Mushroom
Jellyfish By Dr. Joe Richardson
One of the characteristics of southeastern US coastal seaweeds,
invertebrates and fish that I’ve noticed during my 4 decades of study and
research in the area is that species abundance can be very variable. Most
all the same species tend to be present during their particular season from
year to year. But often I’ll find that one or another animal or seaweed will be
unexpectedly abundant one year, and then the next year, something else will
be more common than usual. There are probably many different possible
reasons for this, ranging from environmental conditions during a critical life
history stage, to seasonal ocean current patterns. But this phenomenon sure
keeps coastal ecology around here interesting because you don’t know what
species is going to be most common from one season to the next.
A good example of this year-to-year variation in abundance among our
winter-time beach animals along Tybee is the Mushroom Jellyfish. Mushroom
Jellies are easily the largest jellyfish that we find on our beach at any time
of the year, and fortunately they are harmless and don’t sting. Like all jellies,
they produce copious amounts of slime that helps entrap tiny, microscopic
planktonic algae and animals for food; so when you touch it or pick it up, you
26 TYBEE BEACHCOMBER | JAN 2018
will get slimed! This is especially true of the underside of the large round
“bell” and of the long finger-like mouth extensions that hang from the middle
of the bell. These long mouth extensions form the “stalk” and the large round
bell forms the “cap” that make this jellyfish look like a giant mushroom.
Although the long finger-like mouth extensions might look like thick
tentacles, they are not actually tentacles. The stinging tentacles of a jellyfish
most often are attached and hang from the outer rim of its bell, and not
from the middle mouth area. With Mushroom Jellies and their close relative
Cannonball Jellies, there aren’t any stinging tentacles hanging from the
outer rim of the bell; so both of these jellies are non-stingers. Another
characteristic they share is that, compared to most other jellyfish, the
Mushroom and Cannonball are stiffer and harder and feel more like rubber
or plastic, rather than soft and mushy like other jellyfish feel. As a result,
when a Mushroom Jellyfish washes up on the beach, it will often still be in
one piece. Lying in the wet sand, it will look like a big, round, clear dome with
some long, clear, finger-like extensions sticking out.
One other thing I’ve noticed about the Mushroom Jellies that wash up here
during the winter is that we will find them in a variety of sizes. Small ones
will be 4 or 5 inches across, and large ones may be more than a foot across.
Now is the time they will be showing up, so we will just have to get out there
on the beach to see if this winter is a big year for our biggest jellyfish!
Dr. Joe Richardson is a retired marine science professor with 35+ years of
research and teaching experience along GA and the southeastern coast and
Bahamas. Besides research, he conducts Tybee Beach Ecology Trips year
round (www.TybeeBeachEcology.com) and frequently posts pictures of what
they are finding on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe