Papers by Brent Boscarino
Limnology and Oceanography, 2007
The extent to which temperature, temperature gradients, predator smell, and prey availability inf... more 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.
Journal of Great Lakes Research, 2012
We investigated the seasonal occurrence of Hemimysis anomala in the diets of fish that prey on ma... more We investigated the seasonal occurrence of Hemimysis anomala in the diets of fish that prey on macroinvertebrates at two sites with established Hemimysis populations east of Oswego, NY, during 2009-2010. In 2009, we examined 320 stomachs from 10 species and found Hemimysis only in alewife (Alosa pseudoharengus), rockbass (Ambloplites rupestris), and yellow perch (Perca flavescens). Of those species, alewife consumed Hemimysis most frequently and it represented a greater proportion of their diets. During 2009, the dry weight composition of Hemimysis in alewife diets varied seasonally between b 1% in June, 5% in July, 98.5% in August, and 18.8% in September. In contrast, we examined 667 stomachs from 15 species in 2010 and observed Hemimysis in only one alewife and two rockbass stomachs. For alewife from September 2009, we found no relationship between predator size and the number of Hemimysis consumed, or between the presence of Hemimysis in fish diets and the presence of other diet taxa or diet diversity. Fish diets collected as bycatch from other assessments revealed large numbers of Hemimysis in fishes that had not previously been observed consuming Hemimysis in Lake Ontario, including cisco (Coregonus artedi) and white perch (Morone americana).
Journal of Great Lakes Research, 2012
Hemimysis anomala is one of the latest macroinvertebrates to invade the Laurentian Great Lakes. S... more Hemimysis anomala is one of the latest macroinvertebrates to invade the Laurentian Great Lakes. Since first reported in 2006, Hemimysis have been confirmed in several locations within the Great Lakes basin. However, little is known about the seasonal and spatial variation in demographics and dynamics of Hemimysis populations. We used a standardised pier-based methodology to describe the distribution of Hemimysis
Journal of Great Lakes Research, 2012
We use a combination of spectral sensitivity analyses, laboratory behavioral observations and fie... more We use a combination of spectral sensitivity analyses, laboratory behavioral observations and field distributions of a vertically migrating invertebrate, Hemimysis anomala (a recent invasive species to the Laurentian Great Lakes of North America), to determine if light preference and timing of emergence has an ontogenetic component. Juvenile Hemimysis (b 4.5 mm) preferred light levels between 10 −3.4 and 10 −2.4 mylux-a Hemimysis-specific unit of brightness derived from visual pigment analyses (wavelength of maximum absorbance = 500 nm; 1 mylux~159 lx). These preferred light levels are equivalent to those present during nautical twilight on the Earth's surface and were several orders of magnitude brighter than those most preferred by adults (N 4.5 mm) in the laboratory (10 −6.4 to 10 −7.4 mylux). Both size classes completely avoided light levels of 10 −0.4 mylux and greater, which are representative of daytime light levels at the Earth's surface. Net hauls taken at~20-min intervals from sunset to the end of nautical twilight on two sampling occasions on Seneca Lake, New York (sampling depth = 2 m) revealed that juveniles emerged into the water column during civil twilight. Adult Hemimysis emerged later during nautical twilight when juveniles had already reached their maximum abundance in the water column. Laboratory-derived light preferences successfully predicted the timing of emergence and time of maximal abundance of both size classes on both sampling occasions. This study is one of the first to demonstrate that Hemimysis diel vertical migration has an ontogenetic component and to report the specific light levels likely to initiate and limit vertical movements.
Hydrobiologia, 2013
Hemimysis anomala is a near-shore mysid native to the Ponto-Caspian region that was discovered to... more Hemimysis anomala is a near-shore mysid native to the Ponto-Caspian region that was discovered to have invaded Great Lakes ecosystems in 2006. We investigated feeding rates and prey preferences of adult and juvenile Hemimysis in laboratory experiments to gain insight on the potential for Hemimysis to disrupt food webs. For both age groups (AGs), we measured feeding rates as a function of prey abundance (Bosmina longirostris as prey), prey type (B. longirostris, Daphnia pulex, and Mesocyclops sp.), and light levels (no light and dim light). Mean feeding rates on Bosmina increased with prey density and reached 23 ind. (2 h) -1 for adults and 17 ind. (2 h) -1 for juveniles. Dim light had little effect on prey selection or feeding rate compared to complete darkness. When feeding rates on alternate prey were compared, both AGs fed at higher rates on Bosmina than Daphnia, but only juveniles fed at significantly higher rates on Bosmina relative to Mesocyclops. No significant differences were observed between feeding rates on Mesocyclops and on Daphnia. Hemimysis feeding rates were on the order of 30-60% of their body weight per day, similar to predatory cladocerans that have been implicated in zooplankton declines in Lakes Huron and Ontario.
