Sea temperature change in the Mediterranean, Marmara and Black Sea coasts of Turkey and its biodiversity effects are investigated. The surface sea water temperatures of the Mediterranean, Marmara and Black Sea region of Turkey for last 41 years showed increased trends in Mediterranean Sea (Iskenderun, Mersin and Antalya), Marmara Sea (Istanbul) and Black Sea (Samsun). The number of Indo-Pacific species is getting rapidly increased for the last decade that caused increased invasion of the Indo-Pacific species and significant shift of biodiversity in Turkish Seas. This settlement process is probably accelerated or facilitated by global climate change and overfishing of native species. Nowadays, the occurrence of Atlantic-Mediterranean (Lithognathus mormyrus, Serranus hepatus and Callinectes sapidus) and Indo-Pacific (Stephanolepis diaspros, Lagocephalus spadiceus) originated species in the Marmara and Black Seas can also be an important indicator of the process of Mediterranization of the Marmara and Black Seas.

A checklist of non-indigenous marine fishes including bony, cartilaginous and jawless distributed along the Turkish Marine Waters was for the first time generated in the present study. The number of records of non-indigenous fish species found in Turkish marine waters were 101 of which 89 bony, 11 cartilaginous and 1 jawless. In terms of occurrence of non-indigenous fish species in the surrounding Turkish marine waters, the Mediterranean coast has the highest diversity (92 species), followed by the Aegean Sea (50 species), the Marmara Sea (11 species) and the Black Sea (2 species). The Indo-Pacific origin of the non-indigenous fish species is represented with 73 species while the Atlantic origin of the non-indigenous species is represented with 22 species. Only first occurrence of a species in the Mediterranean, Aegean, Marmara and Black Sea Coasts of Turkey is given with its literature in the list.

Three specimens of striped eel catfish, Plotosus lineatus (Thunberg, 1787) were caught by a spear gun at depths of 20 m on 4 April 2016 from Iskenderun Bay (Çevlik harbour), Northeastern Mediterranean coast of Turkey. With the present study, P. lineatus is the first time reported from Turkish marine waters, in the Iskenderun Bay, the Northeastern Mediterranean and also this is the first Plotosid species recorded from Turkish Seas.

The lionfish Pterois miles was first recorded in the Iskenderun Bay on 2014 in Turkish Marine waters, and then its distribution was extended to Mersin and Antalya Bays in 2014 in the Mediterranean part of Turkey. The first observation of P. miles in the Aegean Sea was from Fethiye region in July 2015. The extension of P. miles in Turkish marine waters seems to be fast even though it’s slow moving feature. Second species of the lionfish, red lionfish Pterois volitans, was also recorded from Turkish Marine waters on May 2016 by a commercial purse seine at 30 m depth at İskenderun Bay and underwater observation was also recorded on October 2016 at Antakya Bay. Therefore, the number of Pterois species in the Mediterranean Sea has reached to two, P. miles and P. volitans. Based on underwater observations, P. miles and P. volitans are usually observed in rocky and cave habitats and prefer 10-40 meters for feeding that may cause the reduction of populations of vanikoro sweeper (Pempheris spp.), cardinal fish (Apogon spp.) and red coat (Sargocentron rubrum) species. P. miles and P. volitans also show cohabitation and gathering usually with 2-5 individuals. Grouper species such as dusky gruper Ephinephelus marginatus and goldblotch grouper Ephinephelus costae are the main predators of the lionfishes

In Turkish marine waters, pufferfish belongs to Tetraondontidae family are represented with 8 species, Lagocephalus lagocephalus, L. sceleratus, L. spadiceus, L. suezensis, L. guentheri, Sphoeroides pachygaster, Torquigener flavimaculosus and Tylerius spinosissimus. DNA barcoding can be useful in the assessment of cryptic or morphologically similar species of identification which is widespread in marine environment. DNA barcode identification of the eight puffer species of the Tetraodontidae family in Turkish marine waters were examined by using mtDNA sequencing of the amplified partial mitochondrial cytochrome c oxidase I (COI) gene. COI contained 189 variable and 337 conservative nucleotides of which 183 were parsimony informative over 526 bp. Mean genetic diversity all species was found 0.18164. The highest and lowest nucleotide divergence was observed L.spadiceus (0.0022) and between L. sceleratus, L. suezensis, L. lagocephalus, L. guentheri and S. pachygaster (0.0000) respectively. The number of detected different haplotypes were 10 out of 23 sequences, and haplotype diversity was found to be 1.000.

Underwater visual census (UVC) is a commonly used approach for assessing fish density and biomass. Iskenderun Bay, comprising the Samandağ coast in Turkey, is the most important introduction pathway of alien species in the northeastern Mediterranean. In this study, the density, abundance, distribution and interaction of invasive lionfish or devil firefish Pterois miles were assessed using the UVC method on the Samandağ coast. The total transect area monitored on the Samandağ coast was 4.500 m ² . Species richness, Shannon’s diversity index and rate of biomass were 25, 1.81 and 73.5 m ² , respectively. Reduced diversity was observed with increasing depths. The sandy seafloor was a limiting factor for lionfish distribution. There was a significant positive correlation between lionfish total density and both the Shannon diversity index (r = 0.99, P<0.001) and Shannon evenness index (r = 0.99, P<0.05). A high number of significant positive correlations (P<0.05) were detected between the occurrence of lionfish and the occurrence of both the native species and other alien species. The first stock assessment study of lionfish by the UVC method in Turkish marine waters revealed that native species are under very high pressure from lionfish species, especially Chromis, Sparids and Wrasses, indicating negative effects of lionfish on regional native biodiversity.