Fresh water in the Bay meddles with nettles

The Chesapeake Bay is an estuary, where fresh and salt water mix. Salt water coming in from the Atlantic Ocean meets fresh waters coming from the 150 major streams and more than 100,000 smaller tributaries in the Chesapeake watershed. The mix creates a unique ecosystem where the moderate salinity allows many critters to thrive. However, the salinity of the Bay can change depending on the weather.

Heavy rainfall events have led to above-average river flow to the Bay throughout the summer. August was particularly wet, setting a record for streamflow into the Bay. Rainfall has been particularly heavy around the Susquehanna River. Just since late July, the river has experienced three events with river flows surpassing 200,000 cubic feet per second—compared with an average summer flow of 10,000.

One critter that has been affected by the influx of fresh water is jellyfish—in particular, the bay nettle. The bay nettle is typically found in the Bay’s middle tributaries and prefers salinities of 10 to 20 parts per thousand. Because the high river flows have decreased the salinity of the Bay, these nettles have been significantly less abundant in the Bay this year.

While many people may prefer fewer stinging jellyfish in the Bay, nettles play an important role in the ecosystem. Bay nettles are one of the primary predators for comb jellies, which look similar to jellyfish but are actually in a different phylum. Comb jellies are voracious feeders and prey on oyster larvae. Comb jellies are tolerant of a wider range of salinity, so they may have a greater effect on oyster populations without bay nettles to keep them in check.

Another reason to love the bay nettle: it is named for the Chesapeake Bay. A study published last year revealed that the nettle we see in the Bay is actually a distinct species from the one found in much of the Atlantic. The species, called the bay nettle or Chrysaora chesapeakei, has a smaller bell and fewer tentacles than the ocean-based sea nettle, Chrysaora quinquecirrha.

Learn more about jellyfish in the Chesapeake.