In late summer and early fall, Baltimore visitors and downtown workers are often startled when they glance down into the harbor and see large pulsing Atlantic sea nettles!
The Atlantic sea nettle (Chrysaora quinquecirrha) is a jellyfish species native to the western Atlantic and the tributaries of the Chesapeake Bay. If we ever had a Maryland State jellyfish, it would be the notorious Atlantic sea nettle. While it’s true that most jellyfish species do make their homes in the ocean and are unable to tolerate fresher, “brackish” waters, this sturdy species can actually thrive in it!
Their umbrella-like bell is about the size and shape of grapefruit half. Long stinging tentacles trail from the margin of the bell and are used to capture food which includes plankton, other jellies and small fish. These jellies pulse up and down the water column, day and night, in search of food. During moving tides and windless days, large numbers of nettles may gather near the water’s surface.
Jelly species survive the cold winter in a sedentary, polyp stage attached to hard surfaces like oyster shells, rocks and pier pilings. These polyps resemble tiny sea anemones and capture microscopic plankton with stinging tentacles. In late spring and early summer, when water temperatures start to rise, each polyp will start to produce and release tiny free-swimming sea nettles.
Feeding on the Bay’s abundant supply of plankton these nettles grow and reproduce rapidly. A single sea nettle may release up to 45,000 eggs daily. By July and August, sea nettle populations continue to expand and push north into the upper Bay. By the end of summer and early fall, the lack of rain allows the waters of the Inner Harbor to become saltier. This is usually when Atlantic sea nettles start arriving in decent numbers into the Inner Harbor.
The abundance of good food in these deep harbor waters usually results in some fairly massive nettles! And, just as our downtown sea nettle show starts to attract attention, it will soon come to an abrupt end. As the water temperatures begin to drop, the nettles die off and/or start shrinking rapidly. Though the jellies quickly disappear, it’s exciting to know that millions of tiny Atlantic sea nettle polyps are scattered throughout the Bay waiting for the warming waters of spring to start the annual cycle all over again!