Excretion of total phosphorus,dissolved reactive phosphorus,ammonia, and urea by Lake MichiganMysis relicta

Rates of nutrient release byMysis relicta in Lake Michigan were measured on five nights at a 45-m station near Milwaukee, Wisconsin, U.S.A., in the summer of 1977. Nocturnal vertical migrations of the mysids were monitored with both echosounder tracings and vertical net tows. Estimates of the total areal dry mass of the mysids ranged from 600 to 1 820 mg m–2. Rates of release of dissolved reactive phosphorus, total phosphorus, ammonia, and urea were measured in dark incubations on shipboard. Excretion experiments were initiated immediately after mysids were collected from each of several vertical net hauls. The depths of maximum mysid densities corresponded approximately with a deep phytoplankton peak located in the vicinity of the thermocline. Semiquantitative demands for N and P by phytoplankton within this peak were obtained from¹⁴C estimates of primary production from a previous study, assuming a constant C:N:P ratio for the algae. These algal nutrient demands were compared to potential N and P release by the mysids to obtain a first approximation of the relative rates of nutrient supply and demand for the field phytoplankton populations. Our analysis indicates that mysids may directly supply about 1–10% of the daily N and P demands of the phytoplankton in the deep peak. However, indirect interactions betweenMysis relicta and other organisms, such as small zooplankton and fishes, could be major factors in nutrient recycling within the metalimnion and subthermocline region of Lake Michigan.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin.Contribution No. 238, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Wisconsin.     

Influence of experimental conditions on nitrogenous excretion by Lake MichiganMysis relicta (Lovén): laboratory studies with animals acclimated inFragilaria

In laboratory experiments, rates of excretion of ammonia and urea by Lake MichiganMysis relicta were compared for animals incubated in the presence and the absence of algal food (Fragilaria crotonensis chemostat outflow). Prior to experiments, all animals were acclimated to laboratory conditions and the experimental food for 2–4 weeks. Algae used in experiments were enriched in the dark with nutrients (N and P) prior to experimental incubation.There were no significant differences in the ammonia and urea excretion rates of mysids incubated in filtered water compared to those inFragilaria cultures, or in ammonia excretion rates either as a function of individual size or sex of the mysid or of its having been held at 5 °C, 10 °C, or 15 °C. Ammonia excretion rates measured between 4 and 8 h of incubation were significantly higher than those between 1–3 h and 8–15 h, for mysids held both in filtered water and inFragilaria cultures. The results are compared to those from shipboard incubations in a previous study and are discussed with respect to physiological regulation of nitrogenous waste production.Contribution No. 234, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.Contribution No. 234, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.     

In situ predatory behavior ofMysis relicta in Lake Michigan

Selectivity coefficients (W) and predation rates on Lake Michigan zooplankton were determined forMysis relicta during spring through fall using anin situ method. W values indicated the following ranked order of prey preference: Cladocera > copepod copepodites and copepod nauplii > adult diaptomids and cyclopoids. With few exceptions, W values for different prey categories remained fairly constant despite greatly changing relative abundances of prey. Predation rates and prey selectivity were similar in most cases to those determined in laboratory studies. Ingestion rates (percent dry body weight · day^–1) were correlated to total prey biomass (r = 0.38) and to effective prey biomass (r = 0.85), where the weighting factors were overall mean selectivity coefficients for the different prey categories. This result suggested that seasonally varying composition of prey caused much of the variation in ingestion rates among experiments. Feeding trials performed at the same depth with daytime and nighttime assemblages of zooplankton indicated that Cladocera may escape heavyMysis predation at night by migrating from the metalimnetic-hypolimnetic interface into the epilimnion.Contribution 333 from the Great Lakes Research Division, The University of Michigan and contribution 287 from the Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration.Contribution 333 from the Great Lakes Research Division, The University of Michigan and contribution 287 from the Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration.     

Xenopus laevis larvae (Amphibia,Anura) as model suspension feeders

Larvae of the South African clawed frog, Xenopus laevis (Daudin), are efficient, obligate suspension feeders. We examine the relationship between the ambient particle concentration offered these larvae as food and their filtering, ingestion, and buccal pumping rates. We demonstrate that: (i) the larvae can sense and respond to a broad range of particle concentrations, down to 0.2 mg 1^–1 (dry weight); (ii) their metabolic needs theoretically can be met by particle concentrations as low as 5 mg 1^–1; and (iii) their patterns of regulation of filtering and ingestion fit predictions from certain models used to describe zooplankton feeding dynamics. Two such models are discussed: the modified Monod (Michaelis-Menten) model, with a lower threshold below which the tadpoles do not feed, and an energy optimization model. Both the models and the observed behavior of the tadpoles allow for stability of populations of food organisms. Tadpole feeding dynamics apparently are compatible with both the predictions and assumptions of these models, suggesting similar regulation of feeding by tadpoles and zooplankton. However, the size, morphology, and behavior of X. laevis larvae make their feeding regulation uniquely accessible to direct observation.Contribution No. 223, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.Contribution No. 223, Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.     

