Staghorn coral (Acropora cervicornis) with white band disease. (Credit: Sarah Gignoux-Wolfsohn)
by Kristen Minogue
Parasitic slime nets attacking seagrasses. A disease that melts coral tissue down to the skeleton, whose exact cause remains unknown. If these aren’t the first places you’d look for optimism, you’re not alone.
Katrina Lohan heads SERC’s Marine Disease Ecology Lab. She and postdoc Sarah Gignoux-Wolfsohn studied both ailments in Florida. They look for hope in the microscopic realm of DNA. Click to continue »
Katrina Lohan in New Zealand’s Abel Tasman National Park. (Credit: Chris Lohan)
Weird truth: There are more parasites on Earth than non-parasites. Katrina Lohan would know, having spent over a decade studying them. After five years with the Smithsonian Environmental Research Center’s Marine Invasions Lab, Lohan is now in charge of launching the center’s new Marine Disease Ecology Lab. In this Q&A, meet some of the weirdest parasites she’s encountered and learn how DNA is helping her unlock their secrets.
This is the second of three profiles about the young scientists heading SERC’s newest labs. Edited for brevity and clarity.
What do you find most fascinating about parasites?
I really like it when stories are complicated. And adding parasites certainly complicates any story. But I’m also intrigued by the David and Goliath aspect of it, that parasites are super small, [often] overlooked, and most people don’t even think about them in terms of what role they play in ecosystems or what they could possibly be doing. Most people would sort of shrug off—oh, they’re probably not really that important. And yet, they’re extremely important. The more we learn about parasites, the more we realize that they control their hosts. They can actually completely change the behavior of their hosts. Click to continue »
Zebra mussels in the Great Lakes, lionfish in the Atlantic and pythons in the Everglades: Large creatures like these generally draw the spotlight when talking about ways to combat invasive species. But for every visible invader, there are hundreds more too minuscule to see with the naked eye. These species often slip in unnoticed—and unregulated—in the ballast water of large ships.
Last week Nature magazine published a news piece about how supplies of agar, a research staple in labs around the world, are dwindling. Agar is a gelatinous material from red seaweed of the genus Gelidium, and is referred to as ‘red gold’ by those within the industry. Insiders suggest that the tightening of seaweed supply is related to overharvesting, causing agar processing facilities to reduce production. Most of the world’s ‘red gold’ comes from Morocco. In the 2000s, the nation harvested 14,000 tons per year. Today, harvest limits are set at 6,000 tons per year, with only 1,200 tons available for foreign export outside the country. In typical supply and demand fashion, distributor prices are expected to skyrocket. As a result, things could get tough for scientists who use agar and agar-based materials in their research.
Agar is a scientist’s Jell-O. Just like grandma used to make Jell-O desserts with fruit artfully arranged on top or floating in suspended animation within a mold, scientists use agar the same way. Bacteria and fungi can be cultured on top of nutrient-enriched agar, tissues of organisms can be suspended within an agar-based medium and chunks of DNA can move through an agarose gel, a carbohydrate material that comes from agar. Agar and agar products are the Leathermans of the science world.
Tepolt holding a Humboldt squid at Hopkins Marine Station in Pacific Grove, California. (Tom Hata)
Before I was the science writing intern at the Smithsonian Environmental Research Center (SERC), I volunteered in SERC’s marine invasions lab sorting white-fingered mud crabs with Monaca Noble, researcher and public relations coordinator. The mud crabs are tiny, ranging from the size of a tick to the size of a quarter. They reek of preservative alcohol, and milky mittens glove their pincers. While sorting, I met Carolyn Tepolt, a postdoctoral fellow at SERC.
34-year-old Tepolt (which sounds like a fusion of “teapot” and “catapult”) offered me homemade lemon bars the day we met. Working together, we discovered we were both undergraduates at the College of William and Mary—we lived on the same floor of the same freshman hall 14 years apart. Tepolt visited the lab to learn the crab-sorting process because this summer she will use genetics to study how mud crabs are adapting to their parasite, Loxothylacus panopaei, or Loxo. Click to continue »
A grass shrimp infected with a trematode parasite (photo: Sara Gonzalez)
While the idea of playing host to something out of the movie Alien is decidedly unpleasant, it’s hard not to marvel at the exquisite grossness of microscopic parasites. Parasites take advantage of their hosts for resources and shelter, but research on parasites suggests that they also can manipulate their hosts’ behavior: Crickets will drown themselves, snails position themselves to be eaten by birds, and some theories suggest that cat-lovers infected with the parasite Toxoplasma gondii become self-destructively reckless. More than half the known species in the world are parasites—making parasitism the most popular lifestyle on Earth.
