These scientists, along with the 50,000 tourists and dozens of fishing boats in the offshore waters, pose a threat themselves: accidentally providing\u00a0passage to nonnative species<\/a>. Antarctica and its waters have remained relatively isolated, thanks to its distance from other places, frigid temperatures and ocean currents.<\/p>\n But in recent decades an increase in human traffic and pressures from climate change are opening the door for invasive species \u2014 those nonnatives that can rapidly spread, outcompeting native plants and animals, or become unchecked predators.<\/p>\n So far 11 nonnative invertebrates, including mites and an earthworm, have established themselves on the warmer parts of the continent.<\/p>\n In the water it\u2019s a slightly different story.<\/p>\n A 2019\u00a0study<\/a>\u00a0in\u00a0Global Change Biology<\/em>\u00a0reported five nonnative species in the coastal waters, including a Chilean mussel and a crab. But so far none of these visitors has established populations. And scientists are urging vigilance to keep it that way.<\/p>\n \u201cFor now, Antarctica and the Southern Ocean remain the least invaded marine regions on the planet and represent humanity\u2019s last chance to demonstrate that we can manage and mitigate the risks of invasive species at a continental scale,\u201d Arlie McCarthy, a researcher with the British Antarctic Survey and lead author of the study, wrote in an op-ed for\u00a0The Conversation<\/a><\/em>. \u201cIf we do not, climate change will open the door to the world and our neglect will transform the iconic ecosystems we love.\u201d<\/p>\n Natural forces are Antarctica\u2019s best protection. The ocean current that churns off its shores, known as the Antarctic Circumpolar Current, pushes floating species away from the continent. That defense is buoyed by cold water that makes survival extremely difficult for nonnative species, who aren\u2019t especially adapted to the environment.<\/p>\n Sea ice creates another barrier to movement, with less than one-seventh of the coastline ice-free in summer and none of it ice-free in winter.<\/p>\n \u201cIndividuals that manage to cross the Polar Front are confronted with ice in all its forms, freezing temperatures, physical disturbance from icebergs, and strong seasonal variation in light availability and water chemistry,\u201d researchers explained in the\u00a0Global Change Biolog<\/em>y study. \u201cThese extreme conditions often sit at or are beyond the physiological limits of potentially invading marine species.\u201d<\/p><\/blockquote>\n This natural shield, however, is being weakened by climate-change-warmed waters.<\/p>\n \u201cChanges in physical factors (decreasing ice cover, increasing water temperature) will, if unchecked, in time create an environment more hospitable to nonnative species and less hospitable to native species, reducing the resistance of Antarctic ecosystems (Antarctic biodiversity) to establishment of nonnative marine species,\u201d wrote the researchers.<\/p><\/blockquote>\n Most marine species are likely to arrive on the hulls of ships, known as biofouling, although researchers note that microplastics could be a future concern.<\/p>\n Ships arrive from\u00a0ports all over the world<\/a>\u00a0\u2014 some even making the journey from Arctic to Antarctic, which could carry some cold-loving organisms with them. While tourist ships usually only dock at each port for a few hours, research and resupply vessels can linger for weeks, providing ample time for stowaways.<\/p>\n Visitors in Antarctica. Photo: Ian Duffy, CC BY-NC 2.0 DEED<\/em><\/p>\n More than 180 ships were involved in more than 500 voyages active in the area between 2017 and 2018 \u2014 a big jump from the 30 vessels and 75-100 voyages in 1960. Fishing boats and those carrying researchers or their supplies create other opportunities.<\/p>\n Although it\u2019s difficult with ocean currents, new species could arrive in the Southern Ocean and Antarctica by rafting on aggregates of algae. Millions of these so-called kelp rafts are afloat in the Southern Ocean.<\/p>\n \u201cWe found nonnative kelps, with a wide range of \u2018hitchhiking\u2019 passenger organisms, on an Antarctic beach inside the flooded caldera of an active volcanic island,\u201d wrote researchers in a\u00a02020 study<\/a>\u00a0in\u00a0Scientific Reports<\/em>. \u201cThis is the first evidence of nonnative species reaching the Antarctic continent alive on kelp rafts.\u201d<\/p><\/blockquote>\n Of the four \u201cpassenger\u201d species found alive on the nonnative kelp, the most concerning, they said, is\u00a0Membranipora membranacea<\/em>, a kind of bryozoan invertebrate that can form across seaweed, limiting its ability to reproduce and grow.<\/p>\n The warmer waters inside the caldera may have proved a tolerable temperature, while much of the surrounding coastal waters are too cold \u2014 at least for now.<\/p>\n If nonnative marine species do begin to establish themselves in the Southern Ocean, their impact can ripple across the food web, a\u00a0forthcoming study<\/a>\u00a0concluded.<\/p>\n \u201cWe found that these invasive species can actually cause really catastrophic declines in native species abundances,\u201d says lead author Oakes Holland, a postdoctoral research fellow with\u00a0Securing Antarctica\u2019s Environmental Future<\/a>, an initiative of the Australian Research Council.\u00a0\u201cThings like mytilid bivalves can reproduce quickly and just smother all the hard surfaces on the bottom of the ocean, which will push other species out.\u201d<\/p><\/blockquote>\n Northern Pacific seastars (Asterias amurensis<\/em>), known to be voracious predators, are another concern. So too are crabs, a \u201cniche of predator that has been absent from the region for millions of years,\u201d she says.<\/p>\n Asterias amurensis. Photo by Dean Franklin, CC BY 2.0 DEED<\/em><\/p>\n While Holland\u2019s work has identified species to be wary of, she cautions that what we don\u2019t know is even more problematic. The icy waters of the Southern Ocean are difficult to study. \u201cAt the moment, it\u2019s just such an enormous area and it\u2019s so hard to even know where to start looking,\u201d she says.<\/p>\n There\u2019s not much known yet about what organisms are being carted along on ship hulls either. Current research on nonnative marine species comes from studying just seven ships, including a confiscated illegal fishing vessel.<\/p>\n \u201cWe\u2019re very much in the infancy stage of understanding where the biggest risks are going to come from, specifically on ships, and then how best to manage them in a way that\u2019s not going to be economically limiting,\u201d she says.<\/p><\/blockquote>\n Visiting scientists could be part of the problem \u2014 and solution.<\/p>\n When underwater drones and submersibles are deployed for research, the collected data could be mined using machine learning to search for nonnative species, she says. Researchers have also\u00a0recommended using environmental DNA<\/a>, the genetic material shed by organisms into the air or water, that can help detect a species\u2019 presence in the environment even when it hasn\u2019t been seen.<\/p>\n And although the coastal waters of the continent are vast, efforts to ramp up biosecurity should focus on the most highly visited locations that are likely to be \u201cinvasion hotspots\u201d \u2014 like the Antarctic Peninsula and the South Shetland Islands, say researchers.<\/p>\nStaving Off Invaders<\/strong><\/h3>\n
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<\/p>\nGrowing Risks<\/strong><\/h3>\n
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