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A study was conducted to estimate biometry of an epiphytic micro-calcareous red algae, Hydrolithon boreale found on leaves of a Mediterranean meadow, Posidonia oceanica along the entire Turkish coast of the Mediterranean Sea in time (winter and summer 2019) and space (regions, and bottom type and depth). Percent occurrence of the epiphyte was lower in winter (25%), particularly found in a small bay in the west than summer (44%), entirely along the coast. The epiphyte grew up to 5 mm in diameter, 0.35 mm in thickness of the crust size, and was populated up to 1006 ind/m2 in summer owing to the increased utilization of the carbonate by the epiphyte with the increased water temperature. The size was contrasted to the density (abundance and biomass) in space. The biometry was significantly dependent on the siliciclastic-carbonate deposition as inferred from SiO2 of the water in relation the leaf area index (LAI) of P. oceanica. Therefore, this deposition induced specimens growing in size, followed by the reduced density in relation to N-based nutrient of the water. Further major environmental parameters which negatively affected the biometry were pH and total suspended matter of the water, analogous to the turbidity. Of the trace elements, Ni was negatively correlated with the biometry whereas the LAI was however positively correlated with all the anthropogenic-sourced trace elements (V, Cu, Zn, As, Cd, and Pb) in the leaves. Of the bottom types, the calcite rock had higher density than the other soft bottoms in contrast to the size of the epiphyte.

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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.