By Jennifer Barbour
Thousands of dead or dying sea stars washed ashore on our local beaches as winter storms ravaged the coastline recently, bringing below freezing temperatures and plenty of rain. This phenomenon, know as a “wreck of starfish”, is not unusual for the Atlantic. Residents have most likely observed an onslaught of marine life wash ashore once or twice a year, typically during the winter months. The most commonly given reason for this event is that when winter storms hit our area, these sub-tidal animals (which normally burrow in the sand) are lifted up into the frigid water and die of stress and exposure. The higher surf, driven by freezing northeast winds, wash the animals onto dry land where they are left by the ebbing tide.
Commonly referred to as ‘starfish’, sea stars are not actually fish, but echinoderms (“spiny skin”). Sea urchins, sand dollars, and sea cucumbers all fall under this same classification, and are often strewn on the beaches along with their starfish cousins. Gray or Netted Sea Stars (Luidia clathrata) are the most common species in our area. When viewed with a magnifier, the pattern of the plates on its surface resembles a field of daisies. The Common Sea Star (Asterias forbesi) is not commonly seen in large numbers since it does not form colonies like the Gray Sea Star. It has thicker, purple-orange arms with prominent spines and a small pink or bright orange hard spot on the surface of the body called the madreporite. Before water enters the sea star’s water vascular system it is filtered through pores located in this small spot.
The arms of sea stars regularly break off, but they soon display a new ‘bud’ of an arm. This regeneration of an exposed end begins by sealing the area immediately after damage occurs. In approximately one week, a new tip will appear and then grow about 3.7 mm per month. The most common cause of losing an arm is predation from various species of fish and crustaceans. Complete regeneration is possible as long as one fifth of the central disk and one arm remain.
The next time you come across a sea star on the beach, pick it up and examine the underside. Along each arm, thousands of tube feet line either side of a deep groove in the center. Their water vascular system enables the sea star’s movement by changing the water pressure in their tube feet. The groove running along the center of each of the five arms is kept free of sand with a constant flow of salt water.
Sea stars are carnivorous and like to eat marine worms, crustaceans, gastropods, sea urchins, and bivalves like mussels, clams, and oysters. They’ll pull the shells of mollusks apart just enough to fit their inverted stomach inside, usually digesting the animal in its own shell. The ability to insert its stomach through thin openings, as well as their incredible muscular endurance, allows the sea star to win nearly every battle against a bivalve. Naturalists in the field have reportedly seen the center of a sea star noticeably bulging, and sometimes even rupturing, attesting to their rather gluttonous appetite.
Here at the Kiawah Island Nature Center, we enjoy the enthusiasm and curiosity expressed by guests and residents when an incredible phenomenon like this occurs. Continue to send us any questions or unique observations you have by calling us at 768.6001 or emailing us at NatureProgram@kiawahresort.com.
About the Author: Jennifer is a Naturalist with the Kiawah Island Nature Program. To contact her with comments or personal stories, email her at Jennifer_Barbour@kiawahresort.com.