Lake Michigan

Changes in the status and distribution of Wisconsin's double-crested cormorant (DCCO) breeding population during the 20th century closely approximate a similar pattern throughout the Great Lakes and generally along the Atlantic coast: a gradual increase in popula- tion size from about 1921 until about 1950, followed by a population crash, and then a remarkable population resurgence beginning in the early

Phytoplankton pigment distributions during the spring isothermal periods of 1998 and 1999 and their association with episodic sediment resuspension were characterized in coastal waters of southern Lake Michigan. Total and phylogenetic group chl a concentrations (derived using chemical taxonomy matrix factorization of diagnostic carotenoids) corresponded with assemblage and group biovolumes estimated from microscopic enumeration (P≤ 0.001). Diatoms and cryptophytes dominated assemblages and together typically comprised greater than 85% of relative chl a. Total chl a concentrations and both fucoxanthin·chl a−1 and alloxanthin·chl a−1 ratios were similar across depths (P> 0.05), indicating uniform distributions of and photophysiological states for assemblages and diatoms and cryptophytes, respectively, throughout the mixed water column. Total chl a concentrations were not always spatially uniform from near-shore to offshore waters, with the greatest variability reflecting the influence of tributary inflows upon coastal assemblages. Sediment resuspension strongly influenced water column particle density and light climate; however, total and group chl a concentrations did not correspond with coefficients of Kd and suspended particulate matter concentrations (P> 0.05). The correspondence of both light attenuation and suspended particulate matter concentration with relative diatom chl a (P≤ 0.001) indicated an apparent association between sediment resuspension and diatoms. This, and the negative association (P≤ 0.0001) between relative diatom and cryptophyte chl a, corresponded with the spatial dominance of diatom and cryptophyte chl a in near-shore and offshore waters, respectively. The presence of viable chl a and fucoxanthin within the surficial sediment layer, established this layer as a potential source of meroplanktonic diatoms for near-shore assemblages.

Abstract.— I used a one-dimensional numerical model to estimate the present and possible future temperature structures in Lake Michigan. The estimates were based on model output from sim- ulations of the 1981-1984 offshore temperature field. Once the water temperature ...

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Morphological divergence resulting from differences in resource and habitat use is common in many fishes inhabiting postglacial ecosystems. We tested whether young yellow perch Perca flavescens differ in morphology, genetic composition, or diet in the nearshore (deep open-water) versus wetland and littoral habitats (shallow zones) of Lake Michigan and Saginaw Bay, Lake Huron. Twenty-one morphological measurements and six meristic counts were compared for 132 age-1 yellow perch, and the genetic variation at 12 nuclear DNA microsatellite loci was assessed for a subset of age-1 individuals across habitats and adults from nearshore zones. The results showed morphological and genetic divergence in yellow perch between Lake Michigan and Lake Huron and among those in nearshore versus wetland habitats in Lake Michigan (but not Lake Huron). Lake Huron yellow perch had deeper, longer bodies and larger dorsal fins than those from Lake Michigan. Those in nearshore habitats from both lakes had deeper, longer bodies and larger dorsal fins than did those occupying wetlands, which may reflect an adaptive response to predators and open-water cruising. In Lake Michigan, these differences may have a genetic basis that is not apparent in Lake Huron, suggesting a role for phenotypic plasticity. Piscivorous and zooplanktivorous individuals had similar morphologies, with larger body depths than insectivores, which may be useful for fast-starts during prey capture and provide protection from predation in open water. Comparisons of morphology, population structure, and diet thus reveal that the morphological diversity of yellow perch between habitats and lake basins reflects an interplay between phenotypic plasticity and genetic divergence.

