A broad-scale biometrical response of a pristine meadow, Posidonia oceanica, to winter and summer conditions in the north-eastern Mediterranean coast

Abstract The concept of the present study was derived from a study to ground-truth the acoustical echo energy of the seagrass biometrics in order not to use any destructive method and was scoped to study the estimated environment-related biometrical distribution of a pristine marine phanerogam, Posidonia oceanica meadow, along the entire Turkish Mediterranean coast. This study also provided the first knowledge on the broad-scale extent of the meadow from a significant coast length in the Mediterranean Sea. For this purpose, two surveys were conducted covering bottom depths of 5–35 m in the critical seasons (winter and summer 2019) of a subtropical coast for the growth dynamics of the meadow. The meadow samples were collected in a frame of 0.4 x 0.4 m by SCUBA divers, which was a destructive method. The physicochemical and optical environments of the water were evaluated with the biometrical dynamics of the meadow. Orderly, season, region, bottom types, and bottom depths dictated the biometrical distribution. The meadow shoot density showed the environment to be in good ecological condition without changing the average shoot density in season. Other biometrics grew 2-fold higher in summer compared to winter (water temperature and salinity). The region influenced by the Aegean Sea had lower biometrical values than the other two regions. Hard (rock and matte) and soft (sand and mud) benthic environments differentiated the biometrics as follows: Contrary to the morphometric variables, the density biometrics decreased linearly from the hard bottom to the soft bottom. The density dynamics were partially contrasted with the morphometrical dynamics. Rhizome-related biometrics were independently governed by the leaf-related biometrics, especially by nitrogen-based nutrients in near-bottom water. The optical parameter, especially PAR, a certain percent of the daylight was effective during the growth of the biometrics. The present study provided the first knowledge on a broad-scale biometrical distribution from the entire Turkish Mediterranean coast to the seagrass studies.