Carbon and nitrogen fluxes in sediment inhabited by suspension-feeding (Nereis diversicolor) and non-suspension-feeding (N-virens) polychaetes

The impact of suspension-feeding Nereis diversicolor and non-suspension-feeding N. virens on C and N dynamics in an organic-poor sediment was investigated in a controlled laboratory study simulating periods of high and low phytoplankton (Rhodomonas sp.) concentration. High phytoplankton concentration resulted in a 30-fold higher deposition (clearance) of particulate C and N to the sediment inhabited by N. diversicolor than to N. virens and defaunated sediment. Concurrently, O-2 consumption and NH4+ + NO3- release were increased by a factor of 3 in sediment with N, diversicolor, but only by a factor of about 1.5 in N. virens and defaunated treatments. Steady-state porewater concentrations of TCO2 and NH4+ decreased exponentially with increasing ventilation activity of nereids. Ventilation activity was highest for suspension-feeding N, diversicolor and lowest for deposit-feeding N, virens, About 30% of the deposited algal C and N in the N, diversicolor sediment were lost rapidly as excess CO2 or NH4+ + NO3- flux to the water column. Incorporation into N, diversicolor tissues accounted for 2/3 Of the retained C and N. In the case of N. virens, where no net phytoplankton deposition occurred, organic matter removal due to mineralization resulted in a net loss of both sedimentary C and N. Accordingly, the biology and behaviour of infaunal species are important determinants for sediment biogeochemistry and element cycling in marine areas.