Trophic positioning of meiofauna revealed by stable isotopes and food web analyses

Abstract

Abstract. Despite important advances in the ecology of river food webs, the strength and nature of the connection between the meio-and macrofaunal components of the web are still debated. Some unresolved issues are the effects of the inclusion of meiofaunal links and their temporal variations on the overall river food web properties, and the significance of autochthonous and allochthonous material for these components. In the present study, we conducted analyses of gut content of macro-and meiofauna and stable isotope analyses of meiofauna to examine seasonal food webs of a chalk stream. The results of the gut content analyses, confirmed by the δ 13 C signatures, revealed a seasonal shift from a dependence on autochthonous (biofilm) to allochthonous food sources. Here, we demonstrate that aggregating basal or meiofaunal species into single categories affects key web properties such as web size, links, linkage density, and predator-prey ratios. More importantly, seasonal variation in attributes characterized the entire web and these changes persist regardless of taxonomic resolution. Furthermore, our analyses evidenced discrete variations in δ 15 N across the meiofauna community with a trophic structure that confirms gut content analyses, placing the meiofauna high in the food web. We, therefore, conclude that small-body-sized taxa can occur high in dynamic river food webs, questioning assumptions that trophic position increases with body size and that webs are static.

The food web perspective on aquatic biofilms

“…Investigating gut contents and stable isotopic signatures of meiofauna dwelling in a chalk stream, Schmid‐Araya et al. () found that meiofauna occupied unexpectedly high trophic levels for their body size.…”

“…In fact, some microscopic predators possess traits enabling them to feed on prey larger than themselves, for example some amoebae are capable of body distension (Neury-Ormanni et al 2016) and suction-feeding nematodes possess stylets (Traunspurger 1997), so that body size may not necessarily dictate trophic positioning. Investigating gut contents and stable isotopic signatures of meiofauna dwelling in a chalk stream, Schmid-Araya et al (2016) found that meiofauna occupied unexpectedly high trophic levels for their body size.…”

Are meiofauna a standard meal for macroinvertebrates and juvenile fish?

“…Beyond these empirical studies, analysis of stable isotopes and fatty acids are also suitable tools for examining the position of the meiofauna in benthic food webs. Currently, only a few such investigations have been conducted in freshwater habitats (e.g., Schmid-Araya et al, 2016;. Although our knowledge of this trophic interactions has significantly increased over the last 20 years (summarized in Fig.…”

“…Genetically based examinations of the gut contents or feces of consumers are able to identify consumed organisms at a taxonomically high resolution (Pompanon et al, 2012;Tillner et al, 2015). In addition, approaches based on the use of stable isotopes or fatty acids can be applied to investigate trophic pathways, which allows the integration of meiofauna into benthic food webs, as shown by Goedkoop et al (1998) and Schmid-Araya et al (2016) for the meiofauna of streams and lakes. However, most of our knowledge on the role of meiofauna as food for larger organisms has been obtained in classical gut content analyses that were not confirmed in laboratory experiments (model ecosystems/microcosms) or field trials.…”

Predator-prey interactions between the ciliate Blepharisma americanum and toxic (Microcystis spp.) and non-toxic (Chlorella vulgaris, Microcystis sp.) photosynthetic microbes

“…Top-down pressures by grazers are often viewed as not significant due to the morphology, nutritional value and secondary metabolite production of cyanobacteria (Holm & Shapiro 1984, von Elert et al 2003, Wilson et al 2006, Fink et al 2011. Nevertheless, Microcystis are grazed by a number of organisms, including protozoa (Van Wichelen et al 2016); although some specific interactions have been examined (Fyda et al 2009(Fyda et al , 2010, interactions are generally poorly known, especially when toxic cyanobacteria and ciliates are involved (Finlay & Esteban 1998, Esteban et al 2015, with research mainly focussing on crustacean and metazoan grazers (Ger et al 2014, Schmid-Araya et al 2016. Subsequently, ciliate−cyanobacteria trophic relationships stand out as a significant knowledge gap (Ger et al 2016), where further applied ciliate− cyanobacteria research is needed to identify any species-specific interactions relating to their wider ecological function (Sigee et al 1999, Tillmann 2004, Montagnes et al 2008.…”