Invasive marine species discovered on non–native kelp rafts in the warmest Antarctic island

Abstract

Antarctic shallow coastal marine communities were long thought to be isolated from their nearest neighbours by hundreds of kilometres of deep ocean and the Antarctic circumpolar current. the discovery of non-native kelp washed up on Antarctic beaches led us to question the permeability of these barriers to species dispersal. According to the literature, over 70 million kelp rafts are afloat in the Southern Ocean at any one time. These living, floating islands can play host to a range of passenger species from both their original coastal location and those picked in the open ocean. Driven by winds, currents and storms towards the coast of the continent, these rafts are often cited as theoretical vectors for the introduction of new species into Antarctica and the sub-Antarctic islands. We found non-native kelps, with a wide range of "hitchhiking" passenger organisms, on an Antarctic beach inside the flooded caldera of an active volcanic island. This is the first evidence of non-native species reaching the Antarctic continent alive on kelp rafts. one passenger species, the bryozoan Membranipora membranacea, is found to be an invasive and ecologically harmful species in some cold-water regions, and this is its first record from Antarctica. the caldera of Deception island provides considerably milder conditions than the frigid surrounding waters and it could be an ideal location for newly introduced species to become established. These findings may help to explain many of the biogeographic patterns and connections we currently see in the Southern ocean. However, with the impacts of climate change in the region we may see an increase in the range and number of organisms capable of surviving both the long journey and becoming successfully established. Human activity and shipping have long been considered the principal threats to the "biosecurity" of the remote and isolated shallow marine ecosystems of Antarctica 1. However, recent work has shown that the Southern Ocean's (SO) strong, circumpolar winds, currents and fronts may not be a barrier to natural colonization from the north 2-4. Floating kelp is a potential vector for distributing species across the vast oceanic distances between the sub-Antarctic islands. It has been estimated that there may be over 70 million kelp rafts afloat at any one time in the Sub-Antarctic, 94% of which are Durvillaea antarctica 5. The remote archipelagos distributed between 45 and 60° S are key locations for dispersal either side of the Polar Front (PF) and across 2-4,6. The discovery of the non-Antarctic bull kelp, D. antarctica on Antarctic beaches, coupled with oceanographic models, demonstrate a non-anthropogenic mechanism for species introduction into Antarctica 4. Genomic analyses revealed that the kelp specimens originated in the sub-Antarctic (Kerguelen Island and South Georgia) and dispersed thousands of kilometres to reach the Antarctic coast 4. The only epibionts found on these specimens were goose barnacles (Lepas australis), and this epipelagic species is likely to have col...

Scientists' warning on invasive alien species

“…The dissolution of this northern ice cap now opens a huge corridor, not only for species moving north and for species moving between the Atlantic and Pacific Oceans by ocean currents, but for new fleets of exploratory, cargo, fishing, and tourist vessels, which will inadvertently transport marine and terrestrial species (Ricciardi et al ., 2017; Chan et al ., 2018). By contrast, the Antarctic is land surrounded by ocean, with a circumpolar current that, while long isolating the continent, may now be bridged by increasing climate‐induced storm‐driven dispersal (Fraser et al ., 2018; Avila et al ., 2020). Antarctica has been described as the “final frontier for marine biological invasions” (McCarthy et al ., 2019, p. 2221), with formerly ice‐bound shores now available for colonization by poleward‐moving species.…”

First mussel settlement observed in Antarctica reveals the potential for future invasions

“…on ships visiting Antarctica has already been repeatedly documented 14 (specimens originating from South Africa were identified as M. galloprovincialis although the authors apparently did not conduct genetic analyses) in contrary to other vectors (e.g. plastic and kelp rafts) 13 , but see 25 , we suggest that this latter mechanism was the probable means by which the mussels we observed were released into Antarctic waters.…”

“…However, the position and strength of the Antarctic Polar Front was quite different at that time 20,23 , and it now represents a formidable oceanic barrier to poleward migration from South America and nearby islands 8,10 . For instance, passive dispersal from these locations towards islands of the Antarctic Peninsula likely lasts 1 to 3 years 27 , which may explain the absence or paucity of living non-indigenous biota observed upon biodegradable rafts (kelp) reaching Antarctic shores 13,27 .…”

“…Both dispersal and physiological barriers to the establishment of non-indigenous species (NIS) may thus explain why, to date, no known NIS have become established there 12 . Whereas a few non-indigenous invertebrates have been occasionally found in the field, these records have been limited to observations of one or two adult individuals, colonies, or several larval stages, none of which have been known to successfully settle and establish, a necessary step in the invasion process 12,13 . However, as human activity is increasing in Antarctica, human-mediated transport of propagules is occurring 14,15 and shipping is undoubtedly the primary vector by which this dispersal is occurring 16 .…”

“…For benthic organisms, this involves either the transport of pelagic larval stages in ballast water or adults fouling hulls or other outer surfaces. Indeed, the known NIS observed in Antarctica have been limited to organisms with traits conducive to these mechanisms of transport: decapod larvae in ballast water and fouling species (e.g., bryozoans, hydroids and tunicates) on ship hulls or kelp rafts 12,13 . Transport alone is not, however, sufficient for the establishment of a NIS, which minimally requires further development in the case of larval stages, settlement and subsequent reproduction.…”