David L. Fanslow

Filtration Rates of the Zebra Mussel ( Dreissena polymorpha )on Natural Seston from Saginaw Bay, Lake Huron

Filtration rates of the zebra mussel (Dreissena polymorpha) on natural seston from two different regions in Saginaw Bay were determined on a monthly basis from April to October in 1992 and 1993. The two regions represent contrasting trophic conditions, with the inner bay more eutrophic than the outer bay. Mean filtration rate was 16.2 mUmg/h (range 4.0 to 40.7 mL/mg/h) over the entire 2-year period. Filtration rates on seston from the inner bay were significantly lower than rates on seston from the outer bay in 1992, but no differences were apparent in 1993. Lower rates were attributed to higher concentrations of seston {chlorophyll, paniculate organic carbon, and total suspended solids) found in the inner bay in 1992. In 1992, overall filtration rates were related to seston concentrations as described by a negative exponential function. In 1993, seston concentrations were uniformly low, and a relationship between filtration rates and concentrations was not observed. Further, filtration rates were not related to seston composition, as determined by the ratio of POC’TSS and chl:TSS. Maximum filtration rates were apparently related to temperature, with highest maximum rates occurring at 10–20°C. Based on measured filtration rates and overall standing stocks, the Dreissena population in the inner bay was capable of filtering the volume of the inner bay 1.3 times per day in 1992 and 0.2 times per day in 1993.

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 O2 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.

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

Abstract 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 Akaikes 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 pred...

Trends in benthic macroinvertebrate populations in southern Lake Michigan

Long-term changes in bemhic macroinvertebrate populations have long been used to assess trends in environmemal conditions and trophic status in the Great Lakes (for summary see CooK & joHNSON 1974). Until the late I960s/early 1970s, a!though some sensitive forms declined, the general trend was for an increase in numbers of most bemhic groups, particularly in the bays and nearshore areas. These increases reflected increasing nutrient loads (phosphorus) and greater system productivity, allowing greater inputs of organic material to the bemhic region. This material served as food for the taxa most able to utilize this resource. To reverse eutrophic trends, phosphorus control measures were implemented in the mid-1970s. By the early 1980s, overall productivity declined in many areas and water quality improved as indicated by decreased macroinverrebrate densities and a return of more sensitive taxa (JoHNSON & McNEIL 1986, ScHLOESSER et al. 1995, KRIEGER & Ross 1993). lmerpretations of trophic trends based o n macroinvertebrate populations became confounded in the late 1980s when the zebra mussel, Dreissena polymorpha, became established in the Great Lakes. Many benthic taxa increased in density by utilizing Dreissena biodeposits as a source of food, or by taking advantage of increased substrate complexity and structure resulting from dense mussel clumps (GRIFFITHS 1993, STEWART & HAYNES 1994, STEWART et al. 1998). Dreissena negatively affected other taxa through food competition or physical disruption (NALEPA et al. 1996, DERMOTT & I<EREC 1997). lmplications of Dreissena-induced changes are clearit can no longer be assumed that changes in benthic macroinvertebrate densities and composition are primarily a function of changes in trophic status. This is true not only for areas with high Dreissena abundances, but also for areas without high abundances that are located in well-mixed regions in dose proximity to Dreissena-infested areas (NALEPA & FAHNENSTIEL 1995). In this paper, we summarize trends in densities of the major bemhic macroinvertebrate groups in southern Lake Michigan over the period between the mid-1960s and 1993. Changes in densities between the 1960s and 1980-1981 were reported by NALEPA (1987), and changes between 1980-1981 and 1992-1993 were reported by NALEPA et al. (1998). Our purposes here are to summarize trends over the entire period, and to closely examine potential reasons for the changes observed.