| 1. |
- Weich, R G, et al.
(författare)
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Extracellular alkaline phosphatase activity in Ulva lactuca L
- 1989
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 129:1, s. 33-44
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Tidskriftsartikel (refereegranskat)abstract
- Extracellular alkaline phosphatase activity (APA) was detected in the marine macroalga Ulva lactuca, cultivated in laboratory conditions under phosphate limitation. Algal discs were grown in continuous light and in darkness for a maximum of 205 h in sterilized seawater supplied with ammonium nitrate and various phosphate concentrations. APA and phosphate uptake in U. lactuca was stimulated in light whereas inhibition was detected in darkness. APA increased significantly during the cultivation in a phosphate-deficient medium but was suppressed at high external phosphate concentrations. In addition, pretreatment in penicillin over 48 h markedly enhanced enzyme activity during P limitation. The pretreatment in penicillin reduced the number of surface-associated bacteria. Our results indicate that APA in U. lactuca was dependent on the external phosphate concentration, energy from photophosphorylation and bacteria. Since intracellular polyphosphates and an orthophosphate pool still were displayed in 31P NMR spectra after cultivation at phosphate-limiting conditions, P deficiency was not suggested. Unfortunately, NMR spectra reflect total amounts of P compounds and local differences in the P status of the multicellular tissue could not be distinguished. Postulating a negative correlation between the P status and APA, a lower P status in meristematic areas during P limitation was suggested. Alkalisation of the growth medium during algal growth in light, and/or intracellular pH changes may additionally have affected enzyme production.
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| 2. |
- Aljetlawi, A A, et al.
(författare)
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Effect of food and sediment pre-treatment in experiments with a deposit-feeding amphipod, Monoporeia affinis
- 2000
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Ingår i: Journal of Experimental Marine Biology and Ecology. - Umea Univ, Dept Ecol & Environm Sci, SE-90187 Umea, Sweden.. - 0022-0981 .- 1879-1697. ; 249:2, s. 263-280
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally investigated the effects of different pre-treatments of the sediment, and the effect of daily addition of fresh phytoplankton, on the growth and survival of 1-year-old (1 +) individuals of the deposit feeder Monoporeia affinis (Amphipoda). We used three different types of sieved sediment: pre-frozen muddy clay, non-pre-frozen muddy clay, and fine sand. The muddy clay contained phytoplankton originating from the surface sediment sampled in the field during the late spring bloom. No phytoplankton was initially present in sand. The experiment lasted for 18 days. M. affinis responded to the daily phytoplankton addition by increasing growth. Phytoplankton addition had no significant effects on the survival of M. affinis. Upon phytoplankton addition, the sandy and non-frozen muddy clay gave similar growth and survival responses. In contrast, the pre-frozen sediment resulted in significantly lower growth and survival. The growth was negative in all treatments without phytoplankton. Thus, the high initial chlorophyll content in the muddy clay was not of sufficient quality or concentration to allow a positive growth response in M. affinis. The growth of M. affinis was significantly correlated with the reduction of the chlorophyll. Our results indicated that M. affinis is capable of assimilating settled phytoplankton with no, or only a few days' time delay. (C) 2000 Elsevier Science BN: All rights reserved.
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| 3. |
- Granéli, Edna, et al.
