bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Container Size on Estimates of Mortality and Predation Rates in Experiments with Macrozooplankton and Larval Fish
Authors: Lafontaine Yves De , Leggett William C.
Published: April 2008

We investigated the effect of container size on the predation rate of the jellyfish Aurelia aurita on postemergent capelin (Mallotus villosus) larvae in large in situ cylindrical enclosures. Total depth of the enclosures varied between 1 and 9 m and yielded volumes that ranged from 0.26 to 6.35 m3. Instantaneous mortality rates of capelin larvae due to jellyfish predation varied inversely and nonlinearly with the volume of the enclosure. Over the range of container sizes used, mortality rates differed by one order of magnitude. Container volume explained 80% of the variance in mortality rates, while predator size and larval size accounted for 8.3 and 2.3% of the variability, respectively. Mortality rate was independent of the initial larval density within each container size. Differences in mortality rates among container sizes are explained by the observed differences in the vertical patchiness of larvae among various enclosure sizes. These findings indicate that experiments conducted in small containers typical of those used in laboratory studies seriously overestimate rates of larval mortality due to predation. Direct extrapolation of the results of such laboratory studies to field conditions is therefore not warranted. We conclude that the vertical distributions of predator and prey may be the most important factor controlling predator–prey relationships in situ.
Acoustic Measurement of Fish Schools Using Array Phase Information
Authors: Thomas G. L. , Jackson Darrell R.
Published: April 2008

Array phase information on the azimuth and elevation of fish schools allows for beam directivity corrections of target strength, determinations of school depth, and tracking of school movements. When corrected for beam pattern losses, the target strength of blue whiting (Micromesistious poutassou) and rockfish (Sebastes spp.) schools increased approximately 3 dB. The vertical placement of fish schools with the side-scanning split-beam sonar agreed with the fish school depths observed with an echosounder. Split-beam phase was used to track blue whiting schools in the horizontal plane with azimuthal accuracy considerably better than the 3-dB beam width (approximately 20°).
Chrysophycean Microfossils Provide New Insight into the Recent History of a Naturally Acidic Lake (Cone Pond, New Hampshire)
Authors: Gibson Katherine N. , Smol John P. , Ford Jesse
Published: April 2008

Cone Pond, New Hampshire, is an acidic (pH = 4.5) clearwater lake that is currently fishless. Historical records indicate declining fish populations between 1951 and 1966, but paleolimnological work using diatoms failed to find evidence for further recent acidification of this naturally acid site. We initiated new paleolimnological studies using mallomonadacean chrysophytes to further our understanding of Cone Pond's recent past. Our stratigraphic analyses indicate recent striking changes in the chrysophyte flora of this lake, with Mallomonas hindonii, a species only common in recently acidified lakes, replacing M. crassisquama, a cosmopolitan species that dominated the flora over the preceding 8000 yr; this recent change parallels the declines in fish populations. Because chrysophytes often bloom in early spring and are known, in other lakes, to experience changes in community composition before those expressed by the diatom community, a possibility is that chrysophytes track transient excursions of lake water chemistry associated with early snowmelt conditions. In this scenario, chrysophytes would respond to a constellation of specific short-term chemical changes including, but not restricted to, pH. Such pH associated changes could include changes in concentrations, speciation, or complexation of metals mobilized from the catchment or sediments, all of which are known to affect both chrysophytes and fish.
Permeability of the Isolated Atlantic Salmon (Salmo salar) Chorion to Ions as Estimated by Diffusion Potentials
Authors: Peterson R. H. , Martin-Robichaud D. J.
Published: April 2008

The properties of the teleost chorion and perivitelline fluid may allow the embryo to develop in an ionic medium which differs from ambient. A knowledge of these properties facilitates assessment of the potential impact of environmental perturbations (e.g. low-pH episodes) on the developing embryo. Diffusion potentials are created when differing concentrations of a salt solution are imposed upon the opposite sides of isolated Atlantic salmon (Salmo salar) chorions. These diffusion potentials are related to the mobilities of the cations and anions. The magnitude of the diffusion potentials were measured with NaCl, CaC2, H2SO4, and HCl solutions. The results indicate that both anions and cations permeate the chorion. Chloride appears to have greater mobility through the chorion than does sodium, although the difference in mobility of such ion pairs moving through the chorion is not as great as the difference in their mobilities in aqueous solution. Diffusion potentials obtained with CaCl2solutions, on the other hand, indicate reduced calcium mobility through the chorion relative to chloride. The decreased mobility of Ca2+is probably due to adsorption to fixed negative charges on the chorion. The properties of the perivitelline potential of the intact egg could be simulated qualitatively by placing a solution of negatively charged colloid (hen's egg albumin) inside the isolated chorion.
Effects of Irradiance on the Community Structure and Biomass of Algal Assemblages in Laboratory Streams
Authors: Steinman Alan D. , McIntire C. David
Published: April 2008

