| 1. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Consumers mediate the effects of experimental ocean acidification and warming on primary producers.
- 2013
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Ingår i: Proceedings of the National Academy of Science of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:21, s. 8603-8608
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that ocean acidification can have profound impacts on marine organisms. However, we know little about the direct and indirect effects of ocean acidification and also how these effects interact with other features of environmental change such as warming and declining consumer pressure. In this study, we tested whether the presence of consumers (invertebrate mesograzers) influenced the interactive effects of ocean acidification and warming on benthic microalgae in a seagrass community mesocosm experiment. Net effects of acidification and warming on benthic microalgal biomass and production, as assessed by analysis of variance, were relatively weak regardless of grazer presence. However, partitioning these net effects into direct and indirect effects using structural equation modeling revealed several strong relationships. In the absence of grazers, benthic microalgae were negatively and indirectly affected by sediment-associated microalgal grazers and macroalgal shading, but directly and positively affected by acidification and warming. Combining indirect and direct effects yielded no or weak net effects. In the presence of grazers, almost all direct and indirect climate effects were nonsignificant. Our analyses highlight that (i) indirect effects of climate change may be at least as strong as direct effects, (ii) grazers are crucial in mediating these effects, and (iii) effects of ocean acidification may be apparent only through indirect effects and in combination with other variables (e.g., warming). These findings highlight the importance of experimental designs and statistical analyses that allow us to separate and quantify the direct and indirect effects of multiple climate variables on natural communities.
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| 2. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Experimental warming and toxicant exposure can result in antagonistic effects in a shallow-water sediment system
- 2013
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 488, s. 89-101
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that future warming will exacerbate the effect of local stressors such as toxicants. In this study the individual and combined effects of warming (+4 degrees C above ambient) and a toxicant (the antifouling substance copper pyrithione) on natural intact shallow-water sediment were studied in an outdoor flow-through facility. Functional (oxygen and inorganic nutrient fluxes in light and dark, bacterial production) and structural (biomass and composition of microphytobenthos and meiofauna) variables were measured. Warming was found to modify the toxicant response antagonistically, i.e. warming removed the negative effect of the toxicant exposure. This antagonism was found for functions depending on light (gross primary production, 24 h net oxygen fluxes, oxygen and silica fluxes). Most functional variables were, however, affected by warming alone, while structural variables were affected by the toxicant alone. At the end of the experiment, the system had 2 types of microalgal communities, a typical benthic algal mat and a floating periphytic mat. Both the benthic and floating microalgal mats were significantly affected by the toxicant alone, but in opposite directions. The biomass of the benthic algal mat was significantly higher under toxicant exposure, whereas the biomass of the floating periphytic mat was lower. Our results suggest that the effects of toxicants in aquatic environments may be reduced (rather than amplified) by warming. We also show that autotrophic communities can respond differently within the same ecosystem and that habitat may determine the mode of response to warming-toxicant exposures in aquatic environments.
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| 3. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Functioning of a Shallow-Water Sediment System during Experimental Warming and Nutrient Enrichment
- 2012
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- Effects of warming and nutrient enrichment on intact unvegetated shallow-water sediment were investigated for 5 weeks in the autumn under simulated natural field conditions, with a main focus on trophic state and benthic nitrogen cycling. In a flow-through system, sediment was exposed to either seawater at ambient temperature or seawater heated 4 degrees C above ambient, with either natural or nutrient enriched water. Sediment-water fluxes of oxygen and inorganic nutrients, nitrogen mineralization, and denitrification were measured. Warming resulted in an earlier shift to net heterotrophy due to increased community respiration; primary production was not affected by temperature but (slightly) by nutrient enrichment. The heterotrophic state was, however, not further strengthened by warming, but was rather weakened, probably because increased mineralization induced a shortage of labile organic matter. Climate-related warming of seawater during autumn could therefore, in contrast to previous predictions, induce shorter but more intensive heterotrophic periods in shallow-water sediments, followed by longer autotrophic periods. Increased nitrogen mineralization and subsequent effluxes of ammonium during warming suggested a preferential response of organisms driving nitrogen mineralization when compared to sinks of ammonium such as nitrification and algal assimilation. Warming and nutrient enrichment resulted in non-additive effects on nitrogen mineralization and denitrification (synergism), as well as on benthic fluxes of phosphate (antagonism). The mode of interaction appears to be related to the trophic level of the organisms that are the main drivers of the affected processes. Despite the weak response of benthic microalgae to both warming and nutrient enrichment, the assimilation of nitrogen by microalgae was similar in magnitude to rates of nitrogen mineralization. This implies a sustained filter function and retention capacity of nutrients by the sediment.
