Aegean Sea

Category: Marine and Oceanic Biomes.

Geographic Location: Mediterranean Sea.

Summary: The Aegean Sea, in the northeastern corner of the Mediterranean Sea, is a marine province that shares many climate and biome characteristics with temperate North Atlantic realms.

Within the Mediterranean Sea basin, the Aegean Sea forms an embayment surrounded on the west and north by Greece, on the east by Turkey, and on the south by the island of Crete. The area of the Aegean is 82,625 square miles (214,000 square kilometers). It reaches a maximum depth, near Crete, of 11,624 feet (3,543 meters). The area has a complex topography marked by deep trenches and elevated structures; the eastern Mediterranean is a remnant of an ancient body of water known as the Tethys Ocean. The waters are generally nutrient poor, sustaining an oligotrophic environment (an environment that is characterized by relatively slow growth and metabolic activity).

To the northeast, the Aegean connects through Turkey to the Black Sea via the Sea of Marmara and the straits of the Dardanelles and the Bosphorus. The Aegean is dotted with thousands of mountain peaks peeping up from the seafloor. These island chains and the numerous cragged gulfs and bays surrounding them are unsurpassed in utility to seafarers. The islands include Crete and Euboea (the Mediterranean's fifth-largest and sixth-largest, respectively), the Sporades, the Cyclades, the Saronic, the Dodecanese, and the Northern and Eastern groups.

Salinity and Temperature

Like the Mediterranean as a whole, the Aegean Sea flows counterclockwise, its salty waters rising along its eastern boundary and then falling along its northern boundary, carrying the waters of the Black Sea down along its western Greek shoreline and out into the larger basin. The Aegean is influenced by water exchange with such regional sources as the Adriatic and Ionian Seas, as well as flow from the Nile River delta and the Red Sea via the Suez Canal. Changes in saltwater composition over time have periodically altered the circulation patterns and the fundamental ecology of the Aegean basin area. Rising global temperatures now contribute to fluctuating carbon dioxide (CO₂) levels, in concert with CO₂ escaping from volcanic sources.

One result is acidified marine zones that trigger losses in biodiversity and alter food-web functions. This situation is complicated by the Aegean basin being a somewhat enclosed province; pollutants such as heavy metals cannot be readily discharged and over time their levels are concentrated. These factors contribute to worrisome changes in ecology including the erosion of coral ecosystems and the extinction of species such as the sea turtle, the monk seal, and the Atlantic tuna, all of which spawn only in the Mediterranean.

The effects of climate change on pelagic (deep sea) marine ecologies have only begun to be documented; some effects are unexpectedly beneficial to various life forms. Changes of interest include variations in the metabolic rates of marine organisms, and environmental conditions including changes in currents, column stratification, and nutrient production, all variables that affect food-web structure, population distribution, and community dynamics within an ecosystem.

Researchers marked a “transient event” in the area occurring in two phases during the 1990s. As a result of increased salinity by climate forcing, a mass of dense, warm water formed in the southern Aegean. This process was followed by a drop in temperature of 0.7 degrees F (0.4 degrees C), creating another deeper layer of dense water. These changes triggered an upwelling of deep bottom water, creating an intermediate stratum of nutrient-rich water now known as the Transitional Mediterranean Water. This change, in turn, set into motion a threefold increase in biological activity along the continental shelf and upper slope.

Plankton and Human Needs

The total biomass of the Eastern Mediterranean is 46 percent lower than densities found at the western edge. Since the construction of the Aswan High Dam in Egypt and a major dam on the Ebro River in Spain, freshwater inputs into the Mediterranean Sea were significantly reduced. Continued flows of saltwater from the Atlantic Ocean and Red Sea contributed fractional increases in salinity. This, in turn, affects the quality of marine life throughout the region. The Atlantic Ocean waters that spill into the Mediterranean are poorer in nutrients, having served to feed the ocean's population of plankton. As the waters move eastward toward the Aegean, bacteria and other organisms feed on the remaining nutrients, leaving little left for plankton and other marine life. Bacteria are thought to account for about 56 percent of all organisms found on the shallow shores of the Aegean Sea.

The Suez Canal is effectively a passageway for the migration of over 300 species of Erythraen marine biota from the Red Sea into the Mediterranean, an immigration that adds to environmental changes in the Aegean. This is known as the Lessepsian Migration, named after Ferdinand de Lesseps, the French mastermind of the 19th-century Suez Canal project. Exotic macrophytes, invertebrates, and fish include the bivalve Brachiodontes pharaonis, the gastropods Cerithium scabridum and Strombu persicus, the rock oyster Spondylus spinosus, the jellyfish Rhopilema nomadica, penaeid prawns, the American blue crab, mullids, the barracuda Spyraena chrysotaenia, thriving populations of clupeids, and pearl mollusks.

The competitive displacement of autochthonous species is also the result of coastal mariculture farming. Farm stocks include the Pacific oyster Crassostrea gigas, the soft-shell clam Mya arenariea, and the pearl oyster Pinctada radiata. Changes in bathymetric populations are a direct result of migration and displacement. Human population densities and subsequent coastal development have further decimated marine biota and altered fragile littoral (shoreside) ecosystems.

The general absence of phytoplankton contributes to the amazing clarity of the Aegean's waters. The most notable of the sea fauna include the blennies (Blenniidae), Cardinal Fish (Apogonidae), eels, picarels, electric rays, groupers (Serranidae), lizard fish, red mullets, and scorpion fish. The larger sea mammals include dolphins and seals. Divers and snorkelers enjoy touring the Aegean to study and to admire the habitats of sponges and sea urchins, octopus squids, and cuttlefish. Algae, kelps, and seagrasses are also common to the area.

Coastal Species

The Aegean Sea, its archipelago, Greece, and Turkey together form a distinct ecological region classified by the World Wildlife Fund (WWF) as a zone of sclerophyllous and mixed forests (designated PA1201). The eastern border of this ecoregion extends to plains and lowlands in Turkey, while Greece is replete with sparse, mountainous landscapes. Callabrian pine (Pinus brutia) and maquis are the dominant vegetation; north to south, the maquis are varied and include stands of Arbutus andrachne, A. unedo, Spartium junceum, and Laurus nobilis. Stands of sweetgum and Datça palms, endangered native species, are also found. Varied species of oak grow in areas where the pine stands have been removed.

Each of these types of forests provide habitat for European woodland birds; pine forests echo with the calls of wrens, blackbirds, tits, jays, and Krūper's nuthatch, a bird only found in southeast Turkey. Warblers, buntings, and partridges make their habitat in maquis scrublands. Other native wildlife include loggerhead turtles, wolves, foxes, and boars. The entire basin is noted for its olive trees and viticulture.

Bibliography

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