Impact of the invasive polychaete Marenzelleria viridis on the biogeochemistry of sandy marine sediments

Abstract

This study investigated the effects of the invasive polychaete Marenzelleria viridis (Marenzelleria) on the biogeochemistry of sandy marine sediments. A 27-day microcosm experiment was conducted to evaluate net microbial reactions, fluxes and porewater profiles of key solutes under the presence of Marenzelleria in two sediment types; one containing autochthonous organic matter (0.4 %) and another slightly amended with seagrass detritus (Ruppia maritima; 0.5 %). Fluxes of TCO2 and O2 were two- to three-fold increased in the presence of Marenzelleria and were higher in amended (256 mmol m−2 d−1) than in non-amended sediments (117 mmol m−2 d−1). Marenzelleria stimulated carbon degradation and sulfate reduction in both sediment treatments by influencing porewater chemistry and DOC availability. Marenzelleria flushed out inhibitory porewater metabolites (i.e. TCO2, TH2S and NH4 +) while replenishing SO4 2−. Furthermore, sulfate consumption was significantly higher in Marenzelleria sediment (79–87 mmol m−2 d−1) than in defaunated controls (36–50 mmol m−2 d−1), which indicated a 75–92 % lower DOC availability in the former. DOC excreted by Marenzelleria may have sustained 17–32 % of SO4 2− reduction. Lower C:S ratios (1.6–1.7) in Marenzelleria compared to defaunated sediments (2.4–2.8) suggest basic differences in carbon mineralization pathways, with e.g. H2 as a possible substrate for sulfate reduction in the former treatment and higher fermentative TCO2 formation in the latter. No significant stimulatory effect of Marenzelleria was evident for microbial NH4 + production. Total budgets revealed that Marenzelleria increased C mineralization by 50 % in amended sediment, compared to only 9 % in non-amended sediment. This study suggests that the presence of Marenzelleria may lead to a marked stimulation of sulfate reduction and degradation of refractory organic matter. Marenzelleria invasion may therefore have widespread consequences for microbial pathways and organic matter processing in sandy marine sediments.