Tardigrade Ecology

Abstract

Understudied, but ubiquitous in every biome on Earth, tardigrades have been found in marine, freshwater, and terrestrial habitats, although ecological studies are still rather scarce, especially those that utilize quantitative replicate samples for statistical analysis. In this chapter, we discuss what is currently known about the ecology of tardigrades in the three major habitat categories: marine, freshwater, and terrestrial (including limnoterrestrial). Marine tardigrades have been described from all seas, occurring in intertidal and subtidal areas down to the abyss, while freshwater tardigrades inhabit a diversity of lotic, lentic, and subterranean ecosystems. Terres- trial tardigrade habitats include substrates such as mosses, lichens, and liverworts on rocks, soil, and tree trunks, as well as leaf litter and soil, whereas limnoterrestrial species are found in both freshwater and terrestrial environments. Tardigrades display various morphological adaptations for their associated environments. The high variability within and between samples (patchiness) limits data interpretation and reproducibility of previous studies of population dynamics and zonation. Long- term ecological studies are essential for future research. In addition, our knowledge of the biodiversity and biogeography of tardigrades is rapidly changing with the discovery of cryptic species and integrative taxonomy using combined morpholog- ical and molecular information, now considered essential for subsequent work with tardigrades. D.