Characteristics and Potential Causes of Declining \u3ci\u3eDiporeia\u3c/i\u3e spp. Populations in Southern Lake Michigan and Saginaw Bay, Lake Huron

Populations of the amphipods Diporeia spp. are declining in all of the Great Lakes except Lake Superior. We examine characteristics and potential causes of declines in southern Lake Michigan and outer Saginaw Bay, Lake Huron. Amphipod populations began to decline within 3-4 years after zebra mussels (Dreissena polymorpha) colonized both areas. In Lake Michigan, which was better studied, the decline occurred first in shallow waters (\u3c30 m) and then progressed deeper (51-90 m). Between 1980- 1981 (pre-Dreissena) and 1998-1999 (post-Dreissena), densities at sites in these two depth intervals declined 92% and 58%, respectively. At a 45-m site in southeastern Lake Michigan, densities of Diporeia spp. declined to near zero within six months even though mussels were never collected at the site itself. At a nearby 45-m site, densities declined gradually to zero over a six-year period and correlated with increased mussel densities. Although mussels are likely outcompeting Diporeia spp. populations for food, and food limitation is probably a contributing factor to population declines, populations show no physiological signs of starvation; lipid content is at a maximum as densities approach zero. Pathogens, fish predation, contaminants, and low dissolved oxygen do not appear to be the sole causes of population declines. The decline of Diporeia spp. is likely to continue as dreissenid populations expand

Characteristics and Potential Causes of Declining \u3ci\u3eDiporeia\u3c/i\u3e spp. Populations in Southern Lake Michigan and Saginaw Bay, Lake Huron

Populations of the amphipods Diporeia spp. are declining in all of the Great Lakes except Lake Superior. We examine characteristics and potential causes of declines in southern Lake Michigan and outer Saginaw Bay, Lake Huron. Amphipod populations began to decline within 3-4 years after zebra mussels (Dreissena polymorpha) colonized both areas. In Lake Michigan, which was better studied, the decline occurred first in shallow waters (\u3c30 m) and then progressed deeper (51-90 m). Between 1980- 1981 (pre-Dreissena) and 1998-1999 (post-Dreissena), densities at sites in these two depth intervals declined 92% and 58%, respectively. At a 45-m site in southeastern Lake Michigan, densities of Diporeia spp. declined to near zero within six months even though mussels were never collected at the site itself. At a nearby 45-m site, densities declined gradually to zero over a six-year period and correlated with increased mussel densities. Although mussels are likely outcompeting Diporeia spp. populations for food, and food limitation is probably a contributing factor to population declines, populations show no physiological signs of starvation; lipid content is at a maximum as densities approach zero. Pathogens, fish predation, contaminants, and low dissolved oxygen do not appear to be the sole causes of population declines. The decline of Diporeia spp. is likely to continue as dreissenid populations expand

Seasonal changes in the respiratory electron transport system (ETS) and respiration of the zebra mussel, Dreissena polymorpha in Saginaw Bay, Lake Huron

Electron transport system activity (ETS) and respiration rates (R) of the zebra mussel, Dreissena polymorpha , were determined monthly from April to November over 2 years at two sites in Saginaw Bay, Lake Huron. The sites were located in the inner and outer bay and contrasted in food quantity and quality. ETS ranged from 2 to 40 μg O 2 mg DW −1 h −1 over the study period. Both ETS and respiration were strongly related to temperature, and maximum values were found between June and August. ETS also peaked in June/July when assays were conducted at a constant temperature (25 °C), indicating other factors besides temperature affected metabolic activity. R:ETS ratios decreased with increased temperature at the inner bay site, but trends were minimal at the outer bay site. In late summer, blooms of the cyanophyte Microcystis occurred in the inner bay, likely depressing filtration rates, and leading to lower respiration rates relative to ETS. ETS activity was consistently higher in the outer bay and was likely a result of higher food quality. Despite these spatial differences, annual mean R:ETS ratios varied only from 0.04 to 0.09 at the two sites over the 2-year period. Based on these values, ETS may be useful as an indicator of long-term metabolic activity in annual energy budgets of D. polymorpha . However, food conditions differentially affect respiration relative to ETS, and variability in this ratio must be considered when interested in shorter time scales.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42896/1/10750_2004_Article_334245.pd