(författare)
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Effects of river water of different origin on the growth of marine dinoflagellates and diatoms in laboratory cultures
- 1990
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981 .- 1879-1697. ; 136:2, s. 89-106
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Tidskriftsartikel (refereegranskat)abstract
- The hypothesis that acid humic-rich river water selectively favours dinoflagellates in comparison to diatoms in coastal waters was tested in two sets of laboratory experiments using unialgal cultures of marine phytoplankton. In the first experiment, three dinoflagellates, i.e., Prorocentrum minimum (Pav.) J. Schiller, P. micans Ehrenberg and Amphidinium carterae Hulburt, and three diatoms, i.e., Attheya decora T. West, Skeletonema costatum (Grev.) Cleve and Phaeodactylum tricornutum Bohlin, were grown in a mixture of 80% coastal (S 20%.) and 20% river water. Water from seven different rivers was used. Four rivers had a high humic content (yellow substance 22.1 ± 0.9 · m−1) but lower inorganic N and P concentrations ("forest rivers") while three rivers ("agricultural rivers") had a lower humic content (10.7 ± 1.3 · m−1) but inorganic nutrient concentrations approximately three times as high as the forest rivers. The growth rates for the dinoflagellates were significantly higher in the medium with forest river water compared to the mixtures with agricultural river water while the opposite was true for the diatoms. In the second type of experiment, the diatom Ditylum brightwellii (T. West) Grun and the dinoflagellate P. minimum were grown, as semicontinuous dilution cultures, in mixtures of 90% coastal water (S 20%.) and 10% river water. Water from four different rivers was used, one draining mainly agricultural soils and the other acidified humic-rich forested soils. River water of agricultural origin supported a higher D. brightwellii biomass and growth rate than river water draining forested soils while for P. minimum the opposite was true. Decreasing cell P quotas and increasing alkaline phosphatase activity indicated that D. brightwellii was P-deficient, especially when agricultural river water was added, while these physiological indices suggested that P. minimum cultures were not P-starved. Our results support the hypothesis that the discharge of acidified river water, rich in humic substances, to coastal waters, can play a role in shifting the species composition from diatoms to dinoflagellates.
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| 4. |
- Granéli, Edna, et al.
(författare)
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The response of planktonic and microbenthic algal assemblages to nutrient enrichment in shallow coastal waters, Southwest Sweden
- 1985
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 85:3, s. 253-268
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Tidskriftsartikel (refereegranskat)abstract
- Field and laboratory nutrient (nitrogen and phosphorus) enrichment experiments were performed using natural phytoplankton and microphytobenthic assemblages from the brackish water Öresund, S.W. Sweden. The response of algae from a low-nutrient area (Falsterbo Canal) was compared to that of algae from a polluted, nutrient-rich area (Lomma Bay).The biomass (measured as chlorophyll a) of both phytoplankton and microphytobenthos from the Falsterbo Canal increased after the addition of nitrogen. Phytoplankton growth was stimulated by the addition of phosphorus to the nitrogen-rich water of the polluted Lomma Bay. Sediment chlorophyll a showed no significant increase after the addition of nutrients in the Lomma Bay. In containers without sediment, phytoplankton uptake was calculated to account for ≈ 90% of the disappearance of inorganic fixed nitrogen from the water. In the sediment containers the microphytobenthos was estimated to account for ≈20% of the nitrogen uptake. The rest was presumably lost mainly through denitrification.When containers with microphytobenthos from Lomma Bay were kept in the dark, phosphorus was released at a rate of up to ≈ 180 μM · m−2 · day−1. We suggest that by producing oxygen microbenthic algae keep the sediment surface oxygenated thereby decreasing phosphorus transport from the sediment to the overlying water.
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| 5. |
- Macia, Adriano, et al.
(författare)
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Thorn fish Terapon jarbua (Forskål) predation on juvenile white shrimp Penaeus indicus H. Milne Edwards and brown shrimp Metapenaeus monoceros (Fabricius) : the effect of turbidity, prey density, substrate type and pneumatophore density
- 2003
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981 .- 1879-1697. ; 291:1, s. 29-56
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Tidskriftsartikel (refereegranskat)abstract
- A series of laboratory experiments was conducted at Inhaca Island Marine Biological Station, Mozambique, in order to assess the separate effects of turbidity, prey density, substrate type, pneumatophore density, and the combined effects of turbidity with the latter three, on rate of predation by the thorn fish Terapon jarbua (Forskål, 1775) on white shrimp Penaeus indicus and brown shrimp Metapenaeus monoceros. Significant interactions between turbidity and the other three factors on shrimp predation for both prey species were detected. Regardless of prey density, increasing turbidity decreased predation on P. indicus, but not on M. monoceros, for which increasing densities reduced the protective effect of turbidity. Increasing prey density increased predation on P. indicus in clear water, and increased predation on M. monoceros in low and high, but not in intermediate turbidity or clear water. The presence of a substrate suitable for burying decreased predation on M. monoceros in clear water, but not in the turbidity levels used. In clear water, solely sandy-shell substrate afforded protection to P. indicus, while in turbid water, no substrate offered significant protection and muddy substrate even increased prey vulnerability to fish probably as a result of increased preys' locomotor activity. Raising pneumatophores density seems to lower the protective value of turbidity for both species. In clear water, only low and high structure density provided a deterrent effect on predation on P. indicus; in turbid water, intermediate and higher structure density increased predation. Increasing structural complexity reduced predation on M. monoceros linearly in clear water; but in low turbid water it increased. In high turbid waters, the increase was only significant in intermediate pneumatophore density. High structural complexities impair the pursuing capacity of fish and thus decreased predation rates. The results indicate that the effective provision of shelter of different habitats depends not only on the various environmental parameters analysed, but also on the way they interact and on the behaviour of prey and predator as well.
