June 2026 Critter of the Month
Meet the Atlantic Bay Nettle
The Chesapeake Bay is home primarily to three true jellyfish (Scyphozoans): the Bay Nettle (Chrysaora), the Lion’s Mane (Cyanea), and the Moon jelly (Aurelia). The bay nettles, with their painful stings, are famously and reliably the bane of summer swimmers in the Bay. They are distributed throughout the middle and lower regions and their tributaries from spring through early fall. Just as reliably, they disappear completely in the fall once they reproduce, and their tiny-speck-sized offspring settle on hard substrates, especially oyster shells on the seafloor, where they grow looking more like anemones than adult jellyfish through the cold months. They depend on sufficiently salty waters during this juvenile period, so winter and spring salinity is a good predictor of the next year’s Bay nettles, particularly at the low-salt edges of their range.
Though swimmers know bay nettles for their sting, they occupy an important and beneficial position in the Chesapeake food web. They are voracious predators, feeding on a variety of foods, notably including the comb jelly (in technical terms, a Ctenophore) Mnemiopsis leidyi. Comb jellies are themselves effective predators of copepods and oyster larvae, and compete with a variety of juvenile fish for the same copepod prey. In summers when bay nettles are abundant, they suppress comb jelly populations, allowing copepods to proliferate, and potentially diverting more food to juvenile fish. In low-nettle years, this dynamic may reverse: Mnemiopsis blooms unchecked, copepods decline, and oyster larvae face intensified predation pressure. In short, more bay nettles may mean better-fed juvenile fish and improved oyster larval survival.
An old ‘frenemy’ with a new name
Each of the three main jellyfish in the Chesapeake is fairly easy to distinguish by appearance, as well as where and when it’s found. But it is worth pausing to consider how challenging the earliest species identifications were for jellyfish, or any organism, really. A jellyfish looks different at each life stage, resembling an anemone during development, and can grow to very different sizes depending on temperature, prey availability, or other environmental factors. When you find an organism in one place and then find what appears to be the same organism somewhere else, how do you decide if they are the same thing? If there are small differences, are they meaningful species distinctions, or just the result of different environments? And conversely, two animals that look similar might not be closely related at all, and could be separate lineages that have converged on similar forms by chance.
The Bay nettle was one such cryptic species. For nearly two centuries, the stinging nettle of the Chesapeake was assumed to be the same species as the sea nettle found along the open Atlantic coast from New England to the Gulf of Mexico, Chrysaora quinquecirrha. A few observers had noticed differences: Bigelow (1880), for example, noted that Bay animals seemed to mature with only 24 tentacles, compared to the 40 typical of their coastal counterparts. Even so, the prevailing view held that this simply reflected environmental variation, not a fully separated species.
It took DNA to settle the question. In 2017, Bayha and colleagues sequenced animals from across the genus’ full range and found that the Bay’s nettles form a distinct lineage, now named Chrysaora chesapeakei, appear to be more closely related to jellyfishes off the coasts of Ireland and Namibia than to C. quinquecirrha swimming just offshore near Ocean City. Those morphological differences that Bigelow had noted were, in fact, meaningful all along.
How we track jellyfish with shed DNA
At the PhytoChop Coastal Observatory, we monitor the Choptank River weekly using environmental DNA. This technique examines fragments of genetic material shed by organisms into the water column. Jellyfish are particularly well suited to this approach: they are challenging to capture with nets, but they shed copious DNA into the water. In our growing dataset, we see large blooms in 2023 and 2025 but almost none in 2024, which was a summer preceded by heavy rainfall and consequently low salinity. We are currently in a period of low rainfall and elevated salinity, conditions that favor nettle abundance, and the Lion’s Mane jellyfish made a notable appearance in our dataset this past winter as well.
Looking for More Information?
Chesapeake Bay Program. Jellyfish field guide. https://www.chesapeakebay.net/discover/field-guide/entry/jellyfish
Maryland Sea Grant. Jellyfish. https://www.mdsg.umd.edu/topics/jellyfish/jellyfish
Bayha KM, Collins AG, Gaffney PM. 2017. Multigene phylogeny of the scyphozoan jellyfish family Pelagiidae reveals that the common U.S. Atlantic sea nettle comprises two distinct species (Chrysaora quinquecirrha and C. chesapeakei). PeerJ 5:e3863. https://doi.org/10.7717/peerj.3863
Breitburg DL, Fulford RS. 2006. Oyster-sea nettle interdependence and altered control within the Chesapeake Bay ecosystem. Estuaries and Coasts 29(5):776–784. https://doi.org/10.1007/bf02786528
Decker MB, Brown CW, Hood RR, Purcell JE, Gross TF, Matanoski JC, Bannon RO, Setzler-Hamilton EM. 2007. Predicting the distribution of the scyphomedusa Chrysaora quinquecirrha in Chesapeake Bay. Marine Ecology Progress Series 329:99–113. https://doi.org/10.3354/meps329099