Canadian Journal of Fisheries and Aquatic Sciences, 2009
Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis rel... more 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 different light intensities and lighttemperature gradients in the laboratory and derived a mysid light preference function in units relevant to mysid vision: ''mylux''. Mysids preferred light levels between 10 -8 and 10 -7 mylux (*10 -6 to 10 -5 lux) and rarely moved into waters of 10 -3 mylux (*0.1 lux) and greater. A model that assumed equal weight and independence of mysid light and temperature preference functions successfully predicted the proportion of mysids found in two different temperature-light combinations in the laboratory. This model also predicted the depth of maximum mysid density to within 2 m on two spring nights and within 5 m on two summer nights of varying moon phase and thermal conditions in Lake Ontario. This study provides novel insights into how temperature and light interact to influence the vertical distribution of mysids. Our model may be used to predict mysid vertical distribution in any deepwater system inhabited by mysids in which the primary mysid predators are visual feeders.
Canadian Journal of Fisheries and Aquatic Sciences, 2008
We measured acoustic backscattering from Mysis relicta, a common invertebrate in northern lakes, ... more 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 frequencies. 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.
Aquatic Ecosystem Health & Management, 2008
Mysis relicta can be observed on echograms as a sound scattering layer when they migrate into the... more Mysis relicta can be observed on echograms as a sound scattering layer when they migrate into the water column at night to feed on zooplankton. However, quantitative measures of mysid abundance with hydroacoustics requires knowledge of mysid target strength (TS), a ...
Aquatic Biology, 2008
We investigated growth rate, nucleic acid (DNA, RNA) and protein indices and respiration in juven... more We investigated growth rate, nucleic acid (DNA, RNA) and protein indices and respiration in juvenile (8.5 to 12 mm total body length, 7 to 20 mg wet wt) and young adult (12 to 14 mm, 20 to 30 mg wet wt) Mysis relicta, as a function of temperature, body mass and molt stage in order to develop methods to assess condition or growth in the field. Mysids were exposed to either a preferred temperature (6.5°C) and 3 ration levels, or a range of constant and dielly-cycling (DC) temperatures with ad libitum feeding. Mysid growth parameters (specific rates of growth [SGR], respiration [M O 2 ], and RNA content cell -1 ) integrated the DC temperature experienced as averaged responses weighted by the time spent at each temperature. M O 2 peaked at 12.7°C on acute temperature exposure from 4.2°C. M O 2 compensation with prolonged temperature exposure occurred at mean diel temperatures ≤ 8.5°C. Mysids could not survive at 16°C even for 5 h d -1 . These results confirm behavioral observations of temperature preferences. RNA concentration in M. relicta increased with ration and decreasing temperatures. Protein:DNA ratio, %protein and SGR increased with ration and then plateaued. Protein:DNA ratio, %protein and DNA:weight ratio did not change with temperature with unlimited feeding. Forward, stepwise, multiple regression models for each experiment and the combined data accounted for 31 to 72% of variability in SGR. Our experimental data provide guidance, a preliminary temperature-correction factor for RNA, and benchmarks for use of nucleic acid and protein indices in assessing growth or condition of M. relicta in the field.
Aquatic Biology, 2009
The opossum shrimp Mysis diluviana (formerly M. relicta) performs large amplitude diel vertical m... more The opossum shrimp Mysis diluviana (formerly M. relicta) performs large amplitude diel vertical migrations in Lake Ontario and its nighttime distribution is influenced by temperature, light and the distribution of its predators and prey. At one location in southeastern Lake Ontario, we measured the vertical distribution of mysids, mysid predators (i.e. planktivorous fishes) and mysid prey (i.e. zooplankton), in addition to light and temperature, on 8 occasions from May to September, 2004 and 2005. We use these data to test 3 different predictive models of mysid habitat selection, based on: (1) laboratoryderived responses of mysids to different light and temperature gradients in the absence of predator or prey cues; (2) growth rate of mysids, as estimated with a mysid bioenergetics model, given known prey densities and temperatures at different depths in the water column; (3) ratio of growth rates (g) and mortality risk (μ) associated with the distribution of predatory fishes. The model based on light and temperature preferences was a better predictor of mysid vertical distribution than the models based on growth rate and g:μ on all 8 occasions. Although mysid temperature and light preferences probably evolved as mechanisms to reduce predation while increasing foraging intake, the response to temperature and light alone predicts mysid vertical distribution across seasons in Lake Ontario.
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Papers by Brent Boscarino