HABITATS AND COMMUNITIES

Water mites form discrete communities of species based upon adaptations of post-larval instars that specialize them to exploit particular freshwater habitats and microhabitats. In the Mixedwood Plains, eight reasonably distinct communities can be identified in association with different habitat types. Most species are strongly associated with one particular habitat type, but some are able to exploit a variety of similar types (eg. rheocrene springs and riffle areas, stream pools and lakes), and consequently may be represented in more than one community. These communities are richly polyphyletic and often represent unique assemblages of species that have different post-glacial biogeographic histories and occur together nowhere else.
Freshwater habitats are especially vulnerable to physical disturbance and chemical pollution. Both the quantity and quality of these habitats in the Mixedwood Plains have been significantly degraded by agricultural, industrial, recreational and urban development, especially in the Lake Erie Lowlands. Nearly 80% of the original 2 million hectares of wetland habitat in the Mixedwood Plains has been eliminated or seriously damaged by human activities. Springs and streams have been extensively dammed, diverted, channelled, silted up and polluted. Ponds and lakes have undergone progressive eutrophication and intensive recreational exploitation. All of these activities have had inadvertent impacts on freshwater invertebrate communities. Water mites are useful indicators of biodiversity change in these communities because of their high taxonomic diversity, abundance in all kinds of habitats and robust interactions with other organisms, especially insects. In addition, water mites are relatively easy to collect and identify compared to many other groups of freshwater arthropods because the adult instar is fully aquatic.

Springs About 60 species representing 30 genera and 20 families inhabit springs and seepage areas in the Mixedwood Plains. Communities from individual sites may include up to 20 different species. Deutonymphs and adults are typically specialized for crawling on moss mats and detritus. Most species are cold-adapted crenobionts but some (eg. Laversia berulophila) are more generalized stenophiles also able to live in the profundal zone of oligotrophic lakes. Many crenophilic species are distributed widely in well drained areas of the Boreal Shield and Atlantic-Maritime Ecozones, with scattered populations in the Mixedwood Plains. Most of these species have Northeastern or Boreal distributions. They probably inhabited Pleistocene refugia in discharge areas associated with highlands near the edge of the Laurentide Ice Sheet and dispersed through the Mixedwood Plains early in the Holocene, leaving relict populations in persistent cold springs as they moved north. Spring habitats are common throughout the Mixedwood Plains, but they and their arthropod communities are increasingly threatened by intensive agriculture and residential development in urban areas, especially in the Lake Erie Lowlands. Information on springs and their biota in the Mixedwood Plains Ecozone is fragmentary, despite their importance as sources for surficial watersheds and indicators of ground water quality, respectively . Mites, insects and crustaceans are the dominant animal groups in spring habitats. We need to develop an inventory of springs in the Ecozone and compile a relational database on their arthropod species and communities. This would permit development of baselines for assessing and monitoring biodiversity change in a network of selected springs and permit correlation of documented changes with environmental stressors using Geographical Information System technology.

Groundwater/Hyporheos

Approximately 20 species representing 15 genera and 15 families inhabit subsurface water in the Mixedwood Plains. Communities from individual sites may include up to 10 different species. Deutonymphs and adults are typically specialized for running through subsurface interstices in gravel deposits. They usually lack both pigment and functional eyes (Fig.M-44). Most of these species have Northeastern distributions and are distributed widely in the Atlantic-Maritime Ecozone with scattered populations in the Mixedwood Plains and southern regions of the Boreal Shield Ecozone. Others have Southeastern distributions. All of them probably inhabited Pleistocene refugia in highland and piedmont areas remote from the edge of the Laurentide Ice Sheet and dispersed gradually into the Mixedwood Plains as stable fluvial depositional areas became reestablished during the Holocene. These habitats apparently developed more rapidly in the Atlantic-Maritime Ecozone as a result of its more varied topography and elevation. Subterranean freshwater habitats and their arthropod communities are being degraded in the Mixedwood Plains, especially in agricultural and urban areas of extreme southern Ontario, by chemical pollution, siltation and compaction. Knowledge of groundwater biota in the Mixedwood Plains is rudimentary, but my initial surveys show that some of the water mite species which characterize the rich phreatic communities in unglaciated parts of North America have established populations in the Ecozone. As in the case of spring fauna, we need to develop relational databases for these mites and initiate monitoring in selected aquifers to document biodiversity changes and correlate them with local environmental stressors.

