| 1. |
- Beer, Sven, et al.
(författare)
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Basic Concepts and Key Parameters of Chlorophyll Fluorescence
- 2021
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Ingår i: Research Methods of Environmental Physiology in Aquatic Sciences. - Singapore : Springer. - 9789811553530 - 9789811553547 ; , s. 221-229
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Photosynthetic rates can be measured in several different ways. Classically, phytoplankton productivity has been measured by uptake rates of 14C-labelled inorganic carbon (Ci, i.e. CO2 and HCO3−), which is a sensitive measure even for sparse phytoplankton assemblages. For macrophytes, gas exchange of CO2 or O2 have been used as preferred methods of photosynthetic productivity. All these above mentioned methods have the disadvantage of being slow (minutes to hours or days) and the need for enclosing the plants, the latter of which invariably alters their surroundings from natural ones in terms of light (both irradiance and spectrum), water flow and decreasing nutrient, such as Ci, levels, as well as increasing O2 concentrations, which may impede on rates. For the last 20 years, chlorophyll fluorescence measurements have increasingly replaced the other methods as being both sensitive and speedy, and applicable under natural, non-enclosed, conditions. This chapter explains the background to chlorophyll fluorescence, as well as the principles of pulse-amplitude modulated (PAM) fluorometry and, briefly, fast repetition rate fluorometry (FRRF) measurements.
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| 2. |
- Beer, Sven, et al.
(författare)
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Carbon Dioxide vs. Bicarbonate Utilisation
- 2021
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Ingår i: Research Methods of Environmental Physiology in Aquatic Sciences. - Singapore : Springer. - 9789811553530 - 9789811553547 ; , s. 153-164
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- While CO2 is the external inorganic carbon (Ci) form used for photosynthesis in terrestrial plants, the higher concentration of bicarbonate (HCO3−) in most water bodies renders this ionic Ci form the preferred external Ci source for most cyanobacteria, microalgae, and submerged macrophytes. The equilibrium concentrations of these two Ci forms depend largely on pH. For example, at today’s average seawater pH of 8.1, the HCO3− concentration is approximately 120 times that of dissolved CO2; in most lakes and streams pH values are lower so this ratio is reduced in favour of CO2 (but this Ci form is seldom higher than that of HCO3−), and HCO3− utilisation becomes less advantageous. On the other hand, the affinity of aquatic phototrophs for CO2 is much higher than that for HCO3−, and the preferred Ci form will thus be a compromise between the affinities for, and concentrations of, the two Ci forms. This chapter will outline ways to determine whether, and to what degree, external CO2 or HCO3− is utilised by various aquatic phototrophs.
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| 3. |
- Beer, Sven, et al.
(författare)
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Fluorescence Measurement Techniques
- 2021
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Ingår i: Research Methods of Environmental Physiology in Aquatic Sciences. - Singapore : Springer. - 9789811553530 - 9789811553547 ; , s. 231-238
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Chlorophyll fluorometers are constructed such that the immediate outcomes of the measurements provide information on quantum yields (Y) of electrons passing through photosystem II (PSII). If the photosynthetically active radiation (PAR) absorbed by PSII (PARa) is known, then photosynthetic rates can be calculated as electron transport rates (ETR). If only the incident irradiance (PARi) is known (which often is the case), then relative ETRs (rETR) can be calculated as the product of Y and PARi. There are sometimes easy ways to at least estimate PARa, and they will be described in this chapter, as will other practical means to measure photosynthetic parameters using fluorometry.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Björk, Mats, et al.
(författare)
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Managing Seagrasses for Resilience to Climate Change
- 2008
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Bok (populärvet., debatt m.m.)abstract
- There is growing evidence that seagrasses are experiencingdeclines globally due to anthropogenicthreats (Short and Wyllie-Echeverria 1996, Duarte2002, Orth et al. 2006). Runoff of nutrients andsediments that affect water quality is the greatestanthropogenic threat to seagrass meadows,although other stressors include aquaculture, pollution,boating, construction, dredging and landfillactivities, and destructive fishing practices. Naturaldisturbances such as storms and floods canalso cause adverse effects. Potential threats fromclimate change include rising sea levels, changingtidal regimes, UV radiation damage, sedimenthypoxia and anoxia, increases in sea temperaturesand increased storm and flooding events.Thus, seagrass meadows, the ecosystems thatthey support and the ecosystem services that theyprovide are threatened by a multitude of environmentalfactors that are currently changing or willchange in the future.Seagrasses are flowering plants that thrive in shallowoceanic and estuarine waters around the world.Descendants of terrestrial plants that re-enteredthe ocean between 100 and 65 million years ago,seagrasses have leaves, stems, rhizomes (horizontalunderground runners) and roots. Althoughthere are only about 60 species of seagrassesworldwide, these plants play an important role inmany shallow, near-shore, marine ecosystems.Seagrass meadows provide ecosystem servicesthat rank among the highest of all ecosystems onearth. The direct monetary outputs are substantialsince highly valued commercial catches suchas prawns and fish are dependent on these systems.Seagrasses provide protective shelter formany animals, including fish, and can also be adirect food source for manatees and dugongs,turtles, water fowl, some herbivorous fish and seaurchins. The roots and rhizomes of seagrassesalso stabilise sediments and prevent erosion whilethe leaves filter suspended sediments and nutrientsfrom the water column. Seagrass meadowsare thus linked to other important marine habitatssuch as coral reefs, mangroves, salt marshes andoyster reefs.This paper presents an overview of seagrasses,the impacts of climate change and other threats toseagrass habitats, as well as tools and strategiesfor managers to help support seagrass resilience.
