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Genetic testing reveals Rehoboth Bay, Atlantic jellyfish are two different species

One of the most common jellyfish along the East Coast — and one often feared by tourists — is actually two different species, according to new research from a University of Delaware alumnus and professor.

Ever since the Atlantic Sea Nettle was described in the 1840s, scientists believed it was one species.

But after University of Delaware alumnus Keith Bayha started looking at the jellyfish, he noticed key differences between the type found on the Atlantic coast and the kind found in estuaries like Rehoboth Bay and Chesapeake Bay. He named the new estuary species “Chrysaora Chesapeakei”, — the “Atlantic Bay Nettle”.


“The one on the coast is much bigger — it’s about twice as big,” Bayha said. “The one in the estuary is about twice as long. You could tell them apart by looking at them side by side.”


The two of them are actually more different from each other than they are compared to jellyfish from Ireland, southwest Africa and Argentina, he said.


Bayha collected and compared DNA samples from jellyfish to show their key differences. In the past, scientists mainly compared tentacle numbers. 


He started researching jellyfish in UD Marine Bioscience Professor Patrick Gaffney’s lab, where he looked at high resolution data on gene sequences in jellyfish, that allowed him to find something he wouldn’t have found had he just compared the jellyfish tentacles. Later, he continued to work with Gaffney and Allen Collins from the National Oceanic and Atmospheric Association’s National Systematics Laboratory, in describing the species.


“It’s another illustration of how sometimes basic differences can be hiding in plain site,” Gaffney said.

Gaffney said DNA sequencing has ushered in a new era for research, allowing scientists to look at more than just the features on an organism’s body.


“The first step in any organism is to extract DNA and that’s actually not very easy with things like jellyfish because they have all kinds of gloopy jelly, so Keith spent a fair amount of time working on getting that technique down,” Gaffney said. 


Once they got the DNA, they sequenced it with a technique called“Polymerase Chain Reaction” (PCR) to amplify a portion of the genome. It’s basically a molecular xerox machine, Bayha said. 


Now that scientists know there are two sea nettle species, Bayha says it could help them manage the species.


“We want to know when they’re going to be around and when we need to look out for them. We need to know how many species there are,” he said.


Credit Brian Jones
Keith Bayha with a jellyfish he described five years ago called the pink meanie (Drymonema larsoni).

It could even affect scientists’ annual forecast on what type of sea nettle year next year will be.


“They sting swimmers, they eat the same thing as fish. They have all these ecological impacts,” Bayha said. “In order to predict and understand what those impacts are, you need to know they’re different species. If you don’t you might make broad generalizations that aren’t correct.”


Bayha says he is following up his research and working on another paper on the species found in the Chesapeake Bay to look more at its population genetics. He wants to know if there is one huge population breeding in the Chesapeake Bay and a different one breeding in Rehoboth Bay.

Journal Reference: Keith M. Bayha, Allen G. Collins, Patrick M. Gaffney. 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, 2017, 5:e3863

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