Diel variation in metabolism and ammonia excretion of Marphysa sanguinea (Polychaeta: Eunicidae)

Polychaetes provide an excellent food resource for fish and represent the dominant zoobenthos in marine ecosystems. Diel variation in the rates of metabolism and ammonia-N excretion of Marphysa sanguinea were studied. The worms were grouped according to their wet body weight into small (S; 1.24±0.06 g), medium (M; 4.00±0.30 g), and large (L; 8.54±1.08 g) categories. Their weight-specific metabolic rates, based on aerobic respiration ( R ), were measured at 16°C (±0.2°C) and classed as either routine ( R R ) or standard ( R S ) rates. Both respiration types decreased with increasing body weight. Respiration was described by R = a W b , where b was -0.400 9 and -0.532 0 for R R and R S , respectively. Diurnal changes in R S for each group was relatively flat, with a slightly increasing trend with time, but was relatively stable as a whole. R R of the diurnal variation of worms was higher than R S, but both had similar overall trends. The peak values of specific dynamic action (SDA) ( R SDA ) in the S, M, and L groups were 2.704, 1.149, and 0.682 mg/(g∙h), respectively. The durations of SDA were 13, 6, and 6 h, respectively and the energy expenditures of SDA were 377.98, 117.34, and 74.94 J/g, respectively. These data indicate that the metabolic rates were higher in smaller individuals, which is advantageous for their rapid growth.