Sea Nettle Jellyfish Return To Nantucket Waters In Huge Numbers

The Atlantic sea nettle jellyfish typically show up in the waters around the island in late summer and early fall, and this year they have arrived in huge numbers in Nantucket Harbor and along the north shore of the island.

Some observers, including Nantucket Harbormaster Sheila Lucey, the Nantucket Boat Basin's Sarah Santos, and charter boat captain Carl Bois, told the Current that this year might be the most they've ever seen around the island.

The sea nettle (Chrysaora quinquecirrha) is a jellyfish species that can be found along the Atlantic coast of the United States and is considered planktonic, meaning it cannot swim against the average ocean current. 

"It's almost entirely up to tides and currents," Marian Mitchell Association aquarium manager Christina Norman told the Current. "This year, we didn't see an influx in the harbor until the second half of August, when we had a couple storm fragments that brought strong winds and currents. We typically see influxes late in the summer, and the nettles disperse around mid-September. I've only noticed the nettles dispersing in the last few days. Before then, there were high numbers in the harbor, to the point where we wouldn't pump up harbor water to the aquarium because it was difficult to find a spot along the beach that didn't have sea nettles nearby."

Norman shared the following information about this year's abundance of sea nettles in Nantucket waters:

• It's difficult to say what caused this year's influx compared to last year's very low numbers. Favorable currents and nutrient loads can help jellyfish populations thrive, but all it takes is a stray current to keep them away from the island, so I wouldn't go so far as to "blame" the increased jellies on a specific source like nutrient flow into the harbor.

• Sea nettles do sting. When they wash up on the beach, their tentacles may clump together, making them difficult to see. I've noticed many people this year mistaking them for moon jellies when they look like they don't have tentacles. Never touch a jellyfish on the beach unless you are certain what you're getting into! If, for whatever reason, you want to remove a jellyfish from where it is on the beach, I recommend a shovel.

• Atlantic sea nettles reproduce in the summer. They reproduce both sexually and asexually. The swimming form of the jellyfish (the medusa) reproduces sexually, with eggs carried by females being fertilized by sperm released by males. Their polyps are released and settle down in the water on things like shells, where they asexually make "copies" of themselves and eventually detach from where they were settled down to change into their swimming medusa stage.