Stream Riffles

About 100 species representing 22 genera and 12 families inhabit flowing water in erosional zones of streams and rivers in the Mixedwood Plains (Fig.M-45). Communities from individual sites may include up to 25 different species. The dominant genera in riffle habitats are among the least well known taxa in the Ecozone. Deutonymphs and adults of mites in these habitats are typically specialized for clinging and crawling on rocks and aquatic plants. Most of the species are relatively cold-adapted stenophiles distributed widely in small streams of the Mixedwood Plains, Atlantic-Maritime and southern regions of the Boreal Shield Ecozone. Most of them have Southeastern or Northeastern distributions. They probably inhabited Pleistocene refugia in erosional areas associated with highlands such as the Ozark Plateau, Cumberland Plateau and Appalachian Mountains south of the Laurentide Ice Sheet, and dispersed into the Mixedwood Plains and contiguous eastern Canadian Ecozones as lotic habitats stabilized during the Holocene. A small group of species are relatively warm-adapted and restricted to shallow rivers and streams in Karst areas of the Mixedwood Plains and Atlantic-Maritime Ecozones (Fig.M-46). Several of these species represent clades that apparently invaded North America from South America following establishment of the Panamanian Isthmus during the Pliocene, and have reached the northern limits of their distributions in the Mixedwood Plains.

Stream Pools

Nearly 100 species representing 30 genera and 16 families inhabit pools in depositional zones of streams and rivers in the Mixedwood Plains (Fig. M-47). Communities from individual sites may include up to 60 different species. Deutonymphs and adults are typically specialized for swimming and burrowing in silt. Most of these species are cool-adapted stenophiles with Northeastern or Boreal distributions, found widely in small streams in the Mixedwood Plains, Atlantic-Maritime and Boreal Shield Ecozones. Many of themalso can also exploit sublittoral habitats in small lakes. They probably inhabited Pleistocene refugia in depositional areas south of the Laurentide Ice Sheet and dispersed into the Mixedwood Plains as lotic habitats stabilized during the Holocene.
Streams and their arthropod communities are being degraded by siltation caused by erosion associated with intensive agriculture, chemical pollution and urban development throughout the Ecozone, with the greatest impacts to date in the Lake Erie Lowland Ecoregion. Although a substantial among of research has been done on stream biota in the Mixedwood Plains, this has rarely resulted in well documented inventories of arthropod species that could be used as baselines for monitoring spatial or temporal biodiversity change. This is unfortunate, because mites, along with insects and crustaceans, comprise most of the faunal species diversity in stream habitats. They can be used as sensitive indicators to detect changes in community composition at an early stage, permitting action to be taken to mediate the impact of stressors before profund and irreversible degradation of community structure occurs, with implications for fish and other organisms at higher levels of the food chain. Here again, we need to establish and maintain relational databases on selected taxa that can be linked to information on regional and local stressors using GIS technology. Improving taxonomic knowledge of the most diverse genera of rheobiontic water mites would be a necessary but cost-effective step toward this objective, because the adult mites can be more rapidly and reliably identified than the aquatic larvae of their insect hosts.

Bog Pools

Nearly 50 species representing 17 genera and 12 families inhabit bog pools in the Mixedwood Plains. Communities from individual sites may include up to 20 different species. Deutonymphs and adults are typically specialized for clinging to Sphagnum and swimming. Most of these species are cool-adapted halophiles with Northeastern or Boreal distributions and with scattered populations in relict bogs in the Mixedwood Plains. They probably inhabited tundra pools in periglacial Pleistocene refugia and dispersed through the Mixedwood Plains early in the Holocene leaving relict populations in poorly drained areas as they moved northward.
Bogs and their arthropod communities in the Mixedwood Plains are being degraded by wetland drainage programs and associated agricultural and urban development. Bog communities contain some highly specialized mites that are rare in the Ecozone. The taxonomy of bog- dependent water mite species is sufficiently well known to permit development of a relational database for this fauna. It would be useful to establish baselines for species populations and community composition at selected bog sites, and to monitor for spatial and temporal changes along a transect extending northward to include some relatively large and undisturbed bogs in the Boreal Shield Ecozone.

