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Sunday, May 19, 2024

Warming Water Temperatures in Virginia are Changing Aquatic Life as We Know It

(Photo by Will Parson/Chesapeake Bay Program)

RICHMOND — Throughout Virginia, scientists are documenting significant warming of water temperatures, from inland freshwater streams and rivers to the Chesapeake Bay and the Atlantic Ocean, which experts say has “huge cascading effects on ecosystems.”

Changes in stream water temperatures recorded in the Chesapeake Bay region from 1960 to 2014 (Courtesy of the Environmental Protection Agency)

Rising water temperatures in Virginia are a result of global climate change as well as localized changes in the environment, like a loss of shading from trees that have been removed along streams and riverbanks and a decrease in the amount of freshwater flowing through some ecosystems.

“Even though it might not seem like a big deal, sustained higher temperatures can really damage the intricate balance of species that call those water bodies home,” said Jeremy Hoffman, director of Climate Justice and Impact at Groundwork USA and affiliate faculty in the Department of Geography, Environment and Sustainability at the University of Richmond.

American shad and river herring

Compared to when a Virginia Institute of Marine Science study tracking American shad and river herring returning from the ocean to spawn in Virginia’s rivers and streams first began in 1998, the timing of peak spawning runs now occurs about three weeks earlier, said Eric Hilton, professor at the Virginia Institute of Marine Science at William & Mary and principal investigator of the American shad and river herring monitoring program.

Hilton now sends out his researchers before Valentine’s Day to monitor for the arrival of these fish. He jokes with his team that eventually they will have to start monitoring for spring spawning runs during Christmas.

For a species whose arrival in Virginia historically marked the end of the winter season for Indigenous tribes and later colonists, this shift in the timing of American shad and river herring runs is raising alarms that underwater life as we know it is changing.

American shad and river herring populations are nowhere near what they were historically in Virginia. A moratorium on fishing for American shad in 1994 and the stocking of over 100 million American shad fry in the James River has not reversed a downward trend for the species.

Particularly for American shad in the James River, one of three rivers where surveys are conducted each spring by researchers from the Virginia Institute of Marine Science in conjunction with state and federal partners, populations are in a “very bad state of affairs,” said Hilton.

Not a single American shad was caught in the James River surveys last year, marking a dramatic change for a species that once fed generations of people on the Atlantic Coast and made up one of the largest fishing industries in the region. 

Catch index of female American shad on the James River from 1998 to 2023 (Courtesy of the Virginia Institute of Marine Science)

A multitude of factors are to blame for the shifts in the range and population of American shad and their anadromous counterparts, or species that migrate up rivers from the sea to spawn. Warming water temperatures in Virginia’s rivers and streams as well as in the Atlantic Ocean are thought to be a major part of that equation.

The American shad that do successfully make it back into Virginia’s rivers and streams to spawn are underweight compared to their ancestors; weight is a good indicator of how many eggs they will produce, said Hilton. The loss in weight “is probably a function of living in a warmer changed environment offshore,” he said.

Adding to what he called a self-perpetuating spiral associated with warming waters at sea and in Virginia’s rivers and streams, Hilton said “We know the larvae of American shad have a narrow window before they get cooked or before they get too cold.”

“These things are evolved to work in a certain set of temperatures and regimes that are not there anymore,” said Hilton.

Sensitivities to temperature changes are not just limited to anadromous fish. Freshwater fish are also impacted by rising water temperatures.

Freshwater fish and mussels

Virginia happens to be situated in what Mike Pinder, nongame and endangered fish biologist for the Virginia Department of Wildlife Resources, called the “goldilocks zone.”

“Virginia is very unique in that it’s the northernmost point for a lot of southern species, and it’s the southernmost point for a lot of northern species,” said Pinder.

The state is also home to a lot of western species that occur in the Tennessee, New and Big Sandy drainages, he said.

The wide range of freshwater fish converging in Virginia can be broken down into groups of cold, cool and warm water species. The warming waters would likely impact some species more than others.

“The species that are going to be most vulnerable are going to be those cool and cold water species, because as the temperature warms up, it’s going to affect their reproductive output; it’s going to affect where they’re going to want to inhabit,” said Pinder.

Cold water fish such as brook trout, Virginia’s only species of native trout, are found in cold mountain streams and could be forced to move further upstream to find cooler water at higher elevations if warming trends continue, Pinder said.

“You can only go upstream so far,” said Pinder. “So it’s going to restrict their distribution and probably shrink their range.”

A group of endangered bottom-dwelling fish called darters are also sensitive to changes in water temperature. There are around 42 darter species in Virginia, and they make up one of the most imperiled groups of fish in the nation, Pinder said. 

