Hartmut Koehler

Predatory mites (Gamasina, Mesostigmata)

Abstract Mesostigmata or Gamasida are known from a wide range of habitats. Most of them are free living predators in soil and litter, on the soil surface or on plants. Some are able to disperse rapidly by phoresy. In agroecosystems, edaphic Mesostigmata are important predators of Nematoda, Collembola and insect larvae, and those living on plants may efficiently control pests like spider mites. They are used as bioindicators. This paper reviews recent literature on the participation of soil mesofauna in agroecosystems and focuses on biology and ecology of mesostigmatic mites in particular, with emphasis on the Gamasina. Implications of agricultural practice for diversity and population development and the consequences for ecological processes are highlighted. Results of the author’s studies on the effect of the pesticide Aldicarb on the Gamasina are summarized, which document various patterns of population development following pesticide application.

Mesostigmata (Gamasina, Uropodina), efficient predators in agroecosystems☆

Abstract Mesostigmata or Gamasida are known from a wide range of habitats. Most of them are free living predators in soil and litter, on the soil surface or on plants. Some of them are able to disperse rapidly by phoresy. Most of them feed on small invertebrates. In agroecosystems, edaphic Mesostigmata are important predators of Collembola and Nematoda, and those living on plants may efficiently control pests like spider mites. The paper gives a short introduction to the participation of soil mesofauna in functions of agroecosystems, and focuses on biology and ecology of mesostigmatic mites in particular, by reviewing recent literature. Implications of agricultural practice for diversity and population development and consequences for ecological processes are highlighted. Results from my own studies on the impact of the pesticide Aldicarb on the Gamasina are presented, which document various patterns of population development following the application. Evidence for direct and indirect causes and effects is discussed.

The influence of vegetation structure on the development of soil mesofauna

Abstract Secondary succession of vegetation and soil mesofauna was followed for several years in 3 replicate experiments on artificially created synchronous successional and recultivated (grass) sites in 1980, 1982 and 1985. The data presented cover a period of 2 years, with special reference to the Gamasina (Acari). There is evidence that the grass vegetation has a positive influence on the development of soil mesofauna, which is mainly caused by the specific microclimate. Other indirect effects are discussed. In an ecotoxicological experiment, the succession of the “twin sites” under uncontaminated conditions was compared with that under the influence of 2.5 g m −2 Aldicarb (single application). Different reactions of the soil mesofauna were observed on the two synchronous sites (undisturbed succession and grass).

The use of soil mesofauna for the judgement of chemical impact on ecosystems

Abstract Soil mesofauna has been considered by various authors to be a good indicator in assessing the effect of environmental chemicals. Results are presented from a 4 year study on the succession of soil mesofauna after a single, initial Aldicarb application. The range of reactions is documented, according to organisms concerned, preferred habitat (stratum), type of vegetation, successional status and importance value used. The Gamasina taxocenosis is analyzed on species level. The results show strikingly different successional developments of the gamasine communities of contaminated and control sites. The good indicator properties of these predacious mites are confirmed. Their high sensitivity to external impact combined with their importance for ecosystem functions make soil mesofauna extremely valuable for ecotoxicology. However, theoretical considerations lead to the conclusion, that only when mesofauna investigations are placed into an ecosystem context, can a judgement on the effects of an anthropogenic impact be made. The importance of taxonomy, interdisciplinary and long-term research is stressed.

Natural regeneration and succession : results from a 13 years study with reference to mesofauna and vegetation, and implications for management

Succession of soil mesofauna and vegetation has been studied since 1980 on two experimental plots, one left for undisturbed succession, the other managed as a lawn until 1987 (thereafter ruderalization). Samples of soil mesofauna have been taken every 3 months. The results show the successional dynamics of soil mesofauna taxa and their abundances both at group and species levels (Acari, Mesostigmata: Gamasina) for a period of 13 years, and may be compared to those of the vegetation. Recultivation accelerates colonisation and leads to increased abundances. Although above- and below-ground plant structure influence the development of soil mesofauna, their dynamics are not synchronised. Gamasina communities of the recultivated and successional site diverge with time. Restoration management should consider processes in the soil, e.g. by allowing or introducing patchiness.

Secondary succession of soil mesofauna: A thirteen year study

Abstract Soil mesofaunal succession has been studied since 1980 on two experimental plots, one left undisturbed, the other managed as a lawn until 1987 (thereafter ruderalization). Samples have been taken every three months. The results show the successional dynamics of soil mesofauna taxa and their abundances both at group and species levels (Acari, Mesostigmata: Gamasina) for a period of 13 years. Management (recultivation) allows accelerated colonization and leads to increased abundances of some groups in the long term. Species characteristic of the successional phases and of the plots were identified. Above- and below-ground plant structure influence the development of soil mesofauna. A relationship with plant associations does not become apparent.

