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Brent T. Boscarino - One of the best experts on this subject based on the ideXlab platform.
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laboratory derived temperature preference and effect on the feeding rate and survival of juvenile hemiMysis anomala
Journal of Great Lakes Research, 2013Co-Authors: Jennifer K Sun, Brent T. Boscarino, Lars G. Rudstam, Maureen Walsh, Brian F LantryAbstract:Abstract HemiMysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile HemiMysis , using individuals acclimated to mid (16 °C) and upper (22 °C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0 °C (SE 0.25) when acclimated to 16 and 21.9 °C (SE 0.38) when acclimated to 22 °C, with the σ-values of the curves at 2.6 and 2.5 °C, respectively. No mysids were observed in temperatures below 10 or above 28 °C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32 °C, all mysids died within 8 h at 30.2 °C for 16 °C acclimated mysids, and at 31.8 °C for 22 °C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5 °C to 19 Bosmina eaten per hour at 27 °C. The results of our experiments indicate an optimal temperature for HemiMysis between 21 and 27 °C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.
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light effects on alewife mysid interactions in lake ontario a combined sensory physiology behavioral and spatial approach
Limnology and Oceanography, 2010Co-Authors: Brent T. Boscarino, Lars G. Rudstam, Jill Tirabassi, John Janssen, Ellis R. LoewAbstract:An understanding of the effect of light on predator–prey interactions in aquatic systems requires the integration of sensory physiology, behavioral ecology, and spatial distributions of predator and prey in the field. Here, we present such an integrative approach to a study on the interactions between the alewife, Alosa pseudoharengus, and the mysid shrimp, Mysis diluviana, (formerlyM. relicta) in Lake Ontario at night, when it is unknown whether visual feeding is possible. Visual pigment analyses of alewife rod photoreceptors were used to derive an alewife-specific unit of brightness—the ‘alelux’ (wavelength of maximum absorbance, lmax 5 505 nm)—which formed the basic unit of light intensity in alewife feeding-rate experiments and field applications. At light levels of 1027 alelux (, 1024.1 lux) and greater in the laboratory, alewives engaged in visual search and strike behaviors and fed at rates that were significantly higher than those under completely dark conditions. Field observations from Lake Ontario showed that light levels at the upper edge of the mysid distribution were within the range of those required for visual feeding in the laboratory on a full moon night, but not on a new moon night. These increased light levels translated into feeding rates that were . 30 times higher on the full moon night, despite a larger degree of spatial separation of the two trophic levels. We hypothesize that observed increased water clarity in Lake Ontario in recent years has led to increased consumption of mysids by alewife at night and associated food-web changes. Of the many factors that affect fish feeding success, light may be the most dynamic because light intensity changes over many orders of magnitude throughout the day–night
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early observations on an emerging great lakes invader hemiMysis anomala in lake ontario
Journal of Great Lakes Research, 2010Co-Authors: Brent T. Boscarino, Maureen G Walsh, Kelly L Bowen, Brian F Lantry, Jocelyn Gerlofsma, Ted SchanerAbstract:ABSTRACT HemiMysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, HemiMysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of HemiMysis in the Great Lakes is scarce, the potential for food web disruption by HemiMysis cannot easily be predicted. Preliminary observations indicate widespread invasion of HemiMysis in Lake Ontario. In this study, we confirm the presence of HemiMysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling HemiMysis were horizontal tows ...
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predicting the vertical distribution of the opossum shrimp Mysis relicta in lake ontario a test of laboratory based light preferences
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Brent T. Boscarino, Lars G. Rudstam, Ellis R. Loew, Edward L MillsAbstract:Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis relicta. We monitored the vertical movements and depth selection behavior of mysids exposed to differen...
