Is Amazing, because it features:
Rich biodiversity and provides habitats for 250,000 known species and an estimated 750,000 other species yet to be discovered.
Variety of ecosystems (open oceans, shorelines, seabed)      
Life even in the deep ocean in conditions of absolute darkness and high pressure
Is Life-giving, because it offers:
50% of the oxygen in the atmosphere
Drinking Water through the hydrological cycle
A variety of food, which is rich in proteins
Regulation of global climate through the transfer of heat by ocean currents
A large number of medicines with countless antibacterial and anticancer properties as well as cosmetics derived from marine organisms.
Contributes to economic development through:
Marine Transport, which is the safest and most economical mode for transporting people, goods and raw materials
Raw Materials, since 25% of the global oil and natural gas production originates from the seabed
Renewable energy offered by the sea, which may be viewed as a gigantic energy reservoir (wind, wave and tidal energy)  
Tourism and Recreation. Specifically in Greece, which in 2013 was visited by 18,000,000 tourists, while 500,000 people are employed in the tourism industry