"Nature Guide Journal"

28 June 2001

During minus tides, clam diggers flock to the bays and estuaries of the Oregon Coast seeking empire clams, cockles, and other dinner-bound mollusks.

Estuarine mud can be a very challenging place to live: salinity and temperature may change drastically with the weather and the tide; the shoreline is regularly exposed by low tides; currents and wave action move sediment, burying, scouring, or dislodging residents.

Further, very fine sediments in quiet waters can exclude oxygen, suffocating aerobic (air-needing) animals and fostering anaerobic (air-avoiding) bacteria. The anaerobic bacteria break down the rich organic material in the sediment and produce black, smelly–and rather toxic–hydrogen sulfide.

Most mud-dwelling animals need to reach the surface for the oxygen- and food-laden water. Clams use their siphons (necks) to stretch to the top of the mud; other animals stay near the surface or construct burrows that bring seawater down to their hiding places.

Filtering microscopic, drifting plankton from the water is one way tideflat animals (such as clams and most burrowing shrimp) gather food. Some tideflat residents (such as many of the worms) glean organic material from the sediment; others feed on larger plants; still others feed on larger animals.

As clammers pursue their quarry, they encounter many other denizens of the estuarine tideflat.

By mid-summer, the surface of the mud is often brownish and slick from the large populations of microscopic plants–diatoms. Great beds of slender green eelgrass extend up into the lower intertidal. Tufts of delicate, bright-green sea lettuce and tough, olive-brown rock weed grow attached to exposed rocks and logs.

Many of the larger holes in the upper intertidal may fool inexperienced clammers. Several types of burrowing shrimp excavate and maintain U-shaped burrows in the sediment. The pinkish ghost shrimp (Callianassa californiensis) makes burrows with volcano-shaped tops; darker mud shrimp (Upogebia pugettensis) digs burrows without volcano-shaped tops.

Huge numbers of many different kinds of worms burrow through the mud or work their way along the surface. Notable segmented worms include the lug worm (Abarenicola pacifica), that leaves squiggled coils of fecal castings around it's burrow entry; and the fat innkeeper worm (Urechis caupo), so named because of the other creatures that live inside the pudgy worm and it's burrow.

My favorite segmented worm of the estuarine tideflat is the hooded worm (Pista pacifica). Hooded worms sport a durable tube that arises from perhaps a foot beneath the surface to a couple of inches above, where the top of the tube flares and curves to form a heavily-fringed hood over the opening. At high tide, the worm's tentacles gather plankton from the water.

Sometimes clammers find competition–massive-footed moon snails (Polinices lewisi) prowl the tideflats seeking clams to drill into and eat. The rubbery, coiled collars found on the tideflats in late spring are masses of their eggs, cemented with mucus and sand.

Unseen to most clam diggers, many animals live in the burrows of shrimps and lugworms, and scale worms and pea crabs make their homes inside other animals. Also unseen are the overwhelming numbers of microscopic life living between the sediment particles.

Pools and channels in the tideflats often trap small fish and crab. Nudibranchs, pile anemones, snails, and many other non-burrowing animals may be found on plants rooted in the mud or attached to exposed rocks and wood.

Digging for clams is a great excuse to explore this fascinating environment and encounter some very remarkable inhabitants!

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Visit our pages on related topics:  

tides

low tides for 2002 (on the southern Oregon Coast)

tidepooling

Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.