Poisonous fish, voracious mammals, expansive plants from all corners of the globe, have invaded Greece for good, demonstrating a unique adaptability. The above phenomenon is not happening exclusively in Greece. Species of wildlife, all over the planet, constantly colonize new areas following the paths of humans. As these routes increase and thicken, so more species travel from one side of the world to the other. It has been estimated that already in Europe there are more than 10,000 invasive species, while in Greece they now reach almost 1,000. The spread of these species is caused mainly by human activities, such as navigation, general trade, tourism, trade in garden plants and wild animals, releases of pets and the increase of temperature due to climate change. The effects of their arrival vary from just simple adaptation to extensive alteration or even destruction of habitats and extinction of many native organisms.
An irreversible phenomenon
These invasion seems to grow more and more provoking interest and concern on scientists. In many cases the results are disastrous while other invasions are a unique opportunity to study natural selection in the making. Many biologists even argue, with some philosophical cynicism, that all these invasions are the result of natural selection itself, as Homo sapiens is also a part of it. Besides, are not most of the crops in our countries (potatoes, corn, citrus fruits) foreign species or even domestic cats that, as absolute hunters, are threshing in the surrounding towns and villages? Most scientists, however, are clearly against this massive invasion, trying to address the important problems they create in nature and human activities. It is not many years since various invasive organizations have settled so successfully in Greece that have caused major problems in tourism, fisheries and agriculture, affecting thousands of citizens. But all of them affect thousands of native animals and plants that suddenly see themselves living in a new, inhospitable habitat. Below we present some of the most typical examples of invasive species that have settled in Greece causing irreversible damage to nature and economy.
The American mink (Neovison vison). A very successful semiaquatic hunter who poses a huge threat to the wildest ecosystems in Greece. It has already displaced the European mink in Europe, while among its prey are small mammals, birds, reptiles and actually everything that can be eaten. It is established in lakes Prespa and Orestiada and seems to be an old runaway from the fur industries of the area. The catastrophic mass release of hundreds of American minks from fur industries by eco activists has magnified the problem, as it is a highly adaptable animal, able, in a few years, to change the habitats of the region.
The Coypu (Myocastor coypus). The expansion of the aquatic huge rodent of South America grows every year. Unfortunately it is treated as just another cute fury animal. Few people know that twenty years ago Italy spent 10 million EUR to exterminate over 200,000 coypus that had destroyed ecosystems, wiped out many wading birds and caused serious problems in crops, dams and canals. We haven't seen any major changes in greek habitats yet, but if we don't do something, the catastrophes will come.
The Rose-ringed Parakeet (Psittacula krameri). A common sight with a rather irritating sound of the country's urban parks. The rose-ringed parakeet is highly adaptive, aggressive and has displaced many birds that find shelter in urban parks. Still, it remains in the narrow limits of the cities, but if it escapes it can destroy various crops as it feeds on a huge range of fruits and flowers. Already in Britain they have destroyed hundreds of fruit trees.
The American Bullfrog (Lithobates catesbeianus). Or the swamp monster. Originally from North America this giant frog (up to 18 cm long), feeds on any animal that fits in its mouth. Snakes, fish, frogs, rodents, chicks, insects, bats, etc. It has been introduced to Agia lake, near Chania, Crete, where it has already displaced the rare, endemic Cretan frog (Pelophylax cretensis).
Terrapins of North America. A kind offer of the pet shops to Greek fauna. Already three species of them (Trachemys scripta subsp. elegans, Trachemys scripta subsp. scripta and Pseudemys nelsoni) have invaded dozens of lakes. Their presence has a dramatic impact on the populations of natives Hellenic Pond Terrapin (Emys orbicularis subsp. hellenica) and Balkan Terrapin (Mauremys rivulata). A great example of the ignorance of those who buy them and the irresponsibility of those who sell them. The child wants a turtle, the turtle in a few years reaches 30 cm and thus ends up in the nearest pond. Their sale has been banned by E.U.
The Pumpkinseed (Lepomis gibbosus). The introduction into our lakes and rivers of alien fish species is one of the largest and rather unknown ecological crimes in Greece. In our effort to increase the income of local fishermen, we simply managed to eliminate our own rare narrow endemic fish. Pumpkinseed is perhaps the most characteristic representative of these species. A predatory, highly adaptable fish that feeds on the eggs of other fish and is now established in almost all greek lakes.
