Contribution of biofilm to ecosystem functioning in rock pools with different macroalgal assemblages

Abstract

Research into the role of biodiversity in the functioning of rocky shore ecosystems has ignored the microscopic component of the biota, in particular the microbial films coating most marine surfaces. Yet in other habitats, biofilms are known to be major contributors to ecosystem functioning. The objective of the present study was thus to understand the contribution of epilithic biofilms to rock pool metabolism (oxygen fluxes) and to identify whether this varies under different macroalgal assemblages. A 2-way factorial experiment was run in artificial rock pools on a moderately exposed rocky shore, combining different macroalgal treatments with the presence/ absence of biofilm. Biofilm made significant contributions to rock pool community primary productivity and rock pool residual respiration (rock pool metabolism measured without the macroalgal treatment), independently of the composition of the overlying macroalgal treatment. In rock pools with no macroalgae, biofilm appeared to dominate community metabolism, while the planktonic community was a minor contributor. There was no evidence of any significant effect of the different macroalgal assemblages tested on the metabolism of the biofilm. The presence of both Mastocarpus stellatus and Fucus serratus in pools, however, resulted in a lower photosynthetic activity of the biofilm than any of the other macroalgal treatments. Our results suggest that biofilm is a compartment that contributes significantly to the functioning of rock pool ecosystems, whether in terms of its heterotrophic or autotrophic activity, and should thus be taken into account in future research on these ecosystems. © Inter-Research 2013.