Sieving alive or after fixation: effects of sieving procedure on macrobenthic diversity, density and community structure

Abstract

Although combining datasets is often needed to unravel large-scale or long-term patterns in benthos ecology, this is frequently hampered by diVerences in technical design of the individual studies. One element that often vary among macrobenthic studies is the sieving procedure: sieving alive versus sieving after Wxation. This study therefore aimed at the qualiWcation and quantiWcation of the impact of sieving procedure, using a 1 mm mesh sized sieve, at three levels of ecological organisation: (1) diversity, (2) species and taxon density, and (3) community structure. To include a maximum suite of macrobenthic species and to evaluate the community-speciWc eVects, the impact of sieving procedure was investigated within four widely spread macrobenthos communities in the Belgian part of the North Sea. Sieving alive negatively impacted all tested diversity measures (S, N 1 , N 2 , N 1 , HЈ, ES 100 and JЈ): community-dependent relative losses of up to 35% were observed. However, most trends were ambiguous and statistically non-signiWcant. Community-and taxon-dependent impacts were detected at the level of density. Mainly polychaetes were found to be negatively impacted by sieving alive (relative losses maximum 81%): especially small, interstitial polychaetes (e.g. Hesionura elongata and Spio Wlicornis) tend to actively escape from the sieve (relative loss up to 100%). Next to size, also behaviour, the presence of head appendages, the depth of the sampling stations and sampling season are believed to inXuence the sieving procedure impact. While detailed community composition was impacted (ANOSIM dissimilarity: maximum 85%), no major impact on the diVerentiation between the investigated communities was detected. The present study thus demonstrated that combining data, retrieved with a diVerent sieving procedure can be useful, but its reliability will mainly depend on the type of questions one wants to answer. In all cases caution at all levels of ecological organisation is advised.

Methodological elements for optimising the spatial monitoring design to support regional benthic ecosystem assessments

“…At the same time, agreeing on integrated and harmonised monitoring protocols (cf. ISO 16665 norm; Kingston and Riddle 1989;Lampadariou et al 2005;Degraer et al 2007;Rumohr 2009) before undertaking monitoring will lead to regional datasets of higher quality. This in turn will reduce the work and costs related to harmonisation or calibration of sampling methodologies (Rees et al 2007;Vanden Berghe et al 2009).…”

Biodiversity Trends along the Western European Margin

“…Another problem to be considered is whether the samples should be fixed in formalin prior to, or after, sieving. Sieving after fixation is thought to lead to i) a reduction in the number of animals lost and ii) more intact specimens [36] ; However, sieving prior to fixation results in smaller quantities of formalin being used and lower sample storage requirements on board ship. A technique that is currently being used by some deep-sea researchers is elutriation.…”