Size-frequency estimates of secondary production byMysis relicta in Lakes Michigan and Huron

Data from five Great Lakes studies ofMysis relicta populations were reanalyzed to calculate secondary production estimates using the size-frequency method. Production estimates (P) ranged from 0.25 to 3.2 g dry weight m^–2 yr^–1. Average annual biomass {xxB} and mean annual density (xxD) were 0.11–1.11 g dry weight/ m² and 25–434 animals/ m², respectively. P:{xxB} ratios varied only between 2.2 and 3.3. Maximum and minimum biomass values within a study varied by a factor of 519 for one study but by less than 17 for the others. Highest estimates of P, {xxB} and {xxD} were calculated for collections from a 50-m station in Lake Michigan despite the larger populations suspected to be present at greater depths sampled in the other studies. These conservative estimates provide a basis for scaling trophic interactions involvingM. relicta and emphasize findings by previous workers that night-time sampling with vertical net hauls is the best available technique for quantitative studies ofM. relicta populations in the Great Lakes.     

The influence of phytoplankton composition on the relative effectiveness of grinding and sonification for chlorophyll extraction

The chlorophyll recovery efficiency was compared between control, ground, and sonified samples. The results showed significant improvement between control and ground samples but not between control and sonified samples. Neither prolonging time of sonification nor using an ice bath during filter grinding improved efficiency. Higher chlorophyll a recovery was obtained from ground samples than from sonified ones, when the water samples contained centric diatoms and filamentous blue-green algae. When total phytoplankton numbers were high, there was a distinct advantage in using grinding rather than sonification for chlorophyll c recovery.Contribution no. 313 of the Great Lakes Research Division, University of Michigan.Contribution no. 313 of the Great Lakes Research Division, University of Michigan.     

Primary productivity and nutrients in the sediment retention basin of Lake Monroe

Lake Monroe is the largest body of water in Indiana with a daily mean productivity of 220 mg · C · m⁻² · day⁻¹ in an observed range from 26 to 714 m · C · M⁻² day⁻¹. It is a medium soft reservoir; the acid combining capacity varies from 0.28 to 0.71 meq · l⁻¹ with a mean slightly above 0.5 meq · l⁻¹. The results of diurnal changes in major nutrients, the C, N, and P ratios, and bioassay experiments indicated that phosphorus is the major limiting nutrient on algal photosynthesis in this lake. Surface photo-inhibition may be used to indicate the sufficiency of light for the species of algae in the water. The low productivity in December, January, February, and early March can be attributed to light limitation due to low water transparency. Contribution no. 312 of the Great Lakes Research Division, University of Michigan. Contribution no. 312 of the Great Lakes Research Division, University of Michigan.     

Feeding habits ofMysis relicta — an overview

Mysis relicta has been recognized as an important component of many limnetic food webs. The first approach to studying the feeding habits ofM. relicta was the analysis of stomach contents. Assumptions regarding stomach content analysis have been tested and seasonal feeding estimates ofM. relicta have been reported recently. Laboratory grazing and/or predation experiments have recently been completed usingM. relicta primarily from Lakes Michigan and Tahoe.Mysis relicta is concluded to be opportunistic, capable of utilizing a variety of food resources. It may play an important role in structuring limnetic food webs.     

Seasonal succession of the phytoplankton in the upper Mississippi River

Species composition and seasonal succession of the phytoplankton were investigated on the upper Mississippi River at Prairie Island, Minnesota, U.S.A. Both the numbers and volume of individual species were enumerated based on cell counts with an inverted microscope. A succession similar to algal succession in the local lakes occurred. The diatoms were dominant during the spring and fall and blue-green algae were dominant during the summer. The algal concentrations have increased up to 40 fold the concentrations of the 1920's, since the installation of locks and dams. The maximum freshweight standing crop was 4 mg · l^–1 in 1928 (Reinhard 1931), 13 mg · l^–1 in 1975 a wet year, and 47 mg · l^–1 in 1976, a relatively dry year with minimal current discharge. The diatoms varied from 36–99%, the blue-green algae from 0–44% and the cryptómonads from 0–50% of the total standing crop. The green algae were always present but never above 21% of the biomass. The dominant diatoms in recent years were centric -Stephanodiscus andCyclotella spp. (maximum 50,000 ml^–1). The dominant blue-green algae wereAphanizomenon flos-aquae (L.) Ralfsex Born.et Flahault andOscillatoria agardhii Gomont (maximum 800 ml^–1). These algal species are also present in local lakes. Shannon diversity values indicated greatest diversity of algae during the summer months.     

