Home / Blog / Mad, bad and dangerous to know – invasive biota in the Mediterranean Sea

February 24, 2016

Mad, bad and dangerous to know – invasive biota in the Mediterranean Sea


At 750 the number of recorded multicellular non indigenous species (NIS) in the Mediterranean Sea is far higher than in other European Seas: nearly triple the number of records known from the western European coastline from Norway to Portugal, and between 1970 and 2015, the number has grown by 215%. Of these, 450 were introduced through the Suez Canal, the balance are mostly ship and culture-introductions.

The Suez Canal is one of the most important waterways in the world: 17483 ships transited in 2015. It is also the most potent corridor for invasions by marine species known in the world. The individual and cumulative impacts of these invasions adversely affect the conservation status of particular species and critical habitats, as well as the structure and function of ecosystems and the availability of natural resources. Some species are noxious, poisonous, or venomous and pose clear threats to human health. While global trade and shipping are vital to society, the existing international environmental agreements also recognize the urgent need for sustainable practices that minimize unwanted impacts and long term consequences.

From an unfortunately long list of examples of NIS that have led to profound  environmental, economic, and human-health issues, we cite a few. The recent spread of a lethally poisonous pufferfish (Lagocephalus sceleratus) throughout the Mediterranean, even reaching Sevastopol, in the northeast of the Black Sea, poses severe health hazards: its internal organs contain tetrodotoxin, a strong paralytic neurotoxin, inducing symptoms ranging from vomiting to respiratory arrest, seizures, coma and death. Between 2005 and 2008, 13 persons were treated for poisoning in Israel alone. A scyphozoan jellyfish (Rhopilema nomadica), has formed huge swarms annually along the Levantine coast since the mid 1980s, but recently spread westwards to Tunisia and Pantelleria in the Strait of Sicily. Its painful stings adversely affect tourism, fishers complain of net clogging and inability to sort yield, and jellyfish-blocked water intake pipes interfere with the operation of desalination plants and power plants. The impacts of these planktivorous swarms on the local food web must be considerable. Two herbivorous rabbit fish (Siganus luridus and S. rivulatus) are responsible for an extraordinary shift in the Levantine rocky infralittoral from well-developed native algal meadows to ‘barrens’, bringing about a dramatic decline in biogenic habitat complexity, biodiversity and biomass. Significant and often sudden decline of native species, including local population extirpations, have occurred and are occurring concurrent with proliferation of Canal-introduced NIS. Among many examples, the introduced goldband goatfish (Upeneus moluccensis) has replaced the native red mullet in the Levantine fisheries, and introduced prawns, though considered a boon by local fishers, have been displacing the native prawn in commercial fisheries. Local population losses and niche contraction of native species may not induce immediate extirpation, but they augur reduction of genetic diversity, loss of functions, processes, and habitat structure, increase the risk of decline and extinction, and lead to increased biotic homogenization.

Most NIS spread after long residency period, so we may well expect species introduced in the 1980s or earlier to expand their range and spread – the so called invasion debt. The recent enlargement of the Suez Canal is likely to increase the number of prospective NIS swept through. The individual and cumulative impacts of these species will affect the conservation status of native species and critical habitats, as well as the structure and function of ecosystems and the availability of natural resources. As the sea is warming the spread of tropical species introduced through the Suez Canal may accelerate.

The crucial elements for an effective strategy for slowing the influx of NIS are a scientifically sound policy and coordination among all Mediterranean countries to ensure consistency in legal rules and standards to address all major vectors/pathways. Indeed, the documents adopted in the recent meeting of the Contracting Parties to the ‘Barcelona Convention’ (Convention for the Protection of the Marine Environment and the Coastal Region of the Mediterranean and its Protocols) are rich in pious expressions of concern for the wellbeing of the Mediterranean marine environment. Alas, in the adopted ‘Action Plan’ and ‘Monitoring and Assessment Programme’ that ostensibly deal with non-indigenous and invasive species, the most significant pathway – through the Suez Canal – was strictly avoided. It may seem an expedient compromise, but this bureaucratic act of denialism does not change the actuality that introductions through the Suez Canal contribute the largest number of NIS in the Mediterranean, affecting fisheries, tourism, human health and the wellbeing of the Mediterranean Sea and its biota.

700 marine scientists from 47 countries are involved in raising awareness of the catastrophic costs of bioinvasions in the Mediterranean Sea. With your help this will be but a temporary set-back remembered as an embarrassingly unscientific UN policy.