Non-indigenous species in the Mediterranean and the Black Sea
Abstract
The biota of the Mediterranean and the Black Sea has started to change significantly over the last few decades, due to the introduction of non-indigenous species as a result of Lessepsian migration, ship ballast water, range expansion of Atlantic species, intentional or unintentional introduction and climate change.
The Black Sea has suffered from the non-indigenous invasive comb jelly Mnemiopsis leidyi since the late 1980s, which has led to biodiversity loss and a decrease in fish catch, mainly driven by a sudden collapse of small pelagic species, in particular of the European anchovy. The trend of Mediterranization has also contributed to changes in Black Sea biota, as many species that used to be restricted to the Mediterranean have infiltrated the Black Sea, presumably due to climate change. Rapa whelk (Rapana venosa), a sea snail, is the most harvested non-indigenous invasive species by Black Sea countries and has also been commercially exploited in the Marmara Sea. The Marmara Sea, situated between the Black Sea and the Aegean Sea, plays a crucial role in the range shifts of invasive species due to its exchange of water mass and marine biota. Like the Black Sea, the Marmara Sea has also been negatively impacted by the comb jelly M. leidyi, showing a recovery of small pelagic fish species only in recent years. Lessepsian fishes and invertebrates are increasingly found in the Marmara Sea, but overall impacts are not yet known.
Numerous Lessepsian species have invaded the eastern Mediterranean Sea entering through the Suez Canal, while others have expanded through the central and western sectors of the basin. A number of fish and invertebrate species originating in the Atlantic have also reached the eastern part of the Mediterranean Sea. In total, over 900 non-indigenous species have been reported in the Mediterranean Sea, and almost 300 non-indigenous species in the Black Sea. Over half have established permanent populations and are geographically expanding.
Many Lessepsian fishes have become abundant and commercially relevant, gaining influence in local markets, mostly in the eastern Mediterranean region. Indeed, the new market for nonindigenous species is growing. Due to the lack of overall statistics, the total catch in the entire basin is neither known nor predictable. While non-indigenous species are targeted through various fishing techniques, many others are simply discarded due to a lack of value and there are even some, such as lionfishes, pufferfishes and several jellyfish species, that present immediate dangers to human health. Additionally, important impacts on biodiversity have already been reported, due to habitat displacement and competition with native species.
The creation of marine protected areas and the protection of native species may represent effective measures for mitigating the negative impacts of non-indigenous species. Disseminating information and raising public awareness, in particular on harmful species, are also important tools at the regional level. For the purposes of monitoring and protecting marine biodiversity, regional cooperation on the enforcement of legal measures is essential in order to minimize and reduce the impacts of non-indigenous species both in the Mediterranean and the Black Sea.
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