THE ALLOMETRY OF DEPOSIT FEEDING INCAPITELLASPECIES I (POLYCHAETA:CAPITELLIDAE): THE ROLE OF TEMPERATURE AND PELLET WEIGHT IN THE CONTROL OF EGESTION

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Abstract
This study investigates the relationships between egestion rate, body size, and environmental temperature in the opportunistic marine polychaete Capitella species I. Measurements were made of (1) fecal pellet weight, (2) pellet production rate, and (3) pellet standing stock within the gut of live worms. Egestion rate experiments were conducted with worms ranging in size from 0.27 mm3 to 2.62 mm3 (approx. 1.0-15 mm in length). Pellet production rate measurements were made at 15.degree., 20.degree., and 25%C. Individual fecal pellet weight was related to worm body volume to the 0.70 power. Fecal pellet production rate in Capitella sp. I was independent of body size. The number of pellets maintained on average within the guts of larger animals is at least equal to that of smaller animals. Fecal pellet production rate increased exponentially with increasing temperature between 15.degree.C and 25.degree.C, with an overall Q10 value of 2.49. Power functions relating changes in egestion rate (.mu.g sediment h-1) and size-specific egestion rate [.mu.g dry weight sediment (mm3 worm)-1 h-1] to body size were fit to the data. These curves show that egestion rate scales as body volume to the 0.70 power, indicating that larger Capitella sp. I specimens process relatively less sediment per unit body volume than smaller worms. Capitella sp. I individuals thus control sediment processing rate during ontogeny by reducing the relative pellet weight as they grow. Estimates of the scaling of external surface area in Capitella sp. I show that surface area scales as worm size to the 0.77 power, paralleling the scaling of feeding rate to body size. Date on oxygen uptake rates at different temperatures for Capitella sp. I (Cammen, 1985) are re-examined in light of our results and the implications for a coherent metabolic strategy (senu Newell, 1980) are discussed. We hypothesize that a physiological surface such as the external respiratory surface or the absorptive area of the gut surface may limit growth and anabolism in Capitella species I.