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| 2. |
- Breitbarth, Eike, et al.
(författare)
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Nitrogen fixation and growth rates of Trichodesmium IMS-101 as a function of light intensity
- 2008
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Ingår i: Marine Ecology Progess Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 359, s. 25-36
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Tidskriftsartikel (refereegranskat)abstract
- The diazotrophic cyanobacterium Trichodesmium is a significant contributor to marine nitrogen and carbon cycles and has been incorporated in biogeochemical ocean circulation models. To date, parameterization of light as a controlling factor for nitrogen fixation has been based on field observations, where factors other than light also affect Trichodesmium physiology. Here we present data on light-dependent (15 to 1100 µmol quanta m–2 s–1) diazotrophic growth from controlled laboratory experiments and their implications for modeling approaches. We supply a simple empirical model to describe nitrogen fixation by Trichodesmium in batch cultures. Diazotrophic growth of axenic Trichodesmium IMS-101 was light saturated at 180 µmol quanta m–2 s–1 and did not vary significantly at higher photon irradiances up to 1100 µmol quanta m–2 s–1 (μcarbon based ≈ 0.26 d–1). Chlorophyll a (chl a) normalized N2 fixation rates were significantly affected by light intensity during mid-exponential growth (0.74 to 4.45 mol N fixed mol chl a–1 h–1) over the range of photon irradiances tested. In contrast, nitrogen fixation rates normalized to the cellular carbon content were relatively unaffected by light intensity (0.42 to 0.59, averaging 0.5 mmol N mol particulate organic carbon [POC]–1 h–1). Trichodesmium carbon biomass can be used to estimate the nitrogen input by this diazotroph into the ocean; the maximum input rate is 350 nmol N fixed l–1 h–1.
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| 3. |
- Brock, Elisabet, 1949, et al.
(författare)
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Chemical inhibition of barnacle larval settlement by the brown alga Fucus vesiculosus
- 2007
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 337, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- The possible importance of larval settlement inhibition by Fucus vesiculosus in explaining the low abundance of the barnacle Balanus improvisus on algal fronds compared to adjacent rock was investigated by a combination of field and laboratory studies. A field survey showed that the abundance of adult barnacles was significantly lower on F vesiculosus than on rocks and settlement preference experiments strongly suggested that settlement avoidance for algal fronds during the natural settlement season was chemically mediated. By using a multi-step approach, whereby both exuded and surface associated metabolites were tested on larval settlement, we further investigated the possible existence of chemical antifouling processes in E vesiculosus. For exuded metabolites, seawater was conditioned for 1 and 3 h with both submerged and desiccated algae, Surface extracts at natural concentrations and seawater conditioned with submerged algae had no significant effect on larval settlement, although there was a tendency for reduced settlement in the 3 h samples. Seawater conditioned with desiccated algae consistently inhibited settlement and chemical analyses showed that the mean phlorotannin level in the water was 31.5 mu g ml(-1), which is ca. 30x higher than concentrations previously shown to inhibit barnacle settlement. Seawater conditioned with submerged algae had a mean phlorotannin content of 0.85 mu g ml(-1) and in samples conditioned for 3 h there was a strong and significant negative relationship between phlorotannin concentration and larval settlement, suggesting that the phlorotannin concentration varied around a level inhibitory to barnacle settlement. Altogether, the results from the laboratory experiments strongly suggested that the low larval preference for algae was caused by exudation of waterborne metabolites, primarily phlorotannins. Finally, field measurements showed that phlorotannins exuded from F. vesiculosus can under natural conditions reach concentrations inhibitory to settlement of barnacle larvae.
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| 4. |
- Calliari, Danilo, 1969, et al.
(författare)
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Feeding and reproduction in a small calanoid copepod: Acartia clausi can compensate quality with quantity
- 2005
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 298, s. 241-250
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed the feeding, egg production rate (EPR), and the egg hatching success (EHS) of resulting eggs of adult Acartia clausi subject to realistic food levels (100 mu g C l(-1)) of 7 algae. Feeding was maximum (ca. 20 ml ind.(-1) d(-1)) with Thalassiosira weissflogii and minimum (ca. 0 ml ind.(-1) d(-1)) with Dunaliella tertiolecta and Prymnesium parvum. EPR was highest with T weissflogii, Tetraselmis sp., Rhodomonas sp., and Ditylum brightwellii (21 to 26 eggs ind.(-1) d(-1)) and moderate with Prorocentrum minimum (15 eggs ind.(-1) d(-1)). EHS was highest in R minimum (84%), followed by Rhodomonas sp. (80%), D, brightwellii (60%), T weissflogii (52%) and Tetraselmis sp. (40%). Supplementary nutritional effects (higher EHS and gross growth efficiency) appeared when A. clausi fed on mixtures of algae with contrasting effects on EPR and EFIS (T weissflogii and P. minimum) offered as mixed suspensions, or alternating between unialgal suspensions on a 12:12 h basis. However, realized fecundity (RF) was fairly stable for most single and mixed diets (range 12.3 to 17.3 nauplii female(-1) d(-1)), with the exception of Tetraselmis sp. (8.9 nauplii female(-1) d(-1)). Such stable RF was attained by compensating low EFIS with enhanced feeding and EPR, and consequently lower population growth efficiency. That represents a strategy with a high cost in terms of metabolism and predation risk.
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| 5. |
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| 6. |
- Calliari, Danilo, 1969, et al.
