Federico Betti – Reef Check Italia Associate Project Manager
The project “Watch for jellyfish”, lead by professor Boero of the university of Salento, recorded the first sighting in the Western Mediterranean of the famous Mnemiopsis leidyi; it is a ctenophore, an organism similar to jellyfishes because of the rounded shape, the jelly structure and the transparent body, but lacking of stinging cells, which are substituted by sticky cells, used to catch the zooplankton it feeds on.
This means that ctenophores are harmless for humans; these cells, called colloblasts, are disposed on two long and thin tentacles that flow in the
water column; other important features of this kind of organisms are the presence of ctenids, that is cilia fused in eight lines along the animal body used for moving, and bioluminescence.
Mnemiopsis leidyi comes from the American Atlantic coasts, but during the eighties it was introduced in the Black Sea by means of ballast waters (Vinogradov et al., 1989). There, it found a habitat suitable for its development, in particular thanks to the abundance of prey and the scarcity of competitors and predators, and it began to create great aggregations which, feeding on fish eggs and larvae, in just a few years decimated the already poor (because of the overfishing) ichthyic stocks of the Black Sea. In 1999, again by means of ballast waters, it was introduced in the Caspian Sea (Shiganova et al., 2001; Ivanov et al., 2000), where in some areas it lead to a decrease of the zooplankton of the 80%.
In 2001 it was recorded in the Aegean Sea (Shiganova et al., 2001), where it did not
cause evident effects, maybe because of the higher presence of planktivorous competitors, and in 2006 it was recorded also in the Baltic Sea (Javidpour et al., 2006), where it seems to be always
present even if population may not be stable still.
And now, after some sporadic sightings in the Adriatic Sea, maybe because of animals coming from Aegean Sea, the first record for the Western Mediterranean is arrived: the biologist of the municipality of Lerici Marco Putti found large aggregations of Mnemiopsis leidyi along the coasts of Marinella di San Terenzio and Tellaro (Sp, Italy).
The great tolerance of this species towards different environmental factors (it may bear salinity shifting from 4 to 38 and temperatures between 4 and 32°C) allows it to live in the whole Mediterranean Sea and also out of it; the capacity of this species of compromising the ichthyic stocks, both because of competition and diet, constituted mainly by fish eggs and larvae, give it the possibility to highly modify large ecosystems and to drastically reduce the presence of fishes.
That’s why this species is already a “watched over species”, and why its records are very useful; it is surely an animal we will have a lot to manage with in the future.
Ivanov, V.P., Kamakin, A.M., Ushivtsev, V.B., Shiganova, T.A., Zhukova, O.P., Aladin, N.V., Wilson, S.I., Harbison, G.R., Dumont, H.J., 2000. Invasion of the Caspian Sea by the comb jellyfish Mnemiopsis leidyi (Ctenophora). Biological Invasions 2: 255-258.
Javidpour, J., Sommer, U., Shiganova, T., 2006. First record of Mnemiopsis leidyi A. Agassiz 1865 in the Baltic Sea. Aquatic invasion 1 (4): 299-302.
Shiganova, T.A., Mirzoyan, Z.A., Studenikina, E.A., Volovik, S.P., Siokou-Frangou, I., Zervoudaki, S., Christou, E.D., Skirta, A.Y., Dumont, H.J., 2001. Population development of the invader ctenophore Mnemiopsis leidyi in the Black Sea and other seas of the Mediterranean basin. Marine Biology 139: 431-445.
Vinogradov, M.E., Shushkina, E.A., Musaeva, E.I., Sorokin, Yu.P., 1989. Ctenophore Mnemiopsis leidyii (A. Agassiz) (Ctenophora: Lobata) – a newly introduced species in the Black Sea. Okeanologiya 29 (2): 293-299.