Habitat and human influences on fish assemblages in Les Cheneaux coastal marshes.

Abstract

The Les Cheneaux Islands encompass 176 miles of coastline on Northern Lake Huron. This unique and fragile habitat may be increasingly threatened as human development in this area continues. This study asks the questions: 1) Are there differences in fish assemblages between bays? 2) If so, are the differences correlated to human activity? 3) Are the differences correlated to vegetation present? Wetlands are defined by the Environmental Protection Agency (EPA) and US Army Corps of Engineers as 'areas inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions' (Mitsch and Gosselink, 2000, p.32). Wetlands serve numerous ecological functions, including nutrient cycling, erosion control, water storage, production of peat, carbon cycling, and habitat provision for plants and animals (Costanza et al., 1997; Mitsch and Gosselink, 2000). Costanza et al. (1997) emphasized the economical value of wetlands by approximating the number of US dollars per hectare per year provided by this type of ecosystem. According to this measure of ecosystem service, wetlands afford more ecological value than any other ecosystem category (e.g. marine, terrestrial, coastal). The capacity of Great Lakes coastal marsh wetlands to provide ecological services is being threatened by continued human-induced loss and degradation (Hook et al., 2001). Biological communities such as fish provide valuable information about environmental quality, as these organisms are sensitive to changes in a wide array of environmental factors (Karr, 1981). Freshwater marshes are highly productive systems that serve many functions for larval fish populations (Jude and Pappas, 1992). Marshes are excellent spawning and nursery grounds for many fish species. In the Great Lakes coastal marshes, this is partially because of the great diversity of structural habitat. The water levels of these marshes are subject to periodic fluctuations that allow for a dynamic vegetation composition (Eadie and Keast, 1984). Most larval fish prefer to live in shallow habitats with dense vegetation (Petering and Johnson, 1991). Vegetation protects larval fish from predation by birds and fish, shelters them from wave action, and forms microhabitats that are conducive to food production (Petering and Johnson, 1991; Engel, 1988). Differences in fish species richness, number of tolerant fish species, and number of cyprinid species are considered useful indicators of marsh ecosystem degradation (Karr, 1981; Hocutt, 1981; Hook et al. 2001). For instance, most young fish in the Cyprinidae family are very sensitive to pollution, turbidity, and high temperatures. Their presence or absence in a marsh is a fairly good indicator of the health of the marsh (Hook et at., 2001). Other fish are very tolerant of these circumstances, such as the common carp, Cyprinus carpio, bowfin, Amia calva, and brown bullheads, Amejurus nebulosus. A habitat dominated by these tolerant fish is more likely to have been disturbed and degraded (Jude and Pappas, 1992). Human induced loss and degradation of Great Lakes coastal marsh can significantly alter fish assemblages despite retention of various ecological marsh functions (Poe et al. 1986; Leslie and Timmins 1992; Brazer 1997; Hook et al. 2001). Plant species composition may also change with the addition of pollutants to wetlands, as evidenced by the spread of Typha spp. in wetland areas with increased agricultural runoff laden with phosphorus (Mitsch and Gosselink, 2000, p.625). In severe cases of water pollution, such as acid drainage or oil spilling, wetland vegetation can be killed (Mitsch and Gosselink, 2000, p.625). The proposed survey of the Les Cheneaux fish and plant communities aims to observe changes in these particular populations that may provide evidence of habitat degradation. We expect to observe the mentioned indicators of marsh ecosystem degradation offered by fish population studies in bays which have greater human activity than do less developed bays. We hope to also observe trends in plant communities that relate to human activity, and make correlations between fish and plant community interactions.