Sieve size influence in estimating biomass, abundance and diversity in samples of deep-sea macrobenthos

Abstract

A divergence in sieve size protocols for washing samples has arisen among shallow-and deep-sea benthic biologists, which now affects comparability across the 2 environments. This has come about as a result of a perception of smaller body size among deep-sea benthic organisms. Two box-core samples from ~1900 m depth were examined to see how different sieve size affects estimation of biomass, abundance and diversity of macrofauna in the deep sea. Expressed as cumulative retentions, the coarsest sieve (1 mm mesh) retained 94% of the biomass retained in the finest sieve (0.25 mm), confirming the expectation that rarer, large-sized individuals contribute most to biomass of macrobenthos. There were small increases when progressively finer sieves were used, but the rate of increase declined markedly from 0.425 to 0.25 mm mesh. Numbers of individual organisms increased through the series, with a marked increase from 0.5 to 0.425 mm mesh; numbers of species did not increase as rapidly, but showed a similarly high rate between 0.5 and 0.425 mm mesh. The proportions of the total biomass in coarser sieves, and the total number of specimens retained by the finest sieve were rather similar to those shown in previous studies of inshore and continental shelf benthos. However, the retention of deep-sea species by the 0.5 mm sieve (86%) was about the same as the percentage of inshore species retained by the 1.0 mm sieve (at this sieve size only 54% of deepsea species were retained). Although the finer sieves in both shallow-and deep-sea samples include many postlarval stages, this differing response for species must reflect smaller size of some adult macrobenthos in the deep sea. The effect on diversity depended on index used, with Shannon's index increasing down to the 0.5 mm mesh, but showing a variable response in the finer sieves. This probably mostly reflects increased retention of small-sized juveniles of species already retained, causing increasing unevenness in species abundances with smaller sieve size, rather than addition of smallsized species not previously retained in coarser sieves. Expected numbers of species calculated by rarefaction seems much less affected, with the degree of overlap of rarefaction curves reflecting relative similarity in distribution of species abundances. Degree of overestimation (of expected number of species against number of individuals along the curve) is greatest for the 1 mm mesh, even if the end-points of the curve show decreasing disparity, from 1 to 0.25 mm mesh, in total retention of species as well as individuals. It is argued that, as would apply in shallow water, the great dependence of evenness on sieve size makes shifts in distribution of species abundances caused by disturbance more difficult to detect against the baseline, unless a sufficiently small sieve has been used. When sieve retention was separately considered for the major taxonomic groups of macrobenthos (Polychaeta, Peracarida, Mollusca), differing patterns in relation to sieve size were found in terms of a...

Global bathymetric patterns of standing stock and body size in the deep-sea benthos

“…The macrofauna includes a highly diverse group dominated by polychaete worms, peracarid crustaceans and mollusks. The type of quantitative sampling gear deployed and the sieve mesh size affect estimates of standing stock in the meiofauna and macrofauna (Bett et al 1994, Gage et al 2002. We tested for their potential influence by using partial regression.…”

Biodiversity response to natural gradients of multiple stressors on continental margins

“…North Atlantic) often do not publish associated environmental data. All studies used a sieve size of 0.3 or 0.5 mm, a size that captures the majority of macrofaunal diversity [29] (77 stations used a 0.3 mm sieve and 17 stations used a 0.5 mm sieve). We note that the area of seafloor sampled at each station differs between studies and even within studies (electronic supplementary material, dataset 1), which could differentially affect the accuracy of reported diversity metrics [30].…”

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

“…Gage et al (2002) mentioned that diVerences between sieving a sample alive or after Wxation, might occur in samples from shallow water, where the movement or posture of living animals may aVect the operation of the sieve, but this would not normally occur within deep sea samples because the animals are generally dead by the time they reach the surface.…”

“…This bias in sieving procedure can be largely assigned to the choice between the retention of as much species and individuals as possible (sieving after Wxation) and the avoidance of environmental contamination with large volumes of formalin (sieving alive). While numerous authors mentioned that, for certain species, an actual impact of sieving procedure should be expected (Thorson 1957;Govaere 1978;Bilyard et al 1987;Bachelet 1990;Rumohr 1990;Gage et al 2002;Van Hoey et al 2004), little research was done on the qualiWcation and quantiWcation of the diVerence in sieving procedure. In his study on the eVect or sieving procedure on the benthos retained with a 0.5 mm mesh sized sieve, Ohwada (1988) reported that polychaetes might be far more abundant (up to 20 times) in samples sieved after Wxation compared to samples sieved alive.…”

“…Variations in the elements that constitute such a study design can inXuence the comparability of diVerent data sets. Some elements that vary among studies and that have already been studied intensively are the sampling devices (Thorson 1957;Eleftheriou and Holme 1984;Bilyard et al 1987;Long and Wang 1994), sample replication (McIntyre et al 1984;Bilyard et al 1987), sieve mesh size (Eleftheriou and Holme 1984;Bilyard et altaxonomic discrimination (Bilyard et al 1987;James et al 1995;Gage et al 2002;Thompson et al 2003).…”