On a Saturday in early March, in an attempt to shake off the last of the winter lockdown slump, my partner and I took advantage of the rare sunny day and headed to Constellation Park in West Seattle to explore the shore and soak up a bit of vitamin D. It was low tide in the afternoon — the perfect time to observe the activity of creatures dwelling on the rocky shore.

The intertidal zone, composed of different microhabitats and conditions that are constantly changing due to the tides, is exposed during low tide and submerged during high tide. This habitat is full of a variety of animals that make their home, and the Pacific Northwest intertidal zone is particularly rich in diversity. Each species that lives on the shoreline has adapted to fill a specific niche in order to survive and thrive.

And if you’re interested in finding some crabs, you’re sure to be in luck if you know where to look! Crabs prefer to be out of sight and are masters at seeking out the best hiding spots. On the rocky shore, crabs burrow into the sand, between rock crevices, and under rocks and vegetation.

We carefully turned over rocks to uncover shore crabs, young rock crabs, and hermit crabs all gathered for shelter in a miniature ecosystem left behind by the receding tides. This is the perfect place for defenseless juveniles of various species to hang out and feed on microorganisms until they are large enough to venture out into the big world. However, the shore crabs we found were actually not juveniles — shore crabs generally only reach a maximum size of about two inches.

Our first large find above the rocks was an impressive northern kelp crab, easily identifiable by its smooth, teardrop-shaped shell and spider-like appearance. This individual was missing an arm, likely from surviving an encounter with a shorebird, octopus, or maybe even a sea otter. Immature crabs can lose limbs and regenerate them when they molt, a tactic that helps them survive as common prey animals. However, adult spider crabs (including kelp and decorator crabs) don’t molt, and they can’t regenerate lost limbs.

They are an essential food source for many larger animals. Depending on the species, adult crabs have a few other strategies for defense against predators — the most obvious being their hard carapaces (outer covering) and pinching claws. If you are brave enough to pick up a crab, do so carefully — make sure your hands are out of reach of those claws, or you might regret it!

Kelp crabs can vary in coloration based on their diet. These crabs seemed to be competing for the same rock. photo by Laura Marx

On our way out, we stumbled upon a large red rock crab, distinguishable by its deep reddish coloration and impressively large claws. Its pincers are not just for show — this is a carnivorous species that uses its claws to crack open shelled organisms such as barnacles, clams, and snails to eat. True to its name, it prefers to shelter nestled amongst the rocks in the intertidal zone.

A few weeks later, we went on another venture to the beach at Carkeek Park in Seattle. While we dodged a city of geoducks spraying our ankles, we kept an eye out for critters. Just ahead of us, a flock of hungry seagulls picked through the beach, also keeping an eye out for critters, though for different reasons. This time, we didn’t have as much luck finding many new species of crab. We did find some perfectly intact crab molts. Like all arthropods, crabs must shed their exoskeletons (hard outer covering) in order to grow. We also found many little shore crabs scuttling away or burying themselves in the sand as we peeked under rocks, replacing them gently.

As we circled back, we came upon the grand finale of our crab observations — a Dungeness crab, half buried in the mud. The Dungeness crab is a well known local, named after Dungeness, a community on Washington’s Olympic Peninsula. Related to the red rock crab, the Dungeness crab can be differentiated by its lighter colored claws and large size. The one we found was around eight inches across its armored back. Dungeness crabs are generally found in deeper water, so this was a special find. This individual was a large male guarding a female in a precopulatory embrace. You can see part of the front of the female in the photo.

The next time you take a walk on a Northwest beach, keep an eye out for the kaleidoscope of color and diversity of crustaceans you might find! Plan ahead by looking up the tide times before your visit, and be aware of where you step. One of the biggest causes of damage to intertidal zones is trampling by people who are unaware that each step has a consequence. Even though they may seem rocky and indestructible, beaches are fragile natural areas that many creatures call home.

EZ-ID – Animals (beachwatchers.org)

Massive Crab die-off at Mukilteo? Actually not, but rather an interesting natural phenomenon highlighting a key stage in crabs’ lifecycle. . . | by The Washington Department of Fish and Wildlife | Medium

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