Describing macrofaunal impact on nutrient flux – what is the potential of trait based approaches?

Ever-expanding human activities on land and at sea have amplified the need for easily applicable proxies to effectively predict human mediated changes in ecosystem functioning and biogeochemical cycling. Here we investigate the ability of different proxies to predict macrofaunal impact on nutrient fluxes of ammonium, nitrate, nitrite, silicate and phosphate under different environmental conditions. As proxies we chose simple community descriptors (i.e. density, wet biomass, ash free dry mass) as well as two trait-based indices that were created to describe macrofauna-sediment interactions (i.e. community bioturbation potential (BP_c) and community irrigation potential (IP_c)). We hypothesize that trait based indices, will increase the predictability of macrofaunal impact on nutrient fluxes compared the more simple community descriptors. We correlate all proxies with experimental nutrient flux data measured under different environmental conditions using generalized linear models. Generally environmental conditions significantly affected all analysed nutrient fluxes and mostly provided better predictions than any of the proxies for macrofaunal impact by itself. Yet a combination of the proxies and the environmental conditions always increased prediction accuracy. Hereby the irrigation trait based indices enhanced the predictability of the nutrient fluxes of ammonium, nitrate, nitrite, silicate and phosphate most.