Effects of Collector Sea Urchin (Tripneustes gratilla) on the Reduction of Brown Seaweed (Dictyota spp. and Padina spp.) Cover in Post-Coral Bleached Systems

Anna Karenina C. Dalabajan¹, Suzielette Veve R. Hilay¹, Ma. Cailah Joyce O. Velasco¹, Virna Jane M. Navarro¹ and Angelo P. Olvido^1
1Philippine Science High School Western Visayas Campus – Bito-on, Jaro, Iloilo City 5000, Department of Science and Technology, Philippines

Abstract
The purpose of this research is to determine the effects of Tripneustes gratilla in reducing the abundance of Dictyota dichotoma and Padina spp. in macroalgal-dominated marine ecosystems. Corals attached with macroalgae were exposed to the Tripneustes gratilla for two weeks. Measurement of the macroalgal density before and after the exposure of T. gratilla was administered. The Fleshy Macroalgal Index of the units with sea urchin and without sea urchin were also compared and analyzed. A software, PhotoQuad, was utilized to quantify the FMI of each unit. The results showed that the presence of T. gratilla did not significantly reduce (p=0.23) the macroalgal cover in comparison to the control group. Nevertheless, the compared FMI of the pre-exposure and post-exposure to the urchin showed a significant difference (p=0.023). In conclusion, the reduction of the macroalgal cover may be attributed to the presence of Tripneustes gratilla. Although it is only comparably different, the exposure to Tripneustes gratilla can potentially aid in the recovery of macroalgal-covered post coral bleached systems and in the control of invasive macroalgae population.