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acoustic characterization of Mysis relicta at multiple frequencies
Canadian Journal of Fisheries and Aquatic Sciences, 2008Co-Authors: Lars G. Rudstam, Brent T. Boscarino, Gideon Gal, Frank Reier Knudsen, Helge Balk, Thomas AxenrotAbstract:We measured acoustic backscattering from Mysis relicta, a common invertebrate in northern lakes, using five frequencies (38, 120, 200, 430, and 710 kHz). Acoustic backscattering from mysids was highest at 430 kHz and lowest at 38 kHz (19 dB lower). Maximum difference between the four other frequencies was 5.2 dB. Mysid target strength (TS) ranged from -80.1 dB at 430 kHz to -99.4 dB at 38 kHz (12 mm average length, range 5-21 mm). A theoretical scattering model (Stanton's fluid-like, bent-cylinder model) predicted TS within 0.3-1.9 dB of observed TS for the different frequen- cies. The detection range was lowest at 38 and 710 kHz and greatest at 120 and 200 kHz. Fish were common above the mysid layer and produced higher acoustic backscattering at 38 kHz than at the other frequencies. A combination of 38 kHz and 120 or 200 kHz provides a strong contrast between mysid and fish acoustic backscattering that would help separate these groups using acoustic data. Resume´ : Nous avons mesurela retrodiffusion acoustique causee par Mysis relicta, un invertebrecommun dans les lacs nordiques, a cinq frequences (38, 120, 200, 430 et 710 kHz). La retrodiffusion acoustique par les mysides est maximale a 430 kHz et minimale a ` 38 kHz (inferieure de 19 dB). La difference maximale entre les quatre autres frequences est de 5,2 dB. L'indice de cible (TS) des mysides varie de -80,1 dB a 430 kHz a ` -99,4 dB a 38 kHz (longueur moyenne 12 mm, etendue 5-21 mm). Un modele theorique de retrodiffusion (le modele du cylindre fluide courbe de Stanton) predit des valeurs de TS situees entre 0,3 et 1,9 dB des TS observes aux diverses frequences. La porteed e detection est minimale a ` 38 kHz et 710 kHz et maximale a ` 120 kHz et 200 kHz. Les poissons sont communs au-dessus de la couche de mysidese t produisent une retrodiffusion acoustique plus importante a ` 38 kHz qu'aux autres frequences. Une combinaison de 38 kHz et de 120 ou 200 kHz donne un fort contraste entre la retrodiffusion par les mysides et par les poissons, ce qui aiderait a ` separer ces groupes al'aide de donnees acoustiques. (Traduit par la Redaction)
Lars G. Rudstam - One of the best experts on this subject based on the ideXlab platform.
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� 1999, by the American Society of Limnology and Oceanography, Inc. Acoustic characterization of Mysis relicta
2014Co-Authors: Gideon Gal, Lars G. Rudstam, Charles H. GreeneAbstract:It is possible to increase the sampling resolution and the available information on zooplankton populations by applying acoustic sampling techniques. Knowledge of an organism’s acoustic target strength (TS) is critical for translating acoustic data into meaningful biological information, such as numerical abundance. We have taken several approaches to evaluate the acoustic TS of Mysis relicta, a key benthic-pelagic invertebrate in the Laurentian Great Lakes. This included in situ TS measurements with a dual-beam 420-kHz system and comparison among netbased, optical plankton counter (OPC)-based, and acoustic-based estimates of numerical abundance of mysids. In addition, based on the in situ TS data, we modified a model previously applied primarily to marine zooplankton taxa. The resulting predicted TS was compared to other TS estimates. The estimated mean TSs from the in situ TS measurements and the OPC-acoustic comparison were within a narrow range (�76 to �74.8 dB). Analysis of the net-acoustic data comparison resulted in an estimated average TS of �73.1 dB. We suggest that the net-acoustic discrepancy relative to other methods is due to net avoidance and low filtering efficiency. The model predicted similar mean TSs for the size distribution present when R (reflectivity coefficient) was changed to 0.0675. We hypothesized that the modification of the model parameter values was necessary because of the differences in the medium surrounding marine vs. freshwater zooplankton. The opossum shrimp, M. relicta, is a freshwater species in the mainly marine group of crustaceans belonging to the family Mysidaceae (Mauchline 1980). It is a benthic-pelagic invertebrate that inhabits offshore, hypolimnetic waters. Mysids avoid light, remaining in deep water during the day and moving up to the epilimnion at night (Beeton and Bowers 1982). The extent of vertical migration is primarily lim
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laboratory derived temperature preference and effect on the feeding rate and survival of juvenile hemiMysis anomala
Journal of Great Lakes Research, 2013Co-Authors: Jennifer K Sun, Brent T. Boscarino, Lars G. Rudstam, Maureen Walsh, Brian F LantryAbstract:Abstract HemiMysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile HemiMysis , using individuals acclimated to mid (16 °C) and upper (22 °C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0 °C (SE 0.25) when acclimated to 16 and 21.9 °C (SE 0.38) when acclimated to 22 °C, with the σ-values of the curves at 2.6 and 2.5 °C, respectively. No mysids were observed in temperatures below 10 or above 28 °C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32 °C, all mysids died within 8 h at 30.2 °C for 16 °C acclimated mysids, and at 31.8 °C for 22 °C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5 °C to 19 Bosmina eaten per hour at 27 °C. The results of our experiments indicate an optimal temperature for HemiMysis between 21 and 27 °C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.
