What we found: Our new paper published in Ecography this week shows that kelp rafts, which can carry diverse plants and animals with them, are easily and frequently crossing the Antarctic Polar Front into Antarctic waters.
These kelp species are generally sub-Antarctic, but our research shows they can move south towards Antarctica, carried by ocean currents (especially eddies). This finding shows that Antarctica is not as isolated as we have always thought. For a long time, we have considered the Antarctic Polar Front – where Antarctic and sub-Antarctic waters converge – to be a barrier to dispersal, because many species are found on either side, but not on both sides, of the front. If plants and animals can easily cross the front, however, then many sub-Antarctic species are probably only not found in Antarctica at the moment because of the extreme polar conditions (ice and cold). With global warming, we can therefore expect that more non-native species will establish in Antarctic waters, even without human-assisted transport of plants and animals across the Polar Front.
This figure shows the cruise tracks (star, circle and triangle symbols) and points at which survey recordings were made: green for no kelp, red for Durvillaea, yellow for Macrocystis, and orange for both kelp species. APF positions for each cruise year are shown by lines.
How the study was done, and who did what:
This study was carried out by ship-based observations of kelp rafts at sea, in sub-Antarctic and Antarctic waters. On three different voyages – one in the Atlantic Ocean (2013-2014), and two in the Indian Ocean (2008 and 2014) – observers with the South African National Antarctic Programme counted kelp rafts and recorded their locations. These observers were part of a team led by Professor Peter Ryan (University of Cape Town), who is one of the main authors of the new paper. Geoff Kay, a PhD student in the Fenner School at the Australian National University, and I worked together on analysing the data, and we wrote the manuscript while we were trapped on base in bad weather in Antarctica, in February this year (a good use of blizzard time!). The positions of the Antarctic Polar Front at the time of each voyage were calculated from Maps of Absolute Dynamic Topography (sea surface height anomalies) by Marcel du Plessis, a PhD student in the Department of Oceanography at the University of Cape Town.
Find out more: Read the full article here
Durvillaea is one of the main kelp genera in the sub-Antarctic, and grows in dense populations on rocky shores in the intertidal zone.