|Oregon Coast Notes|
|Searching for the elusive intact Sand Dollar - an Oregon Coast favorite activity|
|Oregon Coast Notes - News|
The best time to hunt for sand dollars is when the tide is going out, especially after a storm.
If there are a lot of rocks on the beach... pick another beach. Waves + Rocks = Broken Sand Dollars
Get there before anyone else.
Walk a mile or more further than other searchers are willing to go and you are more likely to find Sand Dollars that are on top of the sand.
Look for the buried Sand Dollars. Many Sand Dollars are left uncollected because only a small edge is showing above the sand.
The name sand dollar comes from it's shape and color after it dies and washes up on the beach. At that point it is usually missing its velvety covering of minute spines and is often bleached white by the sunlight.
In many species the beach-worn Sand Dollar is quite similar in shape and size to a large coin, and the whiteness makes it resemble a large silver coin, for example the old Spanish Dollar coin, or the American Dollar coin that are between 38 and 40mm in diameter. Other names include sand-cake and cake-urchin. In Spanish, such as in Costa Rica, a sand dollar is known as a "galleta de mar" (sea cookie). In South Africa, they are known as pansy shells from the five-petaled pansy garden flower.
The Sand Dollar found along the Pacific Ocean from Alaska to Baja California is the Dendraster Excentricus, also known as the sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar. It is a member of the order Clypeasteroida, a species of flattened, burrowing sea urchins. Found along the Pacific Ocean from Alaska to Baja California.
The Sand Dollars' natural habitat is just beyond the mean low tide either on top or just below the sand's surface. This is the 'sub tidal' zone and is submerged most of the time, exposed briefly during extreme low tides around full and new moon events.
Sand Dollars live in large social groups and the ones you find on the beach are usually dead. When a sand dollar dies, its skeleton (called a test) will often wash onto shore. At times these tests appear without the velvety coating and have been naturally bleached. This is what you want to collect.
Sand dollars do not have legs or fins. They are able to move around because of the many spines covering their bodies. Next time you gather one; take a close look at the body. If there appears to be fine hairs (called cilia) covering the body, and these hairs seem to move then you have a live sand dollar. Please do not collect this one, but rather let it thrive. If it is low tide or the tide is going out, you can help this beautiful creature by placing it bottom side down on the oceans sandy bottom.
Facts about Oregon Coast Sand Dollars
Dendraster excentricus, also known as the sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a member of the order Clypeasteroida, better known as sand dollars, a species of flattened, burrowing sea urchins. Found along the Pacific Ocean from Alaska to Baja California.
Dendraster excentricus is an irregular echinoid that is flattened and burrows into the sand, unlike the regular echinoids, or sea urchins. It can be found living in the Pacific Ocean from Alaska to Baja California. The range for Dendraster excentricus is larger and includes the range of the other two extant species of Dendraster: D. vizcainoensis and D. terminalis.The flower pattern in this species is off-center, giving it the name excentricus. It's test is compared to that of a sea urchin below
They are colored gray, brown, black or shades of purple. Their size is variable but up to 100mm wide, and a dome shaped carapace varying in height to about 10mm, with a circular body or test. Their body is covered with fine, spiny tube-like feet with cilia, and like other echinoderms they have five-fold radial symmetry.The mouth ,anus and food grooves are on the lower(oral) surface and the aboral surface has a petalidium, or petal shaped structure, with tube feet. Dead individuals have a gray/white test,or skeleton, which is often found washed up on beaches.It has a water-vascular system from the internal cavity or coelom that connect with tube feet.
The tube feet are arranged in five paired rows and are found on the ambulacra – the five radial areas on the undersurface of the animal, and are used for locomotion, feeding, and respiration. Spines are generally club shaped in adults, and less so in juvenilles. The five ambulacral rows alternate with five interambulacral areas, where calcareous plates extend into the test.At the center on the aboral side is the madreporite - a perforated platelike structure, and on the interambulacra are the four tiny genital pores. Radiating out from the genital pores are the five flower petals, which represents the ambulacral radii. The mouth is in the center on the bottom side, with the anus toward the edge.
They are either found subtidally in bays or open coastal areas or in the low intertidal zone on sandy beaches on the Northeast Pacific coast. It can live at a depth of 40 to 90 meters, but usually is found in more shallow areas. Sand dollars are usually crowded together over an area half buried in the sand. As many as 625 sand dollars can live in one square yard (.85 sq m). It is the only sand dollar found in Oregon and Washington.
Behavior and Feeding
It is a suspension feeder which feeds on crustacean larvae, small copepods, diatoms, plankton and detritus. Adult sand dollars move mainly by waving their spines, while juveniles use their tube feet. The tube feet along the petalidium are larger and are used for respiration while tube feet elsewhere on the body are smaller and are used for feeding and locomotion. They frequently move around if they are lying flat.
When feeding they usually lay at an angle with their anterior end buried and catch small prey and algae with its pedicellariae, tube feet, and spines and pass them to the mouth. Their mouth includes a small Aristotle's lantern structure found in most Echinoids. In high currents adults grow heavier skeletons while juveniles swallow heavy sand grains to keep from being swept away.They will bury themselves when they are being preyed on.
Sexes are separate, with no noticeable differences in external features of the two sexes.Reproduction is sexual and D. excentricus reaches sexual maturity between 1 and 4 years of age, spawning in late spring and early summer. Fertilization is external, the female Dendraster discharges the eggs through her gonophores and they are fertilized by the male, who protrudes his genital papilla from his body wall. This is one reason they are believed to live in large groups and tend to release gametes at the same time into the water column. Eggs are pale orange, and covered by a thick jelly coat which keeps adults from eating the eggs.
The first larval stage is called a prism. After this stage the embryo will develop two arms transforming itself into an echinopluteus larva. This is followed by the development of arms, until it reaches 8 arms all together. After this the larva develops an echinus or juvenile rudiment, which will become the juvenile. The nektonic larvae are pelagic and travel away from the parent group with the current. The developed larvae will receive a chemical cue from adults to settle down into a bed of sand dollars and begin to undergo metamorphosis to their adult sand dollar form. As adults they are benthos and stay on the sandy bottom.
Life Span and Predation
Predators include the seastar Pisaster brevispinus and the starry flounder Platichthys stellatus as well as crabs and sea gulls. They are sometimes settled on by a small barnacle Balanus pacificus. Large storms or high temperatures and desiccation can cause mass mortality if low tide coincides with a hot midday and the animals are exposed to air for just 2 to 3 hours or washed up and buried in the sand. Old age is thought to be the main cause of death of Dendraster excentricus. They may live up to 13 years and can be aged by counting growth rings on the plates of the test or by counting the pores in a petal of the petalidium.
The habitat they live in on the sandy seafloor is sometimes damaged by bottom trawling, causing harm to many organisms. Ocean acidification and sea surface warming are also harming populations of sand dollars.