Climate Change Causing Salamanders to Shrink, Leaving Them Vulnerable to Predators and Extinction
Wild salamanders living in some of North America’s best salamander habitat are getting smaller as their surroundings get warmer and drier, forcing them to burn more energy in a changing climate.
That’s the key finding of a new study, published today in the journal Global Change Biology, that examined museum specimens caught in the Appalachian Mountains from 1957 to 2007 and wild salamanders measured at the same sites in 2011-2012. The salamanders studied from 1980 onward were, on average, eight percent smaller than their counterparts from earlier decades. The changes were most marked in the Southern Appalachians and at low elevations—settings where detailed weather records showed the climate has warmed and dried out most.
Scientists have predicted that some animals will get smaller in response to climate change, and this is strong confirmation of that prediction.
“This is one of the largest and fastest rates of change ever recorded in any animal,” said Karen R. Lips, an associate professor of biology at the University of Maryland and the study’s senior author. “We don’t know exactly how or why it’s happening, but our data show it is clearly correlated with climate change.”
And it’s happening at a time when salamanders and other amphibians are in distress, with some species going extinct and others dwindling in number.
“We don’t know if this is a genetic change or a sign that the animals are flexible enough to adjust to new conditions,” Lips said. “If these animals are adjusting, it gives us hope that some species are going to be able to keep up with climate change.”
The study was prompted by the work of University of Maryland Prof. Emeritus Richard Highton, who began collecting salamanders in the Appalachian Mountains in 1957. The geologically ancient mountain range’s moist forests and long evolutionary history make it a global hot spot for a variety of salamander species. Highton collected hundreds of thousands of salamanders, now preserved in jars at the Smithsonian Institution’s Museum Service Center in Suitland, MD.
But Highton’s records show a mysterious decline in the region’s salamander populations beginning in the 1980s. Lips, an amphibian expert, saw a similar decline in the frogs she studied in Central America, and tracked it to a lethal fungal disease. She decided to see whether disease might explain the salamander declines in the Appalachians.
Between summer 2011 and spring 2012, Lips and her students caught, measured and took DNA samples from wild salamanders at 78 of Highton’s collecting sites in Maryland, Virginia, West Virginia, Tennessee and North Carolina. Using relatively new techniques for analyzing DNA from preserved specimens, the researchers tested some of Highton’s salamanders for disease.
Lips found virtually no fungal disease in the museum specimens or the living animals. But when she compared size measurements of the older specimens with today’s wild salamanders, the differences were striking.
Between 1957 and 2012, six salamander species got significantly smaller, while only one got slightly larger. On average, each generation was one percent smaller than its parents’ generation, the researchers found.
The researchers compared changes in body size to the animals’ location and their sites’ elevation, temperature and rainfall. They found the salamanders shrank the most at southerly sites, where temperatures rose and rainfall decreased over the 55-year study.
To find out how climate change affected the animals, Clemson University biologist Michael W. Sears used a computer program to create an artificial salamander, which allowed him to estimate a typical salamander’s daily activity and the number of calories it burned. Using detailed weather records for the study sites, Sears was able to simulate the minute-by-minute behavior of individual salamanders, based on weather conditions at their home sites during their lifetimes.
The simulation showed the modern salamanders were just as active as their forbears had been. But to maintain that activity, they had to burn seven to eight percent more energy. Cold-blooded animals’ metabolisms speed up as temperatures rise, Sears explained.
To get that extra energy, salamanders must make trade-offs, Lips said. They may spend more time foraging for food or resting in cool ponds, and less time hunting for mates. The smaller animals may have fewer young, and may be more easily picked off by predators.
“Right now we don’t know what this means for the animals,” Lips said. “If they can start breeding smaller, at a younger age, that might be the best way to adapt to this warmer, drier world. Or it may be tied in with the losses of some of these species.”
