A cannonball jellyfish in someone's hand

Jellies on the beach!

Recently, beachgoers may have noticed fairly large (eight to ten-inch diameter), brownish, rubbery jellyfish washed up on the shore. This is not a rare occurrence. However, somewhat like the sea butterflies that I wrote about last summer, the timing, location, and abundance for these “strandings” of cannonball jellies is not predictable. The largest such stranding that I have seen was during a cold winter spell several years ago. At that time, thousands of cannonballs washed up on St. Augustine Beach. Cannonball jellies are planktonic. This means that although they are capable of swimming, they cannot swim against a current. They are found in the western Atlantic from New England to Brazil. They are most abundant in coastal waters of the southeastern US and the Gulf of Mexico. These jellies can group together in large numbers. Cannonballs have a lifespan of only about three to six months.

A small spider crab hiding under the bell of a cannonball jelly

A small spider crab hiding under the bell of a cannonball jelly

Colder water temperatures, coastal currents, and onshore winds can all play a role in washing cannonball jellies onto local beaches. These jellies often have “hitch-hikers” riding along underneath their bells. A small spider crab uses the jelly for protection. The crab can also feed on plankton on the surface of the jelly. When the cannonballs wash up on shore, gulls and other birds will often feed on these crabs.

Cannonball jellies do not have long tentacles. Although they do have stinging cells, these are very weak and may not penetrate a person’s skin.

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