(författare)
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Salinity modulates the energy balance and reproductive success of co-occurring copepods Acartia tonsa and A-clausi in different ways
- 2006
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 312, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- We assessed metabolic balance, RNA content, and egg hatching success (EHS) in Acartia tonsa and A. clausi over a wide salinity range (2 to 33 and 16 to 33, respectively). For A. tonsa, the energy partitioning between ingestion, production and respiration was relatively constant with small differences in gross growth efficiency (GGE) and cost of growth (CG). In contrast, A. clausi exhibited significantly reduced ingestion and GGE, and highly elevated CG at salinities <= 20. In both species, RNA levels mirrored egg production. EHS was generally high in both species, but decreased by 80% for A. clausi at 16. These results contribute to the understanding of distribution patterns of both species along salinity gradients. The observed responses would allow the dominance of A. tonsa at low salinities, although its higher energetic requirement and feeding activity subject it to stronger predation pressure than competing A. clausi.
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| 7. |
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| 8. |
- Cervin, Gunnar, 1967, et al.
(författare)
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Small-scale disturbance in a stable canopy dominated community: implications for macroalgal recruitment and growth
- 2005
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 305, s. 31-40
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Tidskriftsartikel (refereegranskat)abstract
- The long-living species Ascophyllum nodosum dominates the mid-shore of sheltered rocky sites in NW Europe, forming near-monospecific stands. We aimed to determine the effects of small-scale disturbance on such shores, through manipulative experiments over a long period (almost 7 yr). We tested the general hypothesis that small-scale disturbance allows co-existence of Fucus canopy (F. vesiculosus, F serratus) and promotes recruitment of Ascophyllum itself. Two factorial experiments were established to determine the interactive effects of the Ascophyllum canopy with: (1) the red algal turf which covers approximately 90% of the substratum at the experimental sites, and (2) the dominant grazer, the limpet Patella vulgata, which maintains small patches of open substratum free from turf. Disturbance to plots 25 x 25 cm resulted in significant changes to the understorey community. Removal of limpets led to high levels of Ascophyllum and Fucus recruitment, irrespective of the presence of the canopy. In the presence of limpets recruitment of fucoids was negligible. In contrast, removal of turf alone led to high Fucus spp. but not Ascophyllum recruitment. Loss of the canopy and a consequent degradation of the turf was required to promote Ascophyllum recruitment. Despite high recruitment in some treatments beneath an intact canopy, low growth rates in shade prevented development of mature plants. Loss of the overlying Ascophyllum canopy was followed by development of a mixed F serratus/F. vesiculosus canopy that was still present nearly 7 yr after manipulation. Ascophyllum recruits, while showing enhanced growth in the absence of the canopy, were too slow-growing to form a canopy.
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| 9. |
- Dedieu, K, et al.
(författare)
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Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective
- 2007
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Ingår i: Marine ecology progress series. - 0171-8630. ; 346, s. 45-59
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data and simulations were used to investigate the seasonal coupling between carbon, nitrogen and oxygen cycles in marine sediments from a eutrophic shallow lagoon in the Mediterranean Sea area. A negative seasonal correlation was observed between oxygen consumption and coupled nitrification–denitrification rates in surface sediments. Elevated values of oxygen consumption rates were reached during warm periods (up to 87.7 mmol m–2 d–1) whereas nitrification and denitrification rates remained close to the lowest rates reported for coastal sediments (values around 0.021 to 0.35 mmol N m–2 d–1 for nitrification and 0.014 to 0.045 mmol N m–2 d–1 for denitrification). A steady-state diagenetic model closely represented the seasonal negative correlation of oxygen uptake, coupled nitrification–denitrification rates, the vertical distribution patterns of pore water oxygen and the solid phase distribution of organic carbon when nitrification inhibition by sulfide was included. Simulation adjusted to field data also highlighted the importance of oxygen penetration depth in the seasonal variation of nitrification. The modelling indicated that anaerobic metabolism was the most significant pathway (65 to 80%) during organic matter mineralization with a clear seasonal increase during warm periods. These warm periods were also characterized by the higher benthic demand of oxygen mostly used to re-oxidize the by-products from anaerobic reactions (from 57 to 82%), the other part being used for carbon mineralization.
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| 10. |
- Degerholm, Jenny, et al.
(författare)
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Seasonal significance of N2 fixation in coastal and offshore waters of the northwestern Baltic Sea
- 2008
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 360, s. 73-84
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Tidskriftsartikel (refereegranskat)abstract
- Annual rates of N2 fixation were measured over 3 yr (1998–2000) at an open water station (BY31) and 2 coastal stations (H4 and X1) in the Baltic Sea. This is the first report on depth-integrated rates of N2 fixation from more than one complete growth season in the Baltic Sea. Annual estimates of N2 fixation ranged from 56000 to 125000 t N in the Baltic Proper, and 18000 to 162000 t N at the inshore stations (Himmerfjärden). Rates of N2 fixation were measured in situ at 4 depths between 0 and 25 m using the 15N tracer technique for size fractionated organisms larger and smaller than 20 µm. Maximum rates of N2 fixation were found in surface waters (0 to 4 m depth), and a major part of this activity (80% in coastal and 89% in offshore waters) took place during daylight hours. Integrated rates of N2 fixation in cells >20 µm followed the average abundance of filamentous cyanobacteria (primarily Aphanizomenon sp.) in the water column. Molar C:N mass ratios in particles >20 µm, i.e. filamentous cyanobacteria, suggest that this size fraction was N-sufficient during summer, whereas the molar C:P mass ratios indicated P-limitation during this period. A reduction in sewage discharge to the Himmerfjärden bay area during the study period appears not to have been compensated for by increased rates of N2 fixation. The patchy distribution of cyanobacteria and the high seasonal variability in N2 fixation rates emphasize the need for adequate spatial and temporal sampling strategies in studies of N2 fixation in coastal and open waters of the Baltic Sea.
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