The research team’s next step will be to compare the salamander species that are getting smaller to the ones that are disappearing from parts of their range. If they match, the team will be one step closer to understanding why salamanders are declining in a part of the world that once was a haven for them.
Visit EcoWatch’s BIODIVERSITY page for more related news on this topic.
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Two decades ago scientists and volunteers along the Virginia coast started tossing seagrass seeds into barren seaside lagoons. Disease and an intense hurricane had wiped out the plants in the 1930s, and no nearby meadows could serve as a naturally dispersing source of seeds to bring them back.
Restored seagrass beds in Virginia now provide habitat for hundreds of thousands of scallops. Bob Orth, Virginia Institute of Marine Science / CC BY 2.0<p>The paper is part of a growing trend of evidence suggesting seagrass meadows can be easier to restore than other coastal habitats.</p><p>Successful seagrass-restoration methods include <a href="https://www.sciencedirect.com/science/article/abs/pii/S0304377099000078?via%3Dihub" target="_blank">transplanting shoots</a>, <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1061-2971.2004.00314.x" target="_blank" rel="noopener noreferrer">mechanized planting</a> and, more recently, <a href="https://www.nature.com/articles/s41467-020-17438-4" target="_blank" rel="noopener noreferrer">biodegradable mats</a>. Removing threats, proximity to donor seagrass beds, planting techniques, project size and site selection all play roles in a restoration effort's success.</p><p>Human assistance isn't always necessary, though. In areas where some beds remain, seagrass can even recover on its own when stressors are reduced or removed. For example, seagrass began to recover when Tampa Bay improved its water quality by reducing nitrogen loads from runoff by roughly 90%.</p><p>But more and more, seagrass meadows struggle to hang on.</p><p>The marine flowering plants have declined globally since the 1930s and currently disappear at a rate equivalent to a football field every 30 minutes, according to the <a href="https://www.unep.org/resources/report/out-blue-value-seagrasses-environment-and-people" target="_blank" rel="noopener noreferrer">United Nations Environment Programme</a>. And research published in 2018 found the rate of decline is <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB005941" target="_blank" rel="noopener noreferrer">accelerating</a> in many regions.</p><p>The causes of decline vary and overlap, depending on the region. They include thermal stress from climate change; human activities such as dredging, anchoring and coastal infrastructure; and intentional removal in tourist areas. In addition, increased runoff from land carries sediment that clouds the water, blocking sunlight the plants need for photosynthesis. Runoff can also carry contaminants and nutrients from fertilizer that disrupt habitats and cause algal blooms.</p><p>All that damage comes with a cost.</p>
The Value of Seagrass<p>As with ecosystems like rainforests and <a href="https://therevelator.org/mangroves-climate-change/" target="_blank">mangroves</a>, loss of seagrass increases carbon dioxide emissions. And that spells trouble not just for certain habitats but for the whole planet.</p><p>Although seagrass covers at most 0.2% of the seabed, it <a href="https://www.unenvironment.org/news-and-stories/story/seagrass-secret-weapon-fight-against-global-heating" target="_blank">accounts for 10%</a> of the ocean's capacity to store carbon and soils, and these meadows store carbon dioxide an estimated 30 times faster than most terrestrial forests. Slow decomposition rates in seagrass sediments contribute to their <a href="https://www.researchgate.net/publication/238506081_Assessing_the_capacity_of_seagrass_meadows_for_carbon_burial_Current_limitations_and_future_strategies" target="_blank" rel="noopener noreferrer">high carbon burial rates</a>. In Australia, according to <a href="https://onlinelibrary.wiley.com/doi/10.1111/gcb.15204" target="_blank" rel="noopener noreferrer">research</a> by scientists at Edith Cowan University, loss of seagrass meadows since the 1950s has increased carbon dioxide emissions by an amount equivalent to 5 million cars a year. The United Nations Environment Programme reports that a 29% decline in seagrass in Chesapeake Bay between 1991 and 2006 resulted in an estimated loss of up to 1.8 million tons of carbon.</p>