Distribution and habitat of Nitellopsis obtusa (Characeae) in the Laurentian Great Lakes

Nitellopsis obtusa, a macroalga (Characeae) native to Europe and Asia, was found in U.S. waters of the St. Clair-Detroit River system in 1983, thus extending the range of this taxon into the Laurentian Great Lakes about 850 km from the St. Lawrence River where it was first discovered in North America in 1978. Its occurrence only in water frequented by commercial shipping vessels suggests that it is distributed via this mechanism. In the St. Clair-Detroit River system, N. obtusa was collected with a Ponar grab at four locations, and with a grapnel at one additional location. It was the ninth most frequently found macrophyte and it was most abundant at Belle Isle in the Detroit River, where the mean dry-weight biomass in Ponar samples was 0 g m^-2 in June, 37 g m^-2 in August, and 32 g m⁻² in September. Maximum biomass of this taxon in one Ponar grab at this location was 289 g m^-2 in September. The alga occurred primarily in water of relatively low current velocity (11.3 cm s⁻¹) and in association with Vallisneria americana, Myriophyllum spicatum, Potamogeton richardsonii, Najas flexilis, and Elodea canadensis. Contribution 654, Great Lakes Fishery Laboratory, Ann Arbor, MI 48105, USA Contribution 654, Great Lakes Fishery Laboratory, Ann Arbor, MI 48105, USA     

Clearance rates of sessile rotifers: in vitro determinations

We measured laboratory clearance rates of 10 rotifer and one unidentified bryozoan species from 3 different lakes using ³²P labeled algae (Chlamydomonas) or yeast (Rhodotorula). Clearance rates for all rotifers fed yeast ranged from < 2.0 to > 260 µl · animal^–1 · h^–1 depending on species. The in vitro clearance rates of two sessile rotifers (Ptygura crystallina and P. pilula) were not significantly different from previously measured in situ rates (Wallace and Starkweather 1983). Clearance rates for 5 rotifers fed algae ranged from < 5.0 to > 90.0 µl · animal^–1 · h^–1. Ptygura beauchampi, P. crystallina, P. pilula, Floscularia conifera, and F. melicerta ingested both cell types but their clearance rates varied substantially among species and between cell types. There was a substantial time-dependent loss of 32P from formalin-fixed animals (Sinantherina socialis) awaiting processing. This loss stabilized at approximately 20 hours and was estimated to be about 40% of the initial ingested label. Clearance rates for the bryozoan fed yeast or algae were highly variable, ranging from < 1.0 to > 3 000 µl · animal^–1 · h^–1.     

Uptake of iron byGeotrichum candidum,a non-siderophore producer

Summary Geotrichum candidum (isolate 1–9) pathogenic on citrus fruits, appears to lack siderophore production. Iron uptake byG. candidum is mediated by two distinct iron-regulated, energy-and temperature-dependent transport systems that require sulfhydryl groups. One system exhibits specificity for either ferric or ferrous iron, whereas the other exhibits specificity for ferrioxamine-B-mediated iron uptake and presumably other hydroxamate siderophores. Radioactive iron uptake from⁵⁹FeCl₃ showed an optimum at pH 6 and 35° C, and Michaelis-Menten kinetics (apparentK _m = 3 m,V _max = 0.054 nmol · mg^–1 · min^–1). The maximal rate of Fe²⁺ uptake was higher than Fe³⁺ (V _max = 0.25 nmol · mg^–1 · min^–1) but theK _m was identical. Reduction of ferric to ferrous iron prior to transport could not be detected. The ferrioxamine B system exhibits an optimum at pH 6 and 40° C and saturation kinetics (K _m = 2 M,V _max = 0.22 nmol · mg^–1 · min^–1). The two systems were distinguished as two separate entities by negative reciprocal competition, and on the basis of differential response to temperature and phenazine methosulfate. Mössbauer studies revealed that cells fed with either⁵⁷FeCl₃ or⁵⁷FeCl₂ accumulated unknown ferric and ferrous binding metabolites.     

