The rates of ingestion, egestion, ammonium excretion, and CO2 respiration of Tripneustes gratilla (Echinodermata: Echinoidea) from a shallow water embayment at eastern Mactan Island, central Philippines were examined. There was no significant difference in weight-specific feeding rate with the three macrophytes (Sargassum polycystum, Thalassia hemprichii, and Kappaphycus alvarezii). The power function equation, M=KWb fitted well with the weight-specific egestion rates ((r2=0·93), weight-specific CO2 respiration rates (r2=0·92) and ammonium excretion rates (r2=0·86). Weight-specific egestion rates, CO2 respiration and ammonium excretion were indirectly proportional to body weight. For weight-specific egestion rate (in μg DW faeces/g DW urchin-h), the regression coefficient, b and constant, K were −2·31±0·68 (mean±SE) (P=0·02) and 6359·55±5394·31 (P=0·29), respectively. The b and K for CO2 respiration were −1·28±0·48 (P=0·04) and 39·72±10·59 (P=0·01), respectively. For ammonium excretion, the b and K were −1·03±0·46 (P=0·11) and 262·51±56·89 (P=0·02), respectively.

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