Hörnefors, Sweden
Hörnefors, Sweden

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Paczkowska J.,Umeå University | Paczkowska J.,Umea Marine Science Center | Rowe O.F.,Umeå University | Rowe O.F.,Umea Marine Science Center | And 6 more authors.
Journal of Plankton Research | Year: 2017

It is well-known that nutrients shape phytoplankton communities in marine systems, but in coastal waters allochthonous dissolved organic matter (ADOM) may also be of central importance. We studied how humic substances (proxy of ADOM) and other variables influenced the nutritional strategies, size structure and pigment content of the phytoplankton community along a south-north gradient in the Baltic Sea. During the summer, the proportion of mixotrophs increased gradually from the phosphorus-rich south to the ADOM-rich north, probably due to ADOM-fueled microbes. The opposite trend was observed for autotrophs. The chlorophyll a (Chl a): carbon (C) ratio increased while the levels of photoprotective pigments decreased from south to north, indicating adaptation to the darker humic-rich water in the north. Picocyanobacteria dominated in phosphorusrich areas while nanoplankton increased in ADOM-rich areas. During the winter-spring the phytoplankton biomass and concentrations of photoprotective pigments were low, and no trends with respect to autotrophs and mixotrophs were observed. Microplankton was the dominant size group in the entire study area. We conclude that changes in the size structure of the phytoplankton community, the Chl a:C ratio and the concentrations of photoprotective pigments are indicative of changes in ADOM, a factor of particular importance in a changing climate. © 2016 The Author.

Hunsicker M.E.,Oregon State University | Ciannelli L.,Oregon State University | Bailey K.M.,National Oceanic and Atmospheric Administration | Buckel J.A.,North Carolina State University | And 23 more authors.
Ecology Letters | Year: 2011

Ecology Letters (2011) 14: 1288-1299 Predator-prey interactions are a primary structuring force vital to the resilience of marine communities and sustainability of the world's oceans. Human influences on marine ecosystems mediate changes in species interactions. This generality is evinced by the cascading effects of overharvesting top predators on the structure and function of marine ecosystems. It follows that ecological forecasting, ecosystem management, and marine spatial planning require a better understanding of food web relationships. Characterising and scaling predator-prey interactions for use in tactical and strategic tools (i.e. multi-species management and ecosystem models) are paramount in this effort. Here, we explore what issues are involved and must be considered to advance the use of predator-prey theory in the context of marine fisheries science. We address pertinent contemporary ecological issues including (1) the approaches and complexities of evaluating predator responses in marine systems; (2) the 'scaling up' of predator-prey interactions to the population, community, and ecosystem level; (3) the role of predator-prey theory in contemporary fisheries and ecosystem modelling approaches; and (4) directions for the future. Our intent is to point out needed research directions that will improve our understanding of predator-prey interactions in the context of the sustainable marine fisheries and ecosystem management. © 2011 Blackwell Publishing Ltd/CNRS.

Dahlgren K.,Umeå University | Olsen B.R.,University of Bergen | Troedsson C.,University of Bergen | Bamstedt U.,Umeå University | Bamstedt U.,Umea Marine science Center
Journal of Plankton Research | Year: 2012

Limnocalanus macrurus from Bothnian Bay in the northern part of the Baltic Sea was studied during the ice-free period (AprilDecember) in order to understand its life history and feeding biology. Our data on the population dynamics indicated that reproduction occurred during the ice-covered period, during which lipid storage was reduced to a minimum. From spring to late summer, the lipid reserve increased by a factor of 3, while the gonads of adult females were immature during this period, continuing to December as indicated by the small size of the eggs. Average stomach fullness was always ca. 50 indicating continuous feeding activity. A newly developed denaturing high-performance liquid chromatography method was used to analyse the gut contents over the study period. More than 30 taxa (at different taxonomic levels) could be identified. However, phytoplankton was only represented by one taxon (Diatomophycea), and was restricted to July. Thus, adult L. macrurus seems to have a strongly carnivorous feeding preference in the northern Baltic Sea. © 2012 The Author. Published by Oxford University Press. All rights reserved.

Sundback K.,Gothenburg University | Lindehoff E.,Linnaeus University | Lindehoff E.,Umea Marine Science Center | Graneli E.,Linnaeus University
Aquatic Microbial Ecology | Year: 2011