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| 8. |
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| 9. |
- Felisberto, Paulo, et al.
(författare)
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Acoustic monitoring of O-2 production of a seagrass meadow
- 2015
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 464, s. 75-87
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic data were acquired in October 2011 over a Posidonia oceanica meadow in the Bay of la Revellata, Calvi, Corsica. The purpose was to develop an acoustic system for monitoring the oxygen (O-2) production of an entire seagrass meadow. In a shallow water area (<38 m), densely covered by P. oceanica, a sound source transmitted signals in 3 different bands (400-800 Hz, 1.5-3.5 kHz and 65-8.5 kHz) toward three self-recording hydrophones at a distance of 100 m, over the period of one week. The data show a high correlation between the diel cycle of the acoustic signals' energy received by the hydrophones and the temporal changes in water column O-2 concentration as measured by optodes. The results thus show that a simple acoustic acquisition system can be used to monitor the O-2-based productivity of a seagrass meadow at the ecosystem level with high temporal resolution. The finding of a significant production of O-2 as bubbles in seagrass ecosysterns suggests that net primary production is underestimated by methods that rely on the mass balance of dissolved O-2 measurements.
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| 10. |
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| 11. |
- Procaccini, Gabriele, et al.
(författare)
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Depth-specific fluctuations of gene expression and protein abundance modulate the photophysiology in the seagrass Posidonia oceanica
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the results of a multiple organizational level analysis conceived to identify acclimative/adaptive strategies exhibited by the seagrass Posidonia oceanica to the daily fluctuations in the light environment, at contrasting depths. We assessed changes in photophysiological parameters, leaf respiration, pigments, and protein and mRNA expression levels. The results show that the diel oscillations of P. oceanica photophysiological and respiratory responses were related to transcripts and proteins expression of the genes involved in those processes and that there was a response asynchrony between shallow and deep plants probably caused by the strong differences in the light environment. The photochemical pathway of energy use was more effective in shallow plants due to higher light availability, but these plants needed more investment in photoprotection and photorepair, requiring higher translation and protein synthesis than deep plants. The genetic differentiation between deep and shallow stands suggests the existence of locally adapted genotypes to contrasting light environments. The depth-specific diel rhythms of photosynthetic and respiratory processes, from molecular to physiological levels, must be considered in the management and conservation of these key coastal ecosystems.
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| 12. |
- Procaccini, Gabriele, et al.
(författare)
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Seagrass ecophysiology meets ecological genomics : are we ready?
- 2012
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Ingår i: Marine Ecolocy. - : Wiley. - 0173-9565 .- 1439-0485. ; 33:4, s. 522-527
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Tidskriftsartikel (refereegranskat)abstract
- In March 2011, the Ecophysiology and Genetics Working Groups of the European Science Foundation COST Action ES 0906, entitled Seagrass Productivity: From Genes to Ecosystem Management, organized an exploratory workshop entitled Linking Ecophysiology and Ecogenomics in Seagrass Systems. The goal of the workshop was to discuss how to integrate comparative gene expression studies with physiological processes such as photosynthetic performance, carbon and nitrogen utilization and environmental adaptation. The main questions discussed for integrative research related to mechanisms of carbon utilization, light requirements, temperature effects and natural variation in pH and ocean acidification. It was concluded that the seagrass research community is still in the nascent stages of linking ecophysiology with genomic responses, as carbon and nitrogen metabolism of seagrasses have not been sufficiently well studied. Likewise, genomic approaches have only been able to assign meaningful interpretations to a handful of differentially expressed genes. Nevertheless, the way forward has been established.