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| 4. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Multiple stressors and multifunctionality: limited effects on an illuminated benthic system
- 2014
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Ingår i: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- The bulk of experiments that study stressor effects on ecosystem functioning consider only individual functions one at a time, and such narrow focus may well bias our understanding of the overall impact on ecosystem functioning. We used data from six published experiments in which marine illuminated sediment systems were exposed to nutrient enrichment, toxicants, sedimentation and warming, either alone or in combination. Measured functions were primary production, community respiration, inorganic nitrogen and phosphorus fluxes, and autotrophic biomass. We calculated two indices of multifunctionality that simultaneously considered all six functions: (i) a weighted average level of the functions and (ii) the number of functions that simultaneously exceed a critical threshold level. Stressors affected individual functions both positively and negatively, but multifunctionality was generally unaffected by both single and joint stressors. The filtering capacity of coastal illuminated sediment systems thus appears resilient to exposure to moderate levels of multiple stressors, most probably due to the robustness of the benthic microalgal community. We recommend using a multifunctionality approach in future studies on cumulative stressor effects on ecosystem functioning, particularly when considering functions related to ecosystem services.
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| 5. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Response of a shallow-water sediment system to warming
- 2011
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590. ; 56:6, s. 2147-2160
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT: Effects of predicted global warming (+4°C) on the structure and function of a temperate shallow-water sediment system were studied for 1.5 months during spring (March–April), using intact sediment in a flow-through system under close to natural light conditions. Although significant effects from temperature were observed during the entire experimental period, many were rather moderate and probably a combination of both direct and indirect effects. With the exception of an earlier development of floating microalgal mats at raised temperature, dividing the autotrophic compartment into a benthic and pelagic part, autotrophic variables, such as oxygen production, biomass, and species composition of benthic microalgae did not respond to warming. However, uptake of nutrients did increase, strengthening the role of shallow-water sediments as sinks for inorganic nutrients in spring. As hypothesized, heterotrophic variables (bacterial production, meiofaunal biomass, and dark fluxes of oxygen and total alkalinity) responded more clearly to warming than did autotrophic variables. Warming is generally hypothesized to push ecosystems towards heterotrophy, but there was no support for this in the present study. Although community respiration and anaerobic mineralization increased, the system remained highly autotrophic during the entire experiment due to the photosynthetic activity of benthic microalgae. The presence of a well-developed benthic microalgal community, already in early spring, appeared to moderate the temperature response. It therefore seems that, in spring, benthic microalgae dampen ecological consequences of global warming in illuminated sediment systems by maintaining the system net autotrophic.
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| 6. |
- Andersson, Björn, 1985, et al.
(författare)
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Nitrogen fixation in shallow-water sediments: Spatial distribution and controlling factors
- 2014
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 59:6, s. 1932-1944
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogenase activity (NA) in shallow-water (< 1 m) sediments was investigated at 60 randomly selected sites along a 150 km stretch on the brackish-water Swedish west coast, without targeting any specific type of sediments, such as microbial mats. Benthic nitrogen (N) fixation and diazotrophs (nifH genes) were found at all sites, regardless of the presence of cyanobacterial or microbial mats. The majority of sites showed N fixation rates between 0.03 and 1 mmol N m−2 d−1. These rates were similar to those of benthic denitrification previously measured in the area. Maximum rates up to 3.4 mmol N m−2 d−1 were measured. A structural equation model was used to investigate direct and indirect effects of biogeochemical and physical factors on NA. Number of nifH genes had the largest direct positive influence on NA, whereas increasing wave exposure had an indirect negative effect on NA through its influence on the diazotrophic abundance. Increased salinity, previously been shown to suppress NA in coastal waters, was found to directly stimulate benthic N fixation, likely by generating favorable conditions for diazotrophic sulfate-reducing bacteria. Our field data confirmed previously observed negative effects of dissolved inorganic nitrogen on NA, which have so far mainly been experimentally studied. Both NA rates and the number of nifH genes correlated positively with pore-water dissolved inorganic phosphorus concentrations. These findings show that the potential for N fixation in illuminated sediments can be considerable, stretching beyond cyanobacterial mats, being controlled by complex interactions between biotic and abiotic factors.
