Distribution of epipelagic mesozooplankton in Mediterranean coast of Turkey

Zooplanktonic organisms generally consume primary producers in the marine ecosystem and provide energy and nutrient transfer to consumers at the next level in the food chain. Except for a few mesozooplankton groups in the epipelagic zone, the most common and abundant groups are Copepoda, Cladocera and Chaetognatha species. This study aims to determine the horizontal distribution of these groups in the epipelagic zone in the summer season when these groups are relatively high in diversity and abundance in a wide area covering the Mediterranean Coast of Turkey. Another aim of this study is to determine the ecological parameters affecting the zooplankton distributions and revealing their vertical distribution and diel migration. Therefore, the study area was evaluated by dividing it into four sub-regions depending on the regions; physicochemical, geomorphological and main-coastal current effects. In this thesis, two different samplings were made (horizontal and vertical distribution). In order to determine the horizontal distribution, samples were taken from 64 stations in the field study carried out in June-July 2019, covering the Mersin-Datça distance. Horizontal distribution stations are formed by aligning two shores and one open water. For vertical distributions, samplings were made at a station (0-200 m) located outside the rim current in Anamur offshore, at 20 m intervals, in 4 different periods of the day. All zooplankton sampling was done with WP-2 plankton mesh with 300 µm mesh. For environmental parameters, samples were taken using a 5 L Niskin bottle. A total of 168 systematic groups were identified in the study. From these groups, 24 families and 123 species from Copepoda, two families and six species from Chaetognatha and two families and seven species from Cladocera were identified. In addition, the presence of Acartia (Hypoacartia) adriatica was recorded for the first time on the Mediterranean Coast of Turkey. In the study area, 91% of the identified zooplankton were holoplankton, while 9% were meroplankton members. Among the groups determined at the species level, 26 permanent species, 23 common species and 86 rare species were identified. Among the Copepoda orders, it is the most dominant Calanoida order. This was followed by Poecilostomatoida, Cyclopoida, Monstrilloida and Harpacticoida orders, respectively. The lowest abundance values were found in the Gulf of Antalya. Copepoda abundance is lower in coastal areas than open areas, and Cladocera is higher in coastal waters. For the Chaetognatha abundance value, there is no difference in coastal-open areas. Faunistic characters differed between coastal, open waters and regions. In general, the number of species in the study area was 60 and below, while lower species numbers were found in coastal waters. The highest abundance was found in the east of the study area, and the lowest values were found in the Gulf of Antalya. While Margalef Species Richness Index decreased towards the west, the highest values were recorded in Antalya Bay. Species richness distributions in coastal-open waters varied between regions; The Pielou Evennes Index reached the highest value in the Gulf of Antalya and is relatively low in other regions. Depending on the species richness and evennes index, Antalya Bay is the region with the highest biodiversity. Mesozooplankton assemblage was statistically different in quality and quantity between coastal-open waters and regions. The main species that cause this difference between offshore waters Haloptilus longicornis, Lucicutia flavicornis, Oithona setigera, Corycaeus limbatus, Lucicutia gemina ve Calocalanus pavo, which have a very high abundance in open waters compared to the shore. Antalya Bay was found to be quite different from other regions. Other remaining regions differed relatively from each other. The environmental factors that cause the difference in the zooplankton composition of coastal-open waters are the distance of the stations from the shore and the depth of the bottom. The regional variation is the environmental variable that primarily shapes the water's density and the near-bottom water temperature. These factors were followed by surface water salinity and temperature values. Vertical zooplankton distribution and diel migration examination showed negative distribution and positive phototaxis structure. Generally, it was seen in species with limited distribution with surface waters, water columns and physical layers. Migration movements were not observed in Cladocera species distributed in surface water. Migration was not observed in Flaccisagitta enflata and Mesosagitta minimima species from the Chaetognatha family, but reverse migration was observed in Serratosagitta serratodentata. Reverse migration was also observed in female Temora stylifera, Acrocalanus gibber, Lucicutia gaussae from the Copepoda, partial reverse migration in Copilia mediterranea, Euchaeta marina and Calanopia elliptica, while C.pavo, Agetus typicus, Oithona plumifera and L. flavicornis showed normal migration. No migration movement was in females of H. longicornis and Clausocalanus parapergens. Male individuals of Copepoda belonging to these species generally showed no migration or partial reverse migration.