Christina Stead was on her usual walk along Morro Strand State Beach, south of Cayucos, and saw the shoreline lined with what she thought looked like dead sand crabs.
This is actually good news.
The “dead” sand crabs actually were molted shells. Like any other invertebrate with exoskeletons, such as lobsters, these Pacific mole crabs (Emerita analoga) need to molt their old shells to grow.
According to marine biologist Jenny Dugan at the Marine Science Institute of UC Santa Barbara, these “windrows” of molt skins are particularly evident in the spring months, when millions of young sand crabs land on the beaches, burrow in the wet sand, start feeding and begin to grow in unison.
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The persistent ridge of high pressure over California may be affecting marine life, including sand crabs. This condition helped to create sustained Santa Lucia (northeasterly) winds that compressed and heated the air mass as it flowed down the Santa Lucia Mountains. Not only did this ill-fated condition this year cause the warmest January through March on record, but it also gave rise to well-above-normal seawater temperatures because of the lack of upwelling.
Thankfully, there are indications that we may be shifting back to a more normal weather pattern as the persistent ridge has been replaced by a trough of low pressure off the coastline. This atmospheric condition has given rise to stronger northwesterly winds. These winds have increased the amount of upwelling along the coast, which brings cold and nutrient-rich subsurface water to the surface along the immediate shoreline. This is the type of water that plankton — the primary food source of many marine creatures, such as sand crabs — thrives in.
According to Dugan, these crabs gather in the active swash zone, the areas where the remnants of waves surge up then back down. As the swash zone moves up and down the beach with the ever-changing tides, the crabs effortlessly move with it.
You see, they are some of the fastest-burrowing critters on the face of the earth. Unlike other crabs, sand crabs only move backward and don’t have any claws. They also swim and orient themselves well in turbulent conditions.
Dugan told me, “Overall, they are the most widespread and often the most abundant suspension-feeding invertebrate on the beach.”
In fact, Dugan and her team of researchers have counted as many as 100,000 mole crabs per meter of shoreline!
“To feed, the crabs burrow in the beach facing seaward with only their eyes and first antennae exposed to the sea. As the waves recede, they extend their feathery second antennae to sieve fine particles, primarily phytoplankton, from the turbulent moving water of the swash,” Dugan said.
Their presence is marked by V-shaped marks in the wet sand. Speaking of feeding, these abundant crabs represent 80 to 90 percent of the food available on the beach for birds and for surf-zone fishes. Not only do they provide food for coastal inhabitants, but they can also deliver hours of fun for kids trying to catch them.
In the United States, the generation of electricity is one of the largest contributors of carbon dioxide. However, in PG&E’s service territory, the generation of electricity utilizing nuclear, hydroelectric, solar, wind, geothermal and biomass has made our state one of the cleanest in the country. In fact, more than 50 percent of the electricity that PG&E delivers to its customers is carbon free. With each passing year, it’s expected to become cleaner.
John Lindsey’s column is special to The Tribune. He is the PG&E Diablo Canyon meteorologist and media-relations representative. Email him at firstname.lastname@example.org.