Between 80-90% of Greek mussels (about 30,000 tons annually) are produced along the coastal zone of the National Park of the Axios – Loudias – Aliakmon Delta, in the western Thermaic gulf.
Mussel culture is a very important activity for the regional as well as the national economy, as the majority of mussels produced are exported to Spain, Holland, France and principally Italy.
The production of mussels in the region began in the early 1980’s, using know-how from nearby Italy. At that time, many local fishermen turned towards mussel culture, as conditions are particularly favorable for this lucrative activity. Mussels grow here at a rapid rate, acquiring the desirable size for consumption in less than nine months. This is due to the fact that the region’s rivers – Axios, Loudias and Aliakmonas – flow close to each other, into the west Thermaic gulf and they bring many nutritive ingredients, thus creating the appropriate conditions to cultivate large and delicious mussels.
Cultivation is of the extensive type and utilizes two methods: the long line and the pole-borne culture. Mussel culture is grouped into three parts of the region: in the estuary of the Axios river, at the boundary of the Municipality of Chalastra, at the estuary of the Loudias river, at the boundary of the Municipality of Axios and to the south of the estuary of the Aliakmonas river, on the Pierian coast.
The mussel of the Thermaic
The variety cultivated in the region is the Mytilus galloprovincialis. It is an endemic type in the eastern Mediterranean, the Adriatic and the Black Sea, but today it has spread in all seas of the world, either because it has been imported for culture, or because it was accidentally transferred (for instance, through commercial ships) and it has developed on its own. In fact, it is listed among the one hundred ‘worst world invaders’, since once it has established itself in regions where it is not endemic, it displaces the local varieties of mussels. It is cultivated for commercial purposes at a large scale in Japan and China and its largest European production can be found in Spain.
Mussels can live within a broad range of temperatures and salinities. They feed off phytoplankton and organic matter which they filter from sea water with their gills. A mussel which is 5 centimeters long can filter as much as 5 liters of water per hour.
The culture method
Culture begins with collecting the spat attached on special ropes, called spat collectors. Mussel cultivators detach the spat from the ropes and place it in plastic cylindrical nets, the mussel socks, which are hung inside the water from a rope. Their culture takes place either on poles (pole-borne mussel culture) or on ropes hanging from floats (waterborne or long-line mussel culture).
From May until July, mussel cultivators make sure to open systematically the mussel socks, to space out the growing mussels and replace them inside the culture units, until their development is completed and they are ready to be collected.
Mussel culture requires hard work under tough conditions. Their quality is ensured through regular controls of the quality of water and of the produced goods.
Mussel culture is not free of problems and pressures on the natural environment. The large density of mussel culture units, apart from negatively affecting the movement of sea masses, which are vital to the development of the shells, also causes the accumulation of material in the seabed, at the sites of the units, thus having a negatively impact on the benthic communities living there.
Moreover, the coast receives tons of residues: pieces of rope, plastic barrels and mostly huge quantities of shells, which must be disposed of properly in order to not damage the environment. For these reasons, emphasis should be placed on methods of mussel culture which are more environmentally friendly.