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- Asplund, Maria E., et al.
(författare)
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Water column dynamics of Vibrio in relation to phytoplankton community composition and environmental conditions in a tropical coastal area
- 2011
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Ingår i: Environmental Microbiology. - 1462-2912 .- 1462-2920. ; 13:10, s. 2738-2751
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Tidskriftsartikel (refereegranskat)abstract
- Vibrio abundance generally displays seasonal patterns. In temperate coastal areas, temperature and salinity influence Vibrio growth, whereas in tropical areas this pattern is not obvious. The present study assessed the dynamics of Vibrio in the Arabian Sea, 1-2 km off Mangalore on the south-west coast of India, during temporally separated periods. The two sampling periods were signified by oligotrophic conditions, and stable temperatures and salinity. Vibrio abundance was estimated by culture-independent techniques in relation to phytoplankton community composition and environmental variables. The results showed that the Vibrio density during December 2007 was 10- to 100-fold higher compared with the February-March 2008 period. High Vibrio abundance in December coincided with a diatom-dominated phytoplankton assemblage. A partial least squares (PLS) regression model indicated that diatom biomass was the primary predictor variable. Low nutrient levels suggested high water column turnover rate, which bacteria compensated for by using organic molecules leaking from phytoplankton. The abundance of potential Vibrio predators was low during both sampling periods; therefore it is suggested that resource supply from primary producers is more important than top-down control by predators.
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| 6. |
- Godhe, Anna, 1967, et al.
(författare)
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Quantification of Diatom and Dinoflagellate Biomasses in Coastal Marine Seawater Samples by Real-Time PCR
- 2008
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 74:23, s. 7174-7182
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Tidskriftsartikel (refereegranskat)abstract
- Two real-time PCR assays targeting the small-subunit (SSU) ribosomal DNA (rDNA) were designed to assess the proportional biomass of diatoms and dinoflagellates in marine coastal water. The reverse primer for the diatom assay was designed to be class specific, and the dinoflagellate-specific reverse primer was obtained from the literature. For both targets, we used universal eukaryotic SSU rDNA forward primers. Specificity was confirmed by using a BLAST search and by amplification of cultures of various phytoplankton taxa. Reaction conditions were optimized for each primer set with linearized plasmids from cloned SSU rDNA fragments. The number of SSU rDNA copies per cell was estimated for six species of diatoms and nine species of dinoflagellates; these were significantly correlated to the biovolumes of the cells. Nineteen field samples were collected along the Swedish west coast and subjected to the two real-time PCR assays. The linear regression of the proportion of SSU rDNA copies of dinoflagellate and diatom origin versus the proportion of dinoflagellate and diatom biovolumes or biomass per liter was significant. For diatoms, linear regression of the number of SSU rDNA copies versus biovolumes or biomass per liter was significant, but no such significant correlation was detected in the field samples for dinoflagellates. The method described will be useful for estimating the proportion of dinoflagellate versus diatom biovolume or biomass and the absolute diatom biovolume or biomass in various aquatic disciplines.
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| 7. |
- Härnström, Karolina, 1980
(författare)
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Bloom dynamics and population genetics of marine phytoplankton - Community, species and population aspects
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phytoplankton are the most important primary producers in the world’s oceans and coastal waters, accounting for nearly half of the global net primary production. Although they are such important organisms, little is known about the ecology and dynamics of phytoplankton. The importance of phytoplankton resting stages, the coupling between cells in the sediment and watermass and how environmental changes affect the population structure is uncertain. The record of a specific species in a given area is foregone by either advection of the species from adjacent areas, or by growth of a few cells present in the water. Many groups of phytoplankton have the ability to form resting stages to provide short- or long-term survival, and these stages can be resuspended and subsequently germinate and thereby be re-established in the water mass. Diatoms constitute the single largest group of microalgae and they are mainly marine but found in all aquatic environments. Diatom blooms can develop fast, and they can grow at low levels of light, which gives the cells an advantage during spring blooms in temperate areas where light is a limiting factor. To successfully meet selective pressure in a variety of ecological niches, it is hypothesized that diatoms display high phenotypic and genetic diversity. Skeletonema marinoi (Sarno et Zingone) is a marine diatom, often dominating temperate coastal waters during spring bloom. The mechanisms for dispersal and expansion of populations of this species are, as for most diatoms, complex and difficult to predict. Possibly the presence of different populations at different seasons is caused by strong directional selection in a continuously growing population, or by a complete replacement of one population by another. The general aim of this thesis was to study marine phytoplankton dynamics at community, species and population level, and we used S. marinoi as model organism for the population studies. In order to perform some investigations, appropriate methods have been developed. I have focused on the interaction between water mass and sediment, both in temperate waters and in a tropical area, investigated the importance of resting stages and small-scale hydrographical changes for the phytoplankton community structure as well as population genetics and microevolutional processes of population dynamics. The results from a tropical area show that benthic resting stages contribute to blooms by resuspension, germination, and proliferation as planktonic cells in the water column, and thus, the cells can influence the phytoplankton community in the water column. There can be an alternation of the species composition if a plankton community is seeded by resting stages or by planktonic cells, and geographically the strategies of seeding can differ within the same species. The composition of the phytoplankton community is exceedingly affected by small-scale hydrographic changes and several of these factors are potentially tightly coupled. These changes have implications on the sampling, and therefore frequent sampling is important. When clones of S. marinoi were examined, the morphological character defining another species of the same genus–Skeletonema dohrnii (Sarno et Kooistra)–was found in most of the clones. The phylogenetic variation in LSU rDNA in the S. marinoi clade were of the same magnitude or greater than differences between S. dohrnii and S. marinoi. The two species are not suggested to be merged since there may be a separation in the biogeographical distribution of the two species. A series of molecular methods were used to study various aspects of phytoplankton ecology. For estimating the proportion of dinoflagellate versus diatom biovolume or biomass and the absolute diatom biovolume or biomass, real