ULBPs, Novel MHC Class I–Related Molecules, Bind to CMV Glycoprotein UL16 and Stimulate NK Cytotoxicity through the NKG2D Receptor

AbstractThe human cytomegalovirus glycoprotein, UL16, binds to two members of a novel family of molecules, the ULBPs, and to the MHC class I homolog, MICB. The ULBPs are GPI-linked glycoproteins belonging to the extended MHC class I family but are only distantly related to MICB. The ULBP and MICB molecules are ligands for the activating receptor, NKG2D/DAP10, and this interaction is blocked by a soluble form of UL16. The ULBPs stimulate cytokine and chemokine production from NK cells, and expression of ULBPs in NK cell–resistant target cells confers susceptibility to NK cell cytotoxicity. Masking of NK cell recognition of ULBP or MIC antigens by UL16 provides a potential mechanism by which human cytomegalovirus–infected cells might evade attack by the immune system

Spatial-temporal variability of in situ cyanobacteria vertical structure in Western Lake Erie: Implications for remote sensing observations

Remote sensing has provided expanded temporal and spatial range to the study of harmful algal blooms (cyanoHABs) in western Lake Erie, allowing for a greater understanding of bloom dynamics than is possible through in situ sampling. However, satellites are limited in their ability to specifically target cyanobacteria and can only observe the water within the first optical depth. This limits the ability of remote sensing to make conclusions about full water column cyanoHAB biomass if cyanobacteria are vertically stratified. FluoroProbe data were collected at nine stations across western Lake Erie in 2015 and 2016 and analyzed to characterize spatio-temporal variability in cyanobacteria vertical structure. Cyanobacteria were generally homogenously distributed during the growing season except under certain conditions. As water depth increased and high surface layer concentrations were observed, cyanobacteria were found to be more vertically stratified and the assumption of homogeneity was less supported. Cyanobacteria vertical distribution was related to wind speed and wave height, with increased stratification at low wind speeds (bathymetry and environmental conditions could lead to improved biomass estimates. Additionally, cyanobacteria contributions to total chlorophyll-a were shown to change throughout the season and across depth, suggesting the need for remote sensing algorithms to specifically identify cyanobacteria

Indirect consequences of hypolimnetic hypoxia on zooplankton growth in a large eutrophic lake

Diel vertical migration (DVM) of some zooplankters in eutrophic lakes is often compressed during peak hypoxia. To better understand the indirect consequences of seasonal hypolimnetic hypoxia, we integrated laboratory-based experimental and field-based observational approaches to quantify how compressed DVM can affect growth of a cladoceran, Daphnia mendotae, in central Lake Erie, North America. To evaluate hypoxia tolerance of D. mendotae, we conducted a survivorship experiment with varying dissolved oxygen concentrations, which demonstrated high sensitivity of D. mendotae to hypoxia (≤2 mg O2 l−1), supporting the field observations of their behavioral avoidance of the hypoxic hypolimnion. To investigate the effect of temporary changes in habitat conditions associated with the compressed DVM, we quantified the growth of D. mendotae, using a 3 (food quantity) × 2 (temperature) factorial design laboratory experiment. Neither food quantity nor temperature affected short-term growth in body length of D. mendotae. However, D. mendotae RNA content (an index of short-term condition) decreased under starvation, indicating an immediate response of short-term feeding on condition. We further evaluated the effect of hypoxia-induced upward shifts in vertical distribution by quantifying the RNA content of D. mendotae from central Lake Erie before and during peak hypoxia. Despite high temperature and food quantity in the upper water column, RNA content in field-collected D. mendotae remained low during peak hypoxia. Furthermore, D. mendotae collected during peak hypoxia consisted of only small-bodied

Reliability of Bioelectrical Impedance Analysis for Estimating Whole‐Fish Energy Density and Percent Lipids

