February 22, 2018
Salish Sea, Pacific Northwest
As winter eases into spring, low tides in the Salish Sea are beginning to shift into daylight hours. Beaches widen. Lots more marine life to see. Yesterday I took a stroll on one of the few sandy beaches we have and ran into thousands of tube worms.
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In the title photo, between the rocky upper half of the beach and the seaweedy water’s edge, the muddy sandy area has two distinct zones of tube worms, with each individual worm tucked inside a vertical leathery tube embedded deep into the sand. The upper zone is inhabited by the Bamboo Tubeworm (aka Jointed Three Section Tubeworm), Spiochaetopterus costarum, a filter feeder whose thin tubes extend two feet deep.
Footprints show scale. The holes indicate clams below, different sizes = different species.
The lower zone contains the larger Ornate Tubeworms, Diopatra ornata , which stick bits of sand and debris onto the outside of their tubes. These worm tubes are a foot deep. The worms are scavengers, poking their heads out to munch on whatever loose seaweed or organic fragments drift into their area. Needless to say, tube worms only feed at high tide, when immersed in water, which is why all we see now is tubes.
The field of Ornate tubeworms extends outward, underwater, as well
Closeup shows mostly sand particles covering the tubes.
The gulls seem uninterested in the tubeworms as food. Their favored prey on this beach are crabs and clams.
Glaucous-winged gulls hang out on the beach between meals.
Broken cockle shell, with telltale Beach Crow tracks. Both gulls and crows drop shells onto the road to break them open, and then usually haul them back onto the beach to eat. I see some flesh remaining, an indication food is so plentiful here the bird left the more difficult bits for scavengers.
A rocky island accessible at low tide is packed with invertebrates that require a hard substrate, either to attach to or to wander amongst to feed on. Solid substrate is prime real estate.
Mossy chitons — a type of mollusk — clamp down to wait out the low tide. In a few hours when the water rises they’ll start grazing the algae and bacteria film on the rock surface. Mossys are the type of chiton best adapted to lack of water, so are found highest in the intertidal.
Halichondria, the most common sponge species, comes in many colors. I like the purple. Barnacles and mussels attach to the bedrock too, while whelk snails roam. They eat barnacles.
But most of this beach is loose sediment. It appears to the casual eye as sand and washed up seaweedy debris but underneath all that are thousands upon thousands of invertebrates, which at low tide is a plentiful buffet for birds, like gulls and shorebirds.
Mr and Ms RAy, the local oystercatchers, are visible most days now low tides are in the daytime. Actually they were likely here at night during the winter lower low tides, foraging limpets and purple varnish clams, but I wasn’t out here to see them then.
a killdeer gets a drink of freshwater from the runoff exiting a culvert that drains the wetland nearby
Empty clam shells abound, mostly in fragments but quite a few complete. The most abundant clam species that in this fairly protected bay are littlenecks, purple varnish clams, cockles, softshells, bentnose, and butter clams, with a few horse clams. Some leave telltale holes in the sand where they have squirted out water as they dig deeper to escape predators.
freshly eaten Littleneck clam
Low tide is a time of relative hardship for these intertidal invertebrates but they are well adapted to surviving regular exposure to air and terrestrial predators. At high tide they will wake up and go into their own feeding mode. This bay collects a lot of debris — fragmented seaweed, eelgrass and bits of dead stuff — so there’s abundant food even though spring sunshine hasn’t arrived to trigger plankton blooms. The thousands of tubeworms and empty clam shells attest to that.
Bucket’s open for your daily nature observations.
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