More than 80 species of sea life, including sea bass, gilt-head bream and picarel, have now settled for good in the Black Sea as its waters grow warmer. Scientists presented the data at a meeting of the Black Sea Advisory Council in Constanța, where Bulgarian and Romanian researchers discussed how warmer water is changing fish stocks and fishing in the region. The shift is called Mediterraneanisation: the sea is slowly taking on traits of the Mediterranean, and species once unknown here now find conditions good enough to live and breed.
Through the Bosphorus and in ballast water
Most newcomers arrive through the Bosphorus, as species that have long lived in the Mediterranean move north once Black Sea winters turn mild enough for them to survive. Others arrive by accident, hidden in the ballast water of cargo ships — the way the rapa whelk turned up decades ago and went on to wipe out most of the black mussel stocks along Bulgaria's coast. The latest count of foreign species in the waters of the six Black Sea states shows 148 in Ukraine, 94 in Turkey, 82 in Romania, 80 in Bulgaria, 51 in Russia and 34 in Georgia. Around 20 new species have entered the sea in just the past few years, and about a third of all foreign species come from the Mediterranean, with the rest arriving from the Atlantic and from distant areas such as the Sea of Japan.
Sea bass, bream and picarel in Bulgarian waters
Sea bass is one of the examples scientists cite most often, since it grows even faster in the Black Sea than in its native Mediterranean and Atlantic waters. Gilt-head bream is also turning up more and more along the Bulgarian coast. A third new arrival is the picarel, a small fish from the sea bream family that came from the Aegean Sea, marked by a dark spot in the middle of its body. It grows to about 20 centimetres and tastes similar to gilt-head bream. Spearfishing enthusiasts say they have been spotting it more often near the rocks along the coast lately.
Dr Yordan Gospodinov, who chairs the Black Sea Advisory Council, says many of the new species are adapting fast to local conditions. That does not mean they will stay for good or push out the fish the Black Sea is known for, he says — more applied research is needed to understand what will happen to fish stocks and the wider ecosystem.
The comb jelly and the blue crab
The comb jelly Mnemiopsis, which arrived from the Atlantic in the 1980s, feeds on the same zooplankton that sustains anchovy, and for years it kept fish stocks low until another newcomer, the jellyfish Beroe, began eating it and brought its spread somewhat under control. The Institute of Oceanology in Varna tracks these changes and publishes a report on the state of the sea every six years. Scientists warn that the blue crab and the comb jelly are now competing for food with species long native to the Black Sea, such as sprat, anchovy and turbot.
The warming of the Black Sea goes beyond the arrival of new fish. The basin is among the European waters hit hardest by marine heatwaves, and its structure — fresher water on top, saltier water below — stops oxygen from reaching the depths when the surface stays warm for long periods. The Black Sea Advisory Council is calling for more research to find out whether sea bass, gilt-head bream and picarel will become a lasting part of the Black Sea diet or remain only temporary visitors.