Population Biology of Tripneustes gratilla (Linnaeus) (Echinodermata) in Seagrass Beds of Southern Guimaras, Philippines

The sea urchin Tripneustes gratilla is a major grazer found in seagrass beds of southern Guimaras, Philippines. Monthly length-frequency data from January 2008 to June 2009 were used to estimate the growth, recruitment pattern and mortality rate with the use of FiSAT II. The estimated values for the Von Bertalanffy growth parameters L(n/k)(asymptotic length) and K (growth coefficient) were 114.2 mm and 1.08 respectively. Monthly densities ranged from 0.06 to 0.58 per m2 with a mean value of 0.26 per m2. Monthly biomass ranged from 4.1 to 49.5 grams per m2 with a mean value of 21.15 grams per m2. T. gratilla density and biomass were observed to be highest during the month of November 2008. The recruitment pattern showed a major broad peak and a minor peak separated by four months. Total mortality (Z) from the length-converted catch curve was computed to be 4.74 per year.