Examining the diet of meiofauna: a critical review of methodologies

Meiofaunal organisms are diverse, and so is their diet comprising bacteria, fungi, micro-algae, flagellates, ciliates, and other meiofauna. Studies have inferred diet from correlative evidences, observations of feeding or gut contents. Incubation experiments have also helped to link meiofauna's role to microbially mediated ecosystem processes, reporting in most cases beneficial effects on microbial activity. Nevertheless, our knowledge of meiofauna's trophic ecology still lags far behind that of other aquatic fauna (i.e. zooplankton, macroinvertebrates, vertebrates), probably because the small-size and the cryptic nature of the meiofauna becomes an issue when it comes to detect their isotopic or lipid composition. Here, we provide a critical review of diverse methodologies used while examining meiofaunal diets. Observation of feeding, incubation experiments, gut content analyses, calorimetry, stable isotopic and fatty acid analyses are very helpful and some modifications of standard materials and methods can help reduce the time-consuming sorting of individuals. Other analytic tools used by microbial ecologists like compound-specific stable isotopic analysis, DNA-stable isotopic probing, confocal laser scanning microscopy, coherent anti-stokes Raman spectrometry and nanoscale secondary ion mass spectrometry have the potential to unravel hidden trophic channels between meiofauna and microbes.