Studies in natural streams have implicated irradiance as a factor which has a strong influence on the dynamics of algal communities. In this study, laboratory streams were used in a replicated, experimental design to investigate whether differences in algal biomass, taxonomic structure, and physiognomy result from exposure to different irradiances. Effects of four photon flux densities (15, 50, 150, and 400 μE∙m−2∙s−1) on locally collected benthic stream algae were monitored over a 48-d period. Biomass increased in all streams during the experiment, but the streams exposed to the highest irradiance had 25 times more biomass at the end of the experiment than the channels exposed to the lowest irradiance. Although diatoms were the dominant algal class in all streams, the relative abundance of chlorophytes was much greater in streams exposed to 150 and 400 μE∙m−2∙s−1 than in channels treated with 15 and 50 μE∙m−2∙s−1 Detrended correspondence analysis indicated that the successional trajectories of assemblages exposed to low irradiances were quite distinct from those of assemblages treated with high irradiances. Observations of assemblage physiognomy by scanning electron microscopy revealed that at low irradiances, a densely packed understory of adnate diatoms, with a few overstory diatoms, covered the tile surface. At high irradiances, tiles were overlaid with thick algal mats, composed of filamentous and coenobic chlorophytes and diatoms of various growth forms (rosette, chain-forming, and solitary). The experimental results suggested that differences in biomass and community structure among the laboratory assemblages were a direct result of light energy, and that irradiance is a major factor influencing algal dynamics in lotic ecosystems.
A Durable and Transportable Limnetic Enclosure System Suitable for Wind-Exposed Lakes
Authors: Werf B. Van der , Schrotenboer J. , Richter A. F. , Moed J. R. , Hoogveld H. L. , Haan H. De
Published: April 2008

A2-m-wide, transportable enclosure system suitable for cold, windy lakes is described. Incubation of these enclosures in the shallow (mean depth = 1.5 m) Lake Tjeukemeer, The Netherlands, has shown that its construction resists wind speeds of 14–20 m/s and temperatures below 5 °C. Potentially lethal concentrations of at least five toxic chemicals necessitate preliminary leaching in lake water of the polyvinylchloride material used in bag construction. Phytoplankton inside and outside the enclosures behaved similarly 3 d and 3 wk into incubation.
Development of Ischnura verticalis (Coenagrionidae: Odonata): Effects of Temperature and Prey Abundance
Authors: Baker Robert L. , Feltmate Blair W.
Published: April 2008

Increased food availability increased rate of development within an instar, head width ratio (ratio of headwidth of later instar over head width in previous instar), and weight per unit head width of newly molted larval Ischnura verticalis (Say) (Coenagrionidae: Odonata) reared in the laboratory. Temperature affected rate of development but not weight per unit head width or head width ratio. Mortality was not affected by any treatment. Rate of development was negatively correlated with both weight per unit head width and head width ratio. Results suggest that the developmental process has evolved to reduce risks associated with small size at the expense of a more rapid development.
Slow Process of Wound Repair in Beluga Whales, Delphinapterus leucas
Authors: Geraci J. R. , Bruce-Allen L. J.
Published: April 2008

Wound repair in beluga whales, Delphinapterus leucas, was studied by examining the sequence and timing of regenerative changes in skin incisions. Soon after the epidermis is breached, exposed cells not normally in contact with seawater begin to degenerate. Within 2 d, the degenerating layer becomes thickened to form a barrier protecting underlying tissue. This layer gradually sloughs as advancing epidermal cells fill the breach. Wound repair is complete in 30–40 d, five times longer than in the bottlenosed dolphin, Tursiops truncatus. Although several factors may be involved, we suggest that the difference in timing appears to relate directly to the greater thickness of epidermis in the whales.
Periphyton Response to a Gasoline Spill in Wolf Lodge Creek, Idaho
Authors: Pontasch Kurt W. , Brusven Merlyn A.
Published: April 2008

A post-impact study on a 94438-L unleaded gasoline spill into Wolf Lodge Creek in northern Idaho was undertaken to determine the temporal and spatial response of periphyton following the spill. Periphytic biomass and chlorophyll a concentrations were determined above and below the spill. Downstream areas were mechanically agitated to release substrate-trapped hydrocarbons 35 d after the spill. Periphyton samples taken 26 d after the spill indicated that periphytic biomass, especially of the heterotrophs, was greater in the impacted than unimpacted areas; the Autorophic Index was up to 30 times greater in the impacted reach. Two months after the spill and 1 mo after stream cleaning, the Autotrophic Index was approximately the same in reference and impacted areas.
Analysis of Planktonic Rotifer Assemblages from Sudbury, Ontario, Area Lakes of Varying Chemical Composition
Authors: MacIsaac Hugh J. , Hutchinson Thomas C. , Keller W.
Published: April 2008

Planktonic rotifer samples were collected from 47 Sudbury, Ontario, area lakes to determine factors influential to species distributions. The lakes ranged from highly acidic and metal contaminated to circumneutral with low metal concentrations. Median rotifer abundance was substantially higher in non-acid (pH > 5.2) than in acid (pH < 5.2) lakes, although differences in species distributions were evident. Application of detrended correspondence analysis to rotifer species densities revealed broad separation of communities from acid and non-acid lakes. Assemblages from acid lakes were highly similar in species composition and dominance, while those from non-acid lakes were generally much more heterogeneous. It was hypothesized that planktonic rotifer communities converged in species composition as a consequence of the stress of lake acidification, in a pattern similar to that previously described for planktonic crustaceans. Among the best predictors of rotifer community composition were lake pH and the concentrations of manganese and aluminum.
Modelling the Effects of Accelerated Development and Reduced Fecundity on the Population Dynamics of Aquatic Diptera
Authors: Rempel Robert S. , Carter John C. H.
Published: April 2008

