When I first came to live on Vashon, my attention was absorbed by the woods, filled with lush plants and abundant wildlife. Glancing at the beach, usually from a car window, I saw rocks, sand, water, sea stars, clam shells. Sort of a damp desert, I assumed, under constant assault by cold water, wind, periodic drying out, summer heat and winter temperatures below freezing.
What life forms could survive so much punishment? An astonishing number, it turns out.
The remarkable diversity of beach life, especially in the Maury Island Aquatic Reserve, has inspired a series of annual Low Tide Celebrations, the fourth one coming on Memorial Day Monday, May 25, at Point Robinson. Beach naturalists will explain some of the beach’s many habitats, each with its own community adapted to conditions there.
Like forests, beach habitats are affected by substrate, slope and exposure to sun and prevailing winds. In addition, beaches are affected by other influences, such as the amount of force in the water currents that hit them and the twice-daily tidal movements. Biologists often divide beaches into a splash zone high up on the beach and three intertidal zones: the upper, middle and lower beach.
At Point Robinson, substrates include sandy beach, cobbles, and, on the north side, outcroppings of hard clay. The splash zone up at the top of all these beaches hosts a sparse community of lichens, acorn barnacles, and ribbed limpets clinging to stones, driftwood and boulders.
There are more species at the upper level of intertidal beach, where sand and cobbles remain damp during low tides. The barnacles live more densely here, and whelks prey on them. Several species of limpets, periwinkles and isopods hide in cracks between stones. Rockweed (Fucus distichus), reddish brown Turkish towel and stones all provide shelter for several species of hermit crabs.
The mid-zone of intertidal beach, with less exposure to air, is even more complex, occupied by many species of seaweeds, limpets, snails and crabs, plus anemones, mussels, sea cucumbers, marine worms, purple stars, chitons and tubeworms. Colonies of the anemone, Anthopleura elegantissima, look like wet green lumps when folded up at low tide. This anemone has the endearing habit of collecting shell fragments like white necklaces on the green stalks supporting its pink tentacles. In the clay beach on the north, piddock clams drill burrows that are later used by other animals. Many mid-zone species thrive in shallow tidepools such as those in the sand southeast of the point. One may spot a wriggling gunnel (an eel-like fish) or a red sea cucumber submerged there.
Eelgrass beds extend down the beach toward the lowest zone. Their roots help stabilize the sandy bottom, and their stems buffer water currents. On their blades grows a furry film of algae and diatoms that provides forage for many small animals, forming the base of a food web that extends upward to fish and diving birds. Small snails known as chink shells lay egg cases like miniature yellow life preservers. Transparent caprellids, also called ghost shrimp, wave oddly spaced legs from their jointed skinny bodies when discovered among strands of seaweed and eelgrass.
The lowest intertidal zone, exposed only at very low tides, reveals larger populations of geoducks, additional shellfish such as scallops, other nudibranchs and crabs and other creatures in the most complex community of beach inhabitants. Every visit to this zone will have a new surprise.
Come and tiptoe gingerly among the fragile beings of Vashon’s edges to learn a bit about who the “other half” are and how they survive. Just remember that their adaptations to heat, cold, pounding waves and freezing air do not protect them from our shoes or rough handling. Treat them with gentle respect!
— Rayna Holtz is a librarian and a naturalist.
Low Tide Celebration
The fourth annual Low Tide Celebration takes place at Point Robinson from 10 a.m. to 3 p.m. on Monday, May 25. For more information about the event, see the Calendar on page A7.