Ponds/Marshes

Over 100 species representing 17 genera and 12 families inhabit ponds and marshes in the Mixedwood Plains (Fig.M-48). Communities from individual sites may include as many as 50 different species. Deutonymphs and adults are typically specialized for swimming and clinging to plants. Most of these species exhibit broad temperature tolerance, and some have extensive Northeastern or Boreal distributions. Others, notably certain species of the genus Arrenurus, appear to have limited distributions within the Great Lakes Basin. A number of the species in this group also exploit shallow, littoral habitats in small eutrophic and mesotrophic lakes. They probably inhabited Pleistocene refugia remote from the edge of the Laurentide Ice Sheet and dispersed gradually into the Mixedwood Plains during the Holocene.
Mites and associated arthropod communities that depend on ponds and marshes have been greatly reduced in the Mixedwood Plains by wetland drainage programs associated with agricultural, urban and industrial development. Large areas of many formerly extensive marshes have been drained and filled, and populations of mite species and their host insects have been fragmented and isolated in small remnant patches of habitat. Some of these species are endemic to the Great Lakes Basin and still occur most commonly and abundantly in the Mixedwood Plains Ecozone. Developing a relational database for these mites would permit us to monitor their populations as indicators of the sustainability of arthropod communities in critical wetland habitats.

Vernal Temporary Pools

About 60 species representing 14 genera and 8 families inhabit vernal temporary pools in the Mixedwood Plains (Fig.M-49). Communities from individual sites may include up to 20 different species. Deutonymphs and adults are typically specialized for clinging to plants and detritus or swimming. All of these species exhibit adaptations for either avoiding or withstanding drought that characteristically extends from early summer until the following spring. Most of them exhibit exceptionally broad temperature tolerance and are distributed widely in the Mixedwood Plains, Atlantic-Maritime and Boreal Shield Ecozones. Many of the species in this group have Northeastern or Boreal distributions; some others are known only from the Great Lakes Basin. A few species are halophiles restricted to intermittent pools in fens and bogs, with distributions that may extend to the high Arctic. Mites able to exploit temporary vernal pools probably inhabited seasonally intermittent tundra pools in periglacial Pleistocene refugia, in regions with marked spring melting and summer drought. They apparently dispersed through the Mixedwood Plains early in the Holocene, leaving relict populations in areas with perched water tables as they moved further north.
Vernal temporary pools are common in the Mixedwood Plains Ecozone, but are often disregarded as significant habitats because they are seasonal. They are frequently filled or drained to reduce mosquito populations and permit agricultural or residential development. In fact, many insects breed only in temporary pools, and the water mites associated with them occur exclusively in these habitats (Wiggins et al. 1980). Developing a relational database for these species would permit monitoring of populations of mosquitoes and their parasites at selected sites, and would provide insight on dispersal of these species and other members of this fascinating arthropod community.

Lakes

About 200 species representing 30 genera and 20 families inhabit lakes in the Mixedwood Plains. Communities from certain mesotrophic lakes (Fig.M-50, Fig.M-51) comprise exceptional diversity and may include up to 100 different species. Swarms of 20 or more species in each of the genera Arrenurus and Piona may live sympatrically in some of these lakes. Deutonymphs and adults of mites inhabiting lakes are typically specialized for swimming or clinging to plants. Lake inhabiting water mites of the Mixedwood Plains exhibit a remarkable diversity of post-glacial origins and dispersals, and illustrate all major distribution patterns. Various species also occur in shallow lakes in the eastern United States, the Atlantic-Maritime Ecozone or Boreal Shield Ecozone, and a few have very broad distributions extending westward to the Prairie Ecozone and beyond. The Mixedwood Plains represent a biogeographic crossroads for these mites, and many of the species assemblages that characterize mesotrophic lake communities in this Ecozone occur nowhere else.

TABLE 6: LIST OF NAMED SPECIES OF WATER MITES IDENTIFIED
FROM THE MIXEDWOOD PLAINS ECOZONE
(Unnamed species included are only known representative of genus in Ecozone)

Superfamily - Hydrovolzoidea

Family - Hydrovolziidae

Superfamily - Eylaoidea

Family - Limnocharidae

Family - Piersigiidae

Family - Eylaidae

Superfamily - Hydrachnoidea

Family - Hydrachnidae

Superfamily - Hydryphantoidea

Family - Hydryphantidae

Family - Hydrodromidae

Family - Rhynchohydracaridae

Superfamily - Lebertioidea

Family - Sperchontidae

Family - Teutoniidae

Family - Anisitsiellidae

Family - Lebertiidae

Family - Oxidae

Family - Torrenticolidae

Superfamily - Hygrobatoidea

Family - Limnesiidae

Family - Hygrobatidae

Family - Feltriidae

Family - Unionicolidae

Family - Pionidae

Family - Aturidae

Superfamily - Arrenuroidea

Family - Momoniidae

Family - Nudomideopsidae

Family - Mideidae

Family - Mideopsidae

Family - Chappuisididae

Family - Athienemanniidae

Family - Acalyptonotidae

Family - Neoacaridae

Family - Laversiidae

Family - Krendowskiidae

Family - Arrenuridae

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