The population dynamics of aquatic insects were simulated using a stage-projection matrix model. Transition elements, some of which were specified by nonlinear and stochastic functions, represent the joint probability of development and survivorship from time t to t + 1. For the simulation, stage-specific survivorship was kept unchanged and only development rate and fecundity were altered. The simulation predicts that the intrinsic capacity for population growth (rm) and equilibrium levels of abundance (K) should increase with both faster development rate and higher fecundity, independent of stage-specific mortality. As a test of the effect of accelerated development on population growth, abundance of insects emerging from experimental stream channels was compared in ambient temperature and heated channels. Development was faster in the heated channels, and abundance was greater for 9 of the 11 species compared. These results indicate that changes in development rate, in addition to changes in fecundity, must be considered when predicting the population effects of an altered thermal regime.
Phosphate Requirement, Photosynthesis, and Diel Cell Cycle ofScenedesmus obliquasUnder Fluctuating Light
Authors: Shin C. N. , Rhee G-Y , Chen J.
Published: April 2008

The effect of light fluctuation (0.06 Hz) on P requirement, photosynthesis, and the diel cell-division cycle was investigated in Scenedesmus obliquus in a chemostat under a 12 h day: 12 h night cycle. P requirement was much less under oscillating than under constant daylight of the same photon flux density. However, cell chlorophyll a was significantly higher, indicating an increased N requirement. There was little difference in photosynthetic efficiency (the slope of the photosynthesis–light regression) between oscillating and constant light, but photosynthetic capacity was higher in fluctuating light. Cell C was also higher. A strong diel rhythmicity in steady-state cell numbers was observed with little phase difference between oscillating and constant light. Although steady-state cell numbers under P limitation were significantly higher under fluctuating light, there was no difference in instantaneous growth rates and their diel distribution. At a dilution rate of 0.6∙d−1, cell death occurred at an average rate of −0.56∙d−1between 4 h before and 5 h after the onset of the dark period.
Calcium and Taurine Interaction in the Heart of the CrabCarcinus maenas
Authors: Zatta Paolo
Published: April 2008

Calcium and taurine were analyzed from the neurogenic heart and other tissues of Carcinus maenas. The interaction between calcium and taurine was studied in vitro using a potentiometric method. The hypothesis that calcium can modulate flux through the cell membrane as in the mammalian heart as a consequence of a taurine–calcium complex formation is untenable for the heart of C. maenas.
Fine-spotted Brown Trout (Salmo trutta): Its Phenotypic Description and Biochemical Genetic Variation
Authors: Skaala Øystein , Jørstad Knut E.
Published: April 2008

Initial studies on a small population of brown trout (Salmo trutta) in the Hardangervidda area in Norway revealed specimens with remarkable morphological characteristics. About one third of the population was classified as "fine-spotted trout" due to the occurrence of small black spots on the body and fins. These individuals also have from four to seven black spots located around the pupil of the eye. Genetic data, obtained by electrophoresis of tissue enzymes, demonstrated large differences compared with other brown trout populations. According to the information available, the abundance of fine-spotted trout has decreased during the last eight decades, which focuses on the need for preservation of the population and its habitat.
Evidence that Parasitic and Nonparasitic Life History Types are Produced by One Population of Lamprey
Authors: Beamish Richard J.
Published: April 2008

A population of lamprey in a small stream on Vancouver Island, British Columbia, Canada, was shown to contain the nonparasitic Lampetra richardsoni and a parasitic variety.
Estimation of Fish Length from Acoustic Target Strengths
Authors: Buerkle U.
Published: April 2008

I show that fish length distributions calculated from acoustic target strengths of cod (Gadus morhua) are in error when target strength–length relationships are used that do not account for the orientation distribution of the fish. The magnitude and statistical significance of the errors vary with the length frequency structure of the fish sample and are thought to be large enough to question the value of acoustically determined lengths in fish surveys if corrections for fish orientation are not applied.
Rationalizing the Irrational: A Case Study in User Group Participation in Pacific Salmon Management
Authors: Hilborn Ray , Luedke Wilf
Published: April 2008

Acrimony between industry and government managers is commonplace in the management of many Pacific salmon fisheries. A case study of the chum salmon (Oncorhynchus keta) fisheries in southern British Columbia provides insight into the prevailing distrust between fishermen and managers. A recent attempt to bring planned management into what had often been an irrational and highly political activity is described. A management system called the "clockwork" provides all fishermen an opportunity for greater understanding of the management rationale and greater input into the decision-making process. The results of this attempt and implications for achieving management goals are discussed.
Snowpack Ion Accumulation and Loss in a Basin Draining to Lake Superior
Authors: Stottlemyer Robert
Published: April 2008