Eelgrass in the river delta at Prince William Sound, Alaska. Alaska ShoreZone Program NOAA / NMFS / AKFSC; Courtesy of Mandy Lindeberg / NOAA / NMFS / AKFSC<p>Seagrasses also protect costal habitats. A healthy meadow slows wave energy, reduces erosion and lowers the risk of flooding. In Morro Bay, California, a 90% decline in the seagrass species known as eelgrass caused extensive erosion, according to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0272771420303528?via%3Dihub" target="_blank" rel="noopener noreferrer">paper</a> from researchers at California Polytechnic State University.</p><p>"Right away, we noticed big patterns in sediment loss or erosion," said lead author Ryan Walter. "Many studies have shown this on individual eelgrass beds, but very few studies looked at it on a systemwide scale."</p><p>In the tropics, seagrass's natural protection can reduce the need for expensive and often-environmentally unfriendly <a href="https://www.nioz.nl/en/news/zeegras-spaart-stranden-en-geld" target="_blank" rel="noopener noreferrer">beach nourishments</a> regularly conducted in tourism areas.</p><p>Seagrass ecosystems improve water quality and clarity, filtering particles out of the water column and preventing resuspension of sediment. This role could be even more important in the future. By producing oxygen through photosynthesis, meadows could help offset decreased oxygen levels caused by warmer water temperatures (oxygen is less soluble in warm than in cold water).</p><p>The meadows also provide vital habitat for a wide variety of marine life, including fish, sea turtles, birds, marine mammals such as manatees, invertebrates and algae. They provide nursery habitat for <a href="https://wedocs.unep.org/bitstream/handle/20.500.11822/32636/seagrass.pdf?sequence=1&isAllowed=y" target="_blank" rel="noopener noreferrer">roughly 20%</a> of the world's largest fisheries — an <a href="https://www.floridamuseum.ufl.edu/science/seagrass-meadows-harbor-wildlife-for-centuries/" target="_blank" rel="noopener noreferrer">estimated 70%</a> of fish habitats in Florida alone.</p><p>Conversely, their disappearance can contribute to die-offs of marine life. The loss of more than 20 square miles of seagrass in Florida's Biscayne Bay may have helped set the stage for a widespread <a href="https://www.wlrn.org/2020-08-14/the-seagrass-died-that-may-have-triggered-a-widespread-fish-kill-in-biscayne-bay" target="_blank">fish kill</a> in summer 2020. Lack of grasses to produce oxygen left the basin more vulnerable when temperatures rose and oxygen levels dropped as a result, says Florida International University professor Piero Gardinali.</p>
Damaged Systems, a Changing Climate<p>Governments and conservationists around the world have already put a lot of effort into coastal restoration efforts. And that's helped some seagrass populations.</p><p>Where stressors remain, though, restoration grows more complicated. <a href="https://www.rug.nl/research/portal/en/publications/the-future-of-seagrass-ecosystem-services-in-a-changing-world(3a8c56db-7bed-4c9e-ac7f-c72453e2a102).html" target="_blank">Research</a> published this September found that only 37% of seagrass restorations have survived. Newly restored meadows remain vulnerable to the original stressors that depleted them, as well as to storms — and <a href="https://www.ecowatch.com/tag/climate-crisis">climate change</a>.</p>
Seagrass in Dry Tortugas National Park, Florida. Alicia Wellman / Florida Fish and Wildlife / CC BY-NC-ND 2.0<p>In Chesapeake Bay a cold-water species of seagrass is currently hitting its heat limit, especially in summer, according to Alexander Challen Hyman of University of Florida's School of Natural Resources and Environment. As waters continue to warm due to climate change, the species likely will disappear there.</p><p>Climate-driven sea-level rise complicates the problem as well. Seagrasses thrive at specific depths — too shallow and they dry out or are eaten, too deep and there isn't enough light for photosynthesis.</p>