Effects of sieve mesh-size on the identification of benthic assemblages and their relationships with habitats and environmental gradients

One of the most discussed aspects of the cost-effectiveness sampling of benthic macrofauna is the choice of the sieve mesh size. Although other studies have tested the cost-effectiveness of mesh-size choice, especially in estimating biodiversity, they largely overlook the effect on the perceived species-environment relationship. In this sense, this study aimed to understand the effects of mesh-size choice on the relationship between macro-benthic communities with benthic habitats and environmental gradients. Samples were grouped in biological groups, based on species composition similarity, and in sedimentary habitats, according to environmental var-iables. Using a 0.5 mm mesh size sieve significantly enhanced the abundance and biodiversity, even at the high taxonomic level of class/order. However, its use did not introduce changes in the identified biological clusters. Distinct biological groups matching distinct sedimentary conditions could only be identified for habitats char-acterized by predominance of medium silt and coarse sand. Specific biological groups were not found for very fine sand and coarse silt habitats, which can be attributed to transitional fauna or unmeasured variables. This result indicates the need for caution in using benthic habitat mapping as a direct surrogate of species assem-blages. Although species composition varied in all biological groups with sieve mesh-size choice, no changes were found in the multivariate relationship between macrobenthic assemblages and environmental variables. In conclusion, sieving through 0.5 mm mesh size should be considered in studies aiming at biodiversity assessments, as the number of species and overall abundance more than doubled in comparison to the 1.0 mm mesh size. However, to study the relationship between biological assemblages and the benthic environment and habitats, we recommend the more cost-effective sieving through a 1.0 mm mesh size.