We evaluated bioelectrical impedance analysis (BIA) as a nonlethal means of predicting energy density and percent lipids for three fish species: Yellow perch Perca flavescens, walleye Sander vitreus, and lake whitefish Coregonus clupeaformis. Although models that combined BIA measures with fish wet mass provided strong predictions of total energy, total lipids, and total dry mass for whole fish, including BIA provided only slightly better predictions than using fish mass alone. Regression models that used BIA measures to directly predict the energy density or percent lipids of whole fish were generally better than those using body mass alone (based on Akaike’s information criterion). However, the goodness of fit of models that used BIA measures varied widely across species and at best explained only slightly more than one‐half the variation observed in fish energy density or percent lipids. Models that combined BIA measures with body mass for prediction had the strongest correlations between predicted and observed energy density or percent lipids for a validation group of fish, but there were significant biases in these predictions. For example, the models underestimated energy density and percent lipids for lipid‐rich fish and overestimated energy density and percent lipids for lipid‐poor fish. A comparison of observed versus predicted whole‐fish energy densities and percent lipids demonstrated that models that incorporated BIA measures had lower maximum percent error than models without BIA measures in them, although the errors for the BIA models were still generally high (energy density: 15‐18%; percent lipids: 82‐89%). Considerable work is still required before BIA can provide reliable predictions of whole‐fish energy density and percent lipids, including understanding how temperature, electrode placement, and the variation in lipid distribution within a fish affect BIA measures.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141722/1/tafs1519.pd

Recent changes in density, biomass, recruitment, size structure, and nutritional state of \u3ci\u3eDreissena\u3c/i\u3e populations in southern Lake Michigan

Trends in density, biomass, population structure, and nutritional state of Dreissena polymorpha and Dreissena rostriformis bugensis were examined in southern Lake Michigan between the 1990s and 2008. Density and biomass of D. polymorpha increased to a peak in the early 2000s and then declined. In contrast, D. rostriformis bugensis was first found in the southern basin in 2001 and has continued to increase in density or biomass at all depths ever since. In 2008, maximum mean density of D. rostriformis bugensis occurred at 16–30 m (19,000/m2), but maximum biomass (AFDW) occurred at 31–50 m (43.9 g/m2). D. rostriformis bugensis has only recently (since 2005) began to increase at depths \u3e50 m. When both species were present in 2004 at depths \u3c50 m, a condition index (CI) for D. rostriformis bugensis was 27% higher, and shell weight per shell length was 48% lower compared to D. polymorpha. For D. rostriformis bugensis, CI decreased in 2008 compared to 2004 at 25 m and 45 m, but biochemical content (lipid, glycogen) did not. Seasonal changes in both RNA/DNA ratio (growth) and ETS (metabolic activity) in D. rostriformis bugensis were unaffected by reproductive activity, and only ETS appeared to change seasonally relative to bottom temperatures. Spawning of D. rostriformis bugensis occurred in late summer at 25 m, but occurred in spring at 45 m. Veliger densities peaked in both spring and late summer at both depths. Future population expansion (biomass) is expected to be most rapid at depths \u3e50 m

Recent changes in benthic macroinvertebrate populations in Lake Huron and impact on the diet of lake whitefish (\u3ci\u3ecoregonus clupeaformis\u3c/i\u3e)

Surveys of the benthic macroinvertebrate community were conducted in the main basin of Lake Huron in 2000 and 2003, and corresponding studies of lake whitefish diets were conducted in 2002-2004. Populations of three major benthic taxa, Diporeia spp., Sphaeriidae, and Chironomidae, declined dramatically between 2000 and 2003, with densities declining 57%, 74%, and 75% over this 3-year period. By 2003, Diporeia, an important food source for lake whitefish, was gone or rare at depths \u3c50 m except in the far northeastern portion of the lake. In contrast, densities of the Dreissena bugensis (quagga mussel) increased between 2000 and 2003, particularly at the 31-50 m depth interval, while densities of the zebra mussel Dreissena polymorpha remained stable. As expected, the diet of lake whitefish varied with fish size. Age-0 lake whitefish fed mainly zooplankton, most of which were Daphnia (98%). Medium lake whitefish (\u3c350 mm excluding age-0 fish) fed mainly on zooplankton, Chironomidae, and Dreissena bugensis, and large lake whitefish (350 to 688 mm) fed mainly on D. bugensis and Gastropoda. The diet of medium and large lake whitefish reflected the changing nature of the benthic community; that is, Diporeia was rarely found in the diet while D. bugensis played a prominent role. Since Diporeia has a much higher energy content than D. bugensis, contrasting density trends in the two organisms will have long term consequences to the relative health of lake whitefish populations in the lake