James R. Liebig

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.

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.

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.

Concentration-Variable Interactions Between Calanoid Copepods and Particles of Different Food Quality: Observations and Hypotheses

The two major issues of research in feeding behavior of calanoid copepods and, indeed, in all research on zooplankton feeding have been concentration- variable selection and food quality (Vanderploeg in press). The concentration- variable selectivity hypotheses in its earliest form stated that copepods would track peaks in natural particle-size spectra, that is, focus their efforts on the most abundant food (Vanderploeg 1981a; Vanderploeg et al. 1984). The counter hypothesis is that selectivity, when expressed as W’ or other appropriate measures, remains invariant no matter what the relative proportions or total concentration of the various food types (Vanderploeg and Scavia 1979a,b; Vanderploeg 1981a; Vanderploeg et al. 1984).

Lake Michigan Bythotrephes Prey Consumption Estimates for 1994–2003 using a Temperature and Size Corrected Bioenergetic Model

ABSTRACT Bythotrephes were collected on a regular basis at a 110 m deep reference station in Lake Michigan over a 10-year period 1994–2003. The measured population structure in conjunction with an updated bioenergetic model was used to estimate daily predation demands by Bythotrephes on the Zooplankton community. The bioenergetic model incorporated the effect of temperature on growth and respiration and used a scalable size structure to adjust for a dynamic range in size across the season. A general linear model was developed to apply the bioenergetic results to routinely collected field data for estimating predation needs. Daily population consumption needs were estimated to be approximately equal to Bythotrephes standing biomass but varied as a function of water temperature and percent instar composition. At a temperature of 18 °C the predation needs of the population were equal to the population biomass. At warmer temperatures (22– 24 °C) the daily needs were up to 35% above the population biomass. Within and across years the population was variable, while trend lines from the long-term data indicated biomass and predation needs had an initial peak in mid-August followed by a plateau period with a seasonal high peak mid-October. A decrease in the midseason long-term average size structure suggests that Bythotrephes may experience prey limitation during this time period of the year. Over the course of the 10-year period population cycles and peak biomass were fairly stable with no indication of a change in predation needs.

Vulnerability of Dreissena polymorpha Larvae to Predation by Great Lakes Calanoid Copepods: the Importance of the Bivalve Shell

Abstract Dreissena polymorpha larvae were vulnerable to predation by three different species of calanoid copepods, Diaptomus sicilis, Limnocalanus macrurus , and Epischura lacustris, when presented to these copepods in bottle experiments. The degree of vulnerability was dependent upon the stage of the larva and the type of predator: trochophore larvae (without shells) were much more vulnerable than D-stage larvae (with shells). D. sicilis and L. macrurus were offered algae as alternate food, and each cleared trochophore larvae at a higher rate than algae. However, the clearance rate for D. sicilis feeding on D-stage larvae was not significantly different from zero, suggesting that this suspension-feeding omnivore-herbivore was not able to ingest D-stage larvae. Of the three species, the large cruising predator, L. macrurus , had the highest clearance rate for trochophore larvae (55.8 mL • animal −1 • d −1 ), but had a significantly lower clearance rate for D-stage larvae, only one eighth of that for trochophores. The smaller predator, E. lacustris , was more adept than L. macrurus or D. sicilis at preying on D-stage larvae: its clearance rate for D-stage larvae (17.9 mL • animal-1 • d −1 ) was about one half of its clearance rate for trochophore larvae. Since bivalve larvae, including Dreissena , and copepods co-occur in many aquatic environments, our results suggest that copepod predation may have been a selective force for production of a protective shell early in the larval development of bivalves.

Temporal and spatial separation allow coexistence of predatory cladocerans: Leptodora kindtii, Bythotrephes longimanus and Cercopagis pengoi, in southeastern Lake Michigan

ABSTRACT The predatory cladocerans, Leptodora kindtii, Bythotrephes longimanus, and Cercopagis pengoi coexist in the waters of southeastern Lake Michigan near Muskegon, Michigan. Leptodora is indigenous, whereas Bythotrephes and Cercopagis are nonindigenous and became established in 1986 and 2000, respectively. To observe seasonal changes in their abundances, and relationships to each other, cladocerans were collected from 1994 to 2008 at an offshore (110-m) site, from 1998 to 2008 at a transitional (45-m) site and from 1999 to 2008 at a nearshore (15-m) site. Bythotrephes was most abundant at the offshore site compared to Leptodora and Cercopagis. Bythotrephes peak abundances usually occurred in autumn at all sites. Cercopagis tended to be more abundant at the nearshore site, and peak densities occurred in summer. At the mid-depth site, similar abundances occurred for all three predatory cladocerans, however, the date of peak abundance was usually earliest for Cercopagis, followed by Leptodora, and latest for Bythotrephes. In recent years, 2007 and 2008, densities of all three predatory cladocerans have increased. Temperature preference, fish predation, and competition between the invertebrate predators may all be important in allowing the dominance of one species over the other seasonally or spatially.

Chloroflexi CL500-11 Populations That Predominate Deep-Lake Hypolimnion Bacterioplankton Rely on Nitrogen-Rich Dissolved Organic Matter Metabolism and C1 Compound Oxidation

ABSTRACT The Chloroflexi CL500-11 clade contributes a large proportion of the bacterial biomass in the oxygenated hypolimnia of deep lakes worldwide, including the worlds largest freshwater system, the Laurentian Great Lakes. Traits that allow CL500-11 to thrive and its biogeochemical role in these environments are currently unknown. Here, we found that a CL500-11 population was present mostly in offshore waters along a transect in ultraoligotrophic Lake Michigan (a Laurentian Great Lake). It occurred throughout the water column in spring and only in the hypolimnion during summer stratification, contributing up to 18.1% of all cells. Genome reconstruction from metagenomic data suggested an aerobic, motile, heterotrophic lifestyle, with additional energy being gained through carboxidovory and methylovory. Comparisons to other available streamlined freshwater genomes revealed that the CL500-11 genome contained a disproportionate number of cell wall/capsule biosynthesis genes and the most diverse spectrum of genes involved in the uptake of dissolved organic matter (DOM) substrates, particularly peptides. In situ expression patterns indicated the importance of DOM uptake and protein/peptide turnover, as well as type I and type II carbon monoxide dehydrogenase and flagellar motility. Its location in the water column influenced its gene expression patterns the most. We observed increased bacteriorhodopsin gene expression and a response to oxidative stress in surface waters compared to its response in deep waters. While CL500-11 carries multiple adaptations to an oligotrophic lifestyle, its investment in motility, its large cell size, and its distribution in both oligotrophic and mesotrophic lakes indicate its ability to thrive under conditions where resources are more plentiful. Our data indicate that CL500-11 plays an important role in nitrogen-rich DOM mineralization in the extensive deep-lake hypolimnion habitat.

Plankton survey system

The Plankton Survey System (PSS), developed at the National Oceanic and Atmospheric Administrations (NOAA) Great Lakes Environmental Research Laboratory (GLERL), has been designed to collect high temporal and spatial resolution marine environmental data in three dimensions. The system has proven effective in providing valuable survey information before, during and after sediment re-suspension events in Lake Michigan in support of GLERLs NOAA/NSF funded Episodic Events Great Lakes Experiment (EEGLE) program. The PSS is a towed multi-sensor platform capable of measuring turbidity, chlorophyll a, photosynthetically active radiation (PAR), conductivity, temperature, and zooplankton spatial distributions. All sensors are integrated using a serial data interface. All data are geo-referenced and registered with time, depth, and vehicle pitch, roll, and speed information. A deck unit supplies power for the underwater vehicle components and provides interfaces for data collection and system monitoring. System software provides real-time display of all marine environmental measurements and vehicle status. Zooplankton spatial and individual size distributions are measured using an optical plankton counter (OPC). The OPC measures particle size distributions (0.25-14 mm) using an LED array and a photodiode receiver. Deflections caused by particles crossing the LED generated light beam (4/spl times/20/spl times/100 mm) are detected by the receiver and digitized. Present work is focused on moving the OPC beyond use as merely a survey tool to calibrating the instrument using laboratory and field measurements. Laboratory calibration plans include the use of specified particles to establish a reference and subsequent investigations using live zooplankton samples. A range of issues involving the implications of variations in zooplankton body characteristics on OPC detection threshold, turbidity on OPC signal-to-noise ratio, tow vehicle orientation and vehicle and OPC channel turbulence are also investigated.