The objective of this study was to relate winter precipitation ionic inputs, snowpack retention, and change in first-order stream chemistry with spring snowpack melt. During winter 1982–83, measurement of precipitation inputs, snowpack concentration and loading, and streamwater concentration and discharge of Ca2+, K+, H+, NO3−, and SO42− from a 176-ha watershed reveals that only H+ might be lost from the snowpack before first thaw. Above-freezing soil temperature beneath the snowpack may be a factor in H+ loss. An initial 1-d thaw resulted in loss of over one third (6 eq∙ha−1) of the snowpack Ca2+. Over one half the snowpack load of K+, H+, NO3−, and SO42−, was lost in a subsequent midwinter freeze–thaw period. Snowpack loading of ionic species was reduced by 70–90% before peak spring melting and stream discharge. Ecosystem H+ retention and biological uptake of NO3− further mitigate ionic "pulses" in streamwater. Sulfate discharge exceeds bulk inputs, which suggests significant dry deposition input and little forest soil retention of this anion. The snowpack was relatively small, which limits wider application of these results to the region.
Morphological Divergence and the Organization of Trophic Characters Among Lacustrine Populations of the Threespine Stickleback (Gasterosteus aculeatus)
Authors: Lavin Patrick A. , McPhail J. D.
Published: April 2008

A multivariate solution for dealing with patterns of character covariance, when character genotypic covariances are known, has been applied to the organization of trophic morphology among lacustrine populations of the threespine stickleback (Gasterosteus aculeatus). The quantitative genetics governing eight trophic characters were investigated using representative populations from each of three known trophic ecotypes (open-water, littoral, and intermediate) which occur in the same drainage. Character heritabilities (0.19–0.84) were all significant. Estimates of character genetic correlations (−0.65 < rG < 0.85) were obtained and their standard errors were calculated by bootstrapping. Cluster analyses of the genetic correlation matrices defined two character suites, head shape and gill raker structure. Selection gradients between trophic ecotypes indicated that directional selection had operated most strongly on characters related to food size (upper jaw length and gill raker number). These results support the hypothesis that interpopulation variability in trophic morphology is organized as an adaptive response to local selection pressures.
Genetic Identification of Cutthroat Trout, Salmo clarki, in Glacier National Park, Montana
Authors: Marnell Leo F. , Behnke Robert J., , Allendorf Fred W.
Published: April 2008

Trout populations in 29 lakes in Glacier National Park were identified by meristic and electrophoretic analyses to assess the extent of introgressive hybridization between introduced nonnative trout and the indigenous cutthroat trout, Salmo clarki lewisi. Native cutthroat trout remain in 16 lakes draining to the North and Middle forks of the Flathead River; no native trout were found east of the Continental Divide. Introduced Yellowstone cutthroat trout, Salmo clarki bouvieri, occur in six headwater lakes. Hybrid populations, including both S. c. lewisi × bouvieri and S. clarki × S. gairdneri, inhabit six lakes. Hybridization between native and introduced trouts has been minimal, apparently due to strong selective pressures favoring the indigenous genotype. Close agreement was observed between the meristic and electrophoretic results.
Size-Selective Mortality in Young-of-the-Year Yellow Perch (Perca flavescens): Evidence from Otolith Microstructure
Authors: Post John R. , Prankevicius Andrew B.
Published: April 2008

Large body size and high growth rates can strongly influence the survival of larval and juvenile fish during periods of intense predation pressure. Experimental evidence suggests that piscivorous fish often feed size selectively, but direct field evidence of size-selective mortality and of the effect of rapid growth on the intensity of size-selective mortality is limited. We used the growth record from otolith microstructure to test the hypothesis that young-of-the-year yellow perch (Perca flavescens) that survived their first growing season were the larger and faster growing members of their cohort. Strong size-selective mortality was identified within the first growing season for a slowly growing population. During the same year, a faster growing population showed minimal size-selective mortality. In contrasting the two populations, differences in predator species composition confounded the growth rate size-selectivity relationship, but it was clear that size-selective predation could be intense, favouring the survival of the faster growing individuals within a population.
Food-Induced Granulomatosis in European Smelt, Osmerus eperlanus
Authors: Anders K. , Möller H.
Published: April 2008

Many European smelt, Osmerus eperlanus, in tributary rivers to the North Sea are affected by granulomatosis in the buccal cavity. The granulomas are caused by spines and leg fragments of amphipods, an important food item of smelt. Granuloma prevalence increases with increasing fish size. The rate of increase slows down in very large fish, probably as an effect of changed feeding habits. Fungi and virus-like particles in the granulomas are assumed to be secondary invaders. Granulomas are occasionally found in Atlantic cod, Gadus morhua, and flounder, Platichthys flesus, also.
Comparison of Acoustic Reflections from Spherical Objects and Fish Using a Dual-Beam Echosounder
Authors: Dickie L. M. , Boudreau P. R.
Published: April 2008

Comparison of dual-beam echos from spherical targets and from fish demonstrates that the fish directivity pattern causes significant distortion and enhanced variance in acoustic measurements related to abundance estimates. Dual-beam data on single fish targets in the laboratory and field may be used to define a correction which more accurately describes the observed or field target strengths of fish, permitting a more precise estimate of the associated measures of size, density, and biomass.
Evaluation of Techniques for Fixing, Preserving, and Measuring Salmon Eggs
Authors: Fleming Ian A. , Ng Susan
Published: April 2008

