Sand Crabs
Facts about the Lives of Sand Crabs
Strolling along on a warm sandy beach where the foamy surf rolls into land, it is a common sight to see sand crabs scuttling along the compacted wet soil. A familiar sight on beaches all along the North and South American coastlines, this tiny creature is a fascinating study of nature.
The term “crab” often brings to mind a delicious meal of tender, sweet meat encased in a bright red bony armor. While the tiny crabs found on the surf line are edible, they do take a great deal more effort to collect and eat than their larger cousins. Typically, the largest of this species is the female, who measures only about one and a half inches long. Even at this diminutive size, they do not rate as the smallest within the crab family which consists of approximately 4,500 different species. One of the distinguishing features that people remember about crabs is in the fact that they are able to move in virtually any direction; switching directions can be done easily and rapidly. Sand crabs are one of the exceptions to the rule of maneuverability, as they can only move in one direction: backwards. This fact does not mean that they are speed inhibited, however; they are quite fast.
One reason that this tiny creature is as swift as it is has to do with their method of food collection. A day in the life of a sand crab is an exercise of scurrying to and fro among the ever shifting sands of the wave break line at shore. Burying their bodies into the wet, mucky sand rear first allows the face to stay above the ground level as the crab faces the incoming waves. These waves, tumbling about in turmoil as they roll toward the shore, are teeming with plankton, tiny microorganisms, particles of sand, plant life and other materials. Washing over the shoreline, the waves recede over the heads of the little sand crabs; the antennae of which act as filters to capture the organisms within the receding water line. This categorizes the crustaceans as “filter feeders”; the antennae are equipped with feathery features that are designed to trap the smallest of these organisms and plankton. These serve as their source of food, which is drawn into the body for nourishment.
Throughout any given day, herds of these ten legged miniatures can be found following the wave break lines up and down the beach. The five pair of legs are essential tools for the crabs; enabling them to swim if swept out to sea with the receding waves, crawl to reach the next break point of the ocean waves and to burrow themselves in the sand as their next meal opportunity approaches. From spring until fall, the daily activity of the crabs remains the same. Storms that rage in winter weather will transport the crabs out to distant sandbars that are formed by the violent wave action of the water. As the springtime weather and air flow changes, that sand is carried back to shore again, bringing the sand crabs with it.
The sand crab has a high mortality rate, as numerous shorebirds, water birds, fish and mammals feed upon the crustacean. Although they are a great source of nutrition of these creatures, they also carry a hazard for them. Living in the sand, the crabs absorb any toxins that are present; toxins that are transferred to the predator as digested. This makes the crabs an informative source for environmental scientists who study the conditions of coastlines. They also carry parasitic worms. Both of these situations pose a threat to the health of the predators, even killing them in many cases.
A day in the life of the sand crabs may seem inconsequential, but they are a valuable link in the circle of life in many aspects. Found on many coastlines, their presence is a fascinating study of nature.