smaller creeks or streams and move to bigger
bodies of water as they mature.
If conditions are unfavorable, being too
cold or not having enough salinity, for
example, the polyps can enclose and survive harsh conditions for extended periods.
When the waters are too cold for the nettles, another jellyfish makes its way into the
Bay. The lion’s mane jellyfish, the world’s
largest jelly, can grow up to eight feet across
in far northern waters. In the Bay, they
grow to about four inches, the same size as
our sea nettles.
Summer-time cohorts of the nettle include
the comb jelly and the moon jellyfish. These
non-stinging comb jellies are actually a distant cousin to the jellyfish. Their walnut-shaped forms reach a maximum size of about
five inches and can glow (through bioluminescence) at night if disturbed.
Appearing mostly in the southern Bay, the
moon jelly’s clear, disk-shaped bell is
fringed with hundreds of short tentacles.
These true jellies can grow up to about 12
inches in diameter and temporarily shrink
to one-tenth their size to conserve energy
when no food is available.
Sea nettles eat zooplankton and small fish,
worms, and crustaceans. Their tentacles are
covered in stinging
cells called nematocysts, which stun or
kill prey. The nettle
uses its oral arms,
which hang from
the center of the
bell, to move food to
When oysters are in
their floating larval
stage they are prone
to predation by nettles and comb jellies.
Although both eat
larval oysters, the
sea nettle spits them
out unharmed. And,
sea nettles help protect baby oysters by
eating comb jellies
during the summer
months when oyster
larvae are most
Because the nettle
has few natural
predators (sea turtles being one), their abundance is more
affected by rain and heat. Since they like
warmer saltier water, more nettles are likely during dry, hot summers.
In case you needed another reason to fight
for clean water, getting our Bay back in balance with healthy fish and turtle populations may help control the nettle. In the
meantime, I suggest avoiding swimming on
windward shores, where jellies tend to traffic jam. And, if stung, apply vinegar, which
keeps unfired nematocysts from stinging.
If the sting is still bothersome, remember the
nettle was just drifting around the Bay eating
oyster enemies. Forgiveness is a funny thing.
It warms the heart and cools the sting.
Jellyfish expert Jennie Janssen, the aquarium’s Manager of Changing Exhibits, took
me behind the scenes recently. I highly
recommend visiting this popular exhibit
in person, but don’t wait too long.
Although a replacement exhibit is not
yet scheduled, the
slated for a three-year stint, have
already been around
for twice as long.
The summer afternoon when I visited, Jennie took me
through the exhibit,
stopping to answer
questions from a
passing throng of
excited children. In
this setting, over
a backlit field of
blue, the jellies
The tanks are set up
to take advantage of
the jellyfishes’ need
to swim against the
current. Water flow
inside the tanks is
adjusted based on
the size of the animals and with the aim of keeping the jellies
in good viewing positions for visitors.
Although mature nettles can achieve a
weak swimming motion by contracting
and relaxing their bell, their location is
mostly controlled by winds and currents.
In the larval and polyp stages, sea nettles
are mostly stationary.
The Atlantic sea nettle spawns in late summer through early fall at the end of its short
life cycle. Males release sperm into the
water. Females pump the sperm through
their bodies and release tiny larvae, called
planulae. The larvae float for a few days
before attaching themselves to a hard surface. There the larvae grow into polyps.
When conditions are right, during the
warmer months of May to August, each polyp
swells into a stack of small discs and buds off
as many as 45 miniature jellies smaller than
the head of a pin. Baby jellies float around in
Chesapeake Bay Jellies (Clockwise from top left):
Atlantic Sea Nettle, Moon Jellyfish, Lion’s Mane Jellyfish, Leidy’s Comb Jelly.
(CLOCKWISE FROM TOP LEFT) BEVERLY JACKSON, ISTOCK, NOAA, VIDAR A.
Loren Anne Barnett—CBF’s
Director of Creative Services
and Editor of Save the Bay
magazine—has a new-found
respect for sea nettles.