Verification of a benthic boxcosm system with potential for extrapolating experimental results to the field

A marine mesocosm system (boxcosm system) was developed for ecological and/or ecotoxicological studies of sediment community function and structure. The system consists of continuous flow-through incubations of intact sediment samples, each with a surface area of 0.25 m². The experimental setup enables repeated non-destructive measurements of benthic fluxes, such as of nutrients, oxygen and dissolved inorganic carbon, over the sediment-water interface. The benthic fluxes reflect the function of the sediment community, integrating over the chemical, biological and physical activities in the sediment. The suitability of the boxcosm system for controlled, highly ecologically relevant studies of intact sediment communities was evaluated in two experiments of six weeks and five months duration respectively, where the functional and structural development over time was compared to the development of the sampling site. The function of the sediment was measured as nutrient and oxygen fluxes, and the structural component consisted of microbial functional diversity and meio- and macrofauna composition. Differences between the boxcosm and the sampling site were detected especially in nitrate fluxes and meiofauna diversity and abundance, but all differences fell within seasonal and inter-annual variability at the sampling site. The cause of the differences could be referred to differences in oxygen availability, supply of organic matter particles, and recruitment of larvae. These factors can however be compensated for within the present setup. The study shows that the boxcosms are suitable tools for ecologically relevant studies generating comparable conditions to the natural environment.