Feeding Preference of Sea Urchin Tripneustes gratilla in Ahangama Rocky Reef, Southern Coast of Sri Lanka during Southwest Monsoon

Abstract

Sea urchins play a vital role as grazers in shallow marine ecosystems throughout the world. Among tropical sea urchin species, Tripnuestes gratilla is common in many shallow benthic habitats of the southern coast of Sri Lanka. Tripnuestes gratilla is a delicacy in Southeast Asian countries and is used as a biological control agent against invasive algae. However, the economic benefits of this species are not fully realized in Sri Lanka. Although they are both ecologically and economically important, so far, no baseline data are available in Sri Lanka on the biology and feeding habits of this species. Therefore, the main objective of this study is to determine the feeding habit of T. gratilla population in the Ahangama rocky reef. Fifteen urchins were collected during the Southwest monsoon in 2020. Samples were transported the laboratory, dissected and gut contents were analysed for organic and inorganic components using standard methods. The gut contents of T. gratilla were composed of organic materials (66.47±2.73%), calcium carbonate (26.99±3.06%), and sand (6.53±0.43%). The most abundant dietary items in the gut contents were Thalassia hemprichii (28.03±4.99%), Red fleshy algae (23.74 ± 1.02%) Red filamentous algae (22.71 ±1.02%), and Sargassum sp (19 ± 0.55%). These groups were highly abundant in T. gratilla habitats in the Ahangama reef during the southwest monsoon period. Even though Helimeda sp. was highly abundant in the high tide zone, it was absent in the gut contents of T. gratilla probably be due to less palatability due to the calcified nature of Helimeda sp.. Tripnuestes gratilla is a generalist herbivore and prefers red algae and seagrass. The impact of seasonal changes in algae cover on the food selectivity of T.gratilla is needed to be studied further.