The air flow into the Mediterranean is through gaps in the mountain ranges, except over its southern shores east of Tunisia. The low concentration of phosphates and nitrates, necessary for marine pastures, limits the quantity of marine life in the Mediterranean . Overexploitation of the sea 's marine resources remains a serious problem. Petroleum deposits have been found off Spain, Sicily, Libya, and Tunisia, and natural gas has been discovered in the Adriatic Sea . Specialty crops of the region include olives, citrus fruits, grapes, and cork.
Tourism is a major source of income for many of the countries bordering the Mediterranean .