In early July, I had the privilege of using some new equipment Stillwaters has obtained to do some in-water monitoring in the new bridge area. I donned a dry suit, snorkel and mask and took a camera in the water to get up close and personal with what is living in the area, and how they interact with their environment when the water is flowing.
While it was July and supposedly summer, the water was still cold so I was happy to have the dry suit. It is like a scuba diver’s wet suit but with attached footies and seals at the wrists and neck. Though this is not like the older, thicker neoprene suits that older divers are familiar with, the ones that are hard to move in. This one is light and very flexible and made of a rugged poly material. The hood, however, is the good old neoprene that fits closely to your head and is quite a fashion statement, but does the job. Then with a pair of gloves you are protected and warm.
I photographed and videoed while nets were being pulled to sample the fish and other critters in the area. I observed several types of sculpins, flat fish, and salmon, but one of the most surprising things was the number of crabs I watched. It seemed to be a crab convention!
The main family of crab I saw was the Shore Crabs (Hemigrapsus sp.). There are several species of these tiny shore crabs on Washington beaches, and I saw two that day in the shallow water near and under the new South Kingston Bridge. Contrary to what many believe, these are not the young of larger crabs; rather, they only grow to be 1 or 2 inches long.
The two found that day: the purple shore crab Hemigrapsus nudus and Hemigrapsus oregonensis, the bay shore crab (mud crab). They shelter under rocks when the tide is out or bury themselves fully or partially to protect themselves from their main predators, gulls, blue herons, or other birds. However, birds are not the only animals that eats these crabs. Research shows that mammals also dine on these little crabs. Raccoons, coyotes, rats, minks, deer and even bears have been known to eat these crabs. The crabs primarily eat sea lettuce (Ulva), diatoms (microscopic plants), other green algae and scavenge dead animal matter or other detritus.
The purple shore crab is not always purple. It can range in color from greenish yellows to deep purples. Also it shares the same habitat with a number of bay shore crab, and they can look very similar The bay shore crab is grayish green and has hairy legs and do not have the reddish spot on the “forearms” of their legs with the large claws (cheliped) that you find on the purple shore crab.
They breed in the spring and summer, hatching their eggs in water at high tide to drift off as plankton. Floating for several weeks they change shape several times until settle to the bottom where they begin their adult life.
There are many crabs in intertidal area of the bridge and our nearshore environment. They are wonderful to watch and they are an important part of the food chain.
— Betsy Cooper is a board member and stream monitor at Stillwaters Environmental Center. She also serves on the Kingston Citizens Advisory Council. Contact her at betsycooper1@gmail.com.