We identified and quantified polyaromatic hydrocarbons (PAHs) in six aquatic taxa from the Calumet region of southwestern Lake Michigan in order to examine their differential exposure to and health risks from PAH. There was a high degree of variation in PAH concentrations across and within sites. Mean concentrations of total PAH were high in alewife (1,064 ng/g) and minnows (345 ng/g) collected from the Indiana Ship Canal, when compared to other taxa and locations. Concentrations of PAH in sunfish were relatively low (10 to 79 ng/g), even where environmental concentrations were elevated. In sunfish, regardless of location, concentrations of CHR, FLA, FLU, PHE and PYR were high whereas DBA, IPE, BAP, BBF, BGP and BKF concentrations were low. PAH concentrations in crayfish exceeded those of other taxa at three of four locations where they co-occurred. PAH profiles were similar in crayfish, sunfish and minnows from locations where sediment concentrations were low. Profiles for crayfish and minnows from a location where sediment concentrations were elevated displayed lower concentrations of ACY, and higher concentrations of BAA, BBF, and BKF, than those from the other three locations. In contrast, the profiles in sunfish from those three locations were similar. The PHE/ANT and FLA/PYR ratios for crayfish, minnows and sunfish suggested that the primary sources at most locations were pyrogenic, although some sites had strong petrogenic influences. Toxic equivalency factors in biota generally reflected the magnitude of sediment contamination. In three of four locations where they co-occurred, TEQs were higher in crayfish than in sunfish and minnows. Sunfish had higher TEQs than minnows at most, though not all, locations; TEQs were notably higher in minnows as compared to sunfish from the Little Calumet River. The selection of aquatic species as sentinels of PAH exposure and risks needs to consider differences in ecologies of taxa as well as the relative magnitude of sediment contamination.

The Lake Michigan Recurrent Coastal Plume (LMRCP) may fundamentally affect food web dynamics in Lake Michigan by causing major changes, during the winter-spring transition period, that, in turn, define the annual evolution of the biotic community in the lake. These effects can be observed by examining phytoplankton, zooplankton, and microbial food web structure and function in the field in combination with N-cycling studies that serve as an indicator of autrophic and heterotrophic community dynamics. We hypothesize that: 1. The population growth of phytoplankton and bacteria are enhanced at the edge of the plume, where light levels are higher than inside the plume and nutrients are higher than in surrounding waters. The phytoplankton community structure will shift toward small-sized taxa in the plume relative to offshore waters. 2. The proportion of phytoplankton production consumed in the pelagic zone will, in turn, increase due to increase in herbivory by nano- and microzooplankto...

Recent technological advances have led to the discovery that free-living, planktonic protozoa are ubiquitous in nature and appear to be important components of pelagic food webs (e.g., fluorescent straining, flow cytometry). Despite this, limited information exists tying their seasonality to rate processes that drive succession patterns. The abundance, and seasonal growth and grazing loss of an entire protozoan assemblage were evaluated in Lake Michigan. The protozoan assemblage was species-rich (100 taxa) and abundant throughout the year in Lake Michigan. Nano-sized protozoa (Hnano and Pnano, <20 μm in size) ranged in abundance from 102 to 103 cells ml−1, while micro-protozoa (Hmicro and Pmico, >20 and <200 μm in size) ranged in abundance from 4 to 17 cells ml−1. The biomass of Hnano and Hmicro by itself represented more than 70–80% of crustacean zooplankton biomass, while Pnano and Pmicro constituted nearly 50% of phytoplankton biomass. Protozoa exhibited growth rates comparable to other components of the plankton in Lake Michigan, and some populations grew at rates similar to maximum rates determined in the laboratory (rates of 1–2 day−1). Overall, it appears that macro-zooplankton predation is a major loss factor counter-balancing growth with only small differences between the two rate processes (<0.1 day−1). Discrepancies between growth and grazing loss in the spring were likely attributed to sedimentation losses for larger species of tintinnids and dinoflagellates (Codonella, Tintinnidium, and Gymnodinium) that can account for their occurrence in the deep chlorophyll layer. In the summer, carnivory among similar sized species (Chromulina and small ciliates) may be additional loss factors impinging on the protozoan assemblage.

We use fish and environmental data from 40 wetlands of the Laurentian Great Lakes to develop the Wetland Fish Index (WFI), a tool that can be used to assess the quality of coastal marshes. A partial canonical correspondence analysis was used to ordinate fish species along multidimensional environmental axes that accounted for anthropogenic disturbance based on temperature, conductivity, and the presence of pollutants (e.g., suspended solids and primary nutrients). Compared with other measures of fish habitat quality (e.g., Shannon–Wiener diversity index and species richness), the WFI was the only index that was significantly related to the degree of water quality degradation and wetlands condition, as indicated by an independent index of wetland quality, the Water Quality Index (WQI). WQI ranks sites according to deterioration in water quality and is statistically related to the degree of land-use alteration in wetland watersheds. We demonstrate the usefulness of the WFI for detecti...