Water temperatures, along with light conditions, are major cues for when darters choose to spawn.

“Nature is all timing,” said Pinder. “Certain things need to be there when an animal is ready to reproduce.”

If eggs are laid and hatch prematurely, the right food sources may not be available for the larvae to feed on. When waters warm up too quickly, “it really messes up the timing for a lot of these species,” Pinder said.

Timing of spawning runs is also crucial for many species of freshwater mussels that depend on fish to transport their larvae, called glochidia.

The glochidia develop into juvenile mussels while still attached to the gills, fins or scales of freshwater fish, according to information published by the Department of Wildlife Resources. They then drop off the fish and begin the next phase of their lives on stream bottoms far from their parents’ native waters.

If the timing of spawning runs is off due to shifts in water temperatures, freshwater mussels could miss their opportunity to successfully reproduce, potentially damaging a population with just 30% of its species considered stable and the rest in decline across Virginia.

Aquatic amphibians 

About 40% of the world’s amphibians are threatened or endangered, and climate change is the largest emerging threat for what is now the most threatened class of vertebrates in the world, according to the most recent global amphibian assessment.

Brian Gratwicke, an amphibian conservation biologist at the Smithsonian National Zoo and Conservation Biology Institute, said that some “crazy patterns are emerging” in Virginia’s aquatic amphibians.

In general, warmer winters are interrupting the typical lifecycle of these cold-blooded species. “We had a lot of amphibian movement this year in January,” when normally temperatures are too cold for amphibians to become active, said Gratwicke.

For the group of animals that Gratwicke called the center of the food chain and nature’s soundtrack, the decline of amphibians in Virginia means losing a critical part of the ecosystem as well as the ability for future generations to enjoy these creatures.

“Watching a tadpole metamorphose into a frog, it’s a pretty amazing, magical thing, so we want to ensure that these are going to be present for our kids to learn from, enjoy and explore as they learn observation skills,” said Gratwicke.

Climate is linked to almost every aspect of an amphibian’s biology, but responses to climate change will likely be very dependent on each particular species, Gratwicke said.

In a study co-authored by Gratwicke, researchers set out to discover exactly how one of Virginia’s aquatic amphibians of concern, the eastern hellbender salamander, reacted to temperature changes in a laboratory setting.

Researchers exposed a group of hellbenders to temperatures 1.5 degrees Celsius warmer than water temperatures recorded in one of their natural habitats over the course of a year.

Under the warmer scenario, the hellbenders fared much better during the winter months.

“They didn’t lose as much weight, they didn’t have so much of a stress response as reflected in white blood cell counts, and they seemed to prefer the winters,” said Gratwicke.

But during the summer months, the warmer temperatures caused the hellbenders to “just kind of shut down,” said Gratwicke. They stopped eating for all three months of summer, whereas hellbenders under the current climate scenario only stopped eating for one month of the summer.

This becomes especially problematic during the fall breeding season when males must stop feeding and spend their time strictly guarding their eggs.

“If he hasn’t eaten for three months, at the time those eggs are laid he’s going to be super hungry and look at those big juicy eggs and just eat them,” said Gratwicke.

Gratwicke said he believes the trend scientists are seeing in a lack of recruitment of juvenile hellbenders is probably closely related to climate warming because the males could be eating their young after starving over the summer period.

For species of pond-breeding amphibians like leopard frogs and spotted salamanders, warmer water temperatures can also lead to problems. Warm spells that occur too early in the season can cause these amphibians to lay their eggs prematurely.

“If you come out in January and you lay your eggs and suddenly there’s a huge big cold spell and your pond freezes to the bottom, those eggs will be done for,” said Gratwicke.

For Virginia’s terrestrial species of amphibians, such as the red-backed and Shenandoah salamanders, a host of other threats are also emerging that are associated with warming temperatures.

Freshwater turtles

Broad changes to the natural habitats of freshwater turtles in Virginia are also occurring as a result of warming water temperatures.

For spotted turtles, many of the best remaining habitats in the eastern United States are in low-lying, freshwater overwash ecosystems along the coast, where historically an abundance of freshwater flowing downstream has kept salt water from intruding, said Tom Akre, a conservation ecologist for the Smithsonian’s Working Land and Seascapes Initiative.

With warming water temperatures, sea levels are rising and salt water is entering into these coastal freshwater ecosystems, resulting in what are commonly referred to as “ghost forests.” Adding to that effect, there has been a reduction in the amount of freshwater flowing into these ecosystems as a result of human agriculture and urban environments upstream, as well as an actual sinking of the land along the coastal plain.

