Mites (acari) as Indicators of Soil Biodiversity and Land Use Monitoring: a Review

Soil is an important component for monitoring of sustainability of land use in relation to both the conservation of natural resources and biodiversity of ecosystems. Recently research has focused on the role of mites (Acari) in biomonitoring and their importance as soil bioindicators. Mite communities are extremely sensitive to all types of soil disturbance. This article presents a review of some studies on mite communities in order to discuss whether the diversity and numbers of mites present in the soil can reflect human impact on ecosystems and landscape, and whether mites can be used in monitoring systems. Limited data available about mite communities in agricultural ecosystems (in use and abandoned) in SW Norway from author’s own studies (published and in prep.) are compared with data from ca. 55 papers (mostly concerning Europe). IT was concluded that: (1) Most oribatid mites with their long life span, low fecundity, slow development and low dispersion ability can be a robust indicator of the environment. Changes in the dominance structure of mite communities (Oribatida to Actinedida ratio) are suggested to be an ‘early warning’ criterion for stressed mite communities. (2) Both the number of species and the percentage abundance of Nothroidea and Ptyctimina decrease following human impact on the landscape. Even if individuals cannot be determined to species levels (e.g. Ptyctimina), the percent contribution and frequency of these taxa in relation to stress gradient (input levels) within the landscape provide valuable data. (3) Tectocepheus velatus (Michael 1880) and other oribatid taxa with a similar lifehistory strategy should be evaluated as potential bioindicators for impoverished ecosystems. (4) National and local reference data sets on the biodiversity of mite communities in diverse habitats and along stress gradients need to be collected. (5) Residual natural and semi-natural habitats (such as old woodlands, riparian ecosystems, old hedges and grasslands) with species-rich mite communities found in rural and urban landscapes should be preserved as refuges for dispersion of soil fauna. (6) Comparison of mite communities in traditional, low-input farmland in Norway with those from humandominated landscape in other European countries can contribute to a better understanding of how human activity alters biodiversity along land-use gradients. This will aid the development of a soil bioindicator system. (7) There is a need to develop standardised procedures for the collection of samples and analyses of data sets adapted to ecological soil acarology.