Thursday, Nov. 14, associate professor of marine science David Samuel Johnson presented the 23rd Tack Lecture titled, “Space Fish, Zombie Shrimp, and Other Salt Marsh Tales” in the Commonwealth Auditorium at the Sadler Center. He covered the adaptability and endurance of salt marsh wildlife and climate change’s impacts on these ecosystems in the community lecture.
Established in 2012, the Tack Faculty Lecture series designates a professor to deliver a community talk in their field of expertise once a semester. Martha and Carl Tack donated the endowment for the series, which provides stipends for participating professors.
The event featured a table with several tanks hosting salt marsh creatures such as periwinkle snails and mummichog fish. Attendees examined papers and diagrams with additional information, asking questions to salt marsh experts present at the event. Attendees were also provided programs, stickers and a bubble blowing kit.
Dean and Director of the Virginia Institute of Marine Science Derek Aday introduced Johnson, referencing his prior research on marine life such as crabs and parasites and climate change’s effect on them.
“Most recently, Johnson was featured in Science News for his work documenting the migration of fiddler crabs into northern states as a result of climate change,” Aday said.
Johnson began his lecture by unpacking the definition of a salt marsh.
“So it’s flooded here in Virginia twice a day by the high tides,” Johnson said. “And so to live in a place that is a salt marsh, as beautiful as it is, you have to be tough.”
Johnson then detailed various examples of salt marsh creatures’ survival abilities. One story focused on space fish, commonly known as mummichogs, who became astronauts when NASA sent two of them along with 50 eggs into space in 1973. NASA sent them on the mission to study the species’ endurance in difficult conditions.
“I could take a mummichog and I could put it on a bucket, here on the stage, leave a very thin film of water, and I could come back tomorrow, and it would still be alive. You cannot do that with a goldfish,” Johnson said.
Johnson explained that the fish’s survival in the salt marsh depends on its ability to breathe air via its damp gills. They prevent the fish from suffocating in cases where the high tide falls during feeding, and the fish cannot escape back to deeper waters in time.
Johnson also described the survival strategies of the parasites that create zombie shrimp. These shrimp, which are actually amphipods, changed in appearance and behavior due to infection from a flatworm parasite called trematodes.
“Well, in the marsh, these marsh hoppers like to hide with the grass. But when it’s infected with a parasite, this parasite specifically, it wanders out into the open,” Johnson said.
The parasite also colors the zombie shrimp orange and hinders its traditional defense response of hopping away. These changes result in birds seeing and consuming the infected marsh hopper, allowing the parasite to target a new host.
In addition to discussing these adaptations, Johnson described how climate change has affected various salt marsh creatures. He highlighted fiddler crabs, explaining the effect of warming waters on their migration patterns.
“But again, the waters are warming up there enough that allows these species from the south to break that barrier and go further north,” Johnson said.
He then guided the audience in a demonstration. Using the bubble kit given to attendees, Johnson blew bubbles into the air, likening their upward floating to fiddler crab larvae which can travel north using water currents.
Johnson also performed a rap to explain a hypothesis, which he developed alongside fellow VIMS professor of marine sciences Jeffrey D. Shields. His crafty lyricism explained that decreased parasite levels have resulted in more fiddler crabs traveling northward.
“Because climate change can give you enough velocity to escape your enemies’ animosity,” Johnson said.
Johnson concluded by thanking those working in his lab and expressed his desire for the public to adopt a more diverse view of marine biology that includes salt marshes.
“I hope from this talk that it expanded your idea of what marine biology could be,” Johnson said. “It could be muddy. It could be in our coastal zones.”
Following the lecture, Johnson answered questions from the audience. One attendee asked whether the creatures moving northward were outcompeting native species in the North. Johnson responded that he had not seen this phenomenon with the specific salt marsh species he had mentioned, but that a different species called mangroves are known to disturb salt marshes after migrating from the South.
“They’re a tropical species, but we see them in Florida, which is a subtropical climate, and we’re seeing them move north and they’re starting to displace salt marshes,” Johnson said.
Another attendee asked Johnson if the space mummichogs’ physiology was altered upon return to Earth. Johnson explained that data on physiology had not been collected for the mummichogs, but for rice fish sent into space, they saw decreased bone density, an issue also faced by human astronauts returning from space.
Arianna Rose ’27 commented on the value of the lecture as a student who intends to major in biology and minor in marine science.
“I think this is helping me understand why I’m going to do [biology and marine science] and what I’m doing it for,” Rose said. “So I think this is really eye-opening and it kind of renewed my energy for studying biology and marine science.”
Rose also voiced the importance of conserving marine species, particularly given the impacts of climate change highlighted by the lecture.
Laurel Perchalski ’20, an alumna who majored in chemistry, approached the lecture from the perspective of her current work as a wet chemist.
“In addition to supporting my boyfriend’s brother, I thought [the lecture] would be really interesting because I do a lot of water analysis,” Perchalski said.
The lecture also gave Perchalski a different perspective on the potential consequences of her work, which involves preventing hazardous chemical pollution in aquatic environments through water sample testing.
“So being able to keep an eye open and think that I’m not just protecting the humans that might drink the water or play in the water, I’m protecting the wildlife as well,” Perchalski said.
Valerie Acosta-Rodigruez works as a research technician in Johnson’s lab, and helped set up and operate the salt marsh tank exhibit. Her research focuses on the impacts of the fiddler crab’s northward expansion, including the endangerment of plants and polychaetes, a type of aquatic worm, in the northern habitat.
Acosta-Rodriguez said she would be open to setting up tanks for a similar event in the future to teach the public about salt marshes.
“I love showing people salt marshes because, when they think about a salt marsh, they think about how muddy it is, how disgusting it is,” she said. “But they don’t see that, when everything becomes still, and you just focus on them, it comes to life.”