Introduction

Abstract

The meiobenthos (also called the benthic meiofauna) is a heterogenous group of benthic organisms, both protists and metazoans. Initially distinguished among the benthic organisms on account of their size [as organisms retained on 0.063 (0.032)–1.00 (0.500 or 0.250) mm mesh size sieves], the grouping has become recognised as a distinct ecological category, important by its major contribution to benthic metabolism and secondary production. While marine ecological research usually addresses entire meiobenthic communities considered as assemblages of interacting components represented by high-rank taxonomic units called the major taxa (phyla, orders, families), there is a general awareness of an immense taxonomic richness (diversity) those taxa represent. Whenever detailed taxonomic studies on the meiobenthos have been carried out, a great number of new species, genera and higher-rank taxa has been described. However, the knowledge of this diversity, particularly in the deep sea, is still greatly limited. Ecological research on the meiobenthos revealed the grouping to be a sensitive indicator of environmental changes. Consequently, the meiobenthos is being increasingly frequently used in monitoring and evaluating impacts of factors that disturb the natural state of sedimentary environment. The reliability of such evaluations may be enhanced by refining the resolution of taxonomic analyses and by coupling them with information on functional traits of the meiobenthic taxa present in an assemblage. While such approach is gaining popularity in research on coastal areas, it is still very rare in the deep sea, although the meiobenthos-related variables have been used in evaluating impacts in the deep sea.