Ecology of Testate Amoebae (Protozoa) in Two Lake Superior Coastal Wetlands: Implications for Paleoecology and Environmental Monitoring
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WETLANDS, Vol. 21, No. 4, December 2001, pp. 564±576 q 2001, The Society of Wetland Scientists ECOLOGY OF TESTATE AMOEBAE (PROTOZOA) IN TWO LAKE SUPERIOR COASTAL WETLANDS: IMPLICATIONS FOR PALEOECOLOGY AND ENVIRONMENTAL MONITORING Robert K. Booth Department of Botany University of Wyoming Laramie, Wyoming, USA 82071-3165 E-mail: [email protected] Abstract: Testate amoebae are common inhabitants of moist soils, wetland, and lacustrine habitats. They produce a decay-resistant test, or shell, which can be identi®ed to species in most cases and recovered from sediments in quantities suf®ciently large to permit estimation of relative abundance. The objectives of this study were to assess the potential of testate amoeba assemblages as paleoenvironmental and environmental indicators in two Lake Superior coastal wetlands and to determine if morphological variation in four common taxa (Arcella spp., Assulina spp., Centropyxis cassis type, and Nebela tincta-parvula-collaris group) is related to microenvironment. Study localities included ridge-swale wetland systems adjacent to Grand Traverse Bay and Tahquamenon Bay in the Upper Peninsula of Michigan. Testate amoeba assemblages from 74 microsites were compared with percent moisture, depth to water table, pH, porosity, depth of living moss, and associated moss and vascular plant species. Morphometric analysis (e.g., test length and aperture diameter) was con- ducted on 25 individuals from at least 10 microsites for each of the four selected taxa. Gradient analysis indicated that testate amoeba assemblages are primarily controlled by substrate moisture and pH, consistent with results from other regions. Transfer functions for pH and substrate moisture were developed using `jack- knifed' validation procedures. Little relationship was found between microenvironmental parameters and morphological variation in the investigated taxa, except for the Nebela tincta-parvula-collaris group, where test size was signi®cantly correlated with pH (r2 5 0.68). Results indicate that wetland testate amoeba assemblages in these coastal wetland systems are sensitive environmental and paleoenvironmental indicators that can be used to monitor and reconstruct water-level or pH changes. Key Words: testate amoebae, paleohydrology, paleoecology, paleoenvironment, bioindicators, environmen- tal indicators, Lake Superior wetlands, Great Lakes wetlands INTRODUCTION istry (Woodland et al. 1998, Mitchell et al. 2000a) are Testate amoebae (Protozoa: Rhizopoda) are com- also important factors. The species-speci®c environ- mon inhabitants of moist soils, wetlands, and lacus- mental tolerances of testate amoebae have supported trine habitats (Tolonen 1986, Warner 1990). They pro- qualitative environmental inferences from fossil data duce a decay-resistant test, or shell, that protects the for many years (e.g., Grospietsch 1965, Aaby 1976, cell from desiccation. The shell may be proteinaceous, Tolonen et al. 1985, Beyens and Chardez 1987, Van siliceous, or calcareous and may incorporate extrane- der Molen and Hoekstra 1988). Recent investigations ous materials such as fungal hyphae, diatoms, and have focused on ®nding correlations among quantita- mineral grains (Ogden and Hedley 1980). The mor- tive moisture parameters and modern testate amoeba phology of tests is usually unique, allowing species- assemblages (Charman and Warner 1992, 1997, Warn- level identi®cation (Ogden and Hedley 1980, Tolonen er and Charman 1994, Charman 1997, Woodland et 1986, Warner 1990). Fossil amoeba tests are especially al. 1998, Mitchell et al. 1999). These relationships can abundant and well-preserved in Holocene Sphagnum- be used to develop transfer functions for quantitative derived peats (Jung 1936, SchoÈnborn 1963, Meister- inference of past substrate moisture conditions (Char- feld 1977, Tolonen 1986, Warner 1990). man 1997, Charman and Warner 1997, Woodland et The dominant control on testate amoeba distribution al 1998, Charman et al. 1999, Mitchell et al. 2001). in peatlands is substrate moisture (Tolonen 1986, Many previous calibration studies have focused on Warner 1987, 1990), although trophic status (Tolonen ombrotrophic peatlands due to their sensitivity to cli- et al. 1992), pH (e.g., Charman and Warner 1992, mate change (Blackford 1993, Barber 1994). However, Mitchell et al. 1999), and other aspects of water chem- fossil testate amoebae may have more widespread ap- 564 Booth, WETLAND TESTATE AMOEBAE 565 plicability. Modern studies are needed from different geographic regions and peatland types to fully assess the potential of this proxy data source and to facilitate interpretation of fossil assemblages. Due to their environmental