts is also a good place to find tide pools.

The very best time to go tidepooling is on a minus tide. The average low tide level is represented as zero, so in tide tables and charts minus tides appear as negative numbers. Tide levels vary monthly depending on the location of the moon relative to the sun, but the lowest (and highest) tides always occur either when the moon is full (moon and sun are on exactly opposite sides of the earth) or during the new moon, when the moon is between the sun and the earth. Tide levels also vary seasonally, with extreme low tides occurring near the solstices in December and June. In our area minus tides can be more than three feet lower than the average low tide. Tide tables can be found in guidebooks, the weather section of many newspapers or can be looked up online at freetidetables.com. The exact time of low tide varies by location, so be sure to check a local source of information. The lowest tide of the day occurs in the middle of the night during the winter months, but in summer extreme low tides occur right around midday, providing the perfect excuse to get out to the beach for a picnic and some exploration. In 2013, spring minus tides will occur April 26-29, May 24-28 and June 2-26.

Tidepooling is an easy adventure for all ages. It pays to wear either knee-high rubber boots, or sandals/water shoes that can get wet. Pick footwear with a decent tread, as exposed rocks can be slippery. Watch where you step to avoid crushing or disturbing animals. Lifting a rock can often reveal interesting creatures that are hiding underneath, but take care to replace the rocks in the same position as you found them. Many tidepool creatures are delicate and use rocks for protection when their home is exposed to sunlight and high air temperatures. Many tidepool animals defend themselves against predators with spines or substances that can cause skin irritation, so it is best not to touch them. The Marine Life Center at Squalicum Harbor in Bellingham has a touching pool, great for kids and animal lovers.

Species profiles.

Ocher sea stars are generally either bright orange or a vivid purple. They have five stout legs that radiate out from a central disk that contains the mouth and internal organs. The top of this common starfish is peppered with small bumps that are actually small spines, while the bottom has hundreds of tiny tube feet. While a sea star may seem fixed in place when exposed by the tide they can actually move surprisingly quickly across the sea floor when submerged. Their feet have suckers on the ends that allow them to hang onto rocks and stay put despite the surf’s best efforts to dislodge. Ochre stars eat mussels, chitons, limpets and snails, and can consume larger prey by expelling their stomach outside their body from their mouth to engulf and liquefy the food item. In turn, sea otters and seagulls eat Ochre stars. They have the ability to regenerate legs and it is not uncommon to see one with just two to three stumps.

Green anemones are a species of intertidal anemone that can be as small as a penny or as large as a salad plate. They attach to rocks or pilings by a stalk that is often hidden by a crown of tentacles. These tentacles have stinging cells that provide protection from predators and allow them to capture prey. When exposed to air the crown closes up and looks like a soft brownish-green button, but underwater the tentacles spread and appears bright grayish green. Green anemones eat small fish and crabs and detached mussels, and they are eaten by leather sea stars, nudibranchs and snails.

Barnacles are crustaceans that attach themselves firmly to a hard rock or other shells and then grow shells consisting of a ring of hard bony plates. Their edges are sharp and can give fingers or bare feet a nasty cut. The animals live inside the shell and, when submerged in seawater, extend feathery appendages that wave in the water to draw food into the shell. When exposed at low tide barnacles retreat back into the shell and close tightly. They eat plankton and detritus, and are eaten by snails and starfish.

Sculpins are small bony fish with large heads and long, thin bodies that taper back to a tail with spiny fins. There are hundreds of sculpin species and most have venomous spines on both dorsal fins and pectoral fins, or gill covers. Sculpin stings are generally not deadly, but can be very painful and usually result in swelling and reddening the area of contact. Typically, sculpins’ coloration allows them to blend in with rocks and sand, and are seen only when they dart quickly for cover. They eat small invertebrates, shrimp and worms but are eaten by larger fish and crabs, great blue herons, river otters and raccoons.

Limpets are small sea snails with conical shells. Like barnacles they cling tightly to rocks and other hard surfaces with a muscular ‘foot,’ and are able to survive periodic exposure to the air and sunlight. Limpets feed by grazing on algae that grows on the surface of rocks. They are chow for sea stars, shore birds and fish. X

Sue Madsen is a fluvial geomorphologist who likes to climb, ski, backpack, sea kayak and explore the PNW’s wild places.

Tide Pool Tips
The Washington Department of Ecology offers these tips:

  • Look, learn and leave things as you found them.
  • Resist the temptation to take animals or plants. Most creatures brought home from the shore die and end up smelling in the trash.
  • Be careful where you step. Don’t trample intertidal plants and animals. Walk on bare sand or rocks, if possible.
  • If you pick up a rock, a piece of seaweed or an animal, gently put it back in its place. This will help keep animals safe from predators and temperature extremes.
  • Do not touch or disturb birds or marine mammals.
  • Pick up trash