The contrasting effects of the invasive Marenzelleria viridis and the native Nereis diversicolor on benthic metabolism, partitioning of reaction pathways and distribution of inorganic porewater (C and N) solutes in homogenized sandy sediment were investigated experimentally over a period of 1 mo. The 2 species were studied separately and in combination to observe possible effects
and interactions. Benthic O2 uptake and total CO2 (TCO2) release were affected similarly byM. viridis, N. diversicolor and the two in combination, with roughly a doubling after 1 to 2 wk comparedto defaunated sediment. Sulfate reduction after 1 mo, on the other hand, was more than twiceas high in sediment inhabited by M. viridis alone than in any other treatment, even when combinedwith N. diversicolor. Denitrification estimated from benthic TCO2 release, porewater reaction stoichiometryand nutrient fluxes was largely unaffected by the presence of fauna. Accordingly, the partitioningof reaction pathways after 1 mo revealed that M. viridis stimulated sulfate reduction at theexpense of aerobic respiration. Most of the oxygen uptake in M. viridis sediment was apparently dueto enhanced oxidation resulting from an upward drifting front of sulfide as indicated by low redoxand the appearance of Beggiatoa sp. near the surface. Porewater solute profiles showed that M.viridis was capable of stronger and deeper irrigation than N. diversicolor despite ~10 times higherburrow ventilation by the latter species. This effect was caused by percolation of return water in thedeep (>20 cm) I- or J-shaped burrows of M. viridis compared to the flushing of the more shallow (6 to
8 cm) U- shaped burrows of N. diversicolor. A replacement of the native N. diversicolor with the invasiveM. viridis as the dominant burrow-dwelling polychaete in shallow coastal sediments will probablyaffect the biogeochemical functioning and ecological stability of the ecosystem. Among otherthings, organisms tolerant to sulfide are likely to be favored at the expense of more sensitive species.
- invasiv art