Assessing the threat to Antarctic shallow marine ecosystems from hitchhikers on non-native kelp

Human activity and shipping have long been considered the principal threats to the "biosecurity" of the remote and isolated shallow marine ecosystems of Antarctica (Chown et al., 2015). However, recent work has shown that the Southern Ocean's strong, circumpolar winds, currents and fronts may not be a barrier to natural colonisation from the north (Fraser et al., 2018). The sub-Antarctic (Patagonia, the Falkland Islands, New Zealand and the mid-latitude islands of the Southern Hemisphere) shallow water marine environment is often characterised by highly exposed shores on extremely remote islands (Griffiths & Waller, 2016). The ice-free coastlines are often dominated by dense beds of the kelp Durvillaea antarctica, Macrocystis pyrifera and other large macrophytes. Antarctic shallow coastal marine communities were long thought to be isolated from their subAntarctic neighbours by hundreds of kilometres of deep ocean and the Antarctic Circumpolar Current.

According to the literature, over 70 million kelp rafts are afloat in the Southern Ocean at any one time (Smith, 2002). 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.

Our discovery of non-native kelp and a wide range of 'hitchhiking' passenger organisms washed up on Antarctic beaches led us to question the permeability of these barriers to species dispersal (Avila et al., 2020). 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 (Avila et al., 2020).

The successful applicant will investigate the communities found on floating and beached kelp from southern Chile, the Falkland Islands, South Georgia and Antarctica using existing data and samples, opportunistic collections by scientific expeditions (including partners from University of Barcelona on the Spanish National Antarctic Expeditions), tourist vessels and previous expeditions. The candidate will be expected to undertake a field campaign to the South Atlantic to quantify the potential hitchhikers and conduct physiological experiments. They will be working with collaborators/partners in Chile (University of Magallanes) and the CASE partner in the Falkland Islands (South Atlantic Environmental Research Institute - SAERI).

The candidate will:

Identify the species living on the two main species of kelp in the region, Durvillaea antarctica and Macrocystis pyrifera, and their abundance and location on the kelp plants.
Examine the effect of kelp becoming dislodged from the shore on the fauna and flora that live on the kelp, simulating the effects of storms that lead to kelp rafting (undertaken using scuba diving in the Falkland Islands and potentially in Magellanic Chile).
Investigate biogeographic distribution patterns in the species living on the kelp, using taxonomic and molecular methods; and relating this to oceanographic models and the role of kelp as a vector.
Understanding the ability of sub-Antarctic and Falkland Island native species to tolerate conditions found south of the Polar Front both now and in the future (using physiological experiments and IPCC climate scenarios).
Undertake a risk assessment, using knowledge gained from the PhD, to inform scientists and policy makers about the likely candidate species and centres of colonisation south of the Polar Front, both now and in the future.