You may have seen jellyfish swimming in the Harbor, their long tentacles feeding on zooplankton, tiny microorganisms that are also present in the waters. The jellyfish - and you've likely seen the most common bay nettle species - are seasonal. In the rainier springtime, fresh water pours through the Chesapeake Bay watershed. As rainfall decreases and the level of salt in the Harbor slowly creeps up, jellyfish travel north from the Bay to the Harbor, usually in late summer around September.
Jellyfish like warm, salty water as it helps them digest food, and when the weather is just right, there can be a bloom in the Harbor. This year, Baltimore has cold snaps that set the jellyfish back, and they didn't show up until early October.
"They have just reached the point where they're happy to come and hang out in the Baltimore Harbor," said Adam Lindquist from Waterfront Partnership's Healthy Harbor Initiative. The bay nettles usually start to disappear when the water temperatures drop to about 55 degrees, typically mid-October when they can no longer digest food due to the cold. Climate change will likely increase average temperature sin the Baltimore region, including the Harbor water, and will likely impact jellyfish presence and distribution - it's just hard to predict now.
Climate change will also likely increase extreme rain events and high-flow days, said Ben Zaitchik, a professor in the earth and planetary sciences department at Johns Hopkins University. That would also make the water more turbid, which can decrease dissolved oxygen levels and increase nutrients in the water, which can block sunlight and cause bacterial blooms. "This could be particularly acute on account of our city's again infrastructure and known storm water management issues, Zaitchik added.
Pistachio green tide, when the water becomes milky-green due to a green sulfur bacteria bloom, was spotted in the Harbor in early August. As bacterial blooms become more common with climate change, dissolved oxygen levels in the water could decrease. Jellyfish are fairly tolerant to impaired water, but still need some dissolved oxygen to survive. The blooms could also kill the plankton on which jellyfish prey. Warmer water temperature create a thriving environment for jellyfish, which could help blooms that are more common and last longer, said Jack Cover, the general curator for National Aquarium. Jellyfish could be going up the Bay earlier in the spring and swimming in the Harbor through November. An increased, longer jellyfish bloom would disrupt the food web, creating competition for other animals that feed on zooplankton. Jellyfish could also clog fishing nets and power plants. But increased rainfall could decrease salinity in the water, which would make the Harbor a less favorable habitat, Cover said.
"We do not know what would happen if [jellyfish] permanently disappeared in the Harbor, as we do not fully understand their role in the ecosystem," Cover said. "We do know that areas of the Bay with good water quality and habitat have an abundance of species... they all play a role in the ecosystem function." There are about four species of jellyfish in the Harbor - mnemiopsis leidyi comb jellies, which light up in complete darkness, lion's mane jellyfish, pink comb jellies and bay nettles. Baltimoreans are often surprised when the water is clear and they can see a bay nettle swimming by, Cover said - a vibrant display of life in the Harbor. But the jellies have been in those waters way before the city was ever build, he said. As a young boy, Cover had a love-hate relationship with jellyfish, often getting stung by them as he swam in the Chesapeake Bay. Yet, he found them fascinating. They have a very simple life and body design, Cover said, but are surprisingly resilient. Jellyfish, he said, have been able to take advantage of the alterations humans have made in the environment. "I'd say for an animal that doesn't have a brain," Cover said, "they sometimes are seeming to be a little bit smarter than us."

clara.longo@thebaltimorebanner.com

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