In a comparison of Stockard's solution with 5% buffered formalin for the preservation of coho (Oncorhynchus kisutch) and chum salmon (O. keta) eggs, formalin caused a lesser alteration in weight regardless of whether the eggs were preserved before or after waterhardening or fertilization. Coho and chum salmon eggs responded similarly to the various treatments. Time before preservation (3, 7, and 24 h) and fertilization had little effect on the final size of eggs. Waterhardening, in which the egg was placed in standing water, caused a 23% increase in fresh egg weight. Preservation in Stockard's solution, especially after waterhardening, increased egg weight by 48% and was least consistent in its effect. By contrast, 5% buffered formalin added to fresh eggs caused no significant alteration in weight, even after 5 mo of preservation. The latter was therefore the most suitable technique of preserving egg size. The use of egg weight as a measure of egg size was more accurate and consistent than linear measures of diameter. Finally, some empirical relationships for correcting published data on preserved egg weight are presented.
Homing in Wild Sockeye Salmon (Oncorhynchus nerka) Populations as Inferred from Differences in Parasite Prevalance and Allozyme Allele Frequencies
Authors: Quinn T. P. , Wood C. C. , Margolis L. , Riddell B. E. , Hyatt K. D.
Published: April 2008

Although it is widely accepted that adult Pacific salmon (Oncorhynchus spp.) spawn in their natal stream, there are few quantitative estimates of homing precision in wild populations. The prevalence of two myxosporean parasites, Myxobolus neurobius and Henneguya salminicola, indicated very precise homing in certain sockeye salmon (O. nerka) populations in British Columbia (Long and Owikeno lakes on the central coast and Sproat, Great Central, and Henderson lakes on Barkley Sound, Vancouver Island). These populations were also sampled for electrophoretic differences at 23 loci. Genetic differences were found among all five populations, and estimates of straying from these data corroborated the parasitological evidence that straying is rare (< 1%).
Feeding Habits and Daily Ration of Walleye Pollock (Theragra chalcogramma) in the Eastern Bering Sea, with Special Reference to Cannibalism
Authors: Dwyer Deborah A. , Bailey Kevin M. , Livingston Patricia A.
Published: April 2008

Stomach contents of 3098 walleye pollock (Theragra chalcogramma) collected from the eastern Bering Sea during 1981–83 were examined to (1) describe the diet as influenced by area, season, and fish size, (2) estimate daily ration, and (3) examine the magnitude of cannibalism. Small pollock fed mainly on copepods and shifted to euphausiids and fish with increased size. Stomach contents (percent body weight) were highest in summer and autumn. Laboratory-derived estimates of gastric evacuation rates and age-structured estimates of abundance were used in conjunction with the field data to estimate daily ration of pollock in the eastern Bering Sea. Mean annual daily ration was calculated to be about 0.3% body weight per day. Daily ration was lowest in spring and lower in the northwestern region of the eastern Bering Sea than in the southeastern region. Cannibalism occurred in all seasons, but consumption was highest on age 0 pollock in the southeastern area during autumn. It is estimated that about 400 billion age 0 pollock were consumed annually by larger pollock in the eastern Bering Sea.
A Simulation of the Cape Breton Snow Crab, Chionoecetes opilio, Fishery for Testing the Robustness of the Leslie Method
Authors: Mohn R. K. , Elner R. W.
Published: April 2008

The principal tool for evaluating biomass and, hence, exploitation rate for Atlantic snow crab, Chionoecetes opilio, has been the Leslie method which is based on commercial catch rate and cumulative catch through the fishing season. The method assumes a dosed, homogeneous stock. However, a snow crab stock is often not closed because recruitment can occur during the fishing season as crabs molt into legal size. Also, stocks are not homogeneous and spatial heterogeneity causes fishermen to combine fishing and searching activities. A dynamic simulation of fishing/searching on a heterogeneous sessile stock with within-season recruitment was developed, based on the Cape Breton fishery, to assess the robustness of the Leslie method. In the modelled system, the violations of the assumptions caused by recruitment were shown not to be serious; but those due to the fishing/searching on a heterogeneous stock caused the Leslie method to underestimate initial biomass. Furthermore, the concepts of initial biomass and exploitation rate are seen to be inadequate for heterogeneous, recruiting stocks.
Measurement of Egg Production Rate of Calanus finmarchicus from Preserved Samples
Authors: Runge Jeffrey A.
Published: April 2008

A method for determining Calanus egg production rates from preserved, net-tow samples is proposed. In the sea off Nova Scotia, in situ egg production rates (eggs per female per day) of Calanus finmarchicus are significantly related to an index of gonadal development in preserved females. This relationship could be used in combination with data on female abundance to estimate daily production of eggs in the water column. The method is illustrated with data from a transect across Browns Bank.
Predation on Larval Fish by Atlantic Mackerel Scomber scombrus, with a Comparison of Predation by Zooplankton
Authors: Pepin P. , Pearre jr. S. , Koslow J. A.
Published: April 2008

