Peter Convey

What is so significant about a picture of a hoverfly on a dandelion? After all, there are probably thousands of them doing just that in my garden (aka weed patch) right now, and it’s not even as though it’s a partcularly good picture! But this picture hides a trick question…where was it taken? The answer is the sub-Antarctic island of South Georgia, deep in the South Atlantic Ocean. And there neither dandelions not hoverflies are part of the native flora and fauna. It is a well known truth that, wherever we humans go, we tend to carry other things with us, sometimes deliberately, more often inadvertently. The same is true when we go to the Antarctic but, whereas this process has been happening for many centuries and longer across most of the planet’s continents, our contact with the Antarctic is much more recent, and the intensity of that contact (i.e. numbers of people) much lower. There are still parts of the continent that have seen virtually no human footprints (and I have been privileged to see such places in my work) and, compared to the rest of the world, the actual continent of Antarctica remains largely pristine in the context of alien species. In the Antarctic Treaty system – which effectively is the system used to manage our presence and impacts in Antarctica – we have a clear duty to preserve the Antarctic environment. Which brings me back to the dandelions and the sub-Antarctic islands. These islands are much less extreme than the continent itself, and have typically a couple of hundred years or so of human history, the first three quarters of this being the decades of intense marine exploitation (sealing and whaling) that had such a drastic impact on marine ecosystems. Dandelions arrived on South Georgia at this time, very likely as seeds carried with cargo such as animal fodder. Quite a few other plants arrived at the same time, such that today there are more alien plants on South Georgia than there are native ones (although to be fair most have very limited distributions and haven’t spread far from their introduction site). Of the roughly 200 alien species currently known from the entire Antarctic region, more than 95% are on the sub-Antarctic islands, and half of these are plants and a third insects. Which brings me neatly on to the hoverfly. A peculiarity of sub-Antarctic ecosystems is that they do not include either insect-pollinated flowers, or insects that are pollinators. This is one reason why at least some of the alien plants haven’t spread, as unlike the native species many of them require pollinators. Four years ago, the first hoverfly was seen on South Georgia, and over the last two years it has become clear that this species, which is native to southern South America and the Falkland Islands, is well established in parts of the warmer north-east coast of the island. In terms of how this might impact the local ecosystem, we now have a situation where the ‘brake’ on many alien plants setting fertile seed and spreading rapidly will be taken off, and currently ‘persistent’ species which have little impact may become truly ‘invasive’, possibly leading to major changes in the way the ecosystem functions. Although it seems most likely that the flies would have been carried to South Georgia on a ship, many of which visit each summer, as is often the case noone actually saw the first arrivals, and it is also possible they could simply have been wind-blown from their normal range. However, now they are there, there is no realistic possibility of eradication, hence we simply have to wait and see what the impacts are. And the purpose of highlighting all this? Basically, what has happened so far provides a clear warning of what might happen in future along the Antarctic Peninsula – the ‘next step’ into Antarctica in terms of increasingly severe conditions – especially as this region is one of the three fastest warming parts of the planet at present. The easiest and most practical way of minimising the risks associated with alien species carried by humans is to try and stop them at the point of origin, so they don’t get there in the first place. The reality is that any human activity carries with it a risk of inadvertently carrying a new organism into the Antarctic, but this can be minimised by a whole set of common sense ‘biosecurity’ measures – think about how easy it is to check and clean clothing, boots and rucksacs before you go somewhere new, to pack cargo in clean warehouses and in boxes that do not provide hiding places, to ensure that soil is not carried with fresh foods like potatoes, and so on. If you are ever lucky enough to visit this part of the world, either professionally or as a tourist, keep these simple messages in mind!