The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula and the Apennine Mountains from the Dinaric Alps and adjacent ranges. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the northwest and the Po Valley. The countries with coasts on the Adriatic are Italy, Croatia, Albania, Montenegro, Bosnia-Herzegovina, and Slovenia. The Adriatic contains over 1,300 islands, mostly located along its eastern, Croatian, coast. It is divided into three basins, the northern being the shallowest and the southern being the deepest, with a maximum depth of . The Otranto Sill, an underwater ridge, is located at the border between the Adriatic and Ionian Seas. The prevailing currents flow counterclockwise from the Strait of Otranto, along the eastern coast and back to the strait along the western (Italian) coast. Tidal movements in the Adriatic are slight, although larger amplitudes are known to occur occasionally. The Adriatic's salinity is lower than the Mediterranean's because the Adriatic collects a third of the fresh water flowing into the Mediterranean, acting as a dilution basin. The surface water temperatures generally range from in summer to in winter, significantly moderating the Adriatic Basin's climate.
The Adriatic Sea sits on the Apulian or Adriatic Microplate, which separated from the African Plate in the Mesozoic era. The plate's movement contributed to the formation of the surrounding mountain chains and Apennine tectonic uplift after its collision with the Eurasian plate. In the Late Oligocene, the Apennine Peninsula first formed, separating the Adriatic Basin from the rest of the Mediterranean. All types of sediment are found in the Adriatic, with the bulk of the material transported by the Po and other rivers on the western coast. The western coast is alluvial or terraced, while the eastern coast is highly indented with pronounced karstification. There are dozens of marine protected areas in the Adriatic, designed to protect the sea's karst habitats and biodiversity. The sea is abundant in flora and fauna—more than 7,000 species are identified as native to the Adriatic, many of them endemic, rare and threatened ones.
The Adriatic's shores are populated by more than 3.5 million people; the largest cities are Bari, Venice, Trieste and Split. The earliest settlements on the Adriatic shores were Etruscan, Illyrian, and Greek. By the 2nd century BC, the shores were under Rome's control. In the Middle Ages, the Adriatic shores and the sea itself were controlled, to a varying extent, by a series of states—most notably the Byzantine Empire, the Republic of Venice, the Habsburg Monarchy and the Ottoman Empire. The Napoleonic Wars resulted in the First French Empire gaining coastal control and the British effort to counter the French in the area, ultimately securing most of the eastern Adriatic shore and the Po Valley for Austria. Following Italian unification, the Kingdom of Italy started an eastward expansion that lasted until the 20th century. Following World War I and the collapse of Austria-Hungary and the Ottoman Empire, the eastern coast's control passed to Yugoslavia and Albania. The former disintegrated during the 1990s, resulting in four new states on the Adriatic coast. Italy and Yugoslavia agreed on their maritime boundaries by 1975 and this boundary is recognised by Yugoslavia's successor states, but the maritime boundaries between Slovenian, Croatian, Bosnian–Herzegovinian and Montenegrin waters are still disputed. Italy and Albania agreed on their maritime boundary in 1992.
Fisheries and tourism are significant sources of income all along the Adriatic coast. Adriatic Croatia's tourism industry has grown faster economically than the rest of the Adriatic Basin's. Maritime transport is also a significant branch of the area's economy—there are 19 seaports in the Adriatic that each handle more than a million tonnes of cargo per year. The largest Adriatic seaport by annual cargo turnover is the Port of Trieste, while the Port of Split is the largest Adriatic seaport by passengers served per year.
== Geography ==
The Adriatic Sea is a semi-enclosed sea, bordered in the southwest by the Apennine or Italian Peninsula, in the northwest by the Italian regions of Veneto and Friuli-Venezia Giulia, and in the northeast by Slovenia, Croatia, Bosnia-Herzegovina, Montenegro, and Albania—the Balkan peninsula. In the southeast, the Adriatic Sea connects to the Ionian Sea at the wide Strait of Otranto. The International Hydrographic Organization (IHO) defines the boundary between the Adriatic and the Ionian seas as a line running from the Butrinto River's mouth (latitude 39°44'N) in Albania to the Karagol Cape in Corfu, through this island to the Kephali Cape (these two capes are in latitude 39°45'N), and on to the Santa Maria di Leuca Cape (latitude 39°48'N). It extends from the northwest to the southeast and is wide. It covers and has a volume of . The Adriatic extends northwest from 40° to 45°47' north, representing the Mediterranean's northernmost portion. The sea is geographically divided into the Northern Adriatic, Central (or Middle) Adriatic, and Southern Adriatic. The Adriatic Sea drainage basin encompasses , yielding a land–sea ratio of 1.8. The drainage basin's mean elevation is above sea level, with a mean slope of 12.1°. Major rivers discharging into the Adriatic include the Po, Soča, Krka, Neretva, Drin, Bojana, and Vjosë. In the late 19th century, Austria-Hungary established a geodetic network with an elevation benchmark using the average Adriatic Sea level at the Sartorio pier in Trieste, Italy. The benchmark was subsequently retained by Austria, adopted by Yugoslavia, and retained by the states that emerged after its dissolution.
|+Length in kilometres of Adriatic coastlines
! Coastal fronta
| Croatia || 1,777.3 || 4,058 || 5,835.3 || 526
| Italy || 1,249 || 23b || 1,272 || 926
| Albania || 396 || 10 || 406 || 265
| Montenegro || 249 || 11 || 260 || 92
| Slovenia || 46.6 || 0 || 46.6 || 17
| Bosnia–Herzegovina || 21.2 || 0 || 21.2 || 10.5
| colspan=5|Notes: a The distance between the extreme points of each state's coastline, b Not including islands in coastal lagoons
The Adriatic Sea contains more than 1300 islands and islets, most along the Adriatic's eastern coast—especially in Croatia, with 1,246 counted. The number includes islands, islets, and rocks of all sizes, including ones emerging at ebb tide only. The Croatian islands include the largest—Cres and Krk, each covering about the same area of —and the tallest—Brač, whose peak reaches above sea level. The islands of Cres and the adjacent Lošinj are separated only by a narrow navigable canal dug in the time of classical antiquity; the original single island was known to the Greeks as Apsyrtides. The Croatian islands include 48 permanently inhabited ones, the most populous among them being Krk and Korčula. The islands along the Adriatic's western (Italian) coast are smaller and less numerous than those along the opposite coast; the best-known ones are the 117 islands on which the city of Venice is built. The northern shore of the Greek island of Corfu also lies in the Adriatic Sea as defined by the IHO. The IHO boundary places a few smaller Greek islands (ones northwest of Corfu) in the Adriatic Sea.〔
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