A parasite of unknown origins is destroying the giant pinna clams of the Aegean Sea, where it has spread from other parts of the Mediterranean. The problem first appeared in 2016 in Spain, where it decimated the population of this endemic Mediterranean shellfish species (Pinna nobilis), which resembles a large mussel. Since that time, the disease has spread to the seas of France and Italy, before reaching the Greek archipelago last summer.
Following repeated reports about dead pinna in several parts of the Aegean, a team of research scientists from the University of Mytilene (Oceanography and Sea Bioscience Dept), the University of Thessaly (Veterinary Department) and the Hellenic Centre for Marine Research examined pinna populations in 13 different sites in the seas around the island of Lesvos, finding mass mortality rates that exceeded 93 pct.
“We reached the conclusion that the mass mortality was caused by a protozoan, a small organism that harms only the pinnas. We do not know how it came here. We suppose that it was carried in the ballast water of ships,” marine ecology scientist Stelios Katsanevakis, who works in the University of Mytilene Oceanography Department, said.
Scientists stressed their concern, noting that a fully endemic and iconic Mediterranean species, which can reach up to a metre in length, may be facing the threat of extinction. The Spanish have already classed the pinna as a “critically endangered species” and scientists have focused their efforts on the protection of the existing populations.
Katsanevakis explained that it is not possible to try to kill a parasite in the sea because of the risks that the extermination process poses for other marine organisms. What can be done, he said, is to locate healthy pinna populations and study the environmental conditions, such as combinations of temperature and salinity, that best deter the parasite. Scientists can then try to duplicate these conditions for selected populations of the species, in order to protect them from infection by the parasite and consequently from extinction.