A trip to the beach often involves a starfish encounter. Starfish or Sea Stars, the common name given to an entire class of ocean animals called Asteroidea, or Asteroides for short, inhabit the world’s ocean floors. A walk along the beach at low tides often reveals their presence in the area.
An interesting starfish fact attaches to the name. While it implies five arms, and some starfish such as the purple orchre star (Pisaster ochraceus) pictured at the top of the page show five arms, the number of arms does not define the starfish. Rather, true starfish are characterized as having a symmetrical body with arms extending from the center.
In fact, the two thousand or so different starfish species can have anywhere from four to fifty arms. The sunflower star, for example, a common West Coast starfish, has twenty four arms.
Bat stars (Asterina miniata) present themselves as another variation on the symmetry theme, this time with webbing between the arms.
They live among the rocky and sandy shores along the Pacific coast from Alaska to Southern California, often close to kelp and grassy areas, its food source of choice.
All starfish species tend to move slowly along the ocean floor using the many tube feet situated along the bottom of their bodies. The suction cups attached to the ends of each tube allow them to stay firmly planted in place.
Like all animals, most starfish movement is geared toward a search for food, with mollusks such as barnacles, clams, mussels and snails often their food of choice. Their mouth is located on the bottom of the body, which makes it easy to consume their prey once they can attach their body on top of it.
Living in the ocean can be dangerous for any animal, and although the starfish is a predator, it can also be prey for larger starfish, crabs, fish, birds and sharks. The third picture shows a gull in the process of consuming one.
In instances where they are prey, being slow moving has its drawbacks. To compensate for their slow movement, starfish have evolved with an ability to regrow a limb that is lost to a predator.
Most peoples’ familiarity with starfish comes from the species found close to shore. Near shore starfish normally inhabit the middle and low littoral zones (the areas furthest from the high tide mark on the shoreline).
Low tides can also cause stress for starfish, because it creates a situation where they can be exposed to the air, and their bodies are not designed to be out of the water for extended periods of time.
Are Star Fish Endangered?
Star Fish are not considered endangered, however, like other marine life, their existence depends on healthy oceans.
Recent reports about coastal dead zones along the West Coast, ocean areas that lack oxygen, also include reports of dead sea stars.
The problem, commonly called ‘sea star wasting disease’ slowly turns the sea star into a very soft mast, rendering it incapable of maintaining its ody structure.
As of this date, scientists are unable to point to a specific cause for the disease.
Meet the Starfish Relatives
On a clear, sunny coastal day, sea star relatives can also be found close to the shoreline. Purple spines attached to a Purple Sea Urchin (Strongylocentrotus purpuratus) can be easy to spot. Most of the time, sea urchins remain stationary, attached to rocks or other hard substrate as they spend their day scraping and consuming algae.
Their range extends beyond the shallow intertidal area, to deeper water, often around kelp beds, one of their favorite meals.
The round Sea Urchin bodies, formally called tests, are covered by a hard shell. Like Sea Stars, their mouth is on the bottom of the body. The spines are used as a defense mechanism, and while some sea urchin species are known to be poisonous to humans, the purple sea urchin is not considered poisonous.
Different Sea Cucumber species can be found in the intertidal zone, while other species spend their lives on deeper ocean floors. While their diets change from habitat to habitat, they are considered benthic feeders (animals that feed on the bottom of the ocean), eating algae and other organic materials in their territory.
They are fished commercially in many parts of the world, with Asia serving as the biggest market.
Sand dollars are characterized by a spiny circular shell. As the name suggests, sand dollars live in on the top layer of sand (or just below it) in an area up to one-half mile beyond the lowest of low tide marks. Since they are marine animals, they die if left exposed to sun and air for a period of time.
Their ability to move helps them relocate according to the movement of the tides. They spend their day eating organic material floating on the water or on the top level of sand.