TYBEE BEACHCOMBER | MAR 2019 23
DRIFTWOOD FAUNA
The first thing I do while heading across a boardwalk for some beachcombing is scan along
the beach to see if I see any “clumps” of stuff washed up. I like “clumps!” Sometimes they are
tangles of plant material that might include purple and yellow Sea Whips, Rubbery Bryozoans,
Whelk egg cases, Sponges, Anemones, and other animals. Other times they are chunks of
driftwood, and often the driftwood will include its own fauna or collection of animals.
On larger pieces of wood that have floated offshore for a period of time, you might see Goose
Barnacles attached. Unlike most barnacles that grow attached flat onto rocks and hard structures
close to shore, Goose Barnacles only grow on floating objects far offshore. And they look very
different from normal “acorn” barnacles that we see on our rock jetties. Goose Barnacles are
so named because they have a long, fleshy stalk between its main body and its attachment;
and this stalk was thought to look like a goose’s neck. Like regular barnacles, Goose Barnacles
extend their feather-like feet to capture tiny plankton for food, but some reports indicate that
Goose Barnacles also eat small fish and other floating pelagic animals like Portuguese-Manof
War (That, I’d like to see!). So in many ways (anatomy, where they live, how they live) Goose
Barnacles are weird compared to other barnacles.
Lots of pieces of driftwood will be full of small round holes. Sometimes the holes are empty
and the animal that drilled it will be gone, but other times, if you look closely, you can find that
drilling animal (or pieces of it) still down in there. Martesia, or Wood Piddock, is a small clam-like
bivalve mollusk that drills holes about the diameter of a pencil into all sizes of driftwood. It settles
on the wood and as it grows, it uses its shells to dig and drill deeper into the wood. Its shells are
fairly thin so they will generally crumble when the animal dies, and often all you will see are the
holes in the wood. But sometimes if you look closely down in the hole, you might find some of
the shell fragments.
Probably the most famous driftwood borer is the Ship Worm. A Ship Worm really isn’t a worm,
but is a bivalve mollusk like the Wood Piddock. Although the Wood Piddock uses its wooden
burrow mostly for protection and still filters seawater for food, the Ship Worm is more like a
termite and actually consumes the wood that it is burrowing through. They are thought to have
internal bacteria that can digest cellulose so they can obtain energy from eating wood. On the
surface of the wood, a Ship Worm leaves only a small, pin-hole opening; but as it grows deeper
into the wood, it creates a wider round tunnel. At the end of the tunnel, deep into the wood,
the Ship Worm has a couple of small shells. It lines the long tunnel with a thin coating of white
limestone, and often in a piece of driftwood you can see the white lining of some of the tunnels.
So the next time you notice driftwood drying out along the high tide line, take a closer look and
you might see signs of some of the animals that once called that thing its home.
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)