Effect of upper beach macrofauna on nutrient cycling of sandy beaches: metabolic rates during wrack decay

Abstract

Sandy beaches constitute a dynamic interface between marine and terrestrial environments, where inflows of organic matter occur mainly in the form of beach-cast wrack. Decomposition and processing of these inputs stand out as central components of ecosystem functioning and the biogeochemical processes associated with nutrient and carbon cycling. To investigate the effect of upper-beach macrofauna on wrack decomposition and carbon cycling, a manipulative experiment was carried out on Ladeira beach (42°34.33″N; 9°3.16″W—NW Spain) and ran for 43 days from 1 June 2011, where wrack decomposition rates and metabolism in the presence or absence of invertebrate macrofauna were assessed. The results showed that activities carried out by macrofauna inhabiting the upper beach are relevant in the decomposition of wrack deposits. Both the weight losses and the degradation rates were significantly higher in treatments with macrofauna access. CO2 fluxes measured throughout the experiment showed that wrack patches act as ‘hot spots’ of biogeochemical activity, supporting higher metabolic rates with maximum values of CO2 flux recorded in this study ~ 12 µmol C m−2 s−1. Microbial activity was estimated as being the main contributor to the respiration measured during wrack decay, but fragmentation and activities carried out by the macrofauna had significant effects on the mass loss, degradation rates and carbon fluxes associated with wrack decay process.