Snapshot – Northern Kelp Crab

Shine Tidelands, WA – When it comes to observing intertidal marine life, there is nothing like a good low tide.  June is solid month of stellar daytime low tides. Use apps and websites like NOAA to calendar good low tides and find public tidelands near you. Each beach has a slightly different peak low tide time so plan to reach the beach about an hour before the published time to enjoy the intertidal before the water begins to creep back in.

Once on the beach, slow down and look for subtle movements and colors/textures that stand out. Seasoned tide poolers know to think like a marine animal.  In an environment full of predators, where would be the best place to blend in with the environment to go unnoticed?  Extreme changes in light, heat, moisture, salinity and currents keep intertidal animals vying for spaces to hang on and survive another tide cycle while also avoiding predators.

Natural and man-made structures that stay put, like rocks and pilings, are in high demand and are often crowded with local marine residents. Look on the surfaces that enjoy the most mid-day shade, and if you are tempted to look under smaller rocks, be sure to put them back exactly where you found them.

Underwater forests of marine plant life are another less obvious place to find creatures. Sturdy kelp plants not only provide a good place to hide out, they also come equipped with their own anchors to keep them floating in the same general area.  Moving slowly through the kelp is the northern kelp crab.  This gorgeous spider-like crab is an almost perfect match for glossy olive-brown sugar kelp.

Experience the Northern kelp crab:

• A kelp crab’s diet will determine its color.  When you find them at low tide, an olive-colored kelp crab has been dining on brown kelp. Its’ smooth carapace will blend right in almost unnoticed by passersby.  A red kelp crab has been munching on sargassum and other red algae.  Likewise, a green kelp crab means that it favors eel grass and sea lettuce. 
• Another name for kelp crabs is a spider crab.  This is due to its long legs and small carapace which makes it resemble a spider.  Although spiders have eight appendages, northern kelp crabs have ten. 
• Northern kelp crabs look a lot like decorator crabs, but can be distinguished by their smooth carapace versus the rough carapace of the decorator crab.  Northern kelp crabs will sometimes hook pieces of food on their bodies near their rostrum, but this is for a later snack versus camouflage. 
• Females will lay up to 84,000 eggs.  These eggs also exhibit a range of color as they age.  They start out bright orange, change to red as they mature, and become a purple-gray color when ready to hatch. 
• Watch for kelp crabs up and down the Pacific Coast from Baja California to Alaska.  They are very common and fun to watch.  Can you find one and figure out what it has been munching on?

Cultivate Wonder… Discover Design

Images – SPegany©2000-2020, unless otherwise noted

How many are your works, Lord! In wisdom you made them all; the earth is full of your creatures. There is the sea, vast and spacious, teeming with creatures beyond number— living things both large and small. Psalm 104:24-25