Menacing Marine Species Spotted in Croatian Waters, Fish Stocks in Danger?

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A peculiar species responsible for ravaging fish stocks in the Black Sea has been spotted in Croatian waters

A saltwater animal named Mnemiopsis Leidyi was spotted in the sea near the beach in Baćina, a village in Dubrovnik-Neretva County. For those of us who don’t have a vast knowledge of fishing or aquatic life, the Latin name doesn’t point to much, but it turns out, the creature might present a serious threat to fish stocks in the Croatian Adriatic.

This is the first time the dangerous species has been spotted in the eastern Adriatic, south of the Kvarner bay. Widely known as the warty comb jelly or sea walnut – the latter nickname assigned for its round shape and a very slow moving pace – the animal originates from the western Atlantic waters. It was first spotted in the Black Sea in the 80s, then spread to the Caspian Sea and the Mediterranean.

What looks like a tiny, harmless translucent blob actually presents a real threat to the aquatic life. The sea walnut feeds on zooplankton and fish eggs and larvae, so after it has been present in certain waters for a while, the fish don’t have anything to feed on and the fish stocks start to deteriorate. Another problematic fact is that the animal is a hermaphrodite that self-fertilizes, producing thousands of fertilized eggs at once, so it spreads rapidly and is impossible to stop.

The sea walnut population inflicted serious damage to the fish stocks in the Black Sea, and is currently ravaging the Caspian Sea despite it being a freshwater lake. It was first spotted in the Adriatic in the gulf of Trieste, continuing to spread to the northern Adriatic in the area between Pula and Ravena. According to Dr Paolo Paliago from the Center for Marine Research in Rovinj, only 30% of the catch this summer have been fish, while the rest was made up by the unwanted guest.

Ms Jasmina Čehić from Baćina was the one who spotted the creature in the waters of Ploče, instantly reporting her discovery to the Institute for Marine and Coastal Research in Dubrovnik. The experts went out into the field and confirmed the spotted animal was the Mnemiopsis: they recorded five specimen per cubic metre, a menacing quantity that might grow with time. They measure 3 to 7 centimetres in size, and they probably ended up in these parts along with the ballast water from the international ships that docked in Ploče port.

Experts say the species prefers high sea water temperatures, and once it reproduces, it can lead to fishing nets getting completely covered in mucus. The Institute reported they are prepared to monitor the Mnemiopsis population, but stated they need additional funds. We can only hope the local authorities will react, because otherwise, the already ravaged fish stocks might get completely obliterated in near future.

Source: Slobodna Dalmacija


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