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| 7. |
- Eklöf, Johan, 1978, et al.
(författare)
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Experimental climate change weakens the insurance effect of biodiversity
- 2012
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 15:8, s. 864-872
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystems are simultaneously affected by biodiversity loss and climate change, but we know little about how these factors interact. We predicted that climate warming and CO 2-enrichment should strengthen trophic cascades by reducing the relative efficiency of predation-resistant herbivores, if herbivore consumption rate trades off with predation resistance. This weakens the insurance effect of herbivore diversity. We tested this prediction using experimental ocean warming and acidification in seagrass mesocosms. Meta-analyses of published experiments first indicated that consumption rate trades off with predation resistance. The experiment then showed that three common herbivores together controlled macroalgae and facilitated seagrass dominance, regardless of climate change. When the predation-vulnerable herbivore was excluded in normal conditions, the two resistant herbivores maintained top-down control. Under warming, however, increased algal growth outstripped control by herbivores and the system became algal-dominated. Consequently, climate change can reduce the relative efficiency of resistant herbivores and weaken the insurance effect of biodiversity.
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| 8. |
- Engelsen, Anna, 1964, et al.
(författare)
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Links Between Bottom-Water Anoxia, the Polychaete Nereis diversicolor, and the Growth of Green-Algal Mats
- 2010
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Ingår i: Estuaries and Coasts. - : Springer Science and Business Media LLC. - 1559-2723 .- 1559-2731. ; 33:6, s. 1365-1376
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Tidskriftsartikel (refereegranskat)abstract
- Sediment-water incubations were used to study effects of episodic anoxia on filamentous Ulva sp. Treatments included undisturbed sediment with (AnoxSed) and without (NatSed) exposure to 5 days of anoxia, and cores with only the top 0.5 cm of sediment (SurfSed; no macrofauna, restricted pore-water nutrient pool). All three treatments contained Ulva propagules. An Ulva mat developed in the SurfSed, and after the anoxic period in the AnoxSed cores. No growth was observed in the NatSed treatment. In the AnoxSed, Ulva was progressively removed upon reoxygenation through grazing by Nereis. The results suggest that episodic anoxia stimulates the growth of macroalgal mats not only by increasing the availability of nutrients from the sediment, but also by reducing macrofaunal grazing pressure. Infauna (grazing and bioturbation), benthic microalgae (nutrient competition and retention), and pore-water nutrients appear key components in a biogeochemical network with complex feedbacks controlling the growth of green-algal mats in shallow-water systems.
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| 9. |
- Larson, Fredrik, 1972, et al.
(författare)
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Recovery of microphytobenthos and benthic functions after sediment deposition
- 2012
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 446, s. 31-44
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Tidskriftsartikel (refereegranskat)abstract
- Recovery of microphytobentos (MPB) and benthic processes were followed during 23 d after sediment deposition simulating the effects of 1 wk of nearby dredging or construction work. Cores of natural intact sediment in an outdoor flow-through system were exposed to daily depositions of 1.5 mm fine-grained sediment over 7 d (total load 10.5 mm) Porosity, chlorophyll a (chl a; proxy for MPB biomass), denitrification and sediment-water fluxes of oxygen and inorganic nutrients were measured during day and night on 6 occasions. After deposition stopped, chl a in the uppermost 3 mm of the sediment had decreased to 25% of that in the controls, started to increase linearly, probably due to upward migration of diatoms, but did not converge with the control cores in the course of the experiment. The linear increase of chl a indicated a recovery of algal biomass after similar to 50 d. The proportion of large sigmoid diatoms increased in the deposition cores and this change in MPB composition remained over the 23 d. Deposition resulted in higher porosity and increased flaking of the newly established algal mat. Deposition generally increased release or decreased uptake of nutrients, though effects on nitrate flux and denitrification were less clear. Although alga-related functions (oxygen production and nutrient fluxes in light) recovered faster than algal biomass, the faster recovery of the integrated system function in the dark reflected the impact of deposition on MPB. Sediment deposition in microtidal areas may imply disturbances for MPB, threatening the food supply for grazers and deposit feeders, and, in the end, fish that use the shallow areas as nurseries.
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| 10. |
- McGlathery, Karen, et al.
(författare)
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Estuarine Benthic Algae
- 2012
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Ingår i: Estuarine Ecology. - Hoboken, New Jersy : Wiley-Blackwell. - 9780471755678 ; , s. 203-234
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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