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| 6. |
- Richardson, Katherine, et al.
(författare)
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The relationship between photosynthesis measured by C-14 incorporation and by uptake of inorganic carbon in unicellular algae
- 1984
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 81:3, s. 241-250
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Tidskriftsartikel (refereegranskat)abstract
- The traditional 14C method of estimating photosynthetic rates was compared with net photo-synthesis in two species of unicellular algae. Net photosynthesis was defined as the disappearance of inorganic carbon from the algal medium and was determined using a described infra-red gas analyser (IRGA) technique. For Amphidinium carterae Hulbert, the 14C method always led to lower calculated rates of photosynthesis than the IRGA technique. This difference was, on average, ≈100%. For Scenedesmusobliquus (Turpin) Kützing, the 14C method could lead to over-estimates, good agreement with, or underestimates of net photosynthesis. Although the under-estimates were only of the order of 15%, the over-estimates were in some cases > 100%. There is some indication that respiration rate is an important factor in the relationship between photosynthetic rates calculated by the two methods for this organism.
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| 7. |
- Sakshaug, E, et al.
(författare)
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Chemical composition and alkaline phosphatase activity of nutrient-saturated and P-deficient cells of four marine dinoflagellates
- 1984
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 77, s. 241-254
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Tidskriftsartikel (refereegranskat)abstract
- Four marine dinoflagellates, Amphidinium carterae Hulburt, Ceratium tripos (O.F. Müll.) Nitzsch, Prorocentrum minimum (Pav.) J. Schiller, and Scrippsiella trochoidea (Stein) Loeblich III were grown as dilution cultures at 18°C, S = 29%. and 30 μE·m−2·s−1 at L:D = 14:10 h. In nutrient-saturated cultures, the growth rates (doubl·day−1) ranged from 0.38 for Scrippsiella to 0.80 for Prorocentrum, and carbon content (pg·cell−1) from 83 for Amphidinium to 6900 for Ceratium. The atomic N/C ratio was 0.13–0.15, but for Ceratium it was 0.088, because of its thick, cellulose theca. The atomic N/P ratio ranged from 12–13 for Ceratium and Scrippsiella to 15–17 for Prorocentrum and Amphidinium. Under P-deficient conditions (growth rate 39–70% of the maximum), cellular P decreased considerably, but so did N, so that the N/P ratio was only slightly affected. There was a concomitant increase in carbon content per cell of 1.2- to 1.7-fold. Alkaline phosphatase activity was virtually nil in nutrient-saturated cells, but was readily demonstrable in all species when P-deficient.
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| 8. |
- Angeler, David
(författare)
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Effects of shrimp-farm effluents on the food web structure in subtropical coastal lagoons
- 2011
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 402, s. 65-74
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Tidskriftsartikel (refereegranskat)abstract
- Although numerous studies have reported the negative effects of shrimp aquaculture on water quality, little is known about the ecological effects of these practices in coastal lagoons and near-shore marine habitats. The impact of shrimp-farm effluents on the food webs of an impacted subtropical coastal lagoon in the Gulf of California was evaluated through measurements of isotopic (delta C-13, delta N-15) signatures in sediments, plants and animals, and compared with the results of a near-pristine reference site. Degradation was manifested in a strong reduction on fish diversity at the perturbed site. delta C-13 signatures provided ambiguous evidence of degradation while delta N-15 was a better descriptor of shrimp-farm effluent impact on coastal lagoon food webs. The site receiving nutrient-rich discharges showed significant enrichment of delta N-15 (approximate to 5 parts per thousand) in sediments, macroalgae, benthic algae, filterfeeders and omnivorous feeders, resulting in qualitative differences in foodweb structure between both lagoons. The food web in the perturbed site was sustained by sediment detritus and dominated by opportunistic species. The lowest influence on delta N-15 signatures by aquaculture discharges recorded in the upper trophic levels could be explained by the shift in the composition of biotic communities, and associated feeding strategies. While alterations in resource availability do not affect directly food chain length, trophic linkages between food web compartments can be reduced as a result of shrimp farm impacts. Our study demonstrates that nutrient-enriched discharges from shrimp-farm aquaculture generate changes in the availability of food sources, which reduce biodiversity and alter structural and functional food web characteristics. (C) 2011 Elsevier B.V. All rights reserved.
