The importance of size-dependent physiological processes in the ecology of the deposit-feeding polychaete Capitella species I

The ontogenetic scaling of egestion rate in Capitella sp. I is controlled through the interaction of several factors. They are: (1) the allometry of fecal pellet production rate, (2) relative fecal pellet volume as a function of body size, (3) the allometry of gut fullness. Gut fullness (# pellets {dollar}cdot{dollar} gut{dollar}sp{lcub}-1{rcub}{dollar}) is functionally related to worm length and fecal pellets are added to gut standing stocks as length increases allow. Discrete breaks in the observed scaling relationships are common and not reflected in obvious morphological discontinuities.; Worms lose 8% to 9% of their total carbon content {dollar}cdot{dollar} d{dollar}sp{lcub}-1{rcub}{dollar} at 24{dollar}spcirc{dollar}C. Particulate carbon losses amount to 46% whereas 54% is lost in dissolved form. Dissolved and total carbon losses scale as body volume to a power less than one, while particulate losses scale as body volume to the first power. Total carbon loss is thus relatively greater in smaller worms. Worms starving without sediment decrease their volume-specific loss rate of body tissue to 4%-5% {dollar}cdot rm dsp{lcub}-1{rcub}{dollar} and it is suggested that feeding costs (ingestion, digestion, defecation) are very low with respect to the other costs associated with a burrowing, infaunal existence.; Specific growth rate (G) of individual worms averaged 15% {dollar}cdot rm dsp{lcub}-1{rcub}{dollar} and were independent of body size and sex. G was also independent of the total volume of sediment processed for time lags of up to 28 d. Smaller worms experience both greater growth and degrowth per unit sediment processed than larger worms. This greater growth response in smaller animals is may be due to the lack of stored energy reserves and greater metabolic potential in combination with the effects of absolute body size on scales of resource distribution and availability.; Reduction of pO{dollar}sb2{dollar} and/or food level decreased G in both large and small worms. At high food levels a reduction in pO{dollar}sb2{dollar} exposure from 128 to 37 mmHg decreased growth rates of large and small animals by 27% and 24% {dollar}cdot rm dsp{lcub}-1{rcub}{dollar} respectively. Growth of large worms decreased in response to reductions in both pO{dollar}sb2{dollar} and food level. Growth of small worms decreased only in response to reductions in ambient pO{dollar}sb2{dollar} levels.; A reduction in O{dollar}sb2{dollar} tension from 37 to 20 mmHg decreased the growth of large worms from 1.78% to {dollar}-{dollar}25.08% {dollar}cdot rm dsp{lcub}-1{rcub}{dollar}. The growth rates of small individuals were unaffected. It is predicted that under conditions of near-bottom anoxia or food limitation populations of Capitella sp. I will experience size-dependent growth with large, reproductively mature animals suffering the greatest decline in growth rates.