Isotopic evidence and consequences of the role of microbes in macroalgae detritus-based food webs

Abstract

ABSTRACT: Deep subtidal coastal food webs are increasingly a focus among coastal researchers, largely due to the reliance of these systems on subsidies of organic detritus donated from allochthonous sources. To better understand the dynamics of these food webs, researchers have frequently employed multiple stable isotope (MSI; δ13C, δ15N, δ34S) analysis to gain insights into the relative importance and origins of various sources of detritus. However, the role of microbial decomposition in these detritus-based food webs has been poorly quantified and frequently overlooked in MSI food web mixing models. In this study, we explicitly examined the ecological and MSI methodological effects of microbial decomposition of algal detritus. We found a relationship between δ15N enrichment and microbial abundance on decomposing kelp blades, and evidence that this pattern is influenced by the underlying biochemistry of the kelp. C:N ratios supported the hypothesis that microbial biofilms utilize nitrogen from kelp detritus, rather than augment the detrital nitrogen content. The results also showed that microbial effects can introduce a nonnegligible amount of error to MSI mixing models if left unquantified.© Inter-Research 2013. www.int-res.com.