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| 9. |
- Angove, Charlotte, et al.
(författare)
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Assessing the efficiencies and challenges for nutrient uptake by aquatic plants
- 2018
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 507, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Aquatic plant meadows are valuable components to the 'coastal filter' and it is important to understand the processes that drive their ability to cycle nutrients. However, at present, the field-based evidence for understanding the drivers of nutrient uptake by plants is lacking. This study aimed to investigate how well individual shoots of aquatic plants could meet their nitrogen demands using the sediment nutrient pool (porewater ammonium) and to explore which traits helped to facilitate such uptake. Several species were investigated in shallow, submerged (2-4 m) mixed-species communities in the northern Baltic Sea using incubation experiments with enriched ammonium. After a 3.5 h incubation time, individuals were collected and analysed for nitrogen (% DW) and N-15 (at-%) concentrations. Uptake by plants was calculated per unit nitrogen in response to the N-15 labelled source and to overall nitrogen availability. Background porewater ammonium availability was highly variable between individual plants. Species identity did not significantly affect uptake metrics and the effect of ambient porewater availability was weak. As biomass increased there were significant logarithmic declines in the 95th quantiles of nutrient uptake rates, ambient porewater nutrient availability and aboveground nitrogen tissue concentrations (% DW). Such findings suggested that uptake rates of plants were significantly demand driven and the nutrient conditions of the porewater were significantly driven by the demands of the plant. Findings parameterised the unfulfilled potential for some aquatic plants to cycle nutrients more efficiently and highlighted the potential importance of access to new nutrient sources as a way of enhancing nutrient cycling by aquatic plants. Plant traits and community properties such as the activity of infauna could facilitate such an access and are likely important for nutrient uptake.
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| 10. |
- Arroyo, Nina Larissa, et al.
(författare)
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Interactions between two closely related phytal harpacticoid copepods, asymmetric positive and negative effects
- 2007
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 341:2, s. 219-227
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Tidskriftsartikel (refereegranskat)abstract
- Competition for food is generally thought to exert a strong evolutionary pressure, driving trophic niche separation, either by specialization and/or by widening the choice of potential food resources. Harpacticoid copepods are common inhabitants of phytal assemblages, where several closely related species of the so-called phytal dwelling families often co-occur. However, direct competition among phytal harpacticoids has been thought to be unlikely, due to the abundant and continuously available food supplies. We conducted a series of field and laboratory studies to assess the role of competition in the abundance distribution of two closely related harpacticoid species, Mesochra rapiens and M. aestuari. We found that the abundance of both species co-varied on several seaweed species in the northern Baltic Sea, during a 3-month period. Stable isotope ratios in the green alga Cladophora glomerata field samples indicated different resource utilization of the two species, both in fresh and deteriorated C. glomerata, and in drifting algae. We tested in the laboratory if resource utilization was different between the species in sympatry and allopatry. We used enriched stable carbon isotope ratios (C-13/C-12) of the diatom Phaeodactylum tricornutum to trace the uptake in both species. Results from these experiments showed a much higher assimilation by M. aestuari in sympatry with M. rapiens, while the latter species showed a higher assimilation in allopatry. Our results show that while there is no apparent competition for resources between these two species in the field, there seems to be an asymmetric reaction when in sympatry and provided one single resource in the laboratory. We suggest that M. rapiens may facilitate assimilation by M. acstuari and discuss the mechanisms by which this may take place.
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