Preliminary observations on the recruitment variability in Tripneustes gratilla (echinodermata: echinoidea) in three selected biogeographic regions in the Philippines

摘要

The sea urchin Tripneustes gratilla is an economically important resource found along reef flats in many areas in the Philippines. Monthly field monitoring was conducted in three marine biogeographic regions in the Philippines: Northwestern Luzon, Northern Mindanao and Southern Mindanao, to determine and compare the density and size frequency distribution of T. gratilla benthic recruits (40 mm test diameter) from July 2009 to May 2010. Preliminary results showed that the mean density of recruits was significantly higher in the Southern Mindanao (9.41 individuals/ 100 m~(2)) and Northern Mindanao (5.42 individuals/ 100 m~(2)) compared to Northwestern Luzon (only 0.28 individuals/ 100 m~(2)). On the other hand, most of the larger-sized urchins (up to 92 mm) were recorded in the Northwestern Luzon, and adults (>60 mm) comprised up to 66% of the total density. The observed variability in the density and size frequency distribution of T. gratilla recruits is discussed based on the biophysical profiles of the three regions. Southern and Northern Mindanao seem more favorable for sea urchin recruitment compared to Northwestern Luzon. Our ability to repeatedly induce spawning every month and the prevalence of mature stages (up to 100%) of egg samples in the three regions so far indicate the possible regular supply of larvae in all the regions, however, the vulnerability of the recruit stage to the changing environment may differ across biogeographic regions.