Antarctica vulnerable to invasive species hitching rides on plastic and organic debris

Antarctica's unique ecosystems could be threatened by the arrival of non-native marine species and marine pollution from Southern Hemisphere landmasses, new oceanographic modelling shows.

In a study published today in Global Change Biology, scientists from UNSW Sydney, ANU, University of Otago and the University of South Florida suggest that floating objects can reach Antarctic waters from more sources than previously thought.

"An increasing abundance of plastics and other human made debris in the oceans means there are potentially more opportunities for biota to reach Antarctica," says lead author Dr Hannah Dawson, who completed the study as part of her PhD at UNSW, and is now based at the University of Tasmania.

Non-native species -- including a range of small marine invertebrates -- can reach Antarctica by catching a ride on floating objects like kelp, driftwood, pumice, and plastic. Previously, scientists thought these species only drifted from remote and unpopulated islands in the Southern Ocean. However, this new research suggests they can reach the Antarctic coastline from all southern continents.

"We knew that kelp could raft to Antarctica from sub-Antarctic islands, such as Macquarie and Kerguelen Islands, but our study suggests that floating objects can reach Antarctica from much further north, including South America, New Zealand, Australia, and South Africa," says Dr Dawson.

Co-author Professor Crid Fraser from the University of Otago says that kelp could deal a potential double whammy blow to Antarctica's marine ecosystem.

"Southern bull kelp and giant kelp are very big -- often more than 10 m long -- and create forest-like habitat for a lot of small animals, which they can carry with them on the long rafting trips to Antarctica," she says.

"If they colonise Antarctica, marine ecosystems there could change dramatically."

Southern Ocean modelling

Using modelled surface current and wave data from 1997 to 2015, the team tracked the movement of floating debris from various Southern Hemisphere land sources toward Antarctica, providing valuable new insight into the frequency and pathways of marine dispersal.

"We were able to analyse how frequent these rafting connections are by simulating dispersal pathways across 19 years of differing oceanographic conditions," ANU co-author Dr Adele Morrison says.

"We found that rafting objects reached the Antarctic coastline in each of the years simulated. There seems to be a constant bombardment of anything that floats -- whether it's kelp or a plastic bottle."

Dr Dawson likens the computer modelling process to the game 'Poohsticks' from the children's classic Winnie the Pooh.

"Imagine dropping a stick into a river and then running downstream to see where it ends up -- that's essentially what we do with our modelling, using simulated ocean currents, instead of a river."

"We released millions of virtual particles -- representing drift objects -- from each of the source land masses and modelled their trajectories across 19 years of estimated surface ocean currents and surface waves. After running the simulations, we were able to see where they would likely end up.

"The shortest time it took for particles to reach the Antarctic coastline was from Macquarie Island, south of New Zealand, some of which arrived in just under 9 months. On average, the longest journey was for objects released from South America," she says.

Warmer waters

The research also sheds light on which regions of the Antarctic coastline are most at risk to non-native species arrivals.

"Most of these rafting objects arrive at the tip of the Antarctic Peninsula, a region with relatively warm ocean temperatures and often ice-free conditions. These factors make it a likely area for non-native species to first establish," says UNSW Scientia Professor Matthew England, who is also a co-author.

The dramatic drop in Antarctic sea ice over the last couple of years makes these rafting connections particularly concerning.

"Sea ice is very abrasive and so acts as a barrier for many non-native species to successfully establish around Antarctica," Dr Dawson says.

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Vitamin B12 adaptability in Antarctic algae has implications for climate change, life in the Southern Ocean

Vitamin B12 deficiency in people can cause a slew of health problems and even become fatal. Until now, the same deficiencies were thought to impact certain types of algae, as well. A new study examined the algae Phaeocystis antarctica's (P. antarctica) exposure to a matrix of iron and vitamin B12 conditions. Results show that this algae has the ability to survive without B12, something that computer analysis of genome sequences had incorrectly indicated.

The alga, native to the Southern Ocean, starts as a single-cell that can transform into millimeter scale colonies.

The research published in PNAS, "Flexible B12 ecophysiology of Phaeocystis antarctica due to a fusion B12-independent methionine synthase with widespread homologues," conducted by MIT, WHOI, J.C. Venter Institute, and Scripps Institution of Oceanography (UCSD), found that unlike other keystone polar phytoplankton, P. antarctica can survive with or without vitamin B12.