To test the hypothesis that dissolved organic nitrogen (DON) is important for sustaining primary production by the microphytobenthos (MPB) in nitrogen-limited conditions, we measured the uptake of 15N-labelled urea, the amino acids glycine (GLY) and glutamic acid (GLU), and nitrate and ammonium under simulated in situ light and temperature conditions. Microphytobenthic primary production and chlorophyll a (chl a) were also measured. The MPB was dominated by diatoms attached to sand grains, with cyanobacteria making up ∼30% of the biomass. Activities of the hydrolytic ectoenzymes leucine aminopeptidase (AMA), alkaline phosphatase (APA) and β-glucosidase (GLA) in filter-fractionated sediment showed that the microbenthic community was strongly deficient in nitrogen (N), with the bacterial fraction (<1 μm) also limited in phosphorus. Uptake of DON (urea + GLU + GLY) accounted for ∼50 to 65% of the uptake of 15N- labelled substrates, with a higher proportion of DON uptake at low substrate concentrations (≤2 μM). Except for nitrate, the kinetics fitted a linear model. The calculated relative preference index (RPI), based on pore water concentrations, suggested that the order of preference of the microbenthic community was NH4 + > urea > GLU > NO3 - > GLY. Using a prokaryotic inhibitor (chloramphenicol), and theoretical calculations of algal uptake based on C:chl a ratios, it was estimated that the 'algal' uptake of nitrogen accounted for ∼55 to 90% of DON uptake. Uptake rates were, however, estimated to cover only 26 to 50% of the nitrogen demand of the MPB, suggesting that pore water concentrations of nitrogen were not sufficient to meet the microalgal demand in early summer and that, in sandy sediments of microtidal waters, the MPB may often be severely limited in nitrogen. © Inter-Research 2011.

Dahlgren K.,Umeå University | Dahlgren K.,Umea Marine science Center | Andersson A.,Umeå University | Andersson A.,Umea Marine science Center | And 4 more authors.
Marine Ecology Progress Series | Year: 2010

A 1 yr study was conducted along a brackish-water production gradient to enhance the understanding of factors governing pelagic food web function. This was achieved by measuring carbon transfer efficiency (TE) from the basal resource to an intermediate trophic level. TE was defined as mesozooplankton carbon consumption rate divided by production at the basal trophic level, which is composed of phytoplankton and bacteria. A north-south transect in the Baltic Sea was used as a model system, with 2 stations each in the Bothnian Bay, Bothnian Sea and Baltic Proper being sampled 5 to 8× during 2006. In addition, data from monitoring programmes were used, which comprised 10 to 22 samplings stn-1. TE was expected to be governed by the size distribution of phytoplankton and due to the nutrient gradient, we expected to find an optimal cell size, and thus also a high TE, in the intermediate- productive Bothnian Sea. The basal production during summer/autumn increased 5-fold from north to south, while the mesozooplankton carbon consumption rate exhibited a peak in the Bothnian Sea, being ∼3× higher than in both Bothnian Bay and Baltic Proper. TE was found to be intermediate in the Bothnian Bay (average: 0.8), highest in the Bothnian Sea (1.6), and lowest in the Baltic Proper (0.2). We suggest that the variation in carbon transfer efficiency can be explained by the composition of the phytoplankton community, the abundance balance between copepods and cladocerans, as well as the species composition of mesozooplankton in relation to the size structure of phytoplankton. © Inter-Research 2010.

Lefebure R.,Umeå University | Lefebure R.,Umea Marine Science Center | Degerman R.,Umeå University | Degerman R.,Umea Marine Science Center | And 6 more authors.
Global Change Biology | Year: 2013

Both temperature and terrestrial organic matter have strong impacts on aquatic food-web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food-web dynamics and food-web efficiency in a plausible future scenario with respect to these abiotic variables in a large-scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food-web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food-web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web. © 2013 Blackwell Publishing Ltd.

Andersson A.,Umeå University | Andersson A.,Umea Marine science Center | Hoglander H.,University of Stockholm | Karlsson C.,Umea Marine science Center | Huseby S.,Umea Marine science Center
Estuarine, Coastal and Shelf Science | Year: 2015

Despite cyanobacteria being a key phytoplankton group in the Baltic Sea, the factors governing their community structure are still poorly understood. Here, we studied the occurrence of the orders Chroococcales, Oscillatoriales and Nostocales, and potentially explanatory variables at five locations in the northern Baltic Sea from June-September, 1998-2012. Cyanobacteria constituted 1-36% of the total phytoplankton biomass along the north-south gradient. In the Bothnian Bay, Chroococcales and Oscillatoriales dominated the cyanobacterial community, whereas in the Bothnian Sea and northern Baltic Proper, Nostocales was the dominant group. The dominance of Chroococcales was coupled to low salinity and low total phosphorus, whereas Oscillatoriales correlated with high total nitrogen and low salinity. Nostocales correlated to high total phosphorus, inorganic phosphorus and salinity. Chroococcales showed an increase over time in the offshore Bothnian Bay, whereas Nostocales increased in the coastal Bothnian Sea and coastal Baltic Proper. The increase of Nostocales in the coastal Bothnian Sea was explained by a rise in total phosphorus and decrease in dissolved inorganic nitrogen compared to an increase of total nitrogen and phosphorus in the coastal Baltic Proper. No significant trends were observed in the cyanobacterial community in the offshore Bothnian Sea and the offshore northern Baltic Proper. We concluded that Chroococcales may be a useful indicator for increased phosphorus levels in waters with low phosphorus concentrations, whereas Nostocales could be used as a quality indicator for increasing phosphorus concentrations in waters with low inorganic N/P ratios (<20), such as in the coastal Bothnian Sea and Baltic Proper. © 2015 The Authors.

