RMGN Thilakarathna
Department of Oceanography and Marine Geology, Faculty of Fisheries and Marine Sciences & Technology, University of Ruhuna, Matara, Sri Lanka.
Rocky shores are highly dynamic and the zonation of species is universal despite the geographic location. Pollution and unregulated fishing in many developing nations threaten this sensitive ecosystem altering the species composition. Macroalgae cover of Ahangama Kanda rocky shore in Southern coast of Sri Lanka was analyzed during two monsoon seasons in 2022 (northeast/southwest). Approximately 30-40 photo-quadrates (50 x 50 cm) were used for the analysis of species composition in five zones depending on tidal movement (near shore/intermediate/ sheltered middle zone /sheltered reef edge/ wave breaking zone). Images were analyzed using CPCe software (4.1) and differences between zones were analyzed using ANOSIM in PRIMER V6 software. Sixteen and fifteen species of macroalgae were recorded for the Ahangama Kanda reef in the southwest and northeast monsoon, respectively. ANOSIM results revealed significant differences between species composition of zones (R=0.743, p=0.1%). The Nearshore zone was dominated by crustose coralline algae and the abundance doubled during the southwest monsoon (51.26 ± 4.5%). The intermediate zone was dominated by turf algae (39.38 ± 3.16 %) and Halimeda sp. (40.16 ± 3.82 %) during the northeast monsoon and southwest monsoon respectively. Wave breaking zone was dominated by Carpopeltis sp. whilst the sheltered middle zone was dominated by Sargassum sp. during both seasons. Nearshore zone and wave breaking zone were significantly different (R= 0.937, p=0.1%) and the difference was attributed to Carpopeltis sp. (27.74%) and turf algae (20.70%). The dominance of different species in each zone indicated clear zonation and long-term monitoring is essential to conserve this habitat.