| 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. |
- 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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| 3. |
- 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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