Dahlgren K.,Umeå University | Dahlgren K.,Umea Marine science Center | Wiklund A.-K.E.,University of Stockholm | Andersson A.,Umeå University | Andersson A.,Umea Marine science Center
Aquatic Ecology | Year: 2011

Climate change has been suggested to lead to higher temperature and increased heterotrophy in aquatic systems. The aim of this study was to test how these two factors affect metazooplankton and food web efficiency (FWE was defined as metazooplankton production divided by basal production). We tested the following hypotheses: (1) that lower metazooplankton production and lower FWE would be found in a food web based on heterotrophic production (bacteria) relative to one based on autotrophic production (phytoplankton), since the former induces a larger number of trophic levels; (2) the metazooplankton in the heterotrophic food web would contain less essential fatty acids than those from the autotrophic food web; and (3) that higher temperature would lead to increased FWE. To test these hypotheses, a mesocosm experiment was established at two different temperatures (5 and 10°C) with a dominance of either autotrophic (NP) or heterotrophic basal production (CNP). Metazooplankton production increased with temperature, but was not significantly affected by differences in basal production. However, increased heterotrophy did lead to decreased fatty acid content and lower individual weight in the zooplankton. FWE increased with autotrophy and temperature in the following order: 5CNP < 10CNP < 5NP < 10NP. Our results indicate that in the climate change scenario we considered, the temperature will have a positive effect on FWE, whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality and individual weight of the metazooplankton will be reduced, with possible negative effects on higher trophic levels. © 2011 Springer Science+Business Media B.V.

Lefebure R.,Umeå University | Lefebure R.,Umea Marine Science Center | Larsson S.,Umeå University | Larsson S.,Umea Marine Science Center | Bystrom P.,Umeå University
Journal of Fish Biology | Year: 2011

Specific growth rates of individually reared juvenile three-spined sticklebacks Gasterosteus aculeatus were investigated under laboratory conditions to parameterize a complete temperature-dependent growth model for this species. To test the applicability of experimentally derived optima in growth response rates to natural conditions, the effects of commercial pellets and natural prey on growth rates were investigated. In addition, to test for seasonal effects on growth, laboratory trials were performed in both spring and winter. Growth took place from 5 to 29° C with a temperature for optimum growth reaching a sharp peak at 21° C. Modelled optimal temperature for maximum growth was estimated to be 21·7° C and lower and upper temperatures for growth were estimated to be 3·6 and 30·7° C, respectively. There were no significant differences in growth rates between fish reared on invertebrates or commercial pellets. Seasonal effects on growth were pronounced, with reduced growth rates in the winter despite similar laboratory conditions. On average, 60% higher growth rates were achieved at the optimum temperature in summer compared to the winter. The strong seasonality in the growth patterns of G. aculeatus indicated here reduces the applicability of the model derived in this study to spring and summer conditions. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

Lefebure R.,Umeå University | Lefebure R.,Umea Marine Science Center | Larsson S.,Umea Marine Science Center | Bystrom P.,Umeå University
Journal of Experimental Marine Biology and Ecology | Year: 2014

The three-spined stickleback Gasterosteus aculeatus is a small omnivorous fish, widely distributed in the northern hemisphere. In the Baltic Sea, recently observed increases in their population densities have been attributed to declines of piscivorous predators. Concurrent with this predator release, an alternative hypothesis is that past and present consumption rates and resource limitation thresholds may have contributed to the recent increases in stickleback abundance. To evaluate this hypothesis, we estimated the size- and temperature-dependent attack rate and the critical resource density (CRD) of three-spined sticklebacks. We incorporated laboratory results with time series of zooplankton abundance to estimate historical trends in degrees of resource limitation in sticklebacks and evaluate if increases in individual consumption rates could be a plausible mechanism facilitating the suggested population increase. Attack rates increased with body size and temperature in laboratory experiments. Estimated CRD increased with size but decreased with temperature, suggesting that stickleback scope for individual and population growth might increase at temperatures above 15. °C. Our results further suggest that sticklebacks have been living closer to maximum consumption capacity in the coastal areas of the Bothnian Sea (BS) and Bothnian Bay (BB). Moreover, decreasing levels of resource limitation in the corresponding off-shore zones may have facilitated increases in stickleback densities for these areas. However, in the coastal zones of the Baltic proper (BP), resource levels have declined and are approaching the CRD, suggesting that stickleback populations in BP may not increase further. The decrease in CRD with temperature implies that increasing summer temperatures will increase the scope of individual and population growth in the three-spined stickleback and may favor the three-spined stickleback's competitive ability over other species under a warmer climate. © 2013.

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