For humans, if the temperature rises by a few degrees, the immediate impact is minimal. Some people might peel off a layer of clothing. Others might not even notice a difference.
But for fish living in Lake Erie, such a temperature increase in water could spell disaster. Fish are ectotherms, meaning that their body temperature is dictated by the water they live in. As water heats up, fish metabolism increases, causing fish to work faster and use up more energy.
Temperature also has a direct relationship with the oxygen in the water: As the temperature goes up, dissolved oxygen levels go down. Under hypoxic — or low oxygen — conditions, fish have trouble maintaining basic bodily functions and may decrease activity.
“So the fish have this sort of trade-off of needing more food and needing to be more active because of the higher temperatures but then also needing more oxygen for those metabolic processes when there’s less oxygen available,” said Suzanne Gray, associate director of academic programming and research at The Ohio State University’s Stone Laboratory and associate professor of aquatic physiological ecology at College of Food, Agricultural, and Environmental Sciences School of Environment and Natural Resources.
Ohio Sea Grant researchers Suzanne Gray and Lauren Pintor are looking at how one of Lake Erie’s key fish will be affected by a changing climate. With Stone Lab’s mesocosm facility, their team studied how higher temperatures, more turbidity and less oxygen could affect the growth and health of smallmouth bass. (Photo by Jodi Miller)
Scientists know about these phenomena alongside climate change models that predict an increase in Lake Erie surface temperatures by 3 to 4 degrees Celsius or more in the next 50 years.
What’s unknown, however, is how these climate change “stressors” like increased temperature and hypoxia impact the relationships between fish, such as between predators and their prey. Gray and project collaborator Dr. Lauren Pintor, associate professor of aquatic ecology at Ohio State, hope to discover the answers in their Ohio Sea Grant-funded pilot study on two species of Lake Erie fish, smallmouth bass and the invasive round goby.
“These stressors are going to influence an individual fish’s ability to respond,” said Gray. “So then, what does that look like when you have the interplay between a predator and a prey?”
Round gobies are invasive bottom dwellers that hide under rocks for protection from predators. When a predator like a smallmouth bass is nearby, they tend to freeze in place and then flee if the bass gets too close for comfort.
The relationship between the two fish is relatively new. Smallmouth bass, native to Ohio, are an important sport fish for anglers in the state. Round gobies, on the other hand, are an invasive bottom-dwelling fish from Eurasia that entered Lake Erie in 1994.
“They really came in and their population exploded in a classic kind of invasion,” Gray said. “What’s interesting is that the bass have switched their diet to 80% to 90% gobies. They just started eating them.”
To understand the dynamics between the two fish, Gray and Pintor worked together to combine their expertise. Gray’s research focuses on fish at the individual level, while Pintor generally studies fish populations and communities.
“We’re working in a really complimentary way,” Gray said. “I want to understand, ‘What does this fish do?’ and then together we’re thinking about ‘If the predator does one thing, what does the prey do?’”
Experiments for the pilot study, led by graduate student Noel Schmitz, began last summer at Stone Laboratory. Researchers monitored fish interactions under warm and cool water temperatures as well as high and low oxygen levels. They tagged smallmouth bass with microchips and used cameras to track how bass and gobies interact in tanks.
“We’re looking at things like, how quickly did the bass orient toward the goby? How quickly did the goby seem to notice the bass?” Gray explained. “A lot of the observations are based on timing. How long did it take the bass to strike at the goby? Was it a successful strike, meaning did it catch and then eat the goby, or did the goby flee and hide?”
Noel Schmitz, Gray Lab and Pintor Lab graduate student, left, and Suzanne Gray, associate professor of aquatic physiological ecology at The Ohio State University, right, inspect smallmouth bass held in large tanks at Stone Lab’s Mesocosm Facility. (Photo by Jodi Miller)
This summer, Schmitz continued the experiments based on lessons the team learned from last summer’s pilot study. One change was exposing the fish to conditions for longer periods of time in larger tanks at Stone Lab’s new Mesocosm Facility to better mimic climate change scenarios.
“It’s definitely a learning curve, but they’ve been working really well for the bass,” Schmitz said of the facility’s circular 600-gallon tanks that can pump in water from Lake Erie. “They work really well because it’s a flow-through system. You can filter the lake water so it removes most of the sediment.”
“What is the population of smallmouth bass in particular going to do? Can we predict that if the temperature goes up this much, this is how we see the population potentially changing? That’s how this study will help managers think about populations and how we want to manage them.”
Suzanne Gray
The team also added a new stressor to the study: turbidity, a measure of how cloudy the water is or how much sediment is in the water. More frequent and intense rain events from climate change can increase erosion and wave action that result in greater amounts of suspended sediment in waterbodies like Lake Erie.
“Turbidity affects their visual environment,” Schmitz said. “The water is pretty cloudy and murky, and that might mean they can’t find prey as easily or can’t find mates as easily.”
Researchers held the bass in three mesocosm tanks starting in May before experiments began in early July. Tanks had varying levels of temperature, oxygen and turbidity to reflect conditions in early summer, late summer and under future climate change projections. For the experiments, they moved the bass to tanks holding the gobies under the same conditions at Stone Lab’s wet lab.
“There’s a lot going on, a lot of things to record, but overall it’s been working well,” Schmitz said. “This is really just the starting point for this research.”
Schmitz said she anticipates future experiments will incorporate a factorial design to reveal how the different stressors might interact and influence each other.
Researchers collected smallmouth bass by electrofishing around Gibraltar Island and caught round gobies through regular angling off Stone Lab’s dock. This summer’s experiments required a total of at least 135 gobies. (Photo by Jodi Miller)
Gray hopes the results of the study will inform managers and anglers about how smallmouth bass populations will change, such as taking in less energy content or producing less young, due to climate change.
“What is the population of smallmouth bass in particular going to do? Can we predict that if the temperature goes up this much, this is how we see the population potentially changing?” Gray said. “That’s how this study will help managers think about populations and how we want to manage them and also help us think about ways to mitigate climate change.”
Researchers also aim to explore how fish interactions and behavior can scale up and reveal insights about populations, communities and ecosystems in Lake Erie.
“I think it’s a really cool perspective to take,” Gray said. “It’s just a different way of tackling the issue and thinking about the physiology and behavior of the fish and how that can add to our understanding of scaling to populations and communities.”
For more about this Ohio Sea Grant-funded research, contact Dr. Gray at gray.1030@osu.edu.
Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES), School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.