| 1. |
- Eklöf, J.S., et al.
(författare)
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Sea urchin overgrazing of seagrasses: A review of current knowledge on causes, consequences and management
- 2008
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 79:4, s. 569-580
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Tidskriftsartikel (refereegranskat)abstract
- Sea urchins are one of the most common seagrass macro-grazers in contemporary seagrass systems. Occasionally their grazing rates exceed seagrass growth rates, a phenomenon sometimes referred to as overgrazing. Because of a reported increasing frequency of overgrazing events, concomitant with loss of seagrass-associated ecosystem services, it has been suggested that overgrazing is one of the key threats to tropical and subtropical seagrasses. In light of this, we review the current knowledge on causes, consequences. and management of sea urchin overgrazing of seagrasses. Initially we argue that the definition of overgrazing must include scale and impairment of ecosystem services, since this is the de facto definition used in the literature, and will highlight the potential societal costs of seagrass overgrazing. A review of 16 identified cases suggests that urchin overgrazing is a global phenomenon, ranging from temperate to tropical coastal waters and involving at least 11 seagrass and 7 urchin species. Even though most overgrazing events Seem to affect areas of <0.5 km(2), and recovery often occurs within a few years, overgrazing can have a range of large, long-term indirect effects such as loss of associated fauna and decreased sediment stabilization. A range of drivers behind overgrazing have been suggested, including bottom-up (nutrient enrichment). top-down (reduced predation control due to e.g. overfishing), "side-in" mechanisms (e.g. changes in water temperature) and natural population fluctuations. Based on recent studies, there seems to be fairly strong support for the top-down and bottom-up hypotheses. However, many potential drivers often co-occur and interact, especially in areas with high anthropogenic pressure, suggesting that multiple disturbances-by simultaneously reducing predation control, increasing urchin recruitment and reducing the resistance of seagrasses-could pave the way for overgrazing. In management, the most common response to overgrazing has been to remove urchins, but limited knowledge of direct and indirect effects makes it difficult to assess the applicability and sustainability of this method. Based on the wide knowledge gaps, which severely limits management, we suggest that future research should focus on (1) identification and quantification of ecosystem and societal scale effects of overgrazing; (2) assessment of the relative importance and interactions of different drivers; and (3) development of a holistic proactive and reactive long-term management agenda.
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| 2. |
- George, Rushingisha, et al.
(författare)
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Methane emission and sulfide levels increase in tropical seagrass sediments during temperature stress: A mesocosm experiment
- 2020
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 10:4, s. 1917-1928
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Tidskriftsartikel (refereegranskat)abstract
- Climate change-induced ocean warming is expected to greatly affect carbon dynamics and sequestration in vegetated shallow waters, especially in the upper subtidal where water temperatures may fluctuate considerably and can reach high levels at low tides. This might alter the greenhouse gas balance and significantly reduce the carbon sink potential of tropical seagrass meadows. In order to assess such consequences, we simulated temperature stress during low tide exposures by subjecting seagrass plants (Thalassia hemprichii) and associated sediments to elevated midday temperature spikes (31, 35, 37, 40, and 45°C) for seven consecutive days in an outdoor mesocosm setup. During the experiment, methane release from the sediment surface was estimated using gas chromatography. Sulfide concentration in the sediment pore water was determined spectrophotometrically, and the plant's photosynthetic capacity as electron transport rate (ETR), and maximum quantum yield (Fv/Fm) was assessed using pulse amplitude modulated (PAM) fluorometry. The highest temperature treatments (40 and 45°C) had a clear positive effect on methane emission and the level of sulfide in the sediment and, at the same time, clear negative effects on the photosynthetic performance of seagrass plants. The effects observed by temperature stress were immediate (within hours) and seen in all response variables, including ETR, Fv/Fm, methane emission, and sulfide levels. In addition, both the methane emission and the size of the sulfide pool were already negatively correlated with changes in the photosynthetic rate (ETR) during the first day, and with time, the correlations became stronger. These findings show that increased temperature will reduce primary productivity and increase methane and sulfide levels. Future increases in the frequency and severity of extreme temperature events could hence reduce the climate mitigation capacity of tropical seagrass meadows by reducing CO2 sequestration, increase damage from sulfide toxicity, and induce the release of larger amounts of methane. © 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.
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| 3. |
- Hamisi, M. I., et al.
(författare)
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Plankton composition, biomass, phylogeny and toxin genes in Lake Big Momela, Tanzania
- 2017
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Ingår i: African Journal of Aquatic Science. - : National Inquiry Services Center (NISC). - 1608-5914 .- 1727-9364. ; 42:2, s. 109-121
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Tidskriftsartikel (refereegranskat)abstract
- Lake Big Momela, one of the East African soda lakes in Northern Tanzania characterised by highly saline-alkaline conditions, making them inhospitable to a range of organisms, although supporting massive growths of some adapted planktonic microorganisms that serve as food for birds, such as Lesser Flamingo. The temporal dynamics of plankton, with an emphasis on cyanobacteria, were examined in 2007 using morphological traits and ribosomal genetic markers (16S and 18S rRNA). Cyanobacterial genes encoding for hepatotoxins (mcyE and ndaF) were also screened. Rotifers and copepods dominated the zooplankton, whereas cyanobacteria, such as Anabaenopsis elenkinii and Arthrospira fusiformis dominated the phytoplankton community, and these being related to representatives in other East African soda lakes. The cyanobacteria community also showed distinct seasonal patterns influenced by environmental parameters, mainly salinity, pH and nitrate. Significant positive correlations were found between phytoplankton abundance and nitrate concentrations (r = 0.617, p = 0.033). No signals of the hepatotoxin synthetase genes mcyE and ndaF were retrieved from cyanobacteria during the whole year. In general, our data illustrate the presence of rich planktonic communities, including some unique and potentially endemic cyanobacteria.
