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.
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 gulls seem uninterested in the tubeworms as food. Their favored prey on this beach are crabs and clams.
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.
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.
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.
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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