The Palm Weevil (Rhynchophorus ferrugineus). The females of this beetle lay more than 200 eggs inside palm trees. Once hatched into small caterpillars they begin to eat the trunk, creating large tunnels and drying the tree. Dead palm trees standing with dry leaves, lie almost everywhere in Greece. Of course the palm trees of the gardens are also foreign species but the problem will become huge if palm weevils reach the native forests of the extremely rare Theophrastus Palm Tree (Phoenix theophrasti) in Crete.
The Colorado Potato Beetle (Leptinotarsa decemlineata). This beautiful North American beetle is the ultimate destroyer of potato, tomato, eggplant and bell pepper crops. Although the problem is treated with biological means throughout Greece, Colorado Potato Beetles have also been found in areas without crops, affecting many of native wild plants.
The Silverleaf Nightshade (Solanum eleagnifolium). Descend from America the silverleaf nightshade has spread all over maquis habitats. A particularly adaptive plant -one centimeter of root can give a whole plant- threatens the characteristic type of Mediterranean ecosystems, growing where there should be thyme, oregano and other native shrubs. It is already found in most parts of southern Greece, especially in islands, without any systematic attempt to eradicate it.
The Tree of Heaven (Ailanthus altissima). Coming from China, this particularly adaptive tree has been used extensively as an ornamental on the sides of streets and in cities. It can withstand frost as well as drought and so it is no coincidence to see it appearing in many of our forests next to firs, plane trees, lindens, ashes, willows, etc., occupying their space.
The Silver-cheeked Toadfish (Lagocephalus sceleratus). A dangerous fish, migrant from the Suez Canal. Some organs of the species (skin and entrails) are very toxic and can cause death if eaten. Incidents of fatal poisoning have been recorded in Israel and Lebanon. At the same time it is a fearless fish that attacks any threat. Its numbers are constantly increasing in southern seas, and it seems that with the increase in temperature it will not be long before it expands further north.
The Dusky Spinefoot (Siganus luridus). This expansive fish took its greek name (Germans) from the Nazis, as it appeared here at the time of WW2. It has since expanded all over South Greece, causing huge problems for coastal fishermen. The daily migration of flocks from deep to shallow, traps thousands in the nets. Fishermen often dump their nets because the first dorsal ray of the Dusky Spinefoot contains a toxin that causes swelling and pain and so it is almost impossible to dislodge thousands of them from a net.
Sally Lightfoot (Percnon gibbesi). A crab that reached Greece clinging to large ships. It spreads rapidly across our seabeds, stripping the rocks of every organism that can be eaten. A particularly fast crab with cryptic behavior that makes it very difficult to catch from predators.
The Spotted Sea Hare (Aplysia dactylomela). This large nudibranch has managed to spread to all temperate and tropical waters of the planet. It belongs to the same genus as three other native species of greek seas. However, its defensive behavior, which includes the secretion of a purple ink, makes it resistant to any native predator, thus gaining a survival advantage over our own “sea hares”. Now, it is found in more and more seabeds of Greece.
Oculina patagonica. This coral first appeared in the Mediterranean in 1966 coming from the coasts of North America. Although it spreads slowly, it is now encountered more and more often by scuba divers. One of its characteristics is that it spreads alongside the hard substrate and under right conditions can reach colonies up to one meter, displacing any other animal or algae living attached to the rocks.
Caulerpa racemosa. One of the most famous and old cases of invasion that has so far destroyed large parts of our seabed. Caulerpa comes from Australia and is said to have escaped to the Mediterranean from the laboratories of the Monaco Institute of Oceanography. Especially threatening for the Posidonia oceanica meadows as it creates a dense web that literally "drowns" any organism that tries to grow.
Need for action
From the above, one can come to the conclusion that Greek ecosystems are under a big, new threat. This is the case for some habitats, but it is still early to draw conclusions. What we have to do is take care of our natural heritage. And this is equally true if we are going to buy an exotic pet that we can then release, if we build an unnecessary road that passes through a National Park or if we remain unruffled in front of beautiful trees and animals that have no place in Greece. The massive alien invasion is recent and it's happening now. Some species are dangerous, some adapt without big impact and some do not succeed. Nature, as always, will find the way to balance and there will certainly be losses and changes in Greek nature. Organized action is therefore needed to limit these changes, as far as possible.