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.
