Diversity of the tardigrade communities in the Norwegian forests

Background: Tardigrades are common in most habitats, however few studies have focused on large faunistic survey, specifically on tardigrade diversity in forests. Up to now, only 61 species have been recorded in different types of forest in Norway with an additional 25 found in limnic environments in forests. Although little is known about the ecological preferences of many species, previous studies have found that tardigrade diversity and community composition are significantly affected by ecological variables. In this study we associate georeferenced tardigrade species records with forest type, substrate type and substrate composition in order to see if tardigrade diversity and species communities can be associated with ecological characteristics of Norwegian forests.

Methods: In total 390 moss, lichen and litter samples were collected from 12 forests in central and southern Norway in the summers of 2017 and 2018 and later stored in paper envelopes. For the identification modern literature and keys for specific genera and groups of species were used. For statistical analyses, moss and lichen substrate of each sample was classified according to the main species, life form, growth forms and habitat of substrate and associated with each tardigrade identification and sample metadata.

Results: A total of 17 407 specimens were identified, encompassing in total 132 species (including some new species). Species richness increases with precipitation, but does not change with temperature or precipitation seasonality. The distribution of species richness between life forms and forest types showed considerable variation within and among the variables. Disregarding variables with low sample numbers, among life forms only acrocarpous moss samples appeared to deviate with respect to species richness, containing less species than substrates with other life forms.

Conclusions: Tardigrades in Norwegian forest are extremely abundant, frequent and diverse. Moreover, it appears that that certain species and/or entire communities prefer specific microhabitats.