Feeding preferences of the sea urchin Diadema setosum (Leske, 1778) in Taklong Island National Marine Reserve, Guimaras, Philippines

Abstract

Sea urchins are keystone herbivores that greatly influence primary productivity, algal abundance and scleractinian coral recruitment. The long-spined black sea urchin Diadema setosum is widespread and abundant in reef flats throughout the Philippines. Prior studies regarding the feeding preference of D. setosum have been conducted overseas, but little is known about the impact of the echinoid herbivory on reef flat communities in the Philippines. Feeding preferences of D. setosum on four common marine plant species, Halimeda macroloba, Ceratodictyon spongiosum, Padina sp., and Enhalus acoroides were investigated at the University of the Philippines Visayas Marine Biological Laboratory, located in Taklong Island National Marine Reserve (TINMR), Guimaras. Two food choice experiments were conducted; choice feeding and no-choice feeding. The outcome of choice feeding experiments, expressed as consumption (in g) and percent consumption (%), were used to determine its feeding preferences. The two most preferred feeds determined were then used in no-choice feeding experiment to measure its consumption rate (g⸱echinoid^-1⸱hr^-1). Results of the choice feeding experiment show that D. setosum significantly prefers C. spongiosum (4.83 ± 2.56 g consumption or 32.2%) and H. macroloba (3.73 ± 2.27 g or 24.8%), and avoids E. acoroides (only 0.17 ± 0.22 g or 1.13%) (F= 5.423, p < 0.05). The no-choice feeding experiment between preferred feeds show H. macroloba was consumed more (0.22 ± 0.16 g⸱echinoid^-1⸱hr^-1) than C. spongiosum (0.15 ± 0.05 g⸱echinoid^-1⸱hr^-1) although there was no significant difference (p > 0.05) in consumption rate. Results of the no-choice feeding experiment may have been affected by poor water quality and are considered inconclusive. Nevertheless, the study supports the ecological role of D. setosum as an important herbivore that regulates certain macroalgal species in TINMR through its grazing activities.