Sand dollars, with their distinctive flattened, disc-like shape and star-like patterns, are inhabitants of sandy ocean floors. These marine invertebrates are relatives of sea urchins and starfish, belonging to the echinoderm phylum. They play an integral role in their marine ecosystems, often living in large groups that filter food particles from the water. Understanding their existence involves recognizing the signs of a living organism and the processes that lead to their demise, leaving behind the familiar skeletal structures found on beaches.
Identifying a Live Versus Deceased Sand Dollar
Distinguishing a live sand dollar from a deceased one involves observing physical characteristics. A living sand dollar exhibits a darker coloration, from purplish-brown to reddish, olive, or gray, helping it camouflage within its sandy habitat. Its surface appears velvety or fuzzy due to tiny, flexible spines used for movement, burrowing, and moving food particles towards its mouth. If gently held, a live sand dollar’s spines may show subtle movement, and it might secrete a harmless yellowish substance called echinochrome, which can temporarily stain the skin.
In contrast, a deceased sand dollar, often called a “test,” is bleached white or pale gray, having lost its color and delicate spines. Its surface feels smooth and rigid. These bleached structures are the calcified skeletons that remain after the organism’s soft tissues deteriorate.
Factors Influencing a Sand Dollar’s Demise
A sand dollar dies swiftly when removed from its marine habitat, primarily due to desiccation and lack of water-borne oxygen. Stranded on a beach, these creatures perish within minutes to a few hours, depending on conditions. Direct sunlight, high air temperatures, and dry winds hasten this process, as their specialized gills and soft tissues are not adapted for terrestrial survival. They rely on a consistent aquatic environment for respiration and to maintain their delicate body structure.
Within their natural underwater environment, sand dollars have a lifespan of 6 to 10 years. Their mortality is influenced by ecological factors. Predators like sea stars, crabs, and some fish species consume them. Disease outbreaks within sand dollar populations can also contribute to localized die-offs.
Oceanographic forces also impact their survival. Strong storm surges or powerful currents can dislodge sand dollars from their sandy seafloor habitats, washing them into unsuitable areas or stranding them on shorelines. Sand dollars experience natural aging, which can lead to a decline in physiological functions, making them more susceptible to environmental stresses and predators as they approach the end of their lifespan.
Post-Demise Transformation and Care
After a sand dollar dies, its soft tissues and delicate spines decompose or are consumed by other marine organisms. This process leaves behind the hardened, calcified skeleton, known as a “test,” primarily composed of calcium carbonate. Exposed to sunlight and the abrasive action of ocean currents and sand, the test undergoes bleaching, gradually losing color and becoming the smooth, pale white disc. This transformation can take days or weeks, depending on environmental factors.
For collectors, proper care ensures preservation. Rinse found tests thoroughly in fresh water to remove sand, debris, and organic matter. For a whiter appearance, soak the test in a diluted solution of water and mild bleach (1:1 or 1:4 ratio) for 2 to 30 minutes. Prolonged exposure to bleach can make the test brittle.
After bleaching, rinse the sand dollar thoroughly with fresh water to remove chemical residue and allow it to air dry completely. To enhance durability and prevent breakage, collectors can apply a thin coat of a diluted glue-and-water solution to the dried test. This strengthens the fragile structure, helping preserve the sand dollar for years.