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light effects on alewife mysid interactions in lake ontario a combined sensory physiology behavioral and spatial approach
Limnology and Oceanography, 2010Co-Authors: Brent T. Boscarino, Lars G. Rudstam, Jill Tirabassi, John Janssen, Ellis R. LoewAbstract:An understanding of the effect of light on predator–prey interactions in aquatic systems requires the integration of sensory physiology, behavioral ecology, and spatial distributions of predator and prey in the field. Here, we present such an integrative approach to a study on the interactions between the alewife, Alosa pseudoharengus, and the mysid shrimp, Mysis diluviana, (formerlyM. relicta) in Lake Ontario at night, when it is unknown whether visual feeding is possible. Visual pigment analyses of alewife rod photoreceptors were used to derive an alewife-specific unit of brightness—the ‘alelux’ (wavelength of maximum absorbance, lmax 5 505 nm)—which formed the basic unit of light intensity in alewife feeding-rate experiments and field applications. At light levels of 1027 alelux (, 1024.1 lux) and greater in the laboratory, alewives engaged in visual search and strike behaviors and fed at rates that were significantly higher than those under completely dark conditions. Field observations from Lake Ontario showed that light levels at the upper edge of the mysid distribution were within the range of those required for visual feeding in the laboratory on a full moon night, but not on a new moon night. These increased light levels translated into feeding rates that were . 30 times higher on the full moon night, despite a larger degree of spatial separation of the two trophic levels. We hypothesize that observed increased water clarity in Lake Ontario in recent years has led to increased consumption of mysids by alewife at night and associated food-web changes. Of the many factors that affect fish feeding success, light may be the most dynamic because light intensity changes over many orders of magnitude throughout the day–night
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predicting the vertical distribution of the opossum shrimp Mysis relicta in lake ontario a test of laboratory based light preferences
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Brent T. Boscarino, Lars G. Rudstam, Ellis R. Loew, Edward L MillsAbstract:Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis relicta. We monitored the vertical movements and depth selection behavior of mysids exposed to differen...
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acoustic characterization of Mysis relicta at multiple frequencies
Canadian Journal of Fisheries and Aquatic Sciences, 2008Co-Authors: Lars G. Rudstam, Brent T. Boscarino, Gideon Gal, Frank Reier Knudsen, Helge Balk, Thomas AxenrotAbstract:We measured acoustic backscattering from Mysis relicta, a common invertebrate in northern lakes, using five frequencies (38, 120, 200, 430, and 710 kHz). Acoustic backscattering from mysids was highest at 430 kHz and lowest at 38 kHz (19 dB lower). Maximum difference between the four other frequencies was 5.2 dB. Mysid target strength (TS) ranged from -80.1 dB at 430 kHz to -99.4 dB at 38 kHz (12 mm average length, range 5-21 mm). A theoretical scattering model (Stanton's fluid-like, bent-cylinder model) predicted TS within 0.3-1.9 dB of observed TS for the different frequen- cies. The detection range was lowest at 38 and 710 kHz and greatest at 120 and 200 kHz. Fish were common above the mysid layer and produced higher acoustic backscattering at 38 kHz than at the other frequencies. A combination of 38 kHz and 120 or 200 kHz provides a strong contrast between mysid and fish acoustic backscattering that would help separate these groups using acoustic data. Resume´ : Nous avons mesurela retrodiffusion acoustique causee par Mysis relicta, un invertebrecommun dans les lacs nordiques, a cinq frequences (38, 120, 200, 430 et 710 kHz). La retrodiffusion acoustique par les mysides est maximale a 430 kHz et minimale a ` 38 kHz (inferieure de 19 dB). La difference maximale entre les quatre autres frequences est de 5,2 dB. L'indice de cible (TS) des mysides varie de -80,1 dB a 430 kHz a ` -99,4 dB a 38 kHz (longueur moyenne 12 mm, etendue 5-21 mm). Un modele theorique de retrodiffusion (le modele du cylindre fluide courbe de Stanton) predit des valeurs de TS situees entre 0,3 et 1,9 dB des TS observes aux diverses frequences. La porteed e detection est minimale a ` 38 kHz et 710 kHz et maximale a ` 120 kHz et 200 kHz. Les poissons sont communs au-dessus de la couche de mysidese t produisent une retrodiffusion acoustique plus importante a ` 38 kHz qu'aux autres frequences. Une combinaison de 38 kHz et de 120 ou 200 kHz donne un fort contraste entre la retrodiffusion par les mysides et par les poissons, ce qui aiderait a ` separer ces groupes al'aide de donnees acoustiques. (Traduit par la Redaction)
