Turkey is a country surrounded by three seas with different properties. Nevertheless, there is no estimation on how its terrestrial and marine environment will be affected by climate change. International Panel on Climate Change (IPCC) pointed out that sea levels have risen 10-20 cm on a global scale in the last century, mainly caused by global warming, and that a 40-60 cm rise is expected in this century.
Considering the effect of climate change on our seas and particularly on their biodiversity, one can see that each Turkish sea is going to face different problems.
The Mediterranean Sea is connected with the Atlantic Ocean via Gibraltar Strait and is directly influenced by ecological and oceanographical changes in the Atlantic Ocean. On the other hand, the Mediterranean sea is also vulnerable to variations in the Red Sea and the Indian Ocean. Many marine species entered the Mediterranean sea via the 163 km long, 15 km deep and 365 m wide Suez Channel and still keeps entering. For example, 90 of 650 fish species known to be living in the Mediterranean sea are new species for the Basin. 59 of them entered via the Suez Channel. Others that come from the Atlantic Ocean endeavor to adapt to this new environment. There are actually about 300 species from the Red Sea in the Mediterranean Sea. The number of Indian Ocean originated species recorded in Turkish Seas is already more than 50 and economically valuable ones are exploited by fishermen. Exotic species fished in the Iskenderun Bay constitute 20% of the total catch and this value is expected to rise. In other words, the introduction of new species to the Mediterranean Sea caused changes in fisheries with time. Fish composition of catches changed as many of the Indian Ocean originated colorful exotic species started to be exploited for their commercial value.
One of the major reasons that this species was introduced to and spread throughout the Mediterranean Sea by forming colonies competing with native species is the rise of the seawater temperatures. As such, the tropicalization of the Mediterranean Sea affects the whole basin. Caulerpa taxifolia, known as “killer algae”, and many fish species already successfully spread in the basin and even gained terrain because the seawater temperature rose 0,2°C during the last decade. This rise constitutes a serious threat, especially for deep sea fish adapted to live at a constant 13°C temperature. The Eastern Mediterranean has always been a warmer region of the Mediterranean Sea so sea surface temperatures can reach 28-29°C during summer months. These temperatures reflect waters of tropical seas known to be always warmer than 20°C even during winter months. Besides, the sea level rise in the Eastern Mediterranean is 12 cm on average since 1992. This rise is a threat for all organisms including migratory species. If this change continues, alterations of distributions and reproduction periods of species that are sensitive to temperature rise or that have reproductive capacity in restricted temperature intervals are inevitable.
Mass mortalities of soft corals (gorgonians) observed in the central Mediterranean Sea and the Aegean Sea in recent years are related to global warming. With the descent of surface waters under the thermocline zone, gorgonians, adapted to cold waters, die. It is yet difficult to estimate how many and which species of 12000 marine species living in the Mediterranean Sea are going to be affected by climate change. Sea level changes might have a more pronounced influence on species of mediolittoral and supralittoral zones of long and wide beaches of the Mediterranean Sea. For species like sea turtles, the surface of the beach they utilize as reproductive sites or nesting areas might run a risk because of the shortening of beach surface area. Sea level rise in the Mediterranean would affect, more intensely, sessile and sedentary species with low capacity of moving rather than active swimmers like fish.
Some marine species and particularly some fish species act as indicators of global warming. Seawater temperature is a major determining parameter because it intervenes in reproduction and living area optimum events. Fish are very sensitive to seawater temperature during their pre-adult stages called larvae and juvenile. This is why it is inevitable for fish which migrate between sea and rivers to be affected by this circumstance. Fish like Sardine, Bogue and Salema live in the Mediterranean Sea and were rare in the Black Sea and Marmara Sea until 20 years ago. The fact that they are observed in these seas and are even being exploited in western Black Sea regions such as İğneada is associated with rise in seawater temperatures. The fact that individuals of the species Thalassoma pavo (ornate wrasse) are seen in the Marmara Sea and that its distribution limit has shifted North from South is explained by the effects of climate change.
Frequent observations of a thermophilic (requiring high temperatures for normal development) sea urchin species called “Arbacia lixula” in the Northern Aegean and Marmara Seas are perceived as preliminary signs of faunal shifts in these seas. On the other hand, the process of the Mediterranisation of the Black Sea is continuing. “Black Sea-Mediterranean Sea” connection was reestablished 6000 years ago and Mediterranean originated species entered this sea. At that time, sea levels of the Mediterranean were higher compared to today’s levels. This introduction which has become a continuous process is called “Mediterranisation”. A major characteristic of the species entering the Black Sea from the Mediterranean is the fact that they live in saline and warm waters. For example, the introduction of species like conger, barracuda or john dory to this sea shows that the distribution of thermophilic species is extending. The reason for that is the rise of seawater levels in the basin. The quickening of Mediterranization of the Black Sea, introduction of many new species and alteration of the tropic web as a result can be more pronounced in forthcoming years