| 1. |
- Gasol, Josep M., et al.
(författare)
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Mesopelagic prokaryotic bulk and single-cell heterotrophic activity and community composition in the NW Africa-Canary Islands coastal-transition zone
- 2009
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 83, s. 189-196
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Tidskriftsartikel (refereegranskat)abstract
- Mesopelagic prokaryotic communities have often been assumed to be relatively inactive in comparison to those from epipelagic waters, and therefore unresponsive to the presence of nearby upwelled waters. We have studied the zonal (shelf-ocean), latitudinal, and depth (epipelagic-mesopelagic) variability of microbial assemblages in the NW Africa-Canary Islands coastal-transition zone (CTZ). Vertical profiles of bacterial bulk and single-cell activity through the epi- and mesopelagic waters were combined with point measurements of bacterial respiration, leucine-to-carbon conversion factors and leucine-to-thymidine incorporation ratios. The overall picture that emerges from our study is that prokaryotes in the mesopelagic zone of this area are less abundant than in the epipelagic but have comparable levels of activity. The relationship between prokaryotes and heterotrophic nanoflagellates, their main predators, remains constant throughout the water column, further contradicting the assumption that deep ocean bacterial communities are mostly inactive. Both bulk and single-cell activity showed clear differences between stations, with higher mesopelagic activities closer to the shelf or affected by upwelling features. We also tested whether differences in microbial function between stations could be related to differences in bacterial community structure, and conclude that bacterial communities are very similar at similar depths in the deep ocean, even if the stations present order-of-magnitude differences in bacterial function.
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| 2. |
- Conley, Daniel, et al.
(författare)
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Ecosystem thresholds with hypoxia
- 2009
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 629:1, s. 21-29
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Konferensbidrag (refereegranskat)abstract
- Hypoxia is one of the common effects of eutrophication in coastal marine ecosystems and is becoming an increasingly prevalent problem worldwide. The causes of hypoxia are associated with excess nutrient inputs from both point and non-point sources, although the response of coastal marine ecosystems is strongly modulated by physical processes such as stratification and mixing. Changes in climate, particularly temperature, may also affect the susceptibility of coastal marine ecosystems to hypoxia. Hypoxia is a particularly severe disturbance because it causes death of biota and catastrophic changes in the ecosystem. Bottom water oxygen deficiency not only influences the habitat of living resources but also the biogeochemical processes that control nutrient concentrations in the water column. Increased phosphorus fluxes from sediments into overlying waters occur with hypoxia. In addition, reductions in the ability of ecosystems to remove nitrogen through denitrification and anaerobic ammonium oxidation may be related to hypoxia and could lead to acceleration in the rate of eutrophication. Three large coastal marine ecosystems (Chesapeake Bay, Northern Gulf of Mexico, and Danish Straits) all demonstrate thresholds whereby repeated hypoxic events have led to an increase in susceptibility of further hypoxia and accelerated eutrophication. Once hypoxia occurs, reoccurrence is likely and may be difficult to reverse. Therefore, elucidating ecosystem thresholds of hypoxia and linking them to nutrient inputs are necessary for the management of coastal marine ecosystems. Finally, projected increases in warming show an increase in the susceptibility of coastal marine ecosystems to hypoxia such that hypoxia will expand.
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| 3. |
- Duarte, Carlos M., et al.
(författare)
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Return to Neverland: Shifting Baselines Affect Eutrophication Restoration Targets
- 2009
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Ingår i: Estuaries and Coasts. - : Springer Science and Business Media LLC. - 1559-2731 .- 1559-2723. ; 32:1, s. 29-36
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Tidskriftsartikel (refereegranskat)abstract
- The implicit assumption of many scientific and regulatory frameworks that ecosystems impacted by human pressures may be reverted to their original condition by suppressing the pressure was tested using coastal eutrophication. The response to nutrient abatement of four thoroughly studied coastal ecosystems that received increased nutrient inputs between the 1970s and the 1980s showed that the trajectories of these ecosystems were not directly reversible. All four ecosystems displayed convoluted trajectories that failed to return to the reference status upon nutrient reduction. This failure is proposed to result from the broad changes in environmental conditions, all affecting ecosystem dynamics, that occurred over the 30 years spanning from the onset of eutrophication to the reduction of nutrient levels. Understanding ecosystem response to multiple shifting baselines is essential to set reliable targets for restoration efforts.
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| 4. |
- Håkanson, Lars, 1943-, et al.
(författare)
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Data variability and uncertainty limits the capacity to identify and predict critical changes in coastal systems : A review of key concepts
- 2008
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Ingår i: Ocean and Coastal Management. - : Elsevier BV. - 0964-5691 .- 1873-524X. ; 51:10, s. 671-688
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Tidskriftsartikel (refereegranskat)abstract
- How do inherent variations and uncertainties in empirical data constrain approaches to predictions and possibilities to identify critical thresholds and points of no return? This work addresses this question in discussing and reviewing key concepts and methods for coastal ecology and management. The main focus is not on the mechanisms regulating the concentration of a given variable but on patterns in variations in concentrations for many standard variables in entire lagoons, bays, estuaries or fjords (i.e., on variations at the ecosystem scale). We address and review problems related to: (1) The balance between the changes in predictive power and the accumulated uncertainty as models grow in size and include an increasing number of x-variables. (2) An approach to reduce uncertainties in empirical data. (3) Methods to maximize the predictive power of regression models by transformations of model variables and by creating time and area compatible model variables. (4) Patterns in variations within and among coastal systems of standard water variables. (5) Based on the results of the review, we also discuss the concept “Optimal Model Scale” (OMS) and an algorithm to calculate OMS, which accounts for key factors related to the predictive power at different time scales (daily to yearly prediction) and to uncertainties in predictions in relation to access to empirical data and the work (sampling effort) needed to achieve predictive power at different time scales.
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