Findings may help manage influx of box jellyfish along N.C. coast

BOONE—Unwanted visitors are invading the North Carolina coast, visitors that impact the state’s fishing and tourism industries. These visitors are box jellyfish, known as Carybdea marsupialis and a cousin to the deadly box jellyfish found off the coast of Australia.

The species gets its common name from its four-sided box shape. The box jellyfish has a painful sting, can destroy fishing nets, clog power plant water intakes and close beaches to swimmers.

Biology professor Vicki J. Martin, right, is one of the few biologists in the United States to successfully grow box jellyfish polyps in the lab. Thousands of the tiny creatures are grown in petri dishes and other containers to better understand how they thrive in various conditions. Martin is assisted in her work by senior biology major Lee Stanley, left, from Boone. (Photo by University Photographer Marie Freeman)
Jenna Valley, right, a graduate student in Appalachian State University’s Department of Biology, feeds tiny jellyfish being grown in the lab as part of a study of the animal’s resilience to temperature and pH variations. Monique S. Eckerd, left, research operations manager for the College of Arts and Sciences, is assisting with the study. (Photo by University Photographer Marie Freeman)

This box jellyfish polyp, seen at four times magnification, can grow into a baby jellyfish in just two weeks. Appalachian State University biology professor Vicki J. Martin is one of the few researchers to successfully grow the polyps in laboratory conditions. Her work may help discover ways to manage the explosive growth of jellyfish along North Carolina’s coast, growth that may threaten the shrimp, fishing and tourism industries. (Photo submitted by Vicki J. Martin)

“As the waters off the eastern coast are warming, we are seeing more and more of these jellyfish,” said Vicki J. Martin, a professor of biology at Appalachian.  The jellyfish have migrated from the Caribbean, riding currents that have changed over the past decade.

Martin has studied the box jellyfish’s unique eye structure for more than 10 years. Now, she is looking at factors that contribute to their explosive growth off North Carolina’s coast with hopes of finding ways to reduce or manage the population.

“They are voracious predators of fish and shrimp and have really wreaked havoc on the state’s fishing industry,” Martin said. “The numbers of box jellyfish along the coast have skyrocketed over the last couple of years. They occur in blooms, to the point where entire fishing industries across the world have been destroyed by jellyfish. Beaches have been closed to swimmers along the east coast in past summers.”

The box jellyfish has two adult body forms: the jellyfish form and the polyp form. Its life cycle alternates between the two.

Appalachian is one of a few universities that can grow box jellyfish polyps successfully in the lab. Martin estimates she has billions of the tiny polyps, which are no bigger than the head of a pin, growing in Petri dishes, and mid- and larger-size containers. When fed once a week, they form buds that become more polyps. Each polyp can form a jellyfish no bigger than the tip of a little finger and which eventually can grow to the size of a saucer or larger.

“We can stimulate the polyp to grow into a jellyfish by raising the water temperature and withholding food,” Martin said. The polyps’ ability to reproduce quickly in the lab spurred Martin to look at factors that might inhibit their growth. “I have grown these jellyfish in the lab for years, but no one has done any work in the lab to monitor the various conditions under which they grow,” she explained.

“We have changed the conditions we grow them under—temperature, light, feeding regimes, the pH scale of different sea water concentrations, even the size of the containers they are grown in,” Martin said.

So far, Martin, her undergraduate student assistants and Monique S. Eckerd, research operations manager for the College of Arts and Sciences, have found that the polyps are almost indestructible. They have grown polyps in temperatures ranging from 17 C to 25 C (62.6 F to 77 F), a range in which the polyps thrived. Temperatures lower than 17 C and higher than 25 C tend to kill the polyps.
The polyps’ ability to survive at pH levels from 5.5 to 7.5 pH also was tested.  Seawater is normally 7.9 pH.  A pH of 7 is considered neutral–neither acidic or base. The polyps also survived the pH variations.

“I thought surely at 5.5 pH they would die, but they are not, they are thriving,” Martin said. “That tells us that as oceans become more acidic because of acid rain, and while other organisms are dying, the box jellyfish is thriving. These animals are great at adapting to their environment. So the question becomes how long will they thrive.”

Eckerd said warmer coastal water temperatures have increased the animal’s food supply, which spurs growth. “When we started feeding them twice a week, the number of polyps just exploded,” she said. A polyp can grow into a jellyfish in just 10 days.

Martin next will investigate how the information learned in the lab applies to what is occurring along the coast.  She will monitor water temperature throughout the year at three locations along the N.C. coast, and use a plankton net to trawl for jellyfish to see if the ocean temperature relates to the number of jellyfish caught.

“Think about what’s happening on our planet with global warming. As the temperature is increasing the water is getting warmer, including along the east coast, and this is stimulating the polyps to bud and form jellyfish,” Martin said. “That’s why we are seeing these massive explosions along the coast. The question is, how do we control this. We won’t know until we look at all the parameters that affect their normal growth and reproduction,” she said.

Martin speculates that the jellyfish’s rapid growth may ultimately bring about their demise. “As they reach massive concentrations their food source—fish eggs, shrimp larvae and shrimp—
will become depleted. When the jellyfish loses its food source, I think that’s when we will see the population decline.”

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