Edward L Mills - One of the best experts on this subject based on the ideXlab platform.
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predicting the vertical distribution of the opossum shrimp Mysis relicta in lake ontario a test of laboratory based light preferences
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Brent T. Boscarino, Lars G. Rudstam, Ellis R. Loew, Edward L MillsAbstract:Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis relicta. We monitored the vertical movements and depth selection behavior of mysids exposed to differen...
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the effects of temperature and predator prey interactions on the migration behavior and vertical distribution of Mysis relicta
Limnology and Oceanography, 2007Co-Authors: Brent T. Boscarino, Ora E Johannsson, Lars G. Rudstam, Shylene Mata, Gideon Gal, Edward L MillsAbstract:The extent to which temperature, temperature gradients, predator smell, and prey availability influence the migratory behaviors and vertical distribution of the opossum shrimp, Mysis relicta, was explored through controlled laboratory experiments and comparisons with field distributions of mysids in Lake Ontario. By varying environmental conditions in 2-m tall experimental columns in a temperature-controlled room, we determined that mysids prefer temperatures between 6uC and 8uC with limited movement into waters of 12uC or higher. No mysids moved into waters above 16uC in the absence of prey. However, a higher proportion of mysids moved into temperatures of 14uC and 16uC (but not 18uC) when densities of Daphnia pulicaria exceeding 120 L 21 were present at those temperatures. Mysis avoided waters with kairomones from a primary mysid predator, the alewife (Alosa pseudoharengus). The rate of temperature change with depth did not restrict mysid movements. A temperature preference function based on the experimental data was applied to an existing model of mysid vertical distribution. The modified model predicted the depth of maximum mysid density to within 1 m and yielded high percentage overlap index values when compared with published mysid vertical distributions in Lake Ontario. Our approach may be used to model how diurnal, seasonal, and larger climactic changes can impact both the vertical position and feeding ecology of mysids, a keystone species in many deep-water pelagic food webs.
Risto Vainola - One of the best experts on this subject based on the ideXlab platform.
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opsin gene sequence variation across phylogenetic and population histories in Mysis crustacea mysida does not match current light environments or visual pigment absorbance spectra
Molecular Ecology, 2012Co-Authors: Asta Audzijonyte, Joha Pahlberg, Martta Viljane, Kristia Donne, Risto VainolaAbstract:The hypothesis that selection on the opsin gene is efficient in tuning vision to the ambient light environment of an organism was assessed in 49 populations of 12 Mysis crustacean species, inhabiting arctic marine waters, coastal littoral habitats, freshwater lakes (‘glacial relicts’) and the deep Caspian Sea. Extensive sequence variation was found within and among taxa, but its patterns did not match expectations based on light environments, spectral sensitivity of the visual pigment measured by microspectrophotometry or the history of species and populations. The main split in the opsin gene tree was between lineages I and II, differing in six amino acids. Lineage I was present in marine and Caspian Sea species and in the North American freshwater Mysis diluviana, whereas lineage II was found in the European and circumarctic fresh- and brackish-water Mysis relicta, Mysis salemaai and Mysis segerstralei. Both lineages were present in some populations of M. salemaai and M. segerstralei. Absorbance spectra of the visual pigment in nine populations of the latter three species showed a dichotomy between lake (λmax = 554–562 nm) and brackish-water (Baltic Sea) populations (λmax = 521–535 nm). Judged by the shape of spectra, this difference was not because of different chromophores (A2 vs. A1), but neither did it coincide with the split in the opsin tree (lineages I/II), species identity or current light environments. In all, adaptive evolution of the opsin gene in Mysis could not be demonstrated, but its sequence variation did not conform to a neutral expectation either, suggesting evolutionary constraints and/or unidentified mechanisms of spectral tuning.