This study reports on the feeding selectivity of Atlantic mackerel, Scomber scombrus, on larval fish (3-10 mm in length) presented as part of natural zooplankton assemblages. As with other vertebrate planktivores, prey preference was positively size selective, contrary to the pattern observed for several invertebrate carnivores. Larval fish density did not significantly influence predation rates. Furthermore, there was no evidence of either switching or saturation of the predator's functional feeding response with changes in alternative prey abundance, again unlike invertebrate predators. A review of previous experiments revealed that capture success of larval fish by predators is a function of the size of larval fish relative to the size of the predator, independent of predator taxa (i.e. vertebrate versus invertebrate).
Size Distribution in Periphyton
Authors: Cattaneo Antonella
Published: April 2008

When periphytic organisms growing on artificial plants were grouped in logarithmically increasing size classes, patterns in the distribution of biomass were consistent over the season and under different grazing regimes, despite taxonornical changes in the dominant taxa of algae and invertebrates. The amount in each size class was not constant, and instead, certain classes tended to have values consistently lower or higher than the mean. The locations of these peaks and troughs in the size distributions coincided with those observed in lake plankton. Despite these irregularities, the hypothesis that the biomass in logarithmic size classes is constant apparently applies at a crude level, for the biomass of most size classes lay within an order of magnitude of the mean. This rule of thumb also applies to the littoral fish community, for the minnow biomass was approximately that in a periphyton size class.
Effects of V-Notching on the Lobster, Homarus americanus
Authors: Getchell R. G.
Published: April 2008

No infections were detected in V-notched lobsters, Homarus americanus, held for 56 d in the laboratory. During an outbreak of gaffkemia ("red tail") at a commercial lobster pound, 2 of 20 V-notched lobsters died, but 4 of 10 unnotched controls also became infected. Results from challenge experiments with Aerococcus viridans (var.) homari showed that V-notch wounds healed sufficiently in 24 h to prevent a "red tail" infection. Histological observations of this wound repair of V-notched uropods also demonstrated that within 24 h the wound was sealed by a heavy infiltration of hemocytes.
Response of Lake Ontario to Reductions in Phosphorus Load, 1967–82
Authors: Stevens R. J. J. , Neilson M. A.
Published: April 2008

Total phosphorus (TP) loading to Lake Ontario has declined from 14 600 t∙yr−1 in 1969 to 8900 t∙yr−1 in 1982. Midlake spring TP has responded rapidly to these reductions, decreasing at the rate of 1.09 μg∙L−1∙yr−1 from a maximum of 30.6 μg∙L−1 in 1973 to 12.8 μg∙L−1 in 1982. Spring soluble reactive phosphorus (SRP) exhibited a proportionally larger decrease than TP such that 1982 SRP was 33% of 1973 levels, compared with 42% for TP. A multiple regression equation indicated an 80% response time of spring TP within 2 yr and a 90% response time within 4 yr. Spring nitrate plus nitrite has increased since 1969 at the rate of 9.5 μg∙L−1∙yr−1 causing N:P ratios to increase from 10 to 32. Mean summer epilimnetic TP declined at the rate of only 0.3 μg∙L−1∙yr−1 from 1977 to 1982 so that mean summer TP levels now exceed spring TP by 1–2 μg∙L−1. This suggests that loading to the lake during the stratified period has not shown a similar decline and may be responsible for the lack of a trend in algal biomass indicators during this period.
Phosphorus Deficiency of Lake Ontario Plankton
Authors: Lean D. R. S. , Abbott A. A. , Pick F. R.
Published: April 2008

The phosphate deficiency index (PDI), the ratio of photosynthetic carbon assimilation at optimal light to the maximum uptake velocity for phosphate, showed that P deficiency occurred in the near-shore plankton of Lake Ontario during spring thermal bar conditions and in the midlake plankton immediately after stratification. This condition persisted until October, when deep mixing of the water column occurred. Carbon and phosphate assimilation were by similar size classes, and as the ratio of two rate processes, PDI was independent of both temperature and biomass. Turnover time and alkaline phosphatase activity (APA) correlated with PDI. Short-term photosynthetic depression with phosphate enrichment occurred in only 7 of 23 experiments and may either reflect P-sufficient conditions or high protein to carbohydrate ratios due to physical events common to large lakes. PDI, protein to carbohydrate ratios, and photosynthetic depression respond principally to algal activity. Although turnover time and APA reflect the activity of smaller microorganisms, primarily heterotrophic bacteria, all indices were consistent.
Interpretations of Alkaline Phosphatase Activity in Lake Ontario
Authors: Pick F. R.
Published: April 2008

Alkaline phosphatase activity (APA) in Lake Ontario reached maximum levels of 0.25 μMP released∙h−1 during 1982. Relatively high values were first detected in nearshore surface water in May concurrent with thermal bar development and at a later date (end of June) at a midlake station following transport of nearshore water to the middle. APA remained detectable throughout the summer but declined in mid-August as a result of upwelling events. With fall mixing, APA persisted throughout the entire water column. Additions of phosphate did not inhibit APA until enrichments were much greater than maximum ambient concentrations of soluble reactive P. The findings suggest that APA is not a sensitive indicator of P deficiency. APA activity was correlated with nanoplankton (2–20 μm) plus picopiankton (0.2–2 μm) biomass but not with total algal biornass. APA associated with particles greater than 12 μm was relatively unimportant.
Carbohydrate and Protein Content of Lake Seston in Relation to Plankton Nutrient Deficiency
Authors: Pick F. R.
Published: April 2008