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| 13. |
- Semesi, I. Sware, et al.
(författare)
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Interactions between seagrasses and mussels: CO2, pH and calcification
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Ingår i: Estuarine, Coastal and Shelf Science. - 0272-7714 .- 1096-0015.
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Tidskriftsartikel (refereegranskat)abstract
- Mussels and other bivalves commonly found in tropical seagrass meadows are thought to increase seagrass productivity, and seagrass photosynthesis, through raising the pH of the surrounding water, has been shown to increase rates of calcification in calcareous algae. The effects of seagrass-driven increases in pH on mussel calcification and possible feedback effects of mussel metabolism on seagrass photosynthesis were studied in a seagrass bed on the south-western coast of Zanzibar, Tanzania. Seagrasses and mussels (Pinna muricata) were enclosed, separately or together, in transparent plastic cylinders. The pH and photosynthesis were measured and seawater samples were taken from the experimental cylinders to determine total alkalinity and total inorganic carbon concentration. Cylinders containing only sediments were exposed to light and dark and used as controls. The results showed no effects of increased pH on calcification rates in the mussels. However, photosynthetic rates of the seagrass Thalassia hemprichii rose by up to 15% in the presence of mussels, possibly as a result of water stirring caused by the mussels’ filter feeding and/or CO2 released by their respiration.
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| 14. |
- Semesi, Immaculate Sware, et al.
(författare)
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Mussel, Seagrass and Calcareous Algal Interactions: Influence of CO2 and pH on Photosynthesis and Calcification in a Tropical Bay
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Changes in seawater pH and thus, the inorganic carbon (Ci) composition brought about by photosynthetic carbon uptake have been shown to influence the productivity of marine plants. In this work, we enclosed different combinations of seagrasses Thalassia hemprichii, the mussel Pinna muricata and the calcareous coralline algae Amphiroa fragilissima in open plastic cylinders in a tropical seagrasses meadow at Fumba Bay, Zanzibar, Tanzania, while measuring pH and rates of photosynthesis and calcification. The results showed that the photosynthetic production of seagrasses increased in the presence of mussels (probably due to their supply of respiratory CO2) while the presence of seagrasses supported an increase in calcification of the coralline algae (probably by the higher pH generated by the former). Photosynthetic rates of the seagrasses and the coralline algae were ~20% and ~13% higher, respectively, in the presence of mussels than in their absence. Also, the rate of calcification of the coralline algae was significantly higher (by 11%) in the presence of seagrasses than when alone. Calcification by the mussels, on the other hand, was not affected by the presence of algae or seagrasses. These results illustrate how pH changes induced by fluxes in Ci can act as a factor controlling both productivity and calcification in densely populated shallow marine ecosystems.
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| 15. |
- Semesi, Immaculate Sware, et al.
(författare)
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Seagrass photosynthesis controls rates of calcification and photosynthesis of calcareous macroalgae in a tropical seagrass meadow
- 2009
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 382, s. 41-47
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Tidskriftsartikel (refereegranskat)abstract
- Diel fluctuations in seawater pH can be >1 pH unit (7.9 to >8.9) in the seagrass meadows of Chwaka Bay (Zanzibar, Tanzania). The high daily pH values are generated by the photosynthetic activity of the bay’s submerged seagrasses and macroalgae, and maintained by the relatively low, tide-dominated, water exchange rate. Since pH in principle can affect rates of both calcification and photosynthesis, we investigated whether diel variations in pH caused by photosynthesis could affect rates of calcification and photosynthesis of the calcareous red (Hydrolithon sp. and Mesophyllum sp.) and green (Halimeda renschii) algae growing within these meadows. This was done by measuring rates of calcification and relative photosynthetic electron transport (rETR) of the algae in situ in open-bottom incubation cylinders either in the natural presence of the rooted seagrasses or after the leaves had been removed. The results showed that seagrass photosynthesis increased the seawater pH within the cylinders from 8.3–8.4 to 8.6–8.9 after 2.5 h (largely in conformity with that of the surrounding seawater), which, in turn, enhanced the rates of calcification 5.8-fold for Hydrolithon sp. and 1.6-fold for the other 2 species. The rETRs of all algae largely followed the irradiance throughout the day and were (in Mesophyllum sp.) significantly higher in the presence of seagrasses despite the higher pH values generated by the latter. We conclude that algal calcification within seagrass meadows such as those of Chwaka Bay is considerably enhanced by the photosynthetic activity of the seagrasses, which in turn increases the seawater pH.
