Turkey is a country surrounded by three seas with different properties. Nevertheless there is no estimation on how both its terrestrial and marine environment are going to be affected. International Panel on Climate Change (IPCC) pointed out that sea level has 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 during 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. Otherwise, the Mediterranean sea is also open to variations in the Red Sea and the Indian Ocean. Many marine species entered in 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 of Red Sea origin in the Mediterranean Sea. The number of Indian Ocean originated species determined in Turkish Seas are already more than 50 and economically valuable ones are exploited by fishermen. Exotic species fished in the Iskenderun Bay to its own constitute 20% of the total catch and this value is expected to rise. In other words, the introduction of new species in the Mediterranean Sea induced modifications in fisheries with time. Firstly, fish composition of catches changed with many Indian Ocean originated colourfull exotic species started to be exploited for their commercial value.

One of the major reasons of the introduction of these species in the Mediterranean Sea and of their spread by forming colonies that enter in competition with native species is the rise of the seawater temperature. It is to do with a tropicalisation of the Mediterranean sea affecting the whole basin. Caulerpa taxifolia known as “killer algae” and many fish species already successfully spread in the basin and even gain terrain because the seawater temperature rised 0,2°C during last decade. This rise constitute a serious threat especially for deep sea fish adapted to live at 13°C constant seawater temperature. The Eastern Mediterranean has always been a warmer region of the Mediterranean Sea so that 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 in average since 1992. This rise is a threat for all organisms including migratory species. In case this changement 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 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 among them, the surface of beach they utilize as reproductive site or nesting area 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 itervenes 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 facts that they are observed in these seas and that they are even started to be exploited in western Black Sea regions such as İğneada are associated to seawater temperature rise. Also, the fact that individuals of the species Thalassoma pavo (ornate wrasse) are started to be seen in the Marmara Sea and that its distribution limits has shifted to North from South are explained by the effects of climate change.

Intensive observation of a thermophilic (Requiring high temperatures for normal development) sea urchin species called “Arbacia lixula” in the Northern Aegean Sea and Marmara Sea are perceived as preliminary signs of faunal shifts in these seas. In the other hand, the process of Mediterranisation of the Black sea is continuing. The connection “Black Sea-Mediterranean Sea” is reestablished 6000 years ago and Mediterranean originated species entered in this sea. At that time, sea level of the Mediterranean was higher than today. This introduction is a continued process nowadays and called “Mediterranisation”. A major characteristic of species entering the Black sea from the Mediterranean Sea is the fact that they live in its saline and warm waters. For exemple, the introduction of species like conger, barracuda or john dory in this sea shows that the distribution of thermophilic species is extending. The reason for that is related to seawater rise of the basin. The fastening of Mediterranization of the Black Sea, the introduction of many new species in this sea and the alteration of trophic web as a result can be more pronounced in forthcoming years