High metabolism and periodic hypoxia associated with drifting macrophyte detritus in the shallow subtidal Baltic Sea

Macrophytes form highly productive habitats that export a substantial proportion of their primary production as particulate organic matter. As the detritus drifts with currents and accumulates in seafloor depressions, it constitutes organic enrichment and can deteriorate O2 conditions on the seafloor. In this study, we investigate the O2 dynamics and macrobenthic biodiversity associated with a shallow ∼ 2300 m2 macrophyte detritus field in the northern Baltic Sea. The detritus, primarily Fucus vesiculosus fragments, had a biomass of ∼ 1700 g dry weight m−2, approximately 1.5 times larger than nearby intact F. vesiculosus canopies. A vertical array of O2 sensors placed within the detritus documented that hypoxia ([O2]