Feeding Preference of Sea Urchin, Stomopneustes variolaris in an Intertidal Rocky Reef of Sri Lanka

Abstract

Sea urchins are well-known grazers and bioeroders in marine benthic habitats. Stomopneustes variolaris that play a key role in controlling macroalgae, is the most abundant sea urchin species in the shallow waters of Sri Lanka. The studies on S.variolaris is restricted to few studies on distribution and reproductive biology. Yet, studies on feeding preference is scarce. Thus, present study was carried out to investigate the feeding preference of S. Variolaris during January to April 2021 at Ahangama inetrtidal rocky reef (5º 96’N 80º 37’E). Benthic algae cover of the reef was recorded. Sea urchins (n=20), collected from the rocky intertidal reef were transported to the laboratory, and dissected to preserve 1 cm of gut. Contents in the remaining gut was analyzed for proportions of inorganic and organic components. Further, contents of the preserved gut section were observed under dissecting microscope and percentage frequency of dietary components were recorded. Gut contents of sea urchins consisted of calcium carbonate, organic materials, and siliceous materials 48.06±3.74%, 46.24±3.74%, and 5.66±0.47 % (mean±SE), respectively. The organic component of gut composition included plant (85.4 ±.04 2.83%) and animal materials (14.767±1.57%). The most abundant dietary component of urchin was green fleshy algae (57.81±5.22 %), of which Caulerpa racemosa was the dominant green macroalgae (9.80±2.89%). Foraminiferan shells were the dominant animal dietary component (14.13 ± 5.62%). The presence of animal and plant material in the gut contents indicates that S.variolaris is an omnivorous species. Even though Sargassum sp. and Halimeda sp. were highly abundant in the study area, these species were not observed in the urchins’ gut possibly due to unpalatability. Areas dominated by crustose coralline algae indicate the extensive grazing of sea urchins. Impacts of seasonal changes in the macroalgae cover on the food preference of S. variolaris is reccomended for further studies.