Ontogenetic changes in individual growth and egestion rates in the deposit-feeding polychaete Capitella sp. 1

Abstract

Repeated measurements of individual worms over a 28-d period were used to calculated volumespecific growth (G) and egestion rates at a high, constant food ration (> 1000 mg N · m −2 · d −1). Worm sizes ranged from 0.1–9.0 mm 3 body volume ( BV) (≈20–1600 μg dry weight ( DW)), 1.8–18.7 mm live body length). The relationship between G and BV was highly variable but displayed a plateau at sizes between 0.5–3.5 mm 3 (120–830 μg D W) where G remained in the range of 18–20% · d −1. In contrast to predictions of empirical growth models, G did not show a monotonie decrease with increasing worm volume. Individual volume-specific egestion rates ( V er = mm 3 sediment egested · (mm 3 worm) −1 · d −1) showed an analogous but less broad peak at ≈2 mm 3 B V, suggesting a functional coupling between specific egestion and growth rates. No relationships were found between G and sex or G and body size. G was also independent of the total volume or mass of sediment processed for time lags of up to 28 d. G increased linearly as a function of V er up to specific egestion rates of 2.7 mm 3 sediment egested · (mm 3 worm) −1d −1. With further increases in V er , growth rates remained constant at 25% ·d −1. BV was positively related to cumulative egestion (mm 3 sediment egested) with an average female reaching sexual maturity after egestion of ≈ 20 mm 3 of sediment. Increased variability in measurements of gross individual production efficiency for the smallest animals ( GPE = G · (mm 3 sediment egested) −1 · 100) suggests that the efficiency of energy transfer from ingested food to tissue in smaller worms ⩽ 1 mm 3) may be much more sensitive to environmental or physiological influences. Smaller worms experience both greater growth and degrowth per unit egested sediment than larger worms. The increased variability of GPE in smaller animals may be due to a lack of stored energy reserves in combination with the interaction between absolute body size and the scale of distribution of the sedimentary food resource.