A Broad-scale Biometrical Response of Pristine Posidonia Oceanica Meadow to Winter and Summer Conditions in the North-eastern Mediterranean Coast

Abstract

The present study provided the first knowledge on a broad-scale biometric distribution of the seagrass meadow (Posidonia oceanica) throughout the entire Turkish Mediterranean Sea coast. In this study, two surveys were conducted in winter and summer season of 2019, covering bottom depths range of 5–35 m to assess the growth dynamics and distribution of the P. oceanica. P. oceanica samples were collected from each sampling site by a SCUBA diver with quadrat sampling method for biometrics data. The physicochemical properties and optic characteristics of the water were also determined. Season, site, bottom type, and depth appeared to be determinative on biometric characteristics and distribution of P. oceanica. About one-third of the bottom surface area of the Turkish Mediterranean Sea coast was covered by the P. oceanica. The shoot density did not change seasonally. Leaf biomass and leaf area index were two times higher in summer compared to winter. The biometric characteristics of P. oceanica and distribution pattern differed based on the bottom type of the region. The bottom of Muğla bay is composed of sand and mud, Antalya Bay is mainly composed of rock, and Mersin Bay is mainly composed of matte and mud. Sampling season and region appeared to be determinative on biometric characters (leaf length and width, rhizome length and width or diameter, sheath length and width). The size of the meadows showed a decreasing trend with increasing depth. High variation in morphologic characters was observed in P. oceanica distributed around 15–20 m depth compared to those distributed in shallower or deeper zones. The main seasonal differences were observed in rhizome-related and leaf-related biometrics. Ecological analyses revealed that the biometric characteristics of P. oceanica were affected by season (based on changes in salinity and temperature), region (depending on bottom type), and distribution depth. In winter, the meadow was interacted with salinity, temperature and oxygen of the water. Nitrogen based-nutrients were related to the seasonal growth dynamics of the P. oceanica. The optical parameters (Sechhi depth and percent PAR, Photosynthetically Active Radiation) were not correlated with the biometrics, but the P. oceanica was found in a range of 10% to 30% of PAR. Overall, the density variables were contrasted to the morphometrical variables during the growth dynamics of the meadow. This study has presented SCUBA biometrical data which were used for in situ calibration with the corresponding acoustical echo energy of the seagrass and was an approach to use non-destructive method, the acoustical techniques.