The role of vanadium in green plants

Cells of Chlorella pyrenoidosa, derived from vanadium free agar slants, respond with great sensitivity to microamounts of vanadium, added as NH₄VO₃ to autotrophic liquid cultures. Between 0.01 and 1 g V per litre nutrient medium (2·10^-10-2·10^-8g-at/l), the algae respond with a continuous increase in dry weight. At higher V-concentrations, further enhancement in biomass is accompanied by a additional increase in chlorophyll content. Maximum V-effect on both parameters was found to be at 500g V/l (10^-5 g-at/l). Dry weight as well as chlorophyll content of Chlorella are decreased by concentrations above 25 mg V/l; 100 mg V/l (2·10^-3 g-at/l) stop growth and cause death of the cells. The toxic threshold for the V-content in the algae was determined to be at 150–200 g V/g (3–4·10^-6 g-at/g) dry weight.Two different pH-optima for a positive vanadium action on dry weight and chlorophyll biosynthesis were established, the first at pH 7, the other in the range pH 7.5–8. Two sites of vanadium action in green algae are discussed.Part I: Arch. Microbiol. 105, 77–82 (1975)     

Determining the density dependence of immigration and emigration of benthic stream invertebrates: theoretical considerations

Simple mathematical models are formulated to describe density independent and density dependent dispersal. These models clarify hypotheses of density dependence and may be manipulated easily to suit particular applications. The models demonstrate that the initial composition of a species aggregate must be controlled before valid conclusions can be drawn about the density dependency of the aggregate's dispersal. Stochastic models of emigration are derived to assess the power of particular experimental designs and statistical techniques to discriminate a known form of density dependent emigration. Contribution No. 369, Great Lakes Research Division, University of Michigan Contribution No. 369, Great Lakes Research Division, University of Michigan     

Primary production and phytoplankton in two small,polyhumic forest lakes in southern Finland

Primary production and phytoplankton in polyhumic lakes showed a very distinct seasonal succession. A vigorous spring maximum produced by Chlamydomonas green algae at the beginning of the growing season and two summer maxima composed mainly of Mallomonas caudata Iwanoff were typical. The annual primary production was ca. 6 g org. C · m^–2 in both lakes. The mean epilimnetic biomass was 1.1 in the first lake and 2.2 g · m^–2 (ww) in the second one. The maximum phytoplankton biomass, 14 g · m^–2, was observed during the vernal peak in May.     

Biodegradation of coal slurry transport wastewater organics

Summary Activated sludge was successful in reducing the levels of dissolved organic carbon (DOC) in coal slurry wastewaters. DOC removal by the activated sludge ranged from 61% to 97% with a large percentage (21–41%) of this DOC being completely metabolized to CO₂. Second order kinetic constants (k ₂) developed for DOC removal ranged from 1.39·10^–4 to 2.30·10^–1 liter·day^–1·(mg of sludge)^–1, providing evidence that biological treatment was an effective mechanism for reducing the pollution potential of the slurry wastewaters. After treatment with activated sludge a residual DOC remained in the wastewater and data from ultrafiltration studies indicated that this residual carbon was of MW>1000. The activated sludge preferentially removed the lower (MW<1000) molecular weight compounds and the higher molecular weight DOC was more resistant to biological attack. However, extended acclimation (greater than 1 month) enabled the activated sludge to remove the higher molecular weight DOC from the slurry wastewaters.     

Zooplankton-trophic state relationships in some north and central Florida lakes

In a survey of eight lake systems located in north-central Florida, total zooplankton abundance showed a strong positive correlation (r²=0.87, a=0.01) with trophic state. Zooplankton abundance averaged 1.0 × 10⁵ organisms · m^–2 in oligotrophic systems and up to 8.2 × 10⁵ organisms · m^–2 in the eutrophic systems. Seasonal variations in total abundance were greatest in the eutrophic lakes where rotifers dominated and periodically produced sharp population peaks (approaching 2.0 × 10⁶· m^–2). In contrast, the more oligotrophic systems had relatively stable levels of total abundance and were dominated by copepods. Diversities of the major taxa in the lakes were variable with one to three species of copepods, zero to four species of cladocera, and two to seven species of rotifers dominant at any one time. Planktonic cladoceran communities were often composed of only one or two species. Low cladocera diversity in these subtropical systems was suggestive of increased predation pressure on this group of crustaceans. A comparison of the total crustacean abundance in the Florida systems to those of some of the Great Lakes indicated that lower standing crops of crustacean zooplankton in the Florida lakes may be a response to both predation and temperature.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.     

