Polychaetes provide an excellent food resource for fi sh 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-specifi c metabolic rates, based on aerobic respiration（ R）, were measured at 16℃（±0.2℃） and classed as either routine（ RR） or standard（ RS） 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 RR and RS, respectively. Diurnal changes in RS for each group was relatively flat, with a slightly increasing trend with time, but was relatively stable as a whole. RR of the diurnal variation of worms was higher than RS, but both had similar overall trends. The peak values of specifi c dynamic action（SDA）（ RSDA） 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.
The infaunal polychaete Perinereis aibuhitensis Grube,distributed widely along Asian coasts and estuaries,is considered a useful animal model in ecotoxicological tests and a promising candidate in biomonitoring programs.This paper deals with the activities of antioxidant enzymes including superoxide dismutase(SOD),catalase(CAT),and glutathione peroxidases(GSH-Px) in infaunal polychaete P.aibuhitensis exposed to a series of sublethal water-bound cadmium(Cd) concentrations(0,0.34,1.72,3.44,6.89,and 17.22 mg L-1) under a short-term exposure(1-8 d).The results indicate that the SOD and GSH-Px activities in P.aibuhitensis are stimulated first and then renewed to the original level.The CAT activity of worms decreases at an earlier exposure time but increases to the control values at a later exposure time.Our study suggests that Cd can interfere with the antioxidant defense system of P.aibuhitensis.However,the changes in antioxidant enzyme activities for this species do not show the best promise as biomarkers in Cd biomonitoring of estuarine and coastal zones because weak or non-dose-effect relationships between the antioxidant enzymes activities and Cd levels are found.