Response of vegetation and soil ecosystem to mowing and sod removal in the coastal dunes ‘Zwanenwater’, the Netherlands

This paper investigates the effects of mowing and sod removal on vegetation, soil mesofauna and soil profile, and the restoration of these features in the years following sod removal. The sampling site is located in a primary wet dune slack in the northern part of the province of North-Holland. The original vegetation is a heathland withEmpetrum nigrum andCalluna vulgaris, underlain by a Gleyic Arenosol with an O, Ah and (B) horizon development. Above-ground, the vegetation in the dune slack has been mown since 1940. The sod was removed from restricted areas in the slack at various times in the past (1980, 1985, 1987 and 1991).All three sources of data point to adaptation to wet conditions after mowing and sod removal. The vegetation of the mown area is related to the vegetation in the original heathland, although some species appear to have disappeared. Below-ground, mowing drastically reduces the number and depth of occurrence of microarthropoda. Restriction of depth applies also to the Enchytraeidae. Soil profile development is restricted to an Ah-AC-Cr sequence.Species diversity both above and below-ground is relatively high in plots where the sod has recently been cut, due to the rapid colonization by the first pioneer species. A time series for the vegetation is difficult to establish because hydrological conditions interfere with years since sod removal. Soil profile evolution after sod cutting is poor but consistent, from an AC-Cr sequence since 1991, to an O-Ah-Cr sequence since 1980.The management practices were set up with the intention to interrupt the succession to give pioneer species a chance. Neither the vegetation, nor the soil fauna or soil profile have fully recovered during the 13 yr since the first sod removal. So the goal has been reached.

In-Situ Phytoremediation of TNT-Contaminated Soil

Parts of the area of the derelict World-War-II ordnance plant Werk Tanne (Clausthal-Zellerfeld, Harz, Germany) are heavily contaminated by chemicals resulting from TNT production and particularly by TNT itself. High soil contamination has to be treated with ex-situ methods but for the extended contamination of surface soil, in-situ phytoremediation is appropriate. The TNT-degrading potential of the rhizosphere of the planted trees and shrubs themselves is augmented by highly active mycorrhiza and white-rot fungi. A phytoremediation measure was established to scale with heavy machinery (soil grader), including the incorporation of white-rot fungi into the soil and planting of mycorrhized trees and shrubs. The effects of site preparation, mycorrhized rhizosphere and white-rot fungi on the degradation of TNT were assessed over one year using a complex monitoring scheme, including a battery of five biotests and field investigations of selected indicators (soil mesofauna, decomposition). The results of the monitoring showed the great influence of the grading procedure for site preparation, a diversified sensitivity of the biotest battery and complex reactions of the field indicators. The grading procedure effectively reduced the contamination (almost 90% within the first six months regardless of the initial levels). The phytoremediation measure as a whole reduced hazards of transport of nitro-aromatics by dust or leachate, initiated a secondary succession of the soil ecosystem that could transform the remaining TNT and metabolites over a longer period of time, and thus proved to be an effective decontamination measure applicable in large-scale technology.

Long-Term Observations of Soil Mesofauna

General problems connected with planning, sampling, and data processing of long-term research of soil mesofauna are discussed, based on two case studies: (i) the Bremen study of predatory mites (Gamasina) covering 20 years of secondary succession on a ruderal site in northern Germany and (ii) the Mazsalaca study of the effects of climate warming on Collembola of coniferous stands in the North Vidzeme Biosphere Reserve, Latvia, covering 11 years. The findings from both sites are embedded in an array of environmental data. The results from Bremen document the asynchrony of different biota in successional dynamics. The long-lasting increase of the species numbers of soil predatory mites (Gamasina) is contrasted by a decrease in plant species numbers. In the Baltic forests, climate change is indicated by the dynamics of collembolan community. Gradual decline in species richness has been observed from 1992 to 2002 attributed to global warming. The ‘temporal window’ or time unit to discern changes in soil mesofauna communities seems to span approx. 5 years, highlighting the necessity of long-term observations.

Gamasina in a succession of thirteen years

Succession of soil mesofauna has been studied since 1980 on two experimental plots; one has been left undisturbed, the other was managed as a lawn until 1987. Community structure (species level) of the Gamasina taxocenoses of the two plots was used to form groups according to size classes, preferred humidity, food preference and reproductive performance. The size of the animals seems to be a very important feature, which correlates with other characteristics, particularly feeding. In many cases the guilds exhibit very obvious patterns in successional time and as a consequence of management. Changes of vegetation due to management or succession are reflected in community structure of Gamasina, often because of differences in microclimate. Colonisers reappear with increasing running wild of the managed plot after 1987.