"Vitamin B12 is really important to the algae's metabolism and because it allows them to make a key amino acid more efficiently," said Makoto Saito, one of the study's co-authors and senior scientist at the Woods Hole Oceanographic Institution (WHOI). "When you can't get vitamin B12, life has ways to make those amino acids more slowly, causing them to grow slower as well. In this case, there's two forms of the enzyme that makes the amino acid methionine, one needing B12, and one that is much slower, but doesn't need B12. This means P. antarctica has the ability to adapt and survive with low B12 availability."

Researchers came to their conclusion by studying P. antarctica's proteins in a lab culture, and also searching for key proteins in field samples.

During their observation, they found the algae to have a B12-independent methionine synthase fusion protein (MetE). The MetE gene isn't new, but was previously believed not to have been possessed by P. antarctica. MetE gives the algae the flexibility to adapt to low vitamin B12 availability.

"This study suggests that the reality is more complex. For most algae, maintaining a flexible metabolism for B12 is beneficial, given how scarce the vitamin's supply is in seawater," said Deepa Rao, lead researcher of the study and former MIT postdoc." Having this flexibility enables them to make essential amino acids, even when they can't obtain enough of the vitamin from the environment. Implying that the classification of algae as B12-requiring or not might be too simplistic"

Antarctica, which lives at the base of the food web, has been thought to be entirely controlled by iron nutrition.

The discovery of the MetE gene also indicates vitamin B12 likely plays a factor.

Because of its presence in P. antarctica, the adaptability of the algae gives it a potential advantage to bloom in the early austral spring when the bacteria that produce B12, are scarcer.

This discovery also has implications for climate change. The Southern Ocean, where P. antarctica is found, plays a significant role in the Earth's carbon cycle.

P. antarctica takes in the CO2 and releases oxygen through photosynthesis.

"As our global climate warms, there's increasing amounts of iron entering the coastal Southern Ocean from melting glaciers," Saito said.

"Predicting what the next limiting thing after iron is important, and B12 appears to be one of them. Climate modelers want to know how much algae is growing in the ocean in order to get predictions right and they've parameterized iron, but haven't included B12 in those models yet."

"We are particularly interested in knowing more about the extent of strain level diversity. It will be interesting to see if B12 independent strains have a competitive advantage in a warmer Southern Ocean," said co-author of the study Andy Allen, a joint professor at the J. Craig Venter Institute and the Scripps Institution of Oceanography at the University of California, San Diego.

"Since there is a cost to B12 independence in terms of metabolic efficiency, an important question is whether or not strains that require B12 might become reliant on B12 producing bacteria."

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Researchers identify behavioral adaptations that may help Antarctic fishes adapt to warming Southern Ocean

At first glance, Antarctica seems inhospitable. Known for howling gales and extremely cold temperatures, the continent is blanketed with a mile-thick ice shelf. Occasional elephant seals and seabirds fleck the glacial shorelines.

Yet dipping below the waves, the Southern Ocean teems with biodiversity: vibrant swaths of sea ice algae and cyanobacteria, swarming krill and crustaceans, bristling kelp forests, gigantic polar sea spiders and sponges, whale pods, and abundant Antarctic fish fauna.

These fishes play a vital role in the Southern Ocean's food web of 9,000 known marine species, yet their subzero haven may be at risk. A 2021 climate analysis posited that by 2050 some areas of the Antarctic continental shelf will be at least 1 degree Celsius warmer.

Researchers from Virginia Tech's Fralin Biomedical Research Institute at VTC have published a new study in PLOS ONE describing how two species of Antarctic fish -- one with hemoglobin in its blood cells and one without -- respond to acute thermal stress.

The research team, directed by Virginia Tech Vice President for Health Sciences and Technology Michael Friedlander, observed that both species responded to progressive warming with an elaborate array of behavioral maneuvers, including fanning and splaying their fins, breathing at the surface, startle-like behavior, and transient bouts of alternating movement and rest.

"Remarkably, our team found that Antarctic fishes compensate for increasing metabolic demands by enhancing respiration through species-specific locomotor and respiratory responses, demonstrating resilience to environmental change and possibly to global warming," said Friedlander, who is also the Fralin Biomedical Research Institute's executive director, senior dean for research at the Virginia Tech Carilion School of Medicine, and a professor in the College of Science's Department of Biological Sciences. "Ambient warming presents a multi-faceted challenge to the fish, including increased temperature of the central nervous system and target tissues such as skeletal and cardiac muscles, but also reduced availability of dissolved oxygen in the water that passes through the gills during respiration. While these findings suggest that Antarctic fishes may be able to behaviorally adapt somewhat under extreme conditions, little is known about the effects of environmental warming on their predation habits, food availability, and fecundity,"

Iskander Ismailov, the study's first author and a research assistant professor in Friedlander's laboratory during the study, said, "Behavioral manifestations that we've described show that these fishes have powerful physiological capacities to survive environmental changes," said

Through millions of years of isolation from the rest of the world -- corralled by the Antarctic Circumpolar Current -- Southern Ocean fish species have become well adapted to their frosty ecosystem.

