How much is enough? Adequate sample size for littoral macroinvertebrates in lowland lakes

Abstract

Littoral macroinvertebrates are increasingly used for assessing the ecological status of lakes according to the EU Water Framework Directive. This requires harmonised sampling methods, but information on the appropriate spatial scale of the sampling as well as on the adequate sample sizes are mostly lacking. In this study, we compared the spatial variability of littoral (\1.2 m water depth) macroinvertebrate community composition within habitats and within sites to test whether habitat-specific sampling can reduce their spatial variability. Furthermore, we determined the sample size necessary to obtain maximum species richness for a given habitat type. Spatial variability of macroinvertebrate community composition was significantly lower within habitats than within sampling sites, except for communities of coarse woody debris. Species-area curves revealed that a sample size of 1 m 2 per habitat was not sufficient to obtain the maximum species richness due to the dominance of rare species, which suggests that compilation of taxon inventories may require more exhaustive sampling with sampling sizes substantially larger than 1 m 2 . Separate analysis for species assigned to incidence classes showed that a mean area of 0.63 m 2 per habitat is sufficient to record all species with frequent and medium incidences, and 76% of the rare species. We conclude that habitat-specific sampling is an effective way to reduce the inherent spatial variability of littoral macroinvertebrate communities and that a sample size of 0.63 m 2 per habitat is sufficient to represent their dominant and subdominant elements. The application of this adequate sample size to other lake types than large oligotrophic lakes has to be exercised with caution, in particular if community composition and richness patterns differ. However, our results are based on data from lakes that represent the typical lake type found throughout the Central Baltic ecoregion ensuring its wider applicability in this ecoregion.

Efficient sampling methodologies for lake littoral invertebrates in compliance with the European Water Framework Directive

“…We were able to corroborate the results from our pilot study (Porst et al, 2012) and to demonstrate that the results apply for a wide range of the EU WFD and is in accordance with our preliminary study comparing different sampling methodologies at Lake Werbellin, Germany (Porst et al, 2012). In contrast, Schreiber and Brauns (2010) found variability within habitat-specific macroinvertebrate samples to differ considerably from that of pooled composite samples. The latter study, however, did not account for respective proportional availabilities of individual habitats at each macroinvertebrate sampling location giving each habitat sample equal weight in the computation of artificial pooled samples.…”

“…While the stratified sampling regime might improve signal precision by reducing variability within macroinvertebrate samples, the collection of pooled composite macroinvertebrate samples could, thus, offer an alternative time-and costeffective sampling strategy for routine lake monitoring. So far only a limited number of studies focusing on only a few large oligotrophic and mesotrophic lakes in the Central Baltic region (Schreiber & Brauns, 2010;Porst et al, 2012) and one Mediterranean riverine lake (Mastrantuono et al, in press) have compared the efficiency of habitat-specific and composite sampling techniques for routine assessment of lakes. The suitability of the latter method for routine monitoring purposes has, however, not yet been quantified across a gradient of European lake types.…”

Morphological alterations of lake shores in Europe: A multimetric ecological assessment approach using benthic macroinvertebrates

“…Habitat-specific samples with an area of 1 m 2 each were taken, considering that this area size will be sufficiently large to comprise most of the species present (Schreiber and Brauns, 2010). Three habitat specific samples were taken at all sampling sites and lakes in each country (but see above regarding the sampling scheme).…”

Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes

“…The total sampled area was chosen to capture most of the species occurring at a given habitat, as evaluated at other lowland lakes in northern Germany (Schreiber & Brauns, 2010). An area of 0.14 m 2 was sampled using an Ekman grab in deeper areas.…”

“…An area of 0.14 m 2 was sampled using an Ekman grab in deeper areas. The total sampled area was chosen to capture most of the species occurring at a given habitat, as evaluated at other lowland lakes in northern Germany (Schreiber & Brauns, 2010). The annual production (P, g DW m À2 growing per season) of macrozoobenthos in the three depths was estimated using the allometry-based approach of Plante and Downing (1989), as described in Mehner et al (2016):…”