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| Nov 12 2011 -- Dec 30 2011 Mole Crab Shells Prompt Questions About Life Cycle |   Photo by Jerry Kirkhart
What’s with all the mole crab carcasses on the beach this fall? Fair question, if you’ve been out walking the beach lately. Do they molt like Dungeness and red rock crabs, whose discarded carapaces often litter our beaches in spring and summer? Well, yes and no. Juvenile mole crabs do molt as they grow. But the explanation for the high number of dead adult mole crab shells on the beach this fall probably lies elsewhere in their life history.
Mole crabs (Emerita analoga), also called sand crabs, are the thumb-sized gray critters that are sometimes found in profusion in the surf zone. Close relatives of hermit crabs, mole crabs have 10 legs like other crabs, but no front claws. And they move primarily in one direction: reverse. They dig backwards into the sand not only to hide from predators (gulls, other crabs, fish such as surfperch, and humans, who use them for bait) but to feed. Buried in the sand and facing seaward, with only eyes and antennae exposed, they wait for a wave to wash over them and deliver tiny plankton that they capture with a second set of feathery antennae unfurled for that purpose. Mole crabs reproduce in their first and second summers of life and die in the fall of their second year.
Their distribution pattern has made mole crabs something of a bellwether for scientists observing changing ocean conditions—and it may explain why some years you see lots of them in Oregon and some years none. Mole crabs have been found as far north as Kodiak, Alaska, and south to Baja, but their home turf is California; mole crabs don’t reproduce robustly enough in Oregon to sustain a population here. Typically they arrive as larvae drifting north from California when ocean conditions are right. According to researchers at Hatfield Marine Science Center, especially large numbers tend to drift north in El Niño years, when the sea surface temperature is higher and the Davidson Current, which flows northward off our coast October until March, is especially strong. The larvae may drift at sea as long as four months. So larvae from eggs spawned in late summer or early fall in California can easily reach the beach in Oregon, where they develop into juveniles and, shortly, adults.
Winter 2009-10 was a strong El Niño year, meaning that plenty of mole crab larvae may have drifted north to Oregon in spring, 2010. That robust population would be dying off now, in the autumn of their second year of life. Last winter (2010-11) was a strong La Niña year, with cooler ocean temperatures, and this winter looks to be on the cool side as well. It might be a few years before we see lots of mole crabs on Oregon beaches again.
 Contact: Phillip Johnson, Executive Director, (503) 238-4450, or EMAIL
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MORE SIGHTINGS... | Aug 23 2011 -- Dec 3 2011 Marbled Murrelet Survey Connects Sea and Forest
By Bonnie Henderson. July 14, 4:54 a.m.: It’s still dark when I park at the pullout just south of Gwynn Creek, at the base of Cape Perpetua, and cross the highway to the little trail toward the meadow. Ahead, a dark shrub shifts slightly; turns out it's Yachats mayor Ron Brean, in a brown jacket and rain pants and wide-brimmed hat, sitting in a west-facing camp chair and gazing skyward. ... MORE | | Mar 19 2012 -- Jun 19 2012 Watch for Winter’s Delivery of Egg Cases to the Shore
by Bonnie Henderson There’s no real beachcombing season in Oregon. There’s only beachcombing weather, and that means storms, most common and most boisterous in winter and spring. Storm winds blow long-traveled ocean debris onto the beach. And big enough storm waves can stir the nearshore ocean down to the ocean floor. That’s when skate egg cases are more likely to land on the beach. Commonly ... MORE | | Mar 8 Sightings: Salps Surprise CoastWatchers with Shoreline Appearance
By Bonnie Henderson. This winter CoastWatchers from Clatsop County south to at least Coos County have reported finding an elongated jellyfish-like creature stranded on the beach, sometimes in large numbers. This organism—barrel-shaped and nearly transparent, typically five or six inches long, with two thin, dark, spindly appendages at one end—is an oceanic filter-feeder known as a salp. A pulse ... MORE | | Sep 19 2012 -- Dec 20 2012 Redfish Rocks Community Team Pioneers CoastWatch Strategy
By Kelly Sparks . Collaboration is key. Now repeat these words and I will tell you why. The Redfish Rocks Community Team (RRCT) adopted CoastWatch Mile 46 (Coal Point to Rocky Point, adjacent to the Redfish Rocks Marine Reserve) back in 2010 and has been monitoring that bit of coastline ever since. This past spring an idea was developed to connect students at Driftwood Elementary, in Port ... MORE | | Jul 11 2011 -- Oct 31 2011 Murres and Bald Eagles in a ‘Conservation Collision’
