Effects of two polychaete worms, Nereis diversicolor and Arenicola marina,on aerobic and anaerobic decomposition in a sandy marine sediment

The effects of 2 polychaete species, Nereis diversicolor and Arenicola mari na, on benthic metabolism and decomposition processes in organic-poor (0.06 % POC), sandy sediment were experimentally investigated. Sediment O-2 upta ke and COP release were stimulated by 80 to 90 % and 260 to 270 % for N. di versicolor and A. marina, respectively, from basal rates of approximately 3 0 mmol m(-2) d(-1). These enhancements in benthic fluxes were due to both i ncreased solute exchange due to macrofauna irrigation and increases in tota l benthic metabolism. Although the latter was enhanced by 10 to 35 % and 11 5 to 123 % by N, diversicolor and A, marina, respectively, both species inh ibited anaerobic decomposition as indicated by 66 and 42 % lower sulfate re duction rates. Benthic fluxes and basal rates of benthic metabolism (withou t macrofauna) were 2 to 3 times higher in sediments enriched with organic m atter compared to unamended sediments. Similarly, sulfate reduction rates w ere 3 times higher in enriched sediments. Total benthic metabolism in enric hed sediments was stimulated by N. diversicolor to a similar extent (+ 27 t o 34 %) as in unamended sediments, whereas A. marina stimulated total benth ic metabolism to a slightly lesser extent (+43 to 55%) in enriched sediment s than in unamended sediments. N. diversicolor had little effect on sulfate reduction (-4 %) in enriched sediments, while A, marina reduced sulfate re duction by 85 % in enriched sediments. Porewater profiles reflected the bal ance between stimulating effects on sediment decomposition processes and re moval of porewater solutes by benthic macrofauna. Porewater and sediment pr ofiles of reduced S compounds also showed the effects of these polychaetes on sedimentary S cycling, i.e, lower anaerobic decomposition and increased reoxidation of reduced compounds. Both species affected sediment element cy cles, stimulating C cycling and favoring more oxidized species and processe s in S cycling. Furthermore, both species affected the fate and distributio n of the metabolites produced from decomposition by enhancing the exchange of solutes across the sediment-water interface and porewater flushing. In g eneral, the biogeochemical impact of A. marina was greater than that of N. diversicolor.