Carbohydrate and protein content of seston from Lake Ontario and Jacks Lake, Ontario, were measured during the ice-free season as a means of estimating plankton nutritional status. Despite the similar trophic level of these lakes, protein to carbohydrate ratios were generally above 1 in Lake Ontario, indicating lack of severe phosphorus or nitrogen deficiency, while those of Jacks Lake were always well below 1, indicating severe nutrient stress. However, in Lake Ontario, some discrepancies with other indicators of nutrient status occurred which complicate interpretations of the ratio. The ratio will also not distinguish phosphorus from nitrogen deficiency. On average, 28% (11–80%) of the particulate organic carbon is carbohydrate carbon and 80% (40–100%) of the particulate organic nitrogen is protein-nitrogen in Lake Ontario. Chlorophyll a explained 44% of the variation in carbohydrate but only 22% of the variation in protein. Diurnal as well as seasonal and vertical changes in the ratio of protein to carbohydrate were observed.
Protein Synthesis by Lake Plankton Measured Using in situ Carbon Dioxide and Sulfate Assimilation
Authors: Cuhel Russell L. , Lean David R. S.
Published: April 2008

Sequential 4- to 6-h in situ measurements of carbon dioxide and sulfate uptake showed midday deepening of the depth of Pmax and photoinhibition of upper water column samples. Analysis of subcellular fractions accentuated total uptake measurements, with net protein synthesis providing a direct measure of growth. The percentage of carbon assimilated into protein was smallest at the depth of maximum photosynthesis and increased with light limitation. Summed incubations agreed well with all-day deployments for total carbon fixation and protein synthesis. Assimilation numbers were consistently low (<2.5 g C∙g Chl a−1∙h-1 with integrated (0–20 m) areal production of 616–1467 mg C∙m−2 and 7.5–32.4 mg S∙m−2 during the light day. Nonreductive sulfate assimilation (predominantly ester-SO4−) accounted for up to 40% of the total sulfate uptake when diatoms predominated. Protein synthesis measured with 35S (200–1000 mg protein∙m−2 during the light day) increased 57–89% overnight. Hourly rates were similar during light and scotophase incubations. Night metabolism substantially altered the biochemical composition (e.g. protein, lipid, and carbohydrate) of the plankton with respect to newly incorporated carbon. Combined plant-specific H14CO3− and general microbial 3SSO42− techniques suggested algal dominance in the mixed layer.
Photoinhibition of DCMU-Enhanced Fluorescence in Lake Ontario Phytoplankton
Authors: Putt M. , Harris G. P. , Cuhel R. L.
Published: April 2008

Measurement of 1-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) enhanced fluorescence (FDCMU) suggested that photoinhibition of photosynthesis was frequently an artifact of in situ bottle incubations in Lake Ontario phytoplankton. In a seasonal study, FDCMU of all populations was depressed by bright light in an incubator. However, when the euphotic zone did not exceed the depth of the mixed layer, vertical transport of phytoplankton into either low-light or dark regions apparently allowed reversal of photoinhibition of FDCMU. Advantages of FDCMU as a bioassay of vertical mixing include rapidity of response time, ease of measurement in the field, and insensitivity of this parameter to changes in phosphorus status of the population. Because of seasonal changes in the photoadaptive response of natural populations, the rate constants and threshold light levels required to cause the response must be determined at each use if the method is to be quantitative.
Differences between Nearshore and Offshore Phytoplankton Communities in Lake Ontario
Authors: Gray I. M.
Published: April 2008

Differences between nearshore and offshore phytoplankton biomass and composition were evident in Lake Ontario in 1982. Phytoplankton biomass was characterized by multiple peaks which ranged over three orders of magnitude. Perhaps as a consequence of the three times higher current velocities at the northshore station, phytoplankton biomass ranged from 0.09 to 9.00 g∙m−3 compared with 0.10 to 2.40 g∙m−3 for the midlake station. Bacillariophyceae was the dominant group at the northshore station until September when Cyanophyta contributed most to the biomass (83%). Although Bacillariophyceae was the principal component of the spring phytoplankton community at the midlake station, phytoflagellates (49%) and Chlorophyceae (25%) were responsible for summer biomass, with the Chlorophyceae expanding to 80% in the fall. The seasonal pattern of epilimnetic chlorophyll a correlated with temperature. While chlorophyll a concentrations were similar to values from 1970 and 1972, algal biomass had declined and a number of eutrophic species (Melosira binderana, Stephanodiscus tenuis, S. hantzschii var. pusilla, and S. alpinus) previously found were absent in 1982.
Characterization of Cyanobacterial Picoplankton in Lake Ontario by Transmission Electron Microscopy
Authors: Leppard Gary G. , Urciuoli Dina , Pick F. R.
Published: April 2008

