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

Abstract

14 Background. Sea urchins are keystone herbivores that greatly influence primary productivity, 15 algal abundance and scleractinian coral recruitment. The long-spined black sea urchin Diadema 16 setosum is widespread and abundant in reef flats throughout the Philippines. Prior studies 17 regarding the feeding preference of D. setosum have been conducted overseas, but little is known 18 about the impact of the echinoid herbivory on reef flat communities in the Philippines. Feeding 19 preferences of D. setosum on four common marine plant species, Halimeda macroloba, 20 Ceratodictyon spongiosum, Padina sp., and Enhalus acoroides were investigated at the 21 University of the Philippines Visayas Marine Biological Laboratory, located in Taklong Island 22 National Marine Reserve (TINMR), Guimaras. 23 Methods. Two food choice experiments were conducted; choice feeding and no-choice feeding. 24 The outcome of choice feeding experiments, expressed as consumption (in g) and percent 25 consumption (%), were used to determine its feeding preferences. The two most preferred feeds 26 determined were then used in no-choice feeding experiment to measure its consumption rate 27 (g⸱echinoid⸱hr). 28 Results. Results of the choice feeding experiment show that D. setosum significantly prefers C. 29 spongiosum (4.83 ± 2.56 g consumption or 32.2%) and H. macroloba (3.73 ± 2.27 g or 24.8%), 30 and avoids E. acoroides (only 0.17 ± 0.22 g or 1.13%) (F= 5.423, p < 0.05). The no-choice 31 feeding experiment between preferred feeds show H. macroloba was consumed more (0.22 ± 32 0.16 g⸱echinoid⸱hr) than C. spongiosum (0.15 ± 0.05 g⸱echinoid⸱hr) although there was no 33 significant difference (p > 0.05) in consumption rate. Results of the no-choice feeding 34 experiment may have been affected by poor water quality and are considered inconclusive. 35 Nevertheless, the study supports the ecological role of D. setosum as an important herbivore that 36 regulates certain macroalgal species in TINMR through its grazing activities. 37