Blackfin icefish, Chaenocephalus aceratus, one of the two species studied by the team, have unique opalescent blood. These fish are among the few known vertebrates lacking hemoglobin, a molecule in red blood cells that efficiently carries oxygen from the lungs of land-dwelling vertebrates, or from the gills of aquatic vertebrates, throughout tissues in the body. Instead, blackfin icefish transport oxygen dissolved in blood plasma, harboring roughly 10% of the oxygen carrying capacity of hemoglobin.

Oxygen is more soluble in cold water, allowing white-blooded icefish to thrive in the Southern Ocean. As water temperature rises, however, 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 rockcod, Notothenia coriiceps, in a climate-controlled shoreline laboratory that circulated, and progressively warmed, saltwater straight from the Southern Ocean.

The fishes acclimated to the lab conditions, before being transferred to the experimental tank, where water temperature rose from -1.8 degrees Celsius to 13 degrees, at a rate of 3 degrees per hour. The researchers captured extensive video recordings, allowing them to examine and quantify the fishes' motility, breathing rate, maneuvers in the tank, and fin movements.

As the water temperature rose, the white-blooded icefish displayed intensive pectoral fin fanning -- a behavior previously observed in icefish during egg guarding -- that the researchers suggest may help facilitate respiration. By contrast, the red-blooded fish employed complex maneuvers, including pectoral fin fanning and splaying, followed by startle-like C-turns, which may augment gill ventilation, according to Ismailov.

"The findings provide a new perspective on the effects of rising temperature on these highly cold-adapted species," said George Somero, professor emeritus of marine biology at Stanford University and a leader in studying how marine life adapts to thermal stress, who 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 journey included a flight to Punta Arenas, Chile, then crossing the Drake Passage by boat during the austral fall.

Ismailov was the first to arrive, setting up experimental rigs. Six weeks later, he was joined by Jordan Scharping, then a second-year Virginia Tech Carilion School of Medicine student conducting research in Friedlander's lab. The pair worked in overlapping 12-hour shifts running experiments in the laboratory at near-freezing temperatures.

"Dr. Friedlander drew me to this project. I remember him presenting the Antarctic project proposal to us medical students and everyone just lighting up about it. It was an incredible opportunity and I appreciate him giving it to me," said Scharping, who is now a physician at Northwestern Memorial Hospital.

Researchers were responsible for collecting their own fish specimens during a series of four, week-long fishing trips. At sea, with the help of the research vessel crew, the researchers worked around the clock -- sometimes during harsh conditions.

"One stormy night while we were fishing, a two-story wave overtook the stern, drenching me from head to toe in ice-cold seawater -- the captain of the boat stopped the fishing after that," Ismailov recalled. "As a graduate of medical school, I never could have imagined that my career would lead me to Antarctica to study fish, but this research project has become one of the most extraordinary and memorable in my life."

The field work was funded by a National Science Foundation Grant awarded to Elizabeth Crockett, professor emerita 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 along with collaborators from the University of British Columbia, the University of Leeds, and Valdosta State University.

But the underpinnings of this recent study started 45 years ago. Friedlander, then a graduate student under the mentorship of Prosser 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 to evaluate how temperature change affects molecular, cellular, and behavioral processes in an entire organism. Their landmark study, published in the Journal of Comparative Physiology in 1977, examining the common goldfish, was lauded by Somero in a 2015 review in the Journal of Experimental Biology.

"I find it gratifying that the pathbreaking studies of temperature effects on goldfish behavior carried out by Dr. Friedlander several decades ago have evolved into this fascinating new work on fishes of the Southern Ocean," Somero said.

While the research team observed that stenothermal Antarctic fishes show remarkable capacity to withstand acute thermal stress, Ismailov warns that these vulnerable species still need protection.

"There's a history of severe overexploitation in the Southern Ocean in the '70s and '80s due to unregulated commercial fishing. These activities had depleted the populations of some fish species so badly that the prospects of their recovery are still unclear," Ismailov said.

Friedlander expounds on this, noting that all species play important roles in a fragile ecosystem.

"If left unregulated, anthropogenic activities could produce irreversible damage, impacting not just icefish, but many other species in the Antarctic food webs as well," Friedlander said. "By doing these types 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 what sort of perturbations within complex ecosystems that climate change may trigger, and what type of reserve and adaptive capacity individual species may deploy,"

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