Spotted turtles as well as eastern box turtles are distributed widely from the northeast United States all the way south to Florida. So although these species do face threats associated with sea level rise and habitat loss, their habitat range in Virginia is not likely to be lost entirely in the near future due to rising temperatures alone, said Akre.

Wood turtles, listed as a species in greatest need of conservation in Virginia, are on the other hand very much at risk of being extirpated, or locally extinct, as a result of rising water temperatures.

“The model predicts that we will lose wood turtles in Virginia over the next 50 to 100 years because of temperature changes, and we are beginning to see possible mechanisms for that to happen,” said Akre. 

The wood turtle is listed by the Commonwealth of Virginia as threatened. (Photo by ​​I. T. Wilson/ Department of Conservation and Recreation’s Natural Heritage Program)

Virginia is home to the southernmost habitat for wood turtles in the United States. Although studies have not yet been conducted to prove this hypothesis, Akre said there is speculation that warmer falls and winters combined with drought conditions experienced in parts of the state last year could be part of a growing trend that is negatively impacting the species.

The speculative effect is that “instead of returning to the streams in the fall as they should and having the cool temperatures essentially slow down their metabolisms, they’re basically stranded where there’s not enough water for them to get into the stream, and it’s not cold enough for them to start to hibernate,” said Akre.

This could result in two things: One is that female wood turtles could come out of hibernation with depleted fat stores, resulting in smaller clutches, smaller eggs or both. The other is that males could remain active later into the fall, depleting their vital energy stores by continuing to combat each other to gain access to females for mating.

These hypotheses are “opportunities for us to develop important scientific research to test how these models might manifest and to see if there are avenues for conservation,” said Akre.

There are many threats outside of temperature increases that freshwater turtles are facing in Virginia, including poaching and vehicle strikes on roadways that intersect their habitats.

“None of these threats happen in isolation,” Akre said, “and so as a conservation biologist, we are always thinking about the ways in which these threats are cumulative or additive or both.”

Mitigating against the effects of warming waters

The conservation science and practice community agrees that “the more natural systems that we can conserve, the better off wildlife, people and societies will be in terms of mitigating the risks and impacts of climate change,” said Akre.

He added that large conserved portions of forests and wetlands are carbon sinks and create freshwater and clean air. They also could provide a refuge for species to escape from manmade threats like development and poaching.

Establishing more riparian buffers — trees planted alongside rivers and streams — is another technique being pursued in Virginia to combat rising water temperatures. Riparian buffers provide shade that cool waterways; Gratwicke said if trees are planted along the entire catchment, or natural drainage area, of a stream, they can reduce the amount of hot water entering the ecosystem that drains off of more impermeable surfaces like pavement.

Work is being done in coordination with state, federal, tribal and private landholders to plant more riparian buffers that will benefit aquatic organisms in need of “a nice cool system that’s not going to have wide fluctuations in temperature,” said Pinder.

Allowing aquatic species to move and find suitable habitats that are the right temperature is also important. “One of the biggest problems is that we have a lot of obstructions in our streams and rivers,” such as culverts and low head dams, said Pinder.

Retrofitting or replacing those obstructions is something that environmental organizations and the Virginia Department of Wildlife Resources fish passage program are working on to “allow passage of those aquatic organisms,” Pinder said.

The Cobbs Creek Reservoir in Cumberland County just outside of Henrico is an example of an infrastructural investment that can influence water levels and therefore temperatures in the James River. It can draw up to 75 million gallons of water per day for drinking water during wetter months when the river is at a higher flow volume.

“Then at times of really low flow, which is when you would have the highest impact on the river’s temperature…that reservoir slowly allows more water out into the river system, therefore raising it up and making it not only flow more consistently but also cooling it down at the same time,” said Hoffman.

Creating more vernal pools, or small seasonal pools that fill during the spring and dry up during the summer, is another way humans can be better stewards of aquatic organisms like amphibians, said Gratwicke, who built several vernal pools on his property in Rappahannock. These vernal pools attract “thousands and thousands of tadpoles that are growing into little froglets that go off and eat pests and are just important pieces of our environment.”

“But ultimately,” Gratwicke said, “everything will just be playing around the edges until we stop putting so much carbon dioxide into our atmosphere,” echoing claims made by the majority of sources interviewed for this story.

“We need to be ramping up the amount of renewable energy, getting rid of fossil fuels from our energy mix and reducing our emissions as much as possible to limit the amount of future warming that these water bodies experience,” said Hoffman.

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