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The short-term fate of seagrass and macroalgal detritus in Arenicola marina bioturbated sediments

Alexandra C. G. Thomson, Erik Kristensen, Thomas Valdemarsen, Cintia O. Quintana*

*Corresponding author:

ABSTRACT: Seagrass meadows are globally important ecosystems for carbon (C) sequestration. However, bioturbation by benthic fauna can alter the distribution, degradation and overall preservation of C in the sediment. We performed a 4-week laboratory experiment to investigate the short-term degradation and burial of two major C sources in bare sediments associated with seagrass ecosystems. Eelgrass (Zostera marina) and macroalgal (Fucus vesiculosus) detritus were amended in sediment with and without bioturbation by the common polychaete Arenicola marina. Bioturbation did not significantly affect the loss of eelgrass detritus (>0.5 mm), but caused a rapid burial of this material as a discrete layer (55% recovery) at sediment depths ranging from 8 to 14 cm. A. marina effects on macroalgal detritus were more pronounced, resulting in total 80% loss of macroalgal detritus by microbial degradation and worm ingestion. We conclude that A. marina bioturbation effectively buries eelgrass detritus into deep anoxic sediments, but we cannot confirm that this leads to enhanced C-preservation in coastal ecosystems. In contrast, A. marina bioturbation significantly increases the degradation of macroalgal tissue and it is unlikely that this detritus is a major source for permanent C-burial.