| 1. |
- Hammar, Johan, et al.
(författare)
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Smelt (Osmerus eperlanus): Glacial relict, planktivore, predator, competitor, and key prey for the endangered Arctic char in Lake Vättern, southern Sweden
- 2018
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Ingår i: Journal of Great Lakes Research. - : Elsevier BV. - 0380-1330. ; 44, s. 126-139
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Tidskriftsartikel (refereegranskat)abstract
- Smelts are crucial forage prey for many piscivorous fish species and have, as such, been frequently introduced outside their indigenous ranges, a management measure causing controversy, as smelts are also efficient predators and competitors. In Lake Vattern, relict Arctic char, fourhorn sculpin, smelt and seven species of crustaceans form a deep-water food-web, and interact closely as competitors, predators and prey. Here, we analyzed new and archived data back to the late 1960s in order to understand and relate observed life-history shifts in the smelt population, to concurrent adverse life-history changes observed in the endangered Arctic char population. Smelt growth was sigmoidal and the size frequency distribution dominated by fish up to 110 mm and age 0-4, although smelt occasionally reached 250 mm. Smelt diet shifts as the fish grow, from zooplankton, to Mysis relicta, to piscivory for individuals larger than 150 mm. Recruitment commonly demonstrates regular inter-annual pulses of YOY abundance although strong year classes produced during years with higher spring temperature cause post-annual irregularity of year class strength. Young smelt reside in surface water and older fish in deeper water. This ontogenetic shift in distribution depends on temperature occupied, prey availability and risk of inter- and intra-specific predation. Interestingly, even though very small Arctic char feed on smelt, most small Arctic char are found in deep water together with large smelt, and most large Arctic char are found in shallow water with small smelt. (C) 2017 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Milan, Manuela, et al.
(författare)
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Multiproxy reconstruction of a large and deep subalpine lake's ecological history since the Middle Ages
- 2015
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Ingår i: Journal of Great Lakes research. - : Elsevier. - 0380-1330. ; 41:4, s. 982-994
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Tidskriftsartikel (refereegranskat)abstract
- Two short sediment cores collected at the deepest points of the two sub-basins of Lake Garda (Northern Italy) were radiometrically dated and analyzed for geochemistry, spheroidal carbonaceous particles, photosynthetic pigments and diatoms aimed at reconstructing the lake's ecological evolution over the last ~700 years, and at defining its reference conditions. Both cores showed steady dominance of small Cyclotella spp. and oligotrophic diatom-inferred lake TP concentrations from the Middle Ages until the 1960s. During the successive decades, meso- to eutraphentic elongated Fragilariaceae increased at the expense of small centrics, and diatom-inferred TP concentrations increased. Independent records of subfossil pigments revealed higher pytoplankton biomass and abundance of cyanobacteria in both lake basins since the 1990s. Trends of biological proxies and reconstructed lake TP level agree with modern limnological data collected since the 1990s. Multivariate analyses outlined lake nutrient level as the principal driver of long-term trophic and diatom evolution of Lake Garda and suggested that decadal scale climate dynamics (i.e. air temperature, East Atlantic and North Atlantic Oscillation teleconnection indices) may indirectly modulate the nutrient-driven phytoplankton evolution. The comparison of the two cores revealed that only the larger lake basin responded to major hydrological changes in the catchment during the 1940s. The study emphasizes the vulnerability of large and deep subalpine lakes towards the steadily increasing anthropogenic pressures affecting such lakes, under the present context of global warming.
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| 3. |
- Naddafi, Rahmat
(författare)
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Stomach contents and stable isotopes analysis indicate Hemimysis anomala in Lake Ontario are broadly omnivorous
- 2018
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Ingår i: Journal of Great Lakes Research. - : Elsevier BV. - 0380-1330. ; 44, s. 467-475
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Tidskriftsartikel (refereegranskat)abstract
- Hemimysis anomala is a recent invader to North American aquatic ecosystems and is spreading rapidly throughout the Great Lakes region. This is the first littoral mysid in the North American Great Lakes; and, as such, the ecosystem effects are unknown and could be substantial. These effects depend on the role of Hemimysis in the food web and, therefore, on its diet. We examined the stomach contents of two life stages of Hemimysis from two sites in Lake Ontario during the growing season (May-November 2010). We also report the relationship between zooplankton hard parts and size for a number of potential prey species to allow the back-calculation of prey lengths from stomach contents. Both juvenile (2-5 mm) and adult Hemimysis (5-11 mm) were omnivorous, consuming phytoplankton, zooplankton, and benthos when available. However, adults appeared slightly more carnivorous and incorporated larger prey in their diets. Hemimysis were able to consume zooplankton prey up to 30% of their own length, including Bythotrephes longimanus and Cercopagis pengoi. Daphnia and Bosmina were selected over other prey by both juvenile and adult Hemimysis and were most common in stomachs during July and September when their abundances in the zooplankton were highest. Measurements of delta C-13 and delta N-15 corroborated stomach content materials, indicating an omnivorous diet which included benthic and pelagic sources. Omnivory by Hemimysis is typical of mysids in general and makes them less sensitive to seasonal dynamics of preferred prey items. (C) 2018 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.
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