Thursday, October 13, 2016

What Happens When a Lake Trout Survives a Sea Lamprey Attack?

Study will help fishery managers understand more about Great Lakes lake trout populations
October 13, 2016
By Marie Zhuikov

Despite close attention by fishery managers, the lake trout population in the Wisconsin waters of Lake Superior has been declining in the past decade or so. Recently, this led to emergency limits on the number of lake trout that can be harvested by anglers and commercial and tribal fishermen in Wisconsin waters of the lake.

In an effort to get a better handle on population stressors so that more accurate fishing quotas can be set, fishery managers are looking at a variety of factors that might stress this important population. One of those things are attacks by sea lamprey – the eely vampire of the fisheries world.

Although the number of lake trout deaths by lamprey rank behind those from commercial fishing, natural causes and angling, it is estimated that more than 50 percent of lake trout attacked by lamprey survive. It’s long been assumed that lamprey-attack survivors suffer from impaired growth and reproduction rates, but this has never been studied in the lab.

Tyler Firkus, a fish and wildlife Ph.D. candidate at Michigan State University (MSU), plans to change that. However, first he has a few obstacles to overcome for this unique project. For instance: how to catch lamprey that are in the relatively short feeding stage of their life cycle, how to keep the lamprey alive until they can be introduced to lake trout, and how to expose the trout to lamprey parasitism just long enough so that it’s not lethal.

“It’s a major project with a lot of moving parts,” Firkus said. “There’s different hurdles and different things that keep popping up because nobody’s ever done this before.”

Of the various types of lake trout, Firkus is studying the siscowets (the fat ones) and lean lake trout. They were chosen for the study for comparison purposes. “There’s some evidence that the siscowet are more prone to parasitism from lamprey and they might actually be buffering the lean lake trout from parasitism,” Firkus said.
Why lamprey seem to prefer siscowets could be because lamprey like their fattier taste, or because they live in the same deepwater habitat that feeding lamprey prefer, or it could just be a numbers game because there are more siscowets in Lake Superior than there are lean lake trout, by a ratio of 15:1 (based on 2006-2011 data).

Firkus is conducting his research at the University of Wisconsin-Stevens Point Northern Aquaculture Demonstration Facility (UWSP NADF), a Wisconsin Sea Grant partner organization located in Red Cliff, Wis. The facility currently holds a mature broodstock of both trout types from previous research projects. The UWSP NADF is the only facility in the world that has domestically reared siscowets available. Firkus is just beginning what he suspects will be a four- to six-year project.
As for catching the lamprey, Firkus is getting help from commercial fishermen in the Bayfield area and from the Hammond Bay Biological Station in Michigan, which specializes in lamprey collection and research. So far, he has about 20 lamprey in their feeding stage, with hopes of capturing 30 to 40 total.

As for exposing the lamprey to the research fish, Firkus plans to do this is in a controlled manner, with one lamprey parasitizing one lake trout per tank. For scientific comparison, other lake trout will go into tanks without lamprey.

“We want to look at the sublethal effects of parasitism, “Firkus said. “If the lamprey parasitize longer than five days, it’s likely that the lake trout will die. We will remove the lamprey around three or four days to avoid mortality.”

After the lamprey are removed, he plans to study a number of physical parameters of the fish over the long term. These include growth, reproduction and immune response. He will divide his time between UWSP NADF and MSU depending on whether he needs to collect data, process data or teach.

“The data will be an important tool to refine current physiological and bioenergetics models to better predict how sublethal sea lamprey attacks can affect the lake trout population,” said Greg Fischer, UWSP NADF operations manager. “The information will be vital for proper management strategies in all the Great Lakes.”

Funding for the project is coming from the Great Lakes Fishery Commission. Project leaders are Cheryl Murphy, Michigan State University; Fischer, UWSP NADF; Rick Goetz, National Oceanic and Atmospheric Administration Northwest Fisheries Science Center; and Shawn Sitar, Michigan Department of Natural Resources Marquette Fisheries Research Station.

Tuesday, October 11, 2016

We [Heart] Actinobacteria

Backed by funding from Wisconsin Sea Grant, UW-Madison researcher Trina McMahon has become the worldwide authority on the key bacteria in freshwater lakes.

October 11, 2016

By Aaron R. Conklin
Every ecosystem has a top dog, a species that out-evolves and outcompetes everything else to survive and thrive under a wide range of conditions. In freshwater lakes, that champion is a special group of actinobacteria, small microbes—like, really, really tiny —that make up a superabundant group of bacteria that’s involved in most of what goes on in the freshwater universe.

