March 2018
Salish Sea, PNW
Tides were medium height in the afternoons much of this month so I was looking at shells predominantly, and the birds who turn living bivalves into beautiful beach decore.
This beach is particularly shelly due to its quiet location with a shallow sandy muddy bottom, perfect for these burrowing mollusks who filter plankton from tidal currents washing across the bay. The intermittent storms of winter have sorted thousands of loose shells into drifts high up on the beach face. Many other shells are so abundant in the wet intertidal zone it’s hard to walk along without crunching them underfoot. The vast numbers signify lots of predation, since every one of these bivalves was opened by some critter for its meat. Clams do not die of old age.
The Daily Bucket is a nature refuge.
We amicably discuss animals, weather, climate, soil, plants, waters and note life’s patterns.
We invite you to note what you are seeing around you in your own part of the world, and to share your observations in the comments below.
|
On my walk this past week, I took some photos of a few bivalve species to highlight —
Cockles (
Clinocardium nuttallii) are shallow burrowers, one edge right at the surface, and contain lots of meat inside their rounded shells. At first glance they’re not easy to break open, ribbed and structurally strong. But cockle shells are abundant on the beach. Seastars are subtidal predators who can easily pull the shells apart (although sometimes the cockles escape by energetically engaging their foot...see cool video here
www.centralcoastbiodiversity.org/...).
However I suspect most are eaten by gulls and crows, who dig them up and then access the meat by flying up 10-15 feet and dropping them onto the beach or nearby road. I see this every day, frequently. Sometimes it takes a couple of tries, but then at least one of the cockle’s shells breaks, and it’s all over for the mollusk.
Butter clams (Saxidomus giganteus) burrow deeper (25-30 cm, or about a foot) but there are plenty of their shells on the beach too. Butter clam underwater predators include fish, otters, and big crabs like Dungeness or Red Rock. Even seals will eat them. When actively filter feeding, clams extend their siphons out into the water, making them easily visible to subtidal predators.
I think of Butter clams as the default clam around here, to which all others can be compared/measured. It’s the size of my palm and the quintessentially clam oval shape.
There are several carnivorous snails who use their rasping mouthpart to drill holes in bivalves to access the flesh inside. Could be the native Moon Snail, but the hole doesn’t appear countersunk, the typical sign of the Moons (www.asnailsodyssey.com/...) so it might be either a native whelk or either of the invasive oyster drills. The Eastern and the Japanese Oyster Drills were both brought to the Northwest inadvertently as companions of the introduced and commercially grown Japanese aka Pacific Oysters. All those mollusks have been here in Northwest waters since the early 1900s. (depts.washington.edu/...)
There are many Pacific Oyster (Crassostrea giga) shells on this beach too, having gone feral due to their planktonic larvae ( depts.washington.edu/… ) . They are not burrowers, but glue one shell to a hard surface, usually rock. The oyster shells on the beach were washed in from the nearby reefs, rocks and headlands where they were opened by crabs, seastars, gastropods (like the oyster drill) or birds.
Each oyster grows uniquely, its shape influenced by the rock to which it attaches as well as the presence of neighboring oysters or other things nearby. I love the irregularities in curves and hues, and even iridescence in fresh ones. Here are a couple of empty shells washed up.
While many shells have subtle pretty colors embedded in their calcium carbonate, the most intensely colorful clamshells belong to the Purple Varnish Clams (Nuttalia obscurata). PVCs prefer low salinity water so they aren’t found on every beach. This one gets a lot of freshwater runoff from the wetland behind.
Birds are smart and adaptable. PVCs were accidentally introduced to the West coast from Japan in the 1990s. Fortunately they do not appear to be displacing native clams, unlike Pacific oysters who have displaced native Olympia oysters, possibly because they need such a specific environment: low salinity, gentle water, sandy/muddy bottom, and they prefer the upper third of the intertidal (www.dailykos.com/... ). Oystercatchers very quickly learned how to dig them up. I’m sure the abundance of PVCs is a big reason Mr & Ms RAy so frequently forage on this beach.
Interestingly, PVCs usually burrow about a foot deep (25-30cm) but in this bay the oystercatchers snag them just below the surface, maybe an inch or two. For some reason the PVCs can’t or won't burrow more deeply, where they’d be better protected. Most likely it’s the mix of cobbles and rocks in this sandy/muddy beach that interferes with their burrowing. Predators are happy enough. Judging by the empty shells, the PVC population is keeping up with predation, which is intense. Besides the oystercatchers, omnipresent gulls and crows dig them up steadily as long as the tide is even medium low.
The color in the PVC shells fades quickly so we can tell how old shells are by how bright the purple glows.
The clamming technique, starring Mr RAy. Note how shallow the clam is. Once he’s speared the clam he appears somewhat distracted, looking around as he works on it. But we can see how easily he cuts through the muscles holding the two shells together, and then eat the clam meat inside.
Interestingly, the mix of shells varies from one part of the beach to another. The waves here are very gentle most of the time but when the wind picks up, the water takes on enough force to be able to lift the shells and move them around. They sort into deposits according to a complicated set of dynamic variables far too complex for me to suss out. But clear patterns emerge, like the patches visible in the wide view of the title image. It’s fun to walk from one patch to another and see the variations.
The tide will be getting low again next week, so I’ll have more of the beach to explore.
Bucket’s open for your nature observations today!
"SPOTLIGHT ON GREEN NEWS & VIEWS" IS POSTED EVERY SATURDAY AT 5:00 PM PACIFIC TIME AND WEDNESDAY AT 3:30 ON THE DAILY KOS FRONT PAGE. IT'S A GREAT WAY TO CATCH UP ON DIARIES YOU MIGHT HAVE MISSED. BE SURE TO RECOMMEND AND COMMENT IN THE DIARY. |