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Mysis nordenskioldi n sp crustacea mysida a circumpolar coastal mysid separated from the ne pacific m litoralis banner 1948
Polar Biology, 2007Co-Authors: Asta Audzijonyte, Risto VainolaAbstract:Mysis nordenskioldi n. sp. is a circumpolar, arctic-subarctic coastal mysid crustacean, earlier considered conspecific with M. litoralis (Banner, 1948) and in the past also confused with the circumpolar M. oculata (Fabricius, 1780). Mysis litoralis itself seems to be restricted to the northeastern North Pacific. Formal diagnoses and descriptions of the three species are here given based on morphological and molecular characters (allozymes, mtDNA). The species are morphologically distinguished by features of the telson and by the setation of maxillae and maxillipedes. Molecular differences diagnosing M. nordenskioldi from the two others were found at seven to eight allozyme loci, while M. oculata and M. litoralis differed from each other at five loci. In mitochondrial DNA, M. nordenskioldi is distinguished from the others by 8% nucleotide divergence, whereas M. litoralis and M. oculata make an inseparable cluster (<1%), suggesting post-speciation mitochondrial introgression. Initial phylogeographic data on M. nordenskioldi and M. oculata are presented. A morphological key to marine Mysis species is given.
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spectral sensitivity differences in two Mysis sibling species crustacea mysida adaptation or phylogenetic constraints
Journal of Experimental Marine Biology and Ecology, 2005Co-Authors: Joha Pahlberg, Risto Vainola, Asta Audzijonytė, Magnus LindstromAbstract:Abstract The variation in eye spectral sensitivities of the closely related mysid species Mysis relicta Loven, 1862 and Mysis salemaai Audzijonytė and Vainola, 2005 was studied in sympatric and allopatric populations from the brackish Baltic Sea and from two lakes representing different light environments. In the Baltic Sea the maximum spectral sensitivity of M. relicta, measured by the electroretinogram (ERG) technique, was shifted by ca 20 nm to longer wavelengths than in M. salemaai (564 and 545 nm, respectively). The spectral sensitivity of M. salemaai was closer to that of marine mysid species, which is consistent with its broader euryhalinity and the presumed longer brackish-water history. The species-specific sensitivities in the Baltic Sea were not affected by regional differences in light environments. In two lake populations of M. relicta, the spectral sensitivity was further shifted by ca 28 nm towards the longer wavelengths compared with the conspecific Baltic Sea populations. The spectral sensitivities in the four M. relicta populations were not correlated to the current light conditions, but rather to the phylogeographic histories and fresh- vs. brackish-water environments. A framework to further explore factors affecting spectral sensitivities in Mysis is suggested.
