The biology and ecology of lotic microcrustaceans

1. Copepoda, Ostracoda and 'Cladocera' are important meiobenthic Crustacea which can be both numerically abundant and species rich in running waters. Harpacticoids and ostracods are well adapted to benthic life because they a re typical crawlers, walkers, and burrowers. Many cladocerans are substratu m dwellers, but most benthic species among these can also swim. Cyclopoids which are generally good swimmers are nevertheless often bottom frequenters and actively colonise sediment interstices (the hyporheic zone). 2. The subclass Copepoda includes 10 orders. With 53 families, the order Ha rpacticoida dominates the benthos. Only five of these families are represen ted in fresh waters (ca. 1000 species and subspecies). The order Cyclopoida includes 12 families of which the Cyclopidae is well represented in freshw ater habitats with 900 species and subspecies. Freshwater Ostracods belong to the order Podocopida (5 000 species) with three superfamilies occurring in running fresh waters. The group 'Cladocera' contains four orders, 12 fam ilies, more than 80 genera, and 450-600 freshwater species. Most of the ben thic species are found in the families Chydoridae (39 genera), Macrothricid ae, Ilyocryptidae and Sididae. 3. For each of the three major taxa, morphological characteristics are pres ented, specimen collection and preparation are described and references to available taxonomical keys are provided. 4. Biological characteristics are extremely diverse among and within the th ree taxa, resulting in a great variety of strategies in meiobenthic crustac eans. Characteristics of reproduction, sexual dimorphism, cyclomorphosis an d population parameters (i.e. clutch size, lifespan, growth, moulting) are provided for some of the most common species. 5. Important differences between the three main taxa were found at the spec ies level. Ecological requirements such as hydraulic microhabitats and geom orphologic features of the streambed are the major determinants of species diversity and abundance for benthic microcrustacea of lotic habitats. Many studies on the ecology of these communities are limited by a lack of knowle dge of the life history characterisitics of lotic (especially interstitial) crustacean populations.