PYCNOGONIDS:
SEA SPIDERS!!
One of the things I’ve noticed over the years of studying coastal animals and seaweeds along
the southeastern US is that the abundance of different species changes from year to year. All the
different species are generally present during their particular seasons, but one year one species
will be here in greater numbers than usual; and the next year something else will be overly
abundant. Folks that come and visit Tybee Island every year at about the same time have told me
that they have noticed the same thing. One year a particular kind of animal will be real common,
and the next year something else will be abundant. Reproductive success, slight variations in
environmental conditions during larval stages, food abundance or scarcity, predator abundance,
and even recent weather and oceanographic conditions are just a few of the factors that might
ultimately affect how abundant something is around here each year.
One of the strangest, and to me most interesting, animals that seems to be here some summers
but not so common other summers are Pycnogonids. They are often called Sea Spiders because
they look more like a spider than anything. Although they are classified as Arachnids, along with
real spiders, scorpions and Horseshoe Crabs, Pycnogonids are in a group all to themselves within
the Arachnids and are not spiders at all. They are probably more closely related to Horseshoe
Crabs than spiders. I don’t like spiders! But I don’t mind these mild-mannered, fragile little “Sea
Spiders.”
There’s really not much to a Pycnogonid. It appears to be just 8 (usually) skinny, jointed legs
that come together in one spot. There doesn’t look like there is hardly any main body or head,
because these body parts are very reduced. They live down in the water totally submerged, so
they are true marine animals. I usually find them on hard bottom areas like rocks, dock pilings or
the sides of floating docks, where they slowly crawl around among seaweeds and hairy-looking
hydroids and bryozoans. Because they are small, slow, and nothing but a bunch of skinny legs,
I usually overlook them, and it is usually someone else in our beach ecology trip who finds them
in the tide pools along the jetty rocks.
It amazes me that something this small, fragile, and brittle-looking could survive submerged
among the rock jetties where the waves are crashing and the water is moving swiftly throughout
the crevices between rocks. But somehow they are able to maintain themselves. When we’ve
had them in touch tanks on the beach, I’ve noticed they have the ability to fold up their legs and
make their body much smaller and compact. I wonder if they find a small space between rocks,
curl up and hold on when the water is moving fast and violently around them. But in the quiet,
still water of a tide pool, these gentle, fragile little “Sea Spiders” slowly dance their way among
the seaweeds and hydroids and usually go unnoticed by us tide pool explorers.
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
20 TYBEE BEACHCOMBER | JULY 2018
/(www.TybeeBeachEcology.com)