The Treasure of Sand Dollars la by J. Bruce Neill, Ph.D.
Besides these basic facts, relatively little is known about the biology and life history of sand dollars, so Sanibel Sea School is carrying out a long-term investigation of the populations around Sanibel. Often working with volunteers and students, our team’s goal is to better understand them and the community in which they thrive, meters from our white beaches. Next time you find a sand dollar test, take a minute to consider what a complex life it lived just below the surface of the sea.
their eggs and sperm directly into the ocean, relying on the chance encounters of the two for fertilization to occur. To increase the odds of successful spawning, almost every individual in an area spawns synchronously, usually around the time of the full moon. Any fertilized eggs develop into larvae, which are free-swimming for a period of weeks before they undergo metamorphosis and transform into their adult form. Near Sanibel, most sand dollars live for about seven years.
Sand dollars are iconic treasures for beachcombers in Southwest Florida. They are fairly rare, and do not often wash ashore fully intact. Most people can agree that finding one to take home is a treat, but there is so much more to know about these elusive creatures. Sand dollars are surprisingly active animals that live in the sandy sediments in the shallow, near shore waters of the Gulf of Mexico. What we find on the beach – typically a white, flattened disc — is the skeletal remains of a sand dollar. When they are alive, sand dollars are covered in moving spines, and the white skeletal disc (called the test) is covered with skin that is dark tan or greenish in color. When you go shelling, be sure to leave any live specimens where you found them. Sand dollars belong to the phylum Echinodermata, the spiny skinned animals, which also includes sea urchins, sea stars, sea cucumbers and brittle stars. They have internal skeletons, meaning their skeletal system is covered in skin. This is uncommon among marine invertebrates. Echinoderms are exclusively marine animals – there are no echinoderms that inhabit fresh water or live on land. They are the only animal group entirely restricted to the ocean. Sand dollars make their living by ingesting sand and extracting nutrients from the algal cells and organic matter it contains. This feeding strategy makes them very important members of the near-shore community because their burrowing action keeps the sediment well stirred and aerated. These animals reproduce by releasing
Dr. Bruce Neill is Cofounder and Executive Director of the Sanibel Sea School, a not-for-profit organization dedicated to vibrantly teaching children and adults about marine ecosystems — animals, people, plants, land, ocean and weather — giving students an opportunity to touch, feel and interact with natural surroundings.
Ocean Magic Happens Here
At Sanibel Sea School, each day is filled with moments of wonder in the water. We offer day classes, camps and experiences for kids, families, and grown-ups, so come with us and be amazed. For more information, visit sanibelseaschool.org or call (239) 472-8585.
A nonprofit organization.
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