By Bonnie Henderson. Neal Maine of Gearhart spent much of June with his zoom lens focused on the rocks just off Chapman Point, at the north end of Cannon Beach. Every flat-ish rock, it seems, had common murres crowding it—more murres than he’d ever seen there, 5,000 or more. But murres—the most numerous nesting seabirds on the Oregon coast—were apparently not breeding at Chapman Point. They ... MORE | | Apr 22 2011 -- Jun 22 2011 Crab molts and dead crabs on the beach
by Bonnie Henderson Finding lots of crab shells on the beach? The crabs may have died, or they may have simply molted. The species whose shell is most commonly found on Oregon beaches is the Dungeness crab (Metacarcinus magister), followed by the red rock crab (Cancer productus, smaller than the Dungeness, similar in color but redder, often striped, with black claw tips). Crabs molt when they ... MORE | | Nov 11 2010 -- Dec 11 2010 Beached Northern Fulmars Are a Common Find in Fall
By Bonnie Henderson If you walk your CoastWatch mile late in the fall quarter and you don’t find a dead northern fulmar, perhaps you aren’t looking very closely. Overall it’s the second-most common beached bird found on the Pacific Northwest coast, behind only the common murre, ahead of all gull species combined. At least one in five beached birds found here is a northern fulmar (Fulmarus ... MORE | | Oct 10 2010 -- Dec 31 2010 Strandings of Young Sharks Not Uncommon
By Bonnie Henderson A family on the beach at Face Rock, near Bandon, ran across a live young shark stranded on the beach in September. It had attempted to bite them (and their dog) when they approached, they reported. They were able to return it to the ocean in apparently good health—or so they believed. In fact, says shark expert Wade Smith of Oregon State University, what looked like teeth ... MORE | | Sep 14 2010 -- Oct 31 2010 Dragonflies on the Oregon Coast: An Annual Event
By Terry Morse 1. Scenario Picture, if you will, thousands of dragonflies moving through your town, all flying the same direction, like a miniature zombie Air Force. It has the earmarks of a great Saturday matinee film or an episode of the Twilight Zone: “Small town on the Oregon coast invaded by winged piranhas that strip the flesh from residents before moving on, leaving nothing but bones in ... MORE | | May 14 2010 -- Aug 15 2010 Watch for By-the-wind Sailors Stranded on Our Shores
Every avid Oregon beachcomber is familiar with Velella velella, or by-the-wind sailors: little (typically 4 to 6 cm.) violet-blue floating creatures that are often stranded by the hundreds or thousands on the beach April through July. They live in vast congregations on the sea’s surface, in warm and temperate ocean water around the world. They have no means to propel themselves; rather, they ... MORE | | Feb 25 2010 -- Apr 15 2010 Driftwood Plays a Key Role for Beaches and Estuaries
(Editor's note: This is the second in our “Sightings” series, which provides background information about shoreline phenomena that CoastWatchers might observe. Again, the author is Bonnie Henderson, adopter of Mile 157 and author of Strand: An Odyssey of Pacific Ocean Debris.) Have winter storms deposited new driftwood logs on your mile of beach? Treasure them. Drift logs haven’t actually been ... MORE | | Jan 30 2010 -- Mar 2 2010 The Growing Pelican Presence
(Editor's note: This is the first in what will be an occasional series of brief essays providing background information on phenomena CoastWatchers and other beach visitors may observe out on the shore. This debut "Sightings” article was contributed by Bonnie Henderson, adopter of Mile 157 and author of Strand: An Odyssey of Pacific Ocean Debris.) Recent news about dead or emaciated and ... MORE | |
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CoastWatch, a citizen monitoring program, engages Oregonians in personal stewardship over their shoreline. Volunteers adopt mile-long segments of Oregon's coast, keeping watch for natural changes and human-induced impacts, reporting on their observations, and sounding the alarm about threats and concerns.
CoastWatch is founded on individual vigilance and responsibility for one portion of the ocean shore. But the program also links hundreds of 'mile adopters' in a coastwide network of concerned citizens taking action to conserve shoreline resources. CoastWatchers serve as an early warning system not only for the Oregon Shores Conservation Coalition, but also for neighbors along their miles, local government, regulatory agencies and other conservation groups. |
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