At the Smithsonian Environmental Research Center (SERC), the Marine Invasions Lab has been tracking parasites in grass shrimp, an incredibly common near shore species. Rates of parasitism are extremely high in grass shrimp, with some years 90 percent of the shrimp caught displaying parasite infection. The most common parasite is a trematode that forms cysts in the tail of the shrimp. Sara Gonzalez, who interned with SERC this summer, wanted to see if parasitized shrimp displayed different predator avoidance behaviors than unparasitized shrimp. Because the trematode only reproduces in birds and mammals, the parasite must find a way to make its way up the food chain. Sara suspected that infected shrimp will change their behavior in a way that makes them more vulnerable to predators like mummichogs. The parasite does not infect the mummichogs directly, but mummichogs are prey for mammals and birds. If a mummichog that has ingested an infected shrimp gets eaten by a bird or mammal, then the parasite will be able to reproduce. Click to continue »
Kristy Hill and Michele Repetto hunt for oysters on an exposed marsh in Chincoteague Bay. (Katrina Lohan)
For our final sampling site, we headed north to Chincoteague Bay. Edward Smith, our boat captain, had made sure to find a location that wasn’t currently leased to a local fisherman. He was confident we would find oysters, but he wasn’t sure about mussels or clams.
For some additional manpower, three summer interns from the Eastern Shore Laboratory accompanied us. Our sampling location was adjacent to Wallops Island, a NASA facility. We got to work as soon as Edward stopped the boat. Edward and the interns started raking for clams, while the rest of us grabbed oysters and mussels from the exposed marsh.
The mud here was also thick and deep! Once we had all the oysters and mussels necessary, Kristy and Michele aided in the search for clams while I recorded all the necessary metadata and took sediment and water samples. When the tide started to come in we had to halt our sampling efforts. Though we didn’t find as many clams as we wanted, we had enough to make processing them worthwhile. It was a great time for our final collecting trip of the season!
On Friday, we jumped in the boat for a quick ride to a nearby oyster reef just outside the inlet at Wachapreague. Unfortunately for us there was a storm surge of a few feet, so the area that should have been completely exposed at low tide was still mostly underwater. Our boat captain, Edward Smith, took one look around and told us to hurry, as we probably only had one hour to collect all the bivalves we needed.
Edward and two summer interns started to rake for clams, while Michele, Kristy and I headed for oysters and mussels. It was slow going as the water was mucky and the mud was thick. It was a bit of a leg workout!
I collected at one site and then moved on to the next when I heard Michele yell for me that she had cut her leg on an oyster and needed to head back to the boat. She left her collecting bags so Kristy knew where she had been, and she and Kristy switched out at that location. After I had gotten all I needed, I got back to the boat as fast as I could, while still treading slowly and cautiously through the turbid waters. Thankfully, Michele’s cut wasn’t bad and she was able to clean it out with the first aid kit on board. Next time, we are wearing waders!
Rainbow over the marsh at Wachapreague, Va., following a storm. (Katrina Lohan)
A pretty impressive thunderstorm rolled through one night while we were in Wachapreague. We were so close to finishing that we decided to push through and cross our fingers that the power didn’t go out. Michele and Kristy started cleaning up the lab as soon as they finished processing all of the samples for DNA analysis; however, I still had a few more that I needed to scan under the microscope for metazoan parasites.
It was a little eerie to watch the sky darken and hear the wind, especially when the lights in the lab kept flickering. I contemplated stopping, but I had already dissected all of my samples. It took about 30 more minutes, but I was able to finish up and then we made a mad dash for our rooms in the dormitory. While the power stayed on in the lab, the dorms weren’t so lucky.
As soon as the storm was over, we headed out to dinner at a local restaurant. The view over the marsh was spectacular—rainbows everywhere!
Microscopic slide of a mussel parasite called a trematode. Trematodes often infect small aquatic animals, like mussels or snails, in hope of getting eaten by a larger host they can infect later. Viewed under 400x magnification. (Katrina Lohan)
Just as in previous trips, part of our sampling involved dissecting the bivalves and preparing tissue preps to view under the microscope. I have to admit that the microscopic metazoan parasites that I saw on this trip were not quite as exciting as previous trips—I miss the really cute turbellarians (a.k.a. Urostoma sp.)! Though they weren’t as cute, I did see some parasites through the microscope, including trematode metacercariae in the mussels, three marine mites, a handful of pea crabs and free-swimming harpacticoid copepods. I had never seen a marine mite before and at first thought there were ticks running around the lab. That’s what happens when you spend hours in front of a microscope–you forget how small the things you are viewing actually are!
