People often ask me about black spots sin turquoise sea in island of Vis. It is so called Neptune grass or Posidonia oceanica.
Posidonia oceanica is endemic to the Mediterranean, and is the most-widespread seagrass species in the region. It forms large underwater meadows that are an important part of the ecosystem.It is an important habitat forming species and provides habitat for many species P. oceanica is a very slow growing species and takes a long time to recolonize areas from where it has been removed.
Posidonia oceanica is threatened at depth by mechanical damage from trawling, boat anchoring, and turbidity. Coastal development including shoreline hardening, urban and harbour infrastructure, and sand mining affect the upper limit of Posidonia meadows.