Nobody knows more about freshwater actinobacteria than University of Wisconsin-Madison professor of environmental engineering Trina McMahon. With the support of Wisconsin Sea Grant, McMahon’s laboratory members have spent the last five years studying the little critters from every imaginable angle—and in the process have become the pre-eminent experts on the topic. What they’ve found has enlarged our understanding of how freshwater lakes function and exist.

“If you think of the lake as an entity, a living breathing thing that cycles nutrients, these bacteria are responsible for half of it,” said McMahon. “They’re very, very tiny, but because of their numbers and their level of activity, they’re driving huge amounts of the carbon cycling and nutrient regeneration,” said McMahon. “We’ve had a special place in our heart for a long time for the freshwater actinobacteria.”

The relationship began back in 2007, with Ryan Newton, one of McMahon’s first Ph.D. students. Newton, who’s now an assistant professor with the UW-Milwaukee School of Freshwater Sciences, developed a baseline bar code of actinobacterial RNA sequences that allows researchers to track, classify and enumerate bacteria in lakes. Using that code, Newton and McMahon demonstrated that actinobacteria are the predominant species in inland lakes. 

In 2012, McMahon’s lab used a cutting-edge method to take a single cell of the actinobacteria and sequence its genome. What they found was that the actinobacteria have a rhodopsin protein similar to the protein in the human eye that allows it to sense light. In the actinobacteria, however, the rhodopsin almost certainly does more—converting the light into energy. (Those findings were recently published in the International Society for Microbial Ecology Journal.)

In a 2014-16 funded project with Wisconsin Sea Grant, McMahon and UW-Madison structural biologist Katrina Forest took it further, revealing something even more surprising about freshwater actinobacteria.

“Actinobacteria have the retinal found in most opsin proteins that allows them to harvest light, but we think they also have another light-harvesting structural molecule that allows harvesting of a different wavelength of light, amplifying the energy that gets harvested in a way that not many other bacteria have.”

That extra method of acquiring energy helps explain why they’ve shot to the top of the ecosystem ladder like a supercharged bullet. Currently, a graduate student in Forest’s lab is charting the actinobacterial cell’s biochemical machinery to definitively identify the structure of this second light-capturing molecule. McMahon suggests it might be possible that different groups of actinobacteria harvest different wavelengths of light.

In addition to the light-harvesting mechanism, McMahon’s lab has noted that the actinobacteria also interact extensively with the gunky-green cyanobacteria and algae that often overtake freshwater lakes during the summer months.

“They have in their cell wall/membrane all this machinery to suck up other dead organisms’ parts,” McMahon explained. “We think of them as vultures or scavengers—they wait for other organisms to die and then they eat up their parts. Then they recycle the atoms into carbon dioxide and also into new cell material. They are the foundational recyclers of the lake.”

McMahon said the interactions take a variety of forms—everything from the actinobacteria eating the dead cyanobacteria to sucking up molecules excreted by the cyanobacteria during periods of rapid growth.

“They’re super in one sense but they’re also crippled in another in that they depend on being able to scavenge what they can’t make themselves,” she said. “What’s fascinating is that we haven’t figured out if the actinobacteria help fuel the cyanobacteria blooms or keep them in check,” said McMahon. “There’s some early evidence that maybe they’re actually partners with the cyanobacteria in certain roles, which would mean that understanding actinobacteria might help us control cyanobacteria blooms better.”

McMahon’s well aware that she faces a strong ewwww factor associated with her research—who wants to talk about gross bacteria and smelly, potentially poisonous blue-green algae in our lakes? To get around that, McMahon has begun talking about actinobacteria using the same language people use to talk about the bacteria that live in humans’ guts, performing helpful tasks like digesting our food and bolstering our immune systems.

“People start to feel a little less scared about the bacteria when they think about it that way,” she said. “If we can understand how the actinobacteria function, and all the different ways they get energy and support the ecosystem, then we have that much deeper an understanding of the lake system. Then we can either do some kind of intervention to improve lake quality or at least make a prediction about what’s going to happen if we do make an intervention.”

McMahon’s research focus will now shift to determining how special each of the strains of actinobacteria are. Armed with genome sequences from the Great Lakes, Lake Mendota, lakes in Sweden and other countries around the world, McMahon’s working to determine whether the bacterial strain she’s studied in Madison’s Lake Mendota is endemic to all lakes or has adapted to its specific environments.

“Maybe the cell in Lake Mendota gets carried to a lake in northern Wisconsin, but maybe it can’t live there because it depends on its friends who are in Lake Mendota,” she said. “We would actually prefer if they weren’t too endemic, because we’d like to take what we’ve learned and apply it to all lakes.”