sensitivity and rapid turnover rate, testate amoebae are also potentially sen- sitive bioindicators (Foissner 1987, 1999). Testate amoebae are excellent indicators of calcite precipita- tion (Casper and SchoÈnborn 1985) and heavy metal pollutants (Patterson et al. 1996, Reinhardt et al. 1998) in lakes, and they may be used to assess rates of lake remediation (Patterson et al. 1996). Testate amoeba communities have shown signi®cant compositional changes within 2 ½ years of peatland drainage (Warner and Chiemelski 1992). They have also been used to Figure 1. Location of the two wetland systems in the Up- monitor the restoration and recovery of cutover bogs per Peninsula of Michigan, USA. in Switzerland (Buttler et al. 1996). Additional knowl- edge of testate amoeba ecology would promote more widespread application in biomonitoring and wetland tion in vegetation and hydrology and thus provide a management. wide array of microenvironments for testate amoebae. In this study, I investigated the relationship between Swales at both localities range from oligotrophic bogs testate amoeba assemblages and microenvironmental to highly minerotrophic fens and marshes. parameters (pH, substrate percent moisture, water-ta- Vegetation on the younger ridges at Grand Traverse ble depth, porosity, evaporation potential, depth of liv- Bay is predominantly composed of shrubs (e.g., Myr- ing moss, associated plant species) in two Lake Su- perior coastal wetland systems. I compared assemblage ica gale L., Rosa palustris Marsh., Salix spp., Betula variation between and within the wetlands and deter- pumila L.). Scattered Pinus banksiana Lamb. trees be- th mined controls on testate amoeba distribution in these gin to appear by the 13 ridge inland, becoming more systems. Because morphological variation in some widespread and mixed with Picea mariana (Miller) species has been found to occur in response to envi- BSP. by the 16th ridge. Mixed Picea mariana and Pi- ronmental conditions (Laminger 1978, Foissner 1987, nus banksiana stands continue to characterize the older SchoÈnborn and Peschke 1988, SchoÈnborn 1992, Wan- ridges, with occasional Betula papyrifera Marsh. and ner and Meisterfeld 1994, Bobrov et al. 1995, 1999, Pinus resinosa Aiton. Vegetation in the swales closest Wanner 1999), I compared morphological variation in to the lake is generally characterized by sedges (e.g., four common species groups with microenvironmental Carex spp., Rhynchospora spp., Scirpus spp.). Sphag- conditions. I then developed transfer functions that can num moss is ®rst found in abundance in the 16th swale be used to infer microenvironmental parameters from inland from the lake and is abundant in most of the fossil testate amoeba assemblages. swales further inland. Other species that characterize the inland swales include Chamaedaphne calyculata STUDY SITES (L.) Moench, Kalmia polifolia Wangenh., and Ledum groenlandicum Oeder. Standing water and aquatic Two wetland systems along the southern shore of vegetation (Scirpus subterminalis Torrey, Nymphaea Lake Superior were investigated, one adjacent to odorata Aiton) also occur in several of the swales at Grand Traverse Bay and one adjacent to Tahquamenon Grand Traverse Bay. Bay in the Upper Peninsula of Michigan, USA (Figure The ridges at Tahquamenon Bay are dominated by 1). Each of these systems is characterized by a series of alternating sand ridges and wetland depressions, Pinus strobus L. and Picea mariana. Thuja occiden- which are oriented parallel to the lakeshore. Sand ridg- talis L. and Larix laricina (DuRoi) K. Koch are abun- es were deposited during high stands of Lake Superior. dant on several ridges and swales. The abundance of The inter-ridge wetlands that subsequently developed Thuja occidentalis and Pinus strobus is in contrast to are commonly referred to as swales. The ridges are Grand Traverse Bay, where these species are rare. Like progressively older inland from Lake Superior, and the Grand Traverse Bay, many of the swales are domi- timing of wetland development generally follows the nated by Sphagnum spp.; however, marshes dominated same pattern (Johnston et. al 2000). These wetland by Typha latifolia L. and Carex lasiocarpa Ehrh. also systems are characterized by large inter-swale varia- occur. 566 WETLANDS, Volume 21, No. 4, 2001 METHODS cluded in the analysis and count total. A total of 74 testate amoeba assemblages were analyzed from the Field sampling at both sites was conducted in a two- two wetland systems. Fifty-three taxa were encoun- week period in late July 1999. The sampling procedure tered, although three rare taxa (occurring in fewer than was modeled after previous investigations (Charman 4 samples) were excluded from analysis. and Warner 1992, 1997, Warner and Charman 1994, Morphometric analyses (e.g., test length and aper- Mitchell et al. 1999). Microsites within