There Are Green Crabs, and Then There Are Green Crabs

Ever seen a crab rollercoaster? My kids and I have. Green crabs somersaulting, tumbling, rocking, and rolling underwater. But before I tell you about that, I have a public service announcement: Just because it’s green, doesn’t mean it’s mean.

Seriously. Not all green crabs are the invasive European green crab. In fact, on the Key Peninsula, for now, none of them are.

Recently, a friend in Key Center was telling me about a visit from his out-of-town nephews and how much fun they had on the beach, especially when the youngsters found there were little crabs under every rock, and you could pick them up and watch them run across your palm. I grinned. How many hours as a boy did I spend doing the same?

But my friend continued, the kids really started to have fun when he told them the green ones are bad and should be smashed with rocks.

I cringed. I chastised my friend. The small green crabs along our shores are not invasive.

They are called the Oregon shore crab or green shore crab. They’ve always been here and, as the most abundant species of crab in Puget Sound, they are foundational to the ecosystem. Neither are they the young of a deeper-water species, another common misunderstanding. Their whole adult life plays out in intertidal and subtidal zones.

Also on our beaches is the slightly larger purple shore crab. They too can be green. While most individuals are reddish-purple, they have two other color morphs: “pea soup” and “tomato soup,” as local marine biologist Rachel Easton calls them.

The Salish Sea is home to dozens of different crabs, from small decorator crabs to powerful Dungeness crabs. Other friends have bemoaned to me that when they look down from their kayaks lately, around the southern tip of the peninsula, all they see is the invasive green crab. Their concern makes sense, given the European green crab’s fearsome reputation and ongoing march into other parts of Washington. But it’s not here yet. Several native crabs appear green underwater. The northern kelp crab comes to mind.

It is good for us to be watching our crabs closely. Citizen scientists are an important part of the coastwide effort to detect and slow the European green crab invasion.

But we have to know what to look for. Here is the foolproof way to identify a European green crab: its carapace, or top shell, which maxes out at 4 inches across and will not necessarily be green, has five triangular points on each side of its eyes. No other local crab has five points on each side. Dungeness crabs have ten; kelp crabs two. The native shore crabs have a different carapace shape altogether, with rounded edges and eyes at the corners.

Okay, back to the crab rollercoaster.

My kids and I were down by the mouth of a local lagoon. The day before, we had gone to the state fair, where we gaped at the people whose instinct at the end of summer is to flock to machines that hurl them through the sky with a kind of desperate abandon. Now, an incoming tide poured through the channel. Pilings made wakes. And several crabs were on a rollercoaster ride of their own.

We had been in this place a few weeks before, at low tide, when the channel was nothing more than a narrow stream winding through a landscape of oysters and broken clam shells. Here and there, a few crabs went about their business. But when the tide began to rise, we saw something incredible. Following the leading edge of the rising tidewater, like commuters on a rush hour interstate, a stream of hundreds, then thousands, of shore crabs jostled into the lagoon. They flowed past in uncountable numbers.

And their colors were almost as kaleidoscopic as the rocks on our beaches. Color fascinates me. It can be such a fickle thing. Many of the young crabs were speckled white. Research has shown that beaches with abundant white shell fragments have more white-splotched young shore crabs. I wonder if it’s a similar story with adults and colorful rocks.

Now the tide was much higher. The channel was rough and tumble as seawater rushed in. If there had been a crab commute that day, it was long over. Bits of seaweed flew past.

Then here came an alder leaf, curled like a taco shell, rolling madly across the bottom of the channel. “Dad!” shouted my son. “There’s a crab on it.”

Sure enough, splayed inside the curled leaf, a shore crab hung on for dear life. As it came past, we saw that two more crabs clung to the outside of the leaf. They whirled and bumped as they went.

“Crab rollercoaster!” the kids shouted.

I had never seen this before. While we watched, two more crabs hopped onto the leaf as it passed. Taking advantage of a free ride? Soon, the leaf was out of sight in the lagoon, a bus vanished into the city.

We watched for a while longer. Before long, here came a glob of seaweed weighed down with shell bits. It bounced along the channel bottom with at least five crabs aboard.

I have so many questions.