Department of Natural Sciences, Faculty of Natural and Agricultural Sciences, “Ovidius” University, Constanța,
Human society is currently faced with a series of phenomena which, although caused by man in one form or another, he cannot keep under control. One of the most important of these is the threat of so-called “biological invasions”, a phenomenon the result of which is no less than the drastic and inevitable transformation of natural habitats. A global phenomenon, biological invasions represent a factor which cannot be dismissed. The ability of invasive species to bring about drastic changes to natural habitats and to remodel relationships within ecosystems represent a real danger for the preservation of such habitats.
A large number of plants and animals are classified as invasive species, and the amplitude of the phenomenon and its long-term effects at the global level have already determined a series of states, including the European Union, to react by imposing a series of restrictions and taking a number of legislative measures to combat the problem. Nevertheless, the issue of invasive species is only brought to the forefront of public discourse when either the economy or human health are severely affected. In the case of natural habitats, and with particular regard to natural reservations and other protected areas, invasive species are not only an unwanted presence, but also a considerable medium and long-term perturbation factor.
In Romania, this phenomenon is very poorly taken notice of by non-specialists, and this ignorance places local authorities the uncomfortable position of being unable to adequately manage situations in which invasive species move in. To give but a few examples, this is the case of the North American ctenophore Mnemiopsis leidyi, whose encroachment into the Black Sea had as an ultimate consequence the diminishing of available fishing stocks; of the Ambrosia artemisiifolia species, whose pollen has an allergenic effect on humans, or of various invasive mosquito species carrying exotic diseases.
At present, given the certain prospect of climate change and the fact that we are witnessing an unprecedented growth in the dynamics of economic exchange, the phenomenon of invasive species has gained a new impetus. New species are appearing at an accelerated pace, far from their traditional areas of habitation, and the effects of their forays into new areas are becoming more and more apparent. In Romania, approximately one thousand non-native species have so far been documented, of which some are classified as “invasive”; and Dobrogea is home to a large part of these. In the littoral area, a series of foreign and / or invasive marine species are documented which, in certain cases, have generated considerable changes to marine habitats. Thus, three of the most common mollusc species of the Black Sea littoral – the bivalve Mya arenaria and Anadara kagoshimensis and the gastropod Rapana venosa – are invasive species, two originating in the Far East, and the third in the North-Western Atlantic.
On land, non-native plant species – some voluntarily introduced by man through reforestation projects, and others accidentally introduced and then naturalised – have had the greatest impact on protected areas. Some of these plant species – Pinus nigra, Juniperus virginiana, Amorpha fruticosa, Robinia pseudacacia – were employed both in monospecific populations and in different combinations in the past for reforestation, practically creating vegetal associations entirely inappropriate for our country’s geographic position. Other species – Ambrosia artemisiifolia, Echinocystis lobata – have been accidentally introduced and at times explosively spread, irreversibly altering natural habitats.
In conclusion, we might appreciate the fact that, across protected land areas in Dobrogea, invasive species are an impact factor that cannot be ignored. The monitoring of these species’ development is a requirement for assessing the state of conservation. By far the most important, from the point of view of their impact on autochthonous habitats, are species such as Ailanthus altissima, Amorpha fructosa, Echinocystis lobata, Pinus nigra, which cause radical changes in micro-habitat conditions and perturb the development of autochthonous plant species. Among invertebrates, freshwater bivalve species are most important for consideration, and among insects, species such as Harmonia axyridis and Aedes albopictus which, for separate reasons, must be monitored within settlements as well as within protected areas.