Patterns in fish assemblages from coastal wetland and beach habitats in Green Bay, Lake Michigan: a multivariate analysis of abiotic and biotic forcing factors

Abstract

From May to September in 1990 and 1991, 24 coastal wetland and beach sites in Green Bay, Lake Michigan, were sampled to investigate abiotic and biotic factors influencing fish assemblages; half the sites were modified by human developments, and half were relatively undeveloped. The greatest assemblage differences were observed among regions, but there also were strong differences among assemblages from different habitats. Degree of development had less of an effect on site differences, although assemblages at undeveloped wetlands were unique, and those from developed and undeveloped sites in the upper bay were relatively distinct. The most influential abiotic factors were turbidity, reflecting the trophic gradient in the bay, and a suite of variables associated with macrophyte coverage and diversity, which were critical components of nursery habitats for the primarily immature fishes we captured. The volatile and unpredictable nature of shoreline habitats in the Great Lakes apparently precluded competition and predation from having a strong organizing role. This study demonstrates that undeveloped wetlands are a valuable and intensely utilized fish habitat, particulartly as nursery areas, that should receive special consideration in ecosystem management plans for the Great Lakes.

Coastal wetland insect communities along a trophic gradient in Green Bay, Lake Michigan

“…Several environmental variables expected to reflect the trophic gradient in Green Bay based on previous studies (e.g., Brazner and Beals 1997) were measured concurrently with insect sampling. Water temperature, conductivity, and turbidity were measured daily (n = 4 per season) at mid-depth between the 0.5-m and l-m depth contours with a Hydrolab DataSonde III multiprobe sensing unit (Hydrolab Corp., Austin, TX, USA).…”

“…Water temperature was measured to assess whether wetlands were functioning under similar temperatures seasonally despite their 150-km latitudinal separation. Conductivity is often highly correlated to total dissolved solids and thus was expected to be higher in the lower, eutrophic end of the bay (Brazner and Beals 1997). Similarly, turbidity was expected to be higher in the lower bay due to high productivity and standing-stock biomass of phytoplankton and other suspended solids related to development (Richman et al 1984b, Sager and Richman 1991, Millard and Sager 1994, Brazner and Beals 1997.…”

“…Conductivity is often highly correlated to total dissolved solids and thus was expected to be higher in the lower, eutrophic end of the bay (Brazner and Beals 1997). Similarly, turbidity was expected to be higher in the lower bay due to high productivity and standing-stock biomass of phytoplankton and other suspended solids related to development (Richman et al 1984b, Sager and Richman 1991, Millard and Sager 1994, Brazner and Beals 1997. The number of macrophyte species and the percentage of area covered by macrophytes were estimated visually in the DE, SE, and OW zones where insects were sampled once in each season of sampling.…”

“…These results suggested that turbidity-induced suppression of macrophyte diversity and cover resulted in reduced insect abundance and biomass compared to a nearby diked wetland. These findings may have larger-scale regional implications for fish and wildlife since there is lower turbidity and greater submersed macrophyte diversity and cover in meso-oligotrophic coastzd wetlands in middle and upper Green Bay compared to hypereutrophic wetlands in the lower bay (Brazner and Beals 1997). Low insect production in wetlands could influence waterfowl use and brood survivorship (e.g., Hunter et al 1984, Brlanger and Couture 1988, Pehrsson and Nystrrm 1988, Cox et al 1998, as well as the distribution of insectivorous fish such as centrarchids (Brazner 1997L Based on the limited knowledge of coastal wetland insect communities, their potentially important role in Great Lakes food webs, and their sensitivity to anthropogenic stresses, we set out to characterize insect assemblages from four coastal wetlands that spanned the length of Green Bay.…”

“…The most severe degradation has been within the Fox River watershed, which feeds the southern end of the bay with a high nutrient load (Bertrand et al 1976, Harris et al 1987). This has resulted in highly eutrophic conditions in the lower bay and contributed to a strong north-to-south trophic gradient throughout the bay Richman1991, Brazner andBeals 1997). Nutrient enrichment and associated turbidity has had profound effects on biota, including phytoplankton (Richman et al 1984b, Auer et al 1986, Sager and Richman 1991, zooplankton (Richman et al 1984a, Sager andRichman 1991), macrophytes (Harris et al 1988, Harris et al 199I, Brazner 1997, and fish (Brazner and Beals 1997).…”