Assisted dispersal to the last continent?

K. quadrata

Small (µm –mm scale) aquatic organisms rarely have strong enough morphological features to actively migrate over long distances. Despite this many taxa occur almost everywhere on Earth and the expression “everything is everywhere” has been used regarding these small creatures. During an expedition to one of the most hostile and isolated freshwater systems on Earth, the Dry Valley Lakes in Antarctica, we did, however, not expect a high biodiversity regarding, for example, rotifers and crustacean zooplankton, due to biogeographical borders (salt water oceans). We were therefore very, very surprised when finding, not only the endemic species previously recorded, but also several cosmopolitan species and thereby the highest biodiversity with respect to rotifers ever recorded on the Antarctic mainland! Some of these species, such as Keratella cochlearis and K. quadrata (upper photo)can be found in any pond or lake, even the one outside the Ecology Building in Lund! A plausible question is therefore: how did they come to the Dry Valley lakes? Although we can only speculate, which we do in a recent paper published in Antarctic Science (for a pdf), a likely explanation is that, despite strong restrictions, those animals have unintentionally been brought to the Dry Valleys by the few scientists that have got permission to work there. We can also speculate regarding that this “assisted dispersal” has occurred probably more than ten years ago, since several of the rotifers show relatively high population densities, but probably after the mid-1980ties, since sampling at that time did not register those cosmopolitan species. Although in this case we can only guess regarding the processes, it is likely that small organisms may have a lot of assistance in their dispersal by larger animals, including humans, even to very remote regions. In addition to this surprising dispersal and high biodiversity, we are also proud to show a photo of the most Sothern copepod ever recorded. Hence, we can also extend the southern border of dispersal for Boeckella sp. to 77^oS (photo below)! 

//Lars-Anders Hansson

Boeckella