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| 16. |
- Semesi, Immaculate Sware, 1975-
(författare)
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Seawater pH as a Controlling Factor in Macroalgal Calcification and Photosynthesis
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biological calcification and photosynthesis are important processes with a great influence on both structure and function of oceanic ecosystems. The pH of the seawater has a strong influence on both these processes and therefore the impacts of different pH levels on calcareous macroalgae were investigated in laboratory and field experiments at Chwaka and Fumba Bays in Zanzibar, Tanzania. The levels of pH were manipulated, first in the laboratory by adding HCl, NaOH or by bubbling seawater with CO2 enriched air. Secondly, pH was allowed to fluctuate naturally as a consequence of marine photosynthetic carbon uptake or release through respiration by mussels. The effects on both photosynthesis and calcification were then analyzed on a seagrass (Thalassia hemprichii), and the calcareous red and green algae Mesophyllum sp., Hydrolithon sp., Amphiroa fragilissima and Halimeda renschii, as well as on the mussel Pinna muricata. The laboratory studies revealed a significant decrease in calcification rates in Hydrolithon sp. with decreasing pH, while photosynthesis showed an opposite trend. Also, increased dissolved CO2 lowered pH from 8.1 to 7.8 and caused a ~20% decline in calcification rates. In the field, seagrasses raised pH to ~9, increasing calcification rates significantly in the calcareous algae while photosynthetic rates showed no significant differences with changes in pH expect in Mesophyllum sp., in which rates increased at elevated pH caused by the presence of seagrasses. Conversely, seagrass photosynthesis increased significantly in the presence of mussels. Based on these findings, we conclude that pH is important in shaping biological processes that determines ecological interactions within shallow tidal areas by modifying seawater carbon composition and, thus, influencing calcification and photosynthesis processes.
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| 17. |
- Uku, Jacqueline, et al.
(författare)
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Buffer sensitivity of photosynthetic carbon utilization in eight tropical seagrasses
- 2005
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 147:5, s. 1085-1090
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Tidskriftsartikel (refereegranskat)abstract
- Some of the mechanisms involved in inorganic carbon (Ci) acquisition by tropical seagrasses from the western Indian Ocean were described by Björk et al. (Mar Biol 129:363–366, 1997). However, since then, it has been found that an additional, buffer-sensitive, system of Ci utilisation may operate in some temperate seagrasses (Hellblom et al. in Aquat Bot 69:55–62, 2001, Hellblom and Axelsson in Photos Res 77:173–191, 2003); this buffer sensitivity indicates a mechanism in which electrogenic H+ extrusion may form acidic diffusion boundary layers, in which either HCO3−–H+ is co-transported into the cells, or where HCO3− is converted to CO2 (as catalysed by carbonic anhydrase) prior to uptake of the latter Ci form. Because a buffer was used in the 1997 study, we found it important to reinvestigate those same eight species, taking into account the direct effect of buffers on this potential mode of Ci acquisition in these plants. In doing so, it was found that all seagrass species investigated except Cymodocea serrulata were sensitive to 50 mM TRIS buffer of the same pH as the natural seawater in which they grew (pH 8.0). Especially sensitive were Halophila ovalis, Halodule wrightii and Cymodocea rotundata, which grow high up in the intertidal zone (only ca. 50–65% of the net photosynthetic activity remained after the buffer additions), followed by the submerged Enhalus acoroides and Syringodium isoetifolium (ca. 75% activity remaining), while Thalassia hemprichii and Thalassodendron ciliatum, which grow in-between the two zones, were less sensitive to buffer additions (ca. 80–85% activity remaining). In addition to buffer sensitivity, all species were also sensitive to acetazolamide (AZ, an inhibitor of extracellular carbonic anhydrase activity) such that ca. 45–80% (but 90% for H. ovalis) of the net photosynthetic activity remained after adding this inhibitor. Raising the pH to 8.8 (in the presence of AZ) drastically reduced net photosynthetic rates (0–14% remaining in all species); it is assumed that this reduction in rates was due to the decreased CO2 concentration at the higher pH. These results indicate that part of the 1997 results for the same species were due to a buffer effect on net photosynthesis. Based on the present results, it is concluded that (1) photosynthetic Ci acquisition in six of the eight investigated species is based on carbonic anhydrase catalysed HCO3− to CO2 conversions within an acidified diffusion boundary layer, (2) C. serrulata appears to support its photosynthesis by extracellular carbonic anhydrase catalysed CO2 formation from HCO3− without the need for acidic zones, (3) H. ovalis features a system in which H+ extrusion may be followed by HCO3−–H+ co-transport into the cells, and (4) direct, non-H+-mediated, uptake of HCO3− is improbable for any of the species.
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