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| 4. |
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| 5. |
- Mamboya, F.A, et al.
(författare)
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Influence of combined changes in salinity and copper modulation on growth and copper uptake in the tropical green macroalga Ulva reticulata.
- 2009
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 84:3, s. 326-330
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Tidskriftsartikel (refereegranskat)abstract
- The influence of salinity on growth and Cu uptake in the green macroalga Ulva reticulata collected from the intertidal area in the Western Indian Ocean was studied under controlled laboratory conditions. Exposure concentrations ranged from 5 to 500 μg Cu l−1 at five salinities (ranging 20–40). The accumulation of Cu increased with decreasing salinity, so that the uptake at 500 μg Cu l−1 was approximately 2.7, 2.4 and 2.0 times higher at salinities of 20, 25, and 30 respectively, than uptake at salinity of 35, and with uptake being lowest at salinity of 40. Ulva maintained a positive growth rate over the whole salinity range (20–40), with highest rates at salinity of 35. When exposing to Cu at low salinities (20 and 25), the growth rate of Ulva was strongly inhibited suggesting an increase in toxicity of Cu with decreasing salinity. EC50 and NOEC increased with increase in salinity, implying a reduced Cu toxicity at high salinities. It was concluded that salinity needs to be considered when using macroalgae, such as U. reticulata, as a bioindicator of heavy metals in areas with heavy rainfall, underground fresh water intrusion or in estuaries, as they might accumulate more metals and be more negatively affected.
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| 6. |
- Marwa, Karol J., et al.
(författare)
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Plasmodium falciparum Merozoite Surface Proteins Polymorphisms and Treatment Outcomes among Patients with Uncomplicated Malaria in Mwanza, Tanzania
- 2022
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Ingår i: Journal of Tropical Medicine. - : HINDAWI LTD. - 1687-9686 .- 1687-9694. ; 2022
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Tidskriftsartikel (refereegranskat)abstract
- Background. The severity of malaria infection depends on the host, parasite and environmental factors. Merozoite surface protein (msp) diversity determines transmission dynamics, P. falciparum immunity evasion, and pathogenesis or virulence. There is limited updated information on P. falciparum msp polymorphisms and their impact on artemether-lumefantrine treatment outcomes in Tanzania. Therefore, this study is aimed at examining msp genetic diversity and multiplicity of infection (MOI) among P. falciparum malaria patients. The influence of MOI on peripheral parasite clearance and adequate clinical and parasitological response (ACPR) was also assessed. Methods. Parasite DNA was extracted from dried blood spots according to the manufacture's protocol. Primary and nested PCR were performed. The PCR products for both the block 2 region of msp1 and the block 3 regions of msp2 genes and their specific allelic families were visualized on a 2.5% agarose gel. Results. The majority of the isolates, 58/102 (58.8%) for msp1 and 69/115 (60.1%) for msp2, harboured more than one parasite genotypes. For the msp1 gene, K1 was the predominant allele observed (75.64%), whereas R033 occurred at the lowest frequency (43.6%). For the msp2 gene, the 3D7 allele was observed at a higher frequency (81.7%) than the FC27 allele (76.9%). The MOIs were 2.44 for msp1 and 2.27 for msp2 (p = 0.669). A significant correlation between age and multiplicity of infection (MOI) for msp1 or MOI for msp2 was not established in this study (rho = 0.074, p = 0.521 and rho = -0.129, p = 0.261, respectively). Similarly, there was no positive correlation between parasite density at day 1 and MOI for both msp1 (rho = 0.113, p = 0.244) and msp2 (rho = 0.043, p = 0.712). The association between MOI and ACPR was not observed for either msp1 or mps2 (p = 0.776 and 0.296, respectively). Conclusions. This study reports high polyclonal infections, MOI and allelic frequencies for both msp1 and msp2. There was a lack of correlation between MOI and ACPR. However, a borderline significant correlation was observed between day 2 parasitaemia and MOI.
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| 7. |
- Sjöling, Sara, et al.
(författare)
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Benthic bacterial diversity and nutrient processes in mangroves : impact of deforestation
- 2005
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Ingår i: Estuarine, Coastal and Shelf Science. - United Kingdom : Academic Press. - 0272-7714 .- 1096-0015. ; 63:3, s. 397-406
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Tidskriftsartikel (refereegranskat)abstract
- The bacterial diversity and nutrient dynamics of mangrove sediments in Kisakasaka, Tanzania, was investigated in order to evaluate potential changes associated with deforestation of mangroves. Study sites included relatively undisturbed, recently protected mangroves and clear-cut mangrove areas that were sampled during both the wet and dry seasons. Physicochemical parameters, nitrogenase activity, pore water nutrient concentrations and bacterial diversity were measured in sediment depth profiles using both molecular and chemical techniques. Results show that there are significant differences in sediment pore water nutrient concentrations and bacterial diversity in sediments of mangrove areas which have been deforested compared to those which have been protected. Average measured values for protected and deforested areas, respectively, were: sulphide (S-2-),S- < 42 +/- 10 mu M and > 1.9 +/- 0.5 mM at 30 cm depth; ammonium (NH4+), 58 +/- 2 mu M and 113 +/- 12 mu M at 4-5 cm depth; soluble reactive phosphate, 40.2 +/- 11 mu M and 18.4 +/- 1.2 at 4-5 cm depth. Nitrogen fixation rates were lower in deforested areas during day and night, organic content was higher in protected areas (20 +/- 5%) compared to deforested areas (12 +/- 3%). The bacterial diversity was lower in deforested areas as determined by Shannon index using 16S rRNA gene analysis with terminal restriction fragment length polymorphism.
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