Influence of substratum on the variability of benthic biofilm stable isotope signatures: implications for energy flow to a primary consumer

Abstract

Benthic biofilms have been identified using stable isotope analysis (SIA) as an important resource supporting many freshwater food webs. However, biofilm d 13 C signatures are highly variable in freshwaters, which may hamper our understanding of energy flow through food webs in these systems. There has been little consideration of the influence that substratum may have on biofilm d 13 C signature variability and energy flows to primary consumers. We investigated the effect of organic and inorganic substrata on biofilm dynamics by examining: (1) temporal variability of biofilm stable isotope (d 13 C, d 15 N) signatures on allochthonous leaf-litter (Eucalyptus camaldulensis) and cobble substrata over 12 months in a lowland river in south-eastern Australia; and (2) the effect of substrata on biofilm energy flows to a grazer snail, Physa acuta (Gastropoda: Physidae), using SIA and ecological stoichiometry in a laboratory experiment. The temporal study indicated that cobble biofilm varied significantly in d 13 C signature during the 12 months (up to 11%), whereas the d 13 C signature of leaf biofilm was less variable (less than 2%). In contrast, biofilm d 15 N signatures varied temporally on both cobble (2.6%) and leaf (1%) substrata. This suggests that leaf biofilm was more reliant on leaf tissue for carbon and therefore less limited by carbon supply than cobble biofilm whereas for nitrogen biofilm on both substrata was reliant on external sources. In the laboratory experiment, snails fed leaf biofilm reflected more of an allochthonous d 13 C signature than cobble biofilm fed snails, suggesting assimilation of leaf carbon via the heterotrophic microbial community within the biofilm. Snails grew largest on cobble biofilm, which had lower C:N ratios than leaf biofilm. Our results demonstrate that the type of substratum can influence the temporal variability of biofilm d 13 C signatures and energy flow to primary consumers.

Fungal diversity of marine biofilms on artificial reefs in the north-central Gulf of Mexico

“…Variations in substrate composition can have a substantial influence on the biofilm community and subsequent benthic assemblages (Rahim et al 2004, Hladyz et al 2011. Katrina Reef was composed of limestone, Handkerchief Reef was composed of crushed concrete bridge materials, Legacy Reef was made of limestone rubble, and USM Reef was composed of limestone rock and oyster shells.…”

“…barnacles, mussels (see Rahim et al 2004, Burt et al 2009, Granneman and Steele 2015] which, over time, influence the diversity of a mature artificial reef's fauna. Hladyz et al (2011) reported that substrate composition is a crucial factor in marine biofilm development and later growth of the artificial reef; substrate differences revealed by stable isotope analysis have an effect on energy flow to primary consumers in aquatic food webs. Biofilm microbial communities are important in the production and decomposition of organic matter and in the cycling of limiting nutrients (Mouton et al 2012).…”

Tracing carbon sources in small urbanising streams: catchment‐scale stormwater drainage overwhelms the effects of reach‐scale riparian vegetation

“…We also collected epilithic biofilms, although given the diverse range of primary organic matter sources within biofilms and their potential to affect isotopic signatures (Hladyz et al, 2011), we classified biofilms as a mixture for the purpose of tracing primary organic matter sources. At each study reach, we sampled all visually abundant terrestrial organic matter sources along a 100 m length of stream, including soil, grasses, shrubs and trees.…”

Understanding and Overcoming Baseline Isotopic Variability in Running Waters

“…rocks) (Sabater et al, 1998). These heterotrophs may use the substrate directly as a carbon source, leading to a d 13 C value that resembles the substrate rather than the algae (Walters et al, 2007;Hladyz et al, 2011). One solution to this problem is a technique for purifying algae that employs colloidal silica to create a density gradient (Hamilton et al, , 2005, allowing the denser detritus to settle to the bottom of a collection tube during centrifugation.…”