Alonnisos and the uninhabited islands of the Northern Sporades form an island cluster of incomparable beauty and exceptional ecological value. Of the habitat types, the most significant are the marine Posidonia beds (priority habitat type), the chasmophytic vegetation in calcareous rocks of the Aegean Sea (found in good condition and home to several endemic plants), and the sea caves (refuge of the Mediterranean monk seal). Of the plants species, a number of chasmophytes are endemic to the Sporades and the Aegean Sea, and five species are included in The Red Data Book of rare and threatened plants of Greece. Of the islands’ animal species, the Mediterranean monk seal is one of the most endangered species in the world.
The enormous value of the region’s ecosystems was acknowledged towards the end of the 70s, when attempts were made to protect it. In May 1992, the National Marine Park of Alonnisos and Northern Sporades was founded. It includes all the Northern Sporades except for Skiathos and Skopelos islands.
The Park is not an enclosed area. It is a conservation area of roughly 2,200km2, probably the largest marine conservation area in the Mediterranean. Its purpose is to protect the ecosystems and to promote the development in Alonnisos (the only inhabited island in the park) within renewable parameters and without forced intervention.