Effects of benthic macrofauna and temperature on degradation of macroalgal detritus: The fate of organic carbon

The combined effects of bioturbation by the polychaete Nereis diversicolor and temperature (4°, 8°, 16°C) on diagenesis of short‐term (48 h) 14 C‐labeled Chondrus crispus (new) detritus added to organic‐poor sandy sediment were examined over 20 d. The overall rate of weight‐specific CO 2 production was 5 times higher for C. crispus detritus than for indigenous (old) sediment detritus. N. diversicolor increased sediment O 2 uptake and total CO 2 production by 30–70%; most of this increase was due to worm respiration. Net release of 14 CO 2 was not affected by the worms; microbial 14 CO 2 production was reduced 30%, indicating competitive interaction between worms and bacteria. The activities of N. diversicolor removed 20–50% more of the particulate 14 C label in bioturbated sediment than in defaunated. All of this excess loss was recovered in worm tissues. The increase in total CO 2 production, but not 14 CO 2 production, in the presence of N. diversicolor indicated that bioturbation affected the net mineralization of relatively refractory (old) organic matter more than it affected the labile (new) pools. The temperature dependence of carbon diagenesis was not affected significantly by the worms. The microbial component of total benthic metabolism increased more with temperature (activation energy, E = 53–59 kJ mol −1 ) than worm respiration did ( E = 29 kJ mol −1 ).