TYBEE BEACHCOMBER | FEB 2019 23
IT’S STARFISH TIME!
One of the most exciting animals we find during my beach ecology trips is a Starfish. It’s
usually during this cooler time of the year when we find them. I know they are supposed to be
called Sea Stars, but I’m old school, grew up calling them Starfish, and too old to try to change
now; so I’m going to call them Starfish.
Our winter time star is the Forbe’s Sea Star. It has a reddish-brown, bumpy upper surface.
When we find them, they are usually in the rock jetties hanging onto the oyster-covered rocks
or in the tide pools. This is their preferred habitat because they can grip the rocks and eat just
about any other animal attached to the rocks (oysters, mussels, barnacles). Although it can cling
firmly on the rocks and pry open an oyster, it doesn’t really have much muscle. Instead, it relies
on an internal water vascular system composed of tubes of water that radiate out each arm and
end in tiny, finger-like tube feet that stick out underneath each arm. Each tube foot has a suction
cup on the end, and it is with these tiny suction cups that the Starfish clings onto solid surfaces.
I’ve got to tell you how it eats a mussel or oyster. The Starfish uses its tube feet to pull itself
over the bivalve and position its mouth (small hole at the center of its underside) where the
bivalve would open its two shells. Of course the bivalve will use its strong muscles to hold its
shells tightly shut when disturbed, and the Starfish is not nearly strong enough to pry them apart.
But the Starfish is patient. With those tube feet sucked onto the shells, it will constantly apply
force to open the shells. The Starfish relies on the hydraulic pressure of its water vascular system
to maintain constant force, rather than muscle power. Eventually, the bivalve runs out of energy
and its muscles fatigue, and its shells open slightly. The Starfish then sends its stomach out of
its mouth, through the opening between the shells, and into the inside of the bivalve. In there, the
stomach surrounds the soft body of the bivalve and digests it there. When finished, the Starfish
pulls its stomach back in and crawls to its next victim.
The Forbe’s Sea Star is a cooler water species, and in some northern areas they can be a
problem for commercial oyster beds. Around here, they are more common on offshore hard
bottoms throughout the year; but during the colder months, a few sometimes make their way to
the coast. Some winters, we get a few, and sometimes we don’t get any. But now is the time. So
if you get a chance to explore around the jetties at low tide, be on the lookout.
One last note. With suction cups at the ends of its tube feet, Forbe’s Sea Stars can grip and
move over solid structures and bottoms very well; but they are not good at moving over sand. So
if you happen to find one washed up and you want to rescue it, it will have a much better chance
of surviving if you release it at the rocks rather than just throwing it back out in the water, where
it won’t be able to secure itself.
Dr. Joe Richardson (Ph.D. Marine Sciences) is a retired marine science professor with 40 years
of research and teaching experience along GA, the southeastern coast and Bahamas. Besides
research, he conducts Tybee Beach Ecology Trips (www.TybeeBeachEcology.com) and frequently
posts pictures of their findings on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe
By Dr. Joe Richardson
/(www.TybeeBeachEcology.com)