Impact of the burrow-dwelling polychaete Nereis diversicolor on the degradation of fresh and aged macroalgal detritus in a coastal marine sediment

Abstract

Impacts of the irrigating and detritus-feeding polychaete Nereis diversicolor on degradation of fresh and aged 14 C labeled Fucus serratus detritus deposited into sandy marine sediment were examined in microcosm experiments. The fate of detritus deposited at the surface or buried 3 cm into the sediment was followed over a period of 18 d. Fluxes of solutes (total labeled CO 2 [T 14 CO 2 ] and labeled dissolved organic carbon [DO 14 C]) across the sediment-water interface in the absence and presence of N. diversicolor were compared to changes in pool size and distribution of these solutes and labeled particulate carbon (PO 14 C) within the sediment. The results showed that fresh detritus at the surface of defaunated sediment was degraded twice as fast as aged detritus (k POC = 18 x 10 -3 and 8 x 10 -3 d -1 , respectively, where k is the decay constant). N. diversicolor increased the surface PO 14 C decay by 35 and 90% for fresh and aged detritus, respectively. Competition for food between N. diversicolor and microorganisms reduced the microbial degradation of fresh detritus at the surface by 20 % compared with defaunated sediment. Enhanced microbial degradability after passage through the gut of N. diversicolor was probably responsible for a 20 % increase in microbial decay of surface-deposited aged detritus in faunated compared to defaunated sediment. The decay of subsurface-deposited fresh and aged detritus in defaunated sediment (k POC = 10 x 10 -3 and 3 x 10 -3 d -1 , respectively) was ca. half of that for surface-deposited detritus. Activities of N. diversicolor (irrigation and feeding) increased the degradation of buried PO 14 C by 160 and 270 % for fresh and aged detritus, respectively. The irrigation-associated stimulation of microbial decomposition by injection of oxygen into and removal of toxic metabolites from sediment was 90 and 300% for fresh and aged detritus, respectively. The several-fold enhancement of microbial decay of aged subsurface detritus substantiates the importance of burrow irrigation and oxygenation for degradation of otherwise refractory detritus in sediments. In the absence of irrigated burrows, a larger fraction of partly degraded detritus may remain undegraded and be buried permanently in the sediments.