Researchers identify behavioral adaptations that could help Antarctic fish adapt to warming Southern Ocean – ScienceDaily
At first glance, Antarctica seems inhospitable. Known for its howling gales and extremely cold temperatures, the continent is covered with a kilometer-thick ice shelf. Elephant seals and seabirds sometimes dot the glacial shores.
Yet plunging beneath the waves, the Southern Ocean abounds in biodiversity: vibrant bands of seaweed and cyanobacteria in the pack ice, swarms of krill and crustaceans, spiky kelp forests, gigantic polar spiders and sea sponges, whale pods and an abundance of Antarctic fish fauna.
These fish play a vital role in the Southern Ocean food web of 9,000 known marine species, but their sub-zero refuge may be threatened. A climate analysis from 2021 postulated that by 2050, parts of the Antarctic continental shelf will be at least 1 degree Celsius warmer.
Researchers at Virginia Tech’s Fralin Biomedical Research Institute at VTC published a new study in PLOS ONE describing how two species of Antarctic fish – one with hemoglobin in its blood cells and the other without – respond to acute heat stress.
The research team, led by Virginia Tech vice president for health science and technology Michael Friedlander, observed that both species responded to gradual warming with an elaborate array of behavioral maneuvers, including fanning and spreading their fins, breathing on the surface, startle behavior. , and transient episodes of alternating movement and rest.
âRemarkably, our team found that Antarctic fish compensate for increasing metabolic demands by improving respiration through species-specific locomotor and respiratory responses, demonstrating resilience to environmental change and possibly global warming,â a said Friedlander, who is also director of the Fralin Biomedical Research Institute. Director, Senior Dean of Research at the Virginia Tech Carilion School of Medicine and Professor in the Department of Biological Sciences at the College of Science. âAmbient warming presents a multifaceted challenge for fish, including an increase in the temperature of the central nervous system and target tissues such as skeletal and heart muscles, but also reduced availability of dissolved oxygen in water. that passes through the gills during respiration. these results suggest that Antarctic fish may be able to adapt somewhat behaviorally under extreme conditions, little is known about the effects of environmental warming on their predation patterns, availability food and fertility â,
Iskander Ismailov, first author of the study and assistant research professor at Friedlander’s lab during the study, said: “The behavioral manifestations we have described show that these fish have powerful physiological abilities to survive environmental changes,” said
Thanks to millions of years of isolation from the rest of the world – encircled by the Antarctic Circumpolar Current – fish species in the Southern Ocean have adapted well to their icy ecosystem.
Blackfin icefish, Chaenocephalus aceratus, one of two species studied by the team, has unique opalescent blood. These fish are among the few known vertebrates lacking in hemoglobin, a molecule in red blood cells that efficiently carries oxygen from the lungs of terrestrial vertebrates, or the gills of aquatic vertebrates, through the tissues of the body. Instead, the blackfin icefish carry dissolved oxygen in blood plasma, housing about 10% of hemoglobin’s oxygen carrying capacity.
Oxygen is more soluble in cold water, which allows ice-whitefish to thrive in the Southern Ocean. However, as the water temperature increases, these species experience increased metabolic demand, potentially making white-blooded fish more vulnerable to global warming. To test this hypothesis, the team examined five specimens of white-blooded blackfin icefish and five red-blooded black cod, Notothenia coriiceps, in a climate-controlled coastal laboratory that gradually circulated and heated salt water directly from the Southern Ocean.
The fish acclimatized to laboratory conditions, before being transferred to the experimental tank, where the water temperature rose from -1.8 degrees Celsius to 13 degrees, at a rate of 3 degrees per hour. The researchers captured numerous video recordings, allowing them to examine and quantify the motility, respiratory rate, tank maneuvers and fin movements of the fish.