Many chroococcoid cyanobacteria from Lake Ontario, characterized by epifluorescence in concert with transmission electron microscopy, had a Type I ultrastructure, the major type in oceanic waters. Such cells had a multilayered cell envelope and their polyhedral bodies were interspersed with the central nuclear material. All thylakoids were peripheral and were arranged concentrically, with no intrusion into the nuclear region. Related chroococcoid types were also seen but these were much less abundant. The most numerous cell type in all water samples was a small, Gram-negative, rodlike bacterium. Many of these rods were sufficiently small to pass a filter of 0.45-μm pore size but none had a diameter less than 0.2 μm. Attempts to isolate and describe the cyanobacterial picoplankton presented some unusual difficulties having a potential to mislead limnological analyses. These are described and, to some extent, they are resolved here.
Zooplankton Seasonal Succession in Lake Ontario at Northshore, Midlake, and Southshore Stations in 1982, and a Comparison with 1970
Authors: Taylor W. D. , Fricker H-J. , Lean D. R. S.
Published: April 2008

The seasonal pattern of zooplankton succession in Lake Ontario was similar at three stations along a north–south transect, with differences attributable to physical factors. Because of warming within the thermal bar zone, the spring succession at the northshore station was early relative to the midlake station, but after stratification the northshore station lagged behind due to frequent upwelling events. Thermal bar formation along the south shore was followed by downwelling throughout the summer, giving a deeper epilimnion. These events may have contributed to not only the greater biomass at this location, but also succession which preceded that at the other stations during summer and fall. The species composition and the timing of the summer succession were very similar to those reported for 1970. Lake Ontario zooplankton did not change markedly in response to changes in nutrient loading and salmonid predators during the 1970's.
Reduction of Cladophora Biomass and Tissue Phosphorus in Lake Ontario, 1972–83
Authors: Painter D. S. , Kamaitis G.
Published: April 2008

Cladophora biomass and tissue phosphorus concentrations at seven sites in Lake Ontario have decreased from 1972 to 1983 in response to phosphorus control programs introduced in the early 1970's. Biomass and tissue phosphorus were significantly different between 1972 and 1982–83 (ANOVA, P < 0.001) but not significantly different between 1982 and 1983. The lakewide average tissue phosphorus was 0.49% in 1972 but by 1982 and 1983 had dropped to 0.26 and 0.20%, respectively, on an ash-free dry weight basis. Tissue phosphorus concentrations did not limit growth in 1972 but in 1983 had begun to limit growth. Model-predicted net production for a 6-wk sampling period in 1983 was 1.7 times greater in the western end of the lake than at a remote site in eastern Lake Ontario due to higher soluble reactive phosphorus concentrations.
Differential Thermal and Thermogravimetric Analysis of Sediment-Forming Materials from Lake Ontario
Authors: Zimmermann G. M. , Lean D. R. S. , Charlton M. N.
Published: April 2008

Differential thermal analyses (DTA) and thermogravimetric analyses (TGA) of seston, sediments, and sediment trap material from Lake Ontario were generally similar to each other but were strikingly different from those of the green alga Chlorella pyrenoidosa. Coinciding with the principal weight loss of carbohydrate material, the main exothermic reaction for all lake samples began at 200–250 °C and peaked at 345–355 °C. Trap samples varied over the season and samples from the deep traps (178 m) had exotherms which were broader with less energy content than from traps near the bottom of the metalimnion. This trend continued into the sediments. Compounds likely to be found in sediments (cellulose, chitin, and humic substances) were also analysed. The calcium carbonate endotherm which begins near 675 °C distinguishes this compound from the total "ash" content. DTA and TGA can be used to detect changes in composition of lake organic matter during the sediment-forming process.
Time of Onset of Full Thermal Stratification in Lake Ontario in Relation to Lake Temperatures in Winter
Authors: Rodgers G. Keith
Published: April 2008

Using records from 1965 to 1985 including temperature data from vessel surveys and remote sensing by aircraft and satellite, relationships are explored amongst winter severity, early spring water temperature, and the date on which thermal stratification is established throughout the lake. One extreme event stands out in 1983, in association with the anomolous extent of the El Niño current in the Pacific Ocean. Winter conditions in 1983 in Lake Ontario appear to be within the warmest 5% of winters on record: this is reflected in air and water temperatures and in the very early onset of full thermal stratification of Lake Ontario. The data provide a means of assessing the spring conditions of any particular year and also provide some predictive capability should one wish to schedule experiments to take advantage of particular thermal structures in spring or early summer.
The Lake Ontario Life Support System
Authors: Lean D. R. S. , Fricker H-J. , Charlton M. N. , Cuhel R. L. , Pick F. R.
Published: April 2008

Primary productivity provides most of the energy to support aquatic food chains. The rate is not only influenced by available solar radiation but also by temperature, availability of phosphorus, and the influence of physical mixing processes. The special features of Lake Ontario such as changes in phosphorus concentration, calcium carbonate precipitation, and silica deficiency on primary productivity, concentration of particulate carbon, and chlorophyll are discussed. Our lack of understanding of food chain and nutrient regeneration processes is illustrated through our failure to balance carbon production with losses through zooplankton grazing and sedimentation. It was demonstrated, however, that bacteria are not responsible for nutrient regeneration through "mineralization" but nutrients are effectively recycled in the water column at the second and third trophic levels.