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diversity and distributions of circumpolar fresh and brackish water Mysis crustacea mysida descriptions of m relicta loven 1862 m salemaai n sp m segerstralei n sp and m diluviana n sp based on molecular and morphological characters
Hydrobiologia, 2005Co-Authors: Asta Audzijonytė, Risto VainolaAbstract:Mysid crustaceans of the Mysis relicta species group are widespread throughout the northern Holarctic and play an important role in many fresh- and brackish-water ecosystems. Earlier molecular and morphometric studies already indicated that the conventionally identified Mysis relicta sensu lato comprises several distinct species. Here we present formal taxonomic diagnoses, descriptions and an account of the distributions of Mysis relicta s. str. and three new species split from it, based on comprehensive assessment of both morphological and molecular characters (allozymes, mtDNA). M. relicta Loven s. str. is the prevalent species in lakes of Northern Europe and peripheral parts of the brackish Baltic Sea. M. salemaai n. sp. inhabits offshore habitats of the Baltic Sea and a range of lakes from the British Isles, southern Scandinavia and Karelia to coastal northern Siberia; at several sites M. relicta and M. salemaai are sympatric. M. segerstralei n. sp. has a circumpolar distribution along the Arctic coasts and islands of Eurasia and North America and also occurs in lakes of these northern regions. M. diluviana n. sp. inhabits continental freshwater lakes of the once-glaciated northern North America. The four species are characterised by unique combinations of alleles at a number of allozyme loci, and most of them by specific mitochondrial DNA lineages diverged by c. 7.5% in the COI gene sequence (cytochrome oxidase subunit I). The most important diagnostic morphological characters include the shape of the posterior emargination of carapace, length of setae on the merus of maxillipede 2, length and shape of spine-setae on maxilla endopod distal segment, number and size of lateral spine-setae on telson, and setation of thoracic endopods. A morphological key to the four species is presented.
Maureen G Walsh - One of the best experts on this subject based on the ideXlab platform.
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Mysis diluviana population and cohort dynamics in lake ontario before and after the establishment of dreissena spp cercopagis pengoi and bythotrephes longimanus
Canadian Journal of Fisheries and Aquatic Sciences, 2011Co-Authors: Ora E Johannsson, Kelly L Bowen, Kristen T Holeck, Maureen G WalshAbstract:We investigated population responses of Mysis to ecosystem changes induced by invasion of dreissenids and pred- atory cladocerans, Cercopagis and Bythotrephes. Lake productivity declined as dreissenids invaded the offshore region. Whole-lake mysid biomass was compared before (early 1990s) and after (2002-2007) the invasion period; it declined 40%- 45%. Abundance of young mysids and presence of a summer cohort increased with summer, epilmnetic, nighttime zooplank- ton biomass (i.e., food biomass index). Cercopagis + Bythotrephes biomass was negatively correlated with this index, impli- cating them in the mysid decline. Eggs per gravid female increased with autumn, total-water-column zooplankton biomass, reflecting the greater use of hypolimnetic waters by adults. Reproductive success was below replacement during the period 2002-2005. First-year mysid growth rate was maintained while population abundance declined, suggesting selection for indi- viduals that feed effectively at low food concentrations. Mortality rates in the first and second years were dependent on co- hort density, indicating that competition for food limited abundance in the first 2 years. Fish predation indices (smelt and alewife combined) were correlated positively with mortality rates and negatively with abundance in the third year. Thus, my- sids cannot support as many fish in invaded compared with non-invaded lakes. They may also not be a stable food resource; unusual cohort losses occurred in some years. Resume : Nous etudions les reactions demographiques des Mysis aux changements dans l'ecosysteme causes par l'invasion des dreissenides et des cladoceres predateurs, Cercopagis et Bythotrephes. La productivite lacustre diminue a mesure que les dreissenides envahissent le large. Nous comparons la biomasse des mysides dans le lac entier avant (debut des annees 1990) et apres (2002-2007) l'invasion; elle a decline de 40-45 %. L'abondance de jeunes mysides et la presence d'une co- horte d'ete sont en relation positive avec la biomasse nocturne et epilimnetique du zooplancton en ete (indice de biomasse alimentaire). La biomasse de Cercopagis + Bythotrephes est en correlation negative avec cet indice, ce qui les implique dans le declin des mysides. Les oeufs par femelle gravide augmentent avec la biomasse du zooplancton dans toute la co-
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early observations on an emerging great lakes invader hemiMysis anomala in lake ontario
Journal of Great Lakes Research, 2010Co-Authors: Brent T. Boscarino, Maureen G Walsh, Kelly L Bowen, Brian F Lantry, Jocelyn Gerlofsma, Ted SchanerAbstract:ABSTRACT HemiMysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, HemiMysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of HemiMysis in the Great Lakes is scarce, the potential for food web disruption by HemiMysis cannot easily be predicted. Preliminary observations indicate widespread invasion of HemiMysis in Lake Ontario. In this study, we confirm the presence of HemiMysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling HemiMysis were horizontal tows ...