As the water temperature rose, the white-blooded icefish exhibited intensive pectoral fin venting – a behavior previously seen in icefish during egg protection – which the researchers said could help facilitate breathing. In contrast, red-blooded fish have used complex maneuvers, including venting and spreading the pectoral fins, followed by startle-like C-bends, which can increase gill ventilation, according to Ismailov.
“The results offer a new perspective on the effects of rising temperatures on these very cold-adapted species,” said George Somero, professor emeritus of marine biology at Stanford University and a leader in the study of how marine life adapts to heat stress, which was not involved in the research.
Preparation for the expedition began in early 2014. The research team designed, custom built and shipped laboratory equipment to Palmer Station in Antarctica before living there for three months in 2015. The trip included a flight. towards Punta Arenas, in Chile, then a crossing of the Drake Passage by boat during the austral autumn.
Ismailov was the first to arrive, setting up experimental platforms. Six weeks later, he was joined by Jordan Scharping, then a sophomore at Virginia Tech Carilion School of Medicine conducting research in Friedlander’s lab. The pair worked in overlapping 12-hour shifts to conduct laboratory experiments at near-freezing temperatures.
âDr Friedlander attracted me to this project. I remember he introduced the Antarctic project proposal to us medical students and everyone talked about it. It was an opportunity. amazing and I appreciate that he gave it to me, âsaid Scharping, who is now a doctor at Northwestern Memorial Hospital.
The researchers were tasked with collecting their own fish specimens during a series of four weeklong fishing trips. At sea, with the help of the research vessel’s crew, the researchers worked around the clock, sometimes under difficult conditions.
“One stormy night while we were fishing, a two-story wave passed the stern, drenching me head to toe in icy sea water – the captain of the boat stopped fishing after that,” he said. remembers Ismailov. âAs a graduate of medical school, I could never have imagined that my career would take me to Antarctica to study fish, but this research project has become one of the most extraordinary and memorable of my life. “
The fieldwork was funded by a National Science Foundation grant awarded to Elizabeth Crockett, professor emeritus at Ohio University, and Kristin O’Brien, professor at the University of Alaska Fairbanks. Crockett and O’Brien – both former graduate students of Bruce Sidell, who was trained by C. Ladd Prosser – invited Friedlander to join the expedition with collaborators from the University of British Columbia, the ‘University of Leeds and Valdosta State University. .
But the foundations for this recent study began 45 years ago. Friedlander, then a graduate student under Prosser’s mentorship at the University of Illinois at Urbana-Champaign – a pioneer in the field of comparative animal physiology and thermal biology – conducted research to advance experimental approaches for assess how temperature change affects molecular, cellular and behavioral processes in an entire organism. Their flagship study, published in the Journal of Comparative Physiology in 1977, examining the common goldfish, was praised by Somero in a 2015 review in the Journal of Experimental Biology.
“I find it gratifying that the groundbreaking studies of the effects of temperature on goldfish behavior conducted by Dr. Friedlander decades ago have evolved into this fascinating new work on fish in the Southern Ocean,” said Somero.
While the research team observed that stenothermal Antarctic fish show a remarkable ability to withstand acute heat stress, Ismailov warns that these vulnerable species still need protection.
“There is a history of severe overfishing in the Southern Ocean in the 1970s and 1980s due to unregulated commercial fishing. These activities have depleted populations of some species of fish so much that prospects for their recovery are not yet clear. unclear, âIsmailov said.
Friedlander explains this, noting that all species play an important role in a fragile ecosystem.
“If left unregulated, human activities could produce irreversible damage, affecting not only icefish but also many other species in Antarctic food webs,” Friedlander said. “By performing these type of proof-of-principle experiments now to begin to understand the physiological repertoire available to species at risk, we can begin to make more informed predictions about the type of disturbance within complex ecosystems than change. climate can trigger, and what kind of reserve and adaptive capacity each species can deploy, “
“Behavior is the ultimate manifestation of alterations in the function of molecules, cells, and entire systems of a living organism and can therefore serve as a powerful readout of the underlying effects of thermal challenge.”