Decrease of polypeptides in the PS I antenna complex with increasing growth irradiance in the red alga Porphyridium cruentum

Thylakoids isolated from cells of the red alga Porphyridium cruentum exhibit an increased PS I activity on a chlorophyll basis with increasing growth irradiance, even though the stoichiometry of Photosystems I and II in such cells shows little change (Cunningham et al. (1989) Plant Physiol 91: 1179–1187). PS I activity was 26% greater in thylakoids of cells acclimated at 280 mol photons · m^–2 · s^–1 (VHL) than in cells acclimated at 10 mol photons · m^–2 · s^–1 (LL), indicating a change in the light absorbance capacity of PS I. Upon isolating PS I holocomplexes from VHL cells it was found that they contained 132±9 Chl/P700 while those obtained from LL cells had 165±4 Chl/P700. Examination of the polypeptide composition of PS I holocomplexes on SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 and 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptides belong to a novel LHC I complex, recently discovered in red algae (Wolfe et al. (1994a) Nature 367: 566–568), that lacks Chl b and includes at least six different polypeptides. We suggest that the decrease in PS I Chl antenna size observed with increasing irradiance is attributable to changes occurring in the LHC I-antenna complex. Evidence for a Chl-binding antenna complex associated with PS II core complexes is lacking at this point. LHC II-type polypeptides were not observed in functionally active PS II preparations (Wolfe et al. (1994b) Biochimica Biophysica Acta 1188: 357–366), nor did we detect polypeptides that showed immunocross-reactivity with LHC II specific antisera (made to Chlamydomonas and Euglena LHC II).Abbreviations Bis-Tris bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane - DCPIP 2,6-dichlorophenol indophenol - -dm dodecyl--d-maltoside - HL high light of 150 mol photons · m^–2 · s^–1 - LGB lower green band - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - LL low light of 10 mol photons · m^–2 · s^–1 - ML medium light of 50 mol photons · m^–2 · s^–1 - MES 2-(N-morpholino) ethanesulfonic acid - P700 reaction center of PS I - PFD photon flux density - Trizma tris(hydroxymethyl)aminomethane - UGB upper green band - VHL very high light of 280 mol photons · m^–2 · s^–1     

Bacterial adaptation to low-nutrient conditions as studied with algal extracellular products

Kinetic analyses indicate that members of natural bacterial populations from 2 marine environments near Woods Hole, MA, possess enzyme-mediated transport systems which permit utilization of¹⁴C-labeled extracellular organic C (¹⁴C-EOC) prepared from the algae,Skeletonema costatum, Thalassiosira pseudonana, andDunaliella tertiolecta, and supplied over a concentration range of 15–150C·liter^–1. It is shown that previous exposure of the bacteria to the EOC from these algae cannot explain the linear kinetic patterns obtained. Therefore, the ability to utilize algal EOC at low concentrations is a general feature of metabolically active bacterial populations. Further, as the native bacteria do not restrict this ability to a specific EOC pool, the results are consistent with the hypothesis that bacteria adapted to low nutrient environments possess uptake systems of high substrate affinity and low substrate specificity. Elevation of substrate levels with as little as 10 mg·1^–1 peptone is shown to favor development of a bacterial population that lacks these adaptations. Standard enrichment techniques typically result in the isolation of bacteria that are poor models for evaluating the ecology of native microbiota.Contribution No. 1523 from the University of Maryland Center for Environmental and Estuarine Studies.     

Feeding rate of slimy sculpin and burbot on young lake charr in laboratory reefs

Synopsis Predation and contaminants are two possible factors in the poor recruitment of young lake charr Salvelinus namaycush in the Great Lakes. We measured the feeding rate of slimy sculpins Cottus cognatus and burbot Lota lota on young lake charr (uncontaminated young from eggs of a hatchery brood stock and contaminated young from eggs of Lake Michigan lake charr) in laboratory test chambers with a cobble substrate. The median daily consumption rate of sculpins for all tests was 2 lake charr eggs (N = 22 tests; 95% confidence interval, 0–13) and 2 lake charr free embryos (N = 31 tests; 95% confidence interval, 0–10). Feeding rate did not differ between hatchery and contaminated prey. Slimy sculpins continued to feed on lake charr when another prey organism, the deepwater amphipod Pontoporeia hoyi, was present. Feeding by burbot on free embryos (4–36 d^–1) increased as the mobility of young increased, but burbot consumed about 10% of their body weight weekly in free-swimming young (140–380 d^–1). Predation on lake charr eggs by sculpins could be considerable over the 100 to 140 d incubation period, and burbot could eat large numbers of free-swimming lake charr as the young fish left the reef. Predation pressure on young lake charr may inhibit rehabilitation of self-sustaining populations of lake charr on some reefs unless a critical egg density has been reached.