At two intertidal sites (one sandy and one silty, in the Scheldt estuary, The Netherlands), the fate of microphytobenthos was studied through an in situ ¹³C puls‐chase experiment. Label was added at the beginning of low tide, and uptake of ¹³C by algae was linear during the whole period of tidal exposure (about 27 mg m⁻² h⁻¹ in the top millimeter at both sites). The ¹³C fixed by microphytobenthos was rapidly displaced toward deeper sediment layers (down to 6 cm), in particular at the dynamic, sandy site. The residence times of microphytobenthos with respect to external losses (resuspension and respiration) were about 2.4 and 5.6 d at the sandy and silty stations, respectively. The transfer of carbon from microphytobenthos to benthic consumers was estimated from the appearance of ¹³C in bacterial biomarkers, handpicked nematodes, and macrofauna. The incorporation of ¹³C into bacterial biomass was quantified by carbon isotope analysis of polar lipid derived fatty acids specific for bacteria. The bacterial polar lipid‐derived fatty acids (i14:0, i15:0, a15:0, i16:0, and 18:1ω7c) showed rapid, significant transfer from benthic algae to bacteria with maximum labeling after 1 d. Nematodes became enriched after 1 h, and ¹³C assimilation increased until day 3. Microphytobenthos carbon entered all heterotrophic components in proportion to heterotrophic biomass distribution (bacteria > macrofauna > meiofauna). Our results indicate a central role for microphytobenthos in moderating carbon flow in coastal sediments.

Examination of amino acids in particulate samples from a variety of marine environments (fresh phytoplankton to deep‐sea sediments) revealed systematic compositional changes upon progressive degradation. These consistent trends have been used to derive a quantitative degradation index (DI) that is directly related to the reactivity of the organic material, as indicated by its lability to enzymatic decay and its first‐order degradation rate constant. This direct link between molecular composition and degradation rate allows us to quantify the quality of organic matter based solely on its chemical composition.

Biologically mediated modifications of the abiotic environment, also called ecosystem engineering, can significantly affect a broad range of ecosystems. Nevertheless, remarkably little work has focus...

Physical processes limiting colonization of bare tidal flats by pioneer mangrove species have commonly been described but not yet quantified. Understanding thresholds to early seedling establishment is critical for successful restoration and management of mangrove forests. We determined how seedling establishment of Avicennia alba Bl. is affected by the combination of increasing hydrodynamic forces and sediment dynamics. As the buoyant propagules of A. alba are dispersed by water, early establishment on bare tidal flats requires propagules to quickly anchor to stay in place. Flume studies and field observations showed that 3 thresholds have to be passed until the seedling is successfully established: (1) stranded propagules need an inundation-free period to rapidly develop roots that are long enough to withstand displacement by flooding, (2) roots need to become long enough to withstand seedling dislodgement by hydrodynamic forces from waves and currents, with the required root length being proportional to the force that needs to be resisted, (3) even longer roots are needed to survive high energy events that cause sheet erosion and can thereby induce seedling dislodgement. This sequence of thresholds implies that establishment of the pioneer mangrove species A. alba requires a suitable window of opportunity to pass all thresholds and underlines the importance of rapid root expansion as a crucial pioneer trait for the species