| 1. |
- Odmark, S, et al.
(författare)
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Effects of UVB radiation in a microbenthic community of a marine shallow-water sandy sediment
- 1998
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Ingår i: Marine Biology. - 0025-3162. ; 132:2, s. 335-345
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Tidskriftsartikel (refereegranskat)abstract
- The role of ambient and enhanced ultraviolet-B radiation (UVB; 280 to 315 nm) in a natural sand-associated microbenthic community was studied in a 3-week experiment by incubating intact sediment cores from a shallow bay in an outdoor flow-through system with 27 aquaria. After sampling of initial cores, the remaining cores tone per aquarium) were given one of three treatments: no, ambient, and moderately enhanced UVB, and sampled, nine at a time, after 5, 12, and 19 d. The response of the community was studied by analysing algal and meiofaunal composition and biomass, chlorophyll a content, composition of pigments and fatty acids, and content of UV-absorbing compounds (state variables), as well as carbon fixation and allocation, and bacterial productivity (rate variables). Among rate variables, significant effects of UVB-treatments were found for carbon fixation and allocation, while bacterial productivity was not affected. For state variables, a significant response was observed for the composition of microalgae and fatty acids, and for chlorophyll a content. The effect of treatments was mainly observed as differences in development with time (two-way analysis of variance, treatment x time interaction). Towards the end of the experiment, the no-UVB treatment most often differed from one or both of the two treatments with UVB exposure, the latter showing lower values. There were marked successional changes in the community, irrespective of treatment. The microalgal community changed from being dominated by coccoid cyanobacteria and epipsammic diatoms to a dominance of epipelic diatoms and filamentous cyanobacteria. The pattern of carbon allocation, as well as an increased C/N ratio of the sediment, suggested limitation of growth, perhaps by nutrients, at the end of the experiment. This may possibly have acted synergistically with UVB exposure to create the treatment effects. The new knowledge gained from our experiment is that ambient UVB can exert a stress on the function of sand-associated microbenthic communities in shallow waters and that this effect coincides with structural differences in the community.,More experiments in natural or semi-natural systems are needed to allow better prediction of microbenthic community-level responses to UVB.
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| 2. |
- Sundbäck, Kristina, 1949, et al.
(författare)
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Effects of enhanced UVB radiation on a marine benthic diatom mat
- 1997
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Ingår i: Marine Biology. - 0025-3162. ; 128:1, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the ecophysiological response of a natural diatom-dominated microbial mat to an enhanced level of ultraviolet-B radiation (UVBR), intact sediment cores from a shallow microtidal bay on the Swedish west coast were incubated in an outdoor flow-through system and exposed to either no UVBR or to an artificially enhanced level of UVBR. The microbial mat was cohesive and dominated by the large (approximate to 400 mu m) motile diatom Gyrosigma balticum. Functional response to UVBR was assessed by measuring carbon fixation (C-14) and allocation of photosynthetic products. Sediment oxygen microprofiles were measured as indicators of the balance between the photosynthetic and respiratory activity of the community. Structural variables included biomass and composition of microalgae, pigment composition (HPLC), content of UV-absorbing compounds, and composition of fatty acids. An enhanced level of UVBR resulted in significant functional changes in the microalgal community. Significantly decreased carbon fixation and lower net oxygen production (as calculated from oxygen microprofiles) suggest that primary productivity in the type of microbial mat studied is potentially sensitive to an enhanced level of UVBR. The pattern of carbon allocation hinted a change as to the photosynthetically active part of the community when exposed to UVBR, indicating a differential sensitivity among algal cells. Despite significant functional effects, pigment or algal composition were not significantly affected by enhanced UVBR. The concentration of UV-absorbing compounds was low and did not increase at UVBR exposure. Due to the short duration of the experiment (4 d), a change in algal biomass or composition was not to be expected. Moreover, the thickness of the sampled sediment layer, may have contributed to the lack of observed structural effects of enhanced UVBR. Visual observations suggested that UVBR affected the motility of G. balticum. This study, as well as other experiments with a similar diatom mat, suggest that vertical migration is a key mechanism to be further studied in relation to UVBR exposure of diatom-dominated microbial mats.
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| 3. |
- Underwood, G. J. C., et al.
(författare)
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Short-term effects of UVB radiation on chlorophyll fluorescence, biomass, pigments, and carbohydrate fractions in a benthic diatom mat
- 1999
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Ingår i: Journal of Phycology. - 0022-3646. ; 35:4, s. 656-666
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Tidskriftsartikel (refereegranskat)abstract
- The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated, Chlorophyll fluorescence parameters (F-v/F-m, phi(PSII)), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and +15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels, increases in phi(PSII) values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield (F-s) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G, balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the +15% UVBR treatment also had significantly higher concentrations of beta-carotene after 5 days of treatment, Although G. balticum responded to enhanced UVBR by migration and increased beta-carotene concentrations, significant reduction in maximum quantum yield of PSII (F-v/F-m) and in minimal fluorescence (F-o) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass.
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| 4. |
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| 5. |
- Wulff, Angela, 1963, et al.
(författare)
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Effect of sediment load on the microbenthic community of a shallow-water sandy sediment
- 1997
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Ingår i: Estuaries. - 0160-8347. ; 20:3, s. 547-558
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic activities, such as construction work, dredging, and different kinds of recreation activities, can alter sediment loading in shallow coastal areas. The effect of increased load of fine sediment on the microbenthos (benthic microalgae, bacteria, and meiofauna) was studied in two experiments using undisturbed cores of a sandy sediment from a microtidal bay on the Swedish west coast. In each experiment, a total of 24 cores were incubated in an outdoor flow-through set-up. Twelve cores were treated with a 2.5-mm thick layer of autoclaved fine-grained, (silt) carbon-rich surface sediment. In the first experiment, estimates of the impact were based on measurements of chlorophyll alpha, biomass of microalgae, bacteria, and meiofauna, and bacterial production. The main purpose of the second experiment was to study the effect on sediment oxygen profiles using microsensors. Within a week, after being covered by fine sediment, benthic microalgae (particularly diatoms) had migrated upward and the oxygen profiles were restored at the sediment surface by photosynthesis. However, the oxygen-producing layer became thinner and the algal composition changed. Bacterial biomass was restored to the same level as in the sandy sediment. Meiofauna also appeared to move upward and the meiofaunal composition was reestablished. The results suggest that the microbenthic community of sandy sediment has an inherent capacity to recover after a moderate deposition of fine-particle sediment. Active upward migration of benthic diatoms appears to be a key mechanism for restoring the oxygenation of the sediment surface. The altered sediment type also implies changed species composition, and hence altered benthic trophic interactions, which may affect, for example, flatfish recruitment.
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| 6. |
- Wulff, Angela, 1963, et al.
(författare)
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UV radiation effects on microbenthos - a four month field experiment
- 1999
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 19:3, s. 269-278
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Tidskriftsartikel (refereegranskat)abstract
- A 4 mo field experiment, covering the period May to September, was carried out in a shallow microtidal sandy bay on the Swedish west coast. To test whether the ambient UV radiation (UVR) had any effect on a marine microbenthic community, screens of Plexiglas, Plexiglas + Mylar-D film and polycarbonate were used. This gave 3 different treatments: Ambient (PAR+UVAR+UVBR), NoUVB (PAR+UVAR) and NoUV (PAR) plus Control (areas without screens to test the 'frame effect'). The response of the community was studied on 2 occasions (June, September) by measuring primary productivity (C-14), carbon allocation (C-14) and bacterial productivity (H-3-thymidine) (rate variables), as well as biomass and composition of microalgae and meiofauna, pigment composition (HPLC), content of mycosporine-like amino acids (MAA, HPLC) and composition of fatty acids (GC). The UVR maximum penetration depth (1%) in the sediment, measured by microsensors, was 800 mu m for UVAR and 600 mu m for UVB. No UVR effects were found for any structural variables but ostracodalbiomass, which doubled when exposed to WR compared with the UVR excluding treatments. Significant treatment effects were found for the rate variables primary productivity and carbon allocation. The effects on primary productivity and ostracods were observed in September only. All the treatment effects were found between exclusion of and exposure to UVR. Primary productivity increased in treatments shielded from UVR. For carbon allocation, significant effects on all fractions were found, however, with a partly different outcome in June and September. We conclude that the UVBR part of the spectrum exerted some stress on the microbenthic community, but this was almost exclusively found for rate variables in September, and that the ambient UVAR did not have any harmful effects. It is also concluded that the choice of time scales and experimental approach (laboratory vs field experiments) is crucial for the out come and interpretation of UVBR experiments.
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