Henry A. Vanderploeg

CALCULATION AND USE OF SELECTIVITY COEFFICIENTS OF FEEDING: ZOOPLANKTON GRAZING *

Vanderploeg, H.A. and Scavia, D., 1979. Calculation and use of selectivity coefficients of feeding: zooplankton grazing. Ecol. Modelling, 7: 135--149. A straightforward method of calculating selectivity coefficients (Wii) of predation from raw data, mortality rates of prey, filtering rates, feeding rates and electivity indices is derived. Results from a comparison of selectivity coefficients for the copepod Diaptomus oregonensis grazing under a number of experimental conditions suggest that Wijs for sizeselective feeding are invariant, a conclusion also supported by the leaky-sieve model. Recommendations are made on how to use Wijs in linear and nonlinear feeding constructs for zooplankton and other animals.

Recent changes in primary production and phytoplankton in the offshore region of southeastern Lake Michigan

ABSTRACT Phytoplankton abundance, composition, and productivity were monitored on a bi-weekly basis from March/ April through November/December at two offshore stations in southeastern Lake Michigan in 1983–1987, 1995– 1998 and 2007–2008 (exception 1983–1984 which were sampled from May to August). During the spring isothermal mixing period, surface-mixed layer (SML) chlorophyll a and phytoplankton biomass (carbon) and water column primary productivity decreased substantially in 2007–2008 as compared to 1995–1998 (66%, 87%, and 70% decrease, respectively). Smaller or no decreases were noted between 1983–1987 and 1995–1998 (chlorophyll a 23% decrease, phytoplankton biomass 5% increase, and production 22% decrease). Phytoplankton composition also changed during the spring isothermal mixing period in 2007–2008 as compared to 1983–1987 and 1995–1998; all phytoplankton groups with the exception of cyanobacteria and chlorophytes exhibited dramatic reductions in 2007–2008. The pronounced changes in phytoplankton properties during spring mixing in 2007–2008 were attributed to the filtering activities of the quagga mussel (Dreissena rostriformis bugensis). During mid- and late thermal stratification periods, SML phytoplankton chlorophyll a and phytoplankton carbon and water column primary production exhibited only one significant change across all decades (mid-stratification production in 2007–2008 as compared to 1995–1998 and 1983–1987). Phytoplankton compositional changes in the SML also were limited during thermal stratification. The size of the deep chlorophyll layer (DCL) in 2007–2008 was similar to or smaller than those in 1983–1987 and 1995–1998. However, phytoplankton composition in the DCL changed as net diatoms constituted < 5% of total phytoplankton in the 2007–2008 DCL but over 50% in 1983–1987 and 1995–1998.

Dreissena and the disappearance of the spring phytoplankton bloom in Lake Michigan

ABSTRACT We determined the clearance rates of the profunda morph of the quagga mussel (Dreissena bugensis) using seston and Cryptomonas ozolini, a high-quality algal food, for the temperature range 1–7°C, which is the full temperature range this morph is likely to experience during isothermal conditions or in the hypolimnion of deep lakes. Experiments at 3 °C with the shallow-water morph of the quagga and the zebra mussel provided very similar results. The clearance rates were combined with dreissenid abundance in 0–30 m, 30–50 m, 50–90 m, and >90 m depth zones of the southern basin of Lake Michigan to calculate a maximum (using Cryptomonas) and minimum (using seston) fraction of the water column cleared (FC) per day in the different depth zones at 3 °C to determine dreissenid impact on the spring phytoplankton bloom from 1994 to 2008. Starting in 2003 or 2004 with the replacement of zebra mussels by quagga mussels in shallow water and expansion of quagga mussel biomass in deep water, FC began to exceed likely phytoplankton growth in the 30–50 m zone. In 2007–2008, FC greatly exceeded likely phytoplankton growth by a factor of about 5 in the 30- to 50-m depth zone, where dreissenids were extremely abundant. Low FC in the offshore region led to the hypothesis of a mid-depth carbon (C) and phosphorous (P) sink caused by mussel uptake of seston-associated C and P that affected not only the mid-depth region, but also the offshore region “downstream” of the mid-depth zone.

A model study of the coupled biological and physical dynamics in Lake Michigan

A coupled physical and biological model was developed for Lake Michigan. The physical model was the Princeton ocean model (POM) driven directly by observed winds and net surface heat flux. The biological model was an eight-component, phosphorus-limited, lower trophic level food web model, which included phosphate and silicate for nutrients, diatoms and non-diatoms for dominant phytoplankton species, copepods and protozoa for dominant zooplankton species, bacteria and detritus. Driven by observed meteorological forcings, a 1-D modeling experiment showed a controlling of physical processes on the seasonal variation of biological variables in Lake Michigan: diatoms grew significantly in the subsurface region in early summer as stratification developed and then decayed rapidly in the surface mixed layer when silicate supplied from the deep stratified region was reduced as a result of the formation of the thermocline. The non-diatoms subsequently grew in mid and late summer under a limited-phosphate environment and then declined in the fall and winter as a result of the nutrient consumption in the upper eutrophic layer, limitation of nutrients supplied from the deep region and meteorological cooling and wind mixing. The flux estimates suggested that the microbial loop had a significant contribution in the growth of microzooplankton and hence, to the lower-trophic level food web system. The model results agreed with observations, suggesting that the

Evaluation of Different Phytoplankton for Supporting Development of Zebra Mussel Larvae (Dreissena polymorpha): The Importance of Size and Polyunsaturated Fatty Acid Content

Abstract A marine alga and variety of freshwater algae of known polyunsaturated fatty acid (PUFA) composition were evaluated in the laboratory for their ability to promote development of Dreissena polymorpha from egg through settling and metamorphosis. The three species of algae which promoted development—the marine and the freshwater strain of Chlorella minutissima and the cryptophyte Rhodomonas minuta —were all rich in long-chain (≥ 18 C) n-3 PUFAs, including some 20:5 or 22:6 PUFAs. Dreissena s need for long-chain n-3 PUFAs is consistent with the needs of marine bivalves and freshwater zooplankton. Larval growth rate on the freshwater strain of C. minutissima was about the same as that for R. minuta , but much faster than that for the marine strain of C. minutissima . Mean ages at settling for larvae fed the freshwater C. minutissima were 15 d at 26°C, 17 d at 24°C, and 22 d at 22° C Low survival rates reported for the larvae in nature may be related to low concentrations of long-chain n-3 PUFAs in blue-green and some green algae that dominate eutrophic lakes in summer.

Long-Term and Recent Changes in Southern Lake Michigan Water Quality with Implications for Present Trophic Status

ABSTRACT Southern Lake Michigan has changed in response to alterations in nutrients and invasive species. NOAA and EPA monitoring results are used to examine those changes. NOAA provides detailed seasonal resolution, but limited spatial coverage, whereas the EPA provides more spatial coverage, but limited seasonal resolution. We compare changes in total phosphorus (TP), silica, nitrate plus nitrite, and chlorophyll concentrations from before and after the invasion by the quagga mussel (Dreissena rostriformis bugensis). Although TP at NOAA stations was consistently higher than at EPA stations, both confirm declines in spring and summer surface mixed layer (SML) conditions. Chlorophyll differed at EPA and NOAA stations before quagga mussel invasion, but not after the invasion. Spring chlorophyll decreased at NOAA stations after the invasion, but summer conditions did not change at either set of stations. Pre-invasion silica at NOAA stations was slightly higher than at EPA stations, and the lakes Si reservoir increased over the study period. Basin-scale spring Si increased gradually, whereas summer SML Si increased dramatically after 2003, likely reflecting reduced diatom production. Basin-scale nitrate increased significantly from pre- to post-invasion in both spring and summer. Summer nitrate utilization declined drastically in recent years, likely reflecting reduced phytoplankton production. TP loads decreased; however, the timing of changes in chlorophyll and Si and nitrate utilization suggest the recent increase in dreissenid filtering dramatically reduced spring phytoplankton abundance and production across the entire southern basin. The offshore pelagic zone of the historically mesotrophic southern Lake Michigan is now similar to oligotrophic Lake Superior.

Approaching storm: Disappearing winter bloom in Lake Michigan

ABSTRACT Between 1990 and 2001, late-winter phytoplankton blooms were common in parts of the lower Great Lakes (southern Lake Michigan, Saginaw Bay and southern Lake Huron, and western Lake Erie), providing resources for over-wintering Zooplankton. In Lake Michigan up to 2001, detailed remote sensing and ship studies documented well-developed late-winter blooms in the southern gyre (circular bloom termed the ‘doughnut’). However, from 2001 to 2008, the winter blooms in Lake Michigan also supported early season veliger larvae from the introduced, cold-water adapted “profunda” morph of quagga mussels (Dreissena rostriformis bugensis). Remote sensing and ship studies revealed that settled mussels caused an extraordinary increase in water transparency and a simultaneous decrease of Chl a in the late-winter bloom. Before quagga mussels in 2001, water transparency was 74–85% at deep-water sites, whereas it increased progressively to 89% by 2006 and 94–96% by 2008. Chlorophyll a concentrations in the gyre rings were 1.1–2.6 µg/L in 2001, declining to 0.5–1.7 µg/L by 2006 and 0.4–1.5 µg/L by 2008. The reduction of Chl a in the winter bloom rings from 2001 to 2008 was 56–78% for the western limb and 74–75% for the eastern limb. Zooplankton species abundance, composition and abundance also changed, as cyclopoid copepods became very scarce and overwintering omnivorous calanoid copepods declined. Reduction in late-winter phytoplankton and Zooplankton poses a serious threat to open-water food webs.

Diet and prey selection of alewives in Lake Michigan: Seasonal, depth, and interannual patterns

Abstract To evaluate the current diet of alewives Alosa pseudoharengus and interactions with their prey in light of recent changes in Lake Michigan, we determined the seasonal diet and prey selectivity of large (>100 mm total length) and small (<100 mm) alewives in southeastern Lake Michigan. Selectivity and diet were evaluated on a biomass basis for alewives collected near Muskegon, Michigan, during June, July−August, and October 1999–2001. Fish were sampled from three depth zones: shallow (15–25 m), transitional (35–55 m), and deep (65–90 m). Prey selectivity and diet patterns indicated that alewives had considerable flexibility in adjusting to prey availability, which varied by season, depth zone, and year. Although small copepods were an abundant prey item throughout the year and in all depth zones, they were mainly important in the diet (large and small alewives) in June and at the shallow stations, where many of the other prey types were not available. Despite declining numbers, Diporeia continued t...

Plankton ecology in an ice-covered bay of Lake Michigan: utilization of a winter phytoplankton bloom by reproducing copepods

Plankton ecology was examined during the 1986 winter in Grand Traverse Bay, a 190 m deep, fjordlike bay on Lake Michigan. Before ice cover, algal concentration was low and uniformly distributed with depth, as it is in open Lake Michigan. During ice cover (February and March), a bloom of a typical winter-spring phytoplankton community developed in the upper 40 m, resulting in a 4 to 7-fold increase in feeding rate of adult Diaptomus spp. High algal concentration and zooplankton feeding persisted after ice melt (April). During and after ice cover, lipid concentrations of Diaptomus dropped rapidly from 34% of dry weight to 17 % because of egg production. High incident photosynthetically active radiation (PAR), high (45–50%) PAR transmittance of the ice due to little snow on the ice, and water column stability were probably responsible for the bloom. High ice transparency may be a common feature of large lakes and bays, where strong winds blow snow cover off the ice, or at low latitudes where snowmelt due to occasional rains and warm temperature is common. Winter reproducing calanoid copepods use these blooms to increase their reproductive output.

Feeding ecology of emerald shiners and rainbow smelt in central Lake Erie

ABSTRACT To better understand the feeding ecology of two important Laurentian Great Lakes prey species, rainbow smelt Osmerus mordax and emerald shiners Notropis atherinoides, we quantified the diet composition, selectivity, daily ration, and diet overlap of both species in offshore central Lake Erie during May through October 2005, which spanned a period of severe hypolimnetic hypoxia (<2 mg O2/L). Rainbow smelt fed upon a variety of prey taxa, including zooplankton, chironomid pupae and larvae, and fish, whereas emerald shiners primarily consumed cladocerans, if available. In turn, diet overlap between rainbow smelt and emerald shiners was low except during September when hypolimnetic hypoxia reduced rainbow smelt access to benthic prey. Rainbow smelt most frequently selected chironomid pupae, while emerald shiners generally selected pupae or large predatory cladocerans (Leptodora or Bythotrephes). Daily ration and individual consumption by rainbow smelt were 54–68% less during hypoxia than at the same site during stratified pre-hypoxic or mixed post-hypoxic conditions. Although emerald shiner daily ration and individual consumption decreased between pre-hypoxic and hypoxic periods, it continued to decrease during the post-hypoxic period, suggesting that reduced consumption may not have been linked to hypoxic conditions. Ultimately, our findings suggest that emerald shiners are as important regulator of zooplankton abundance in the Great Lakes as rainbow smelt, given their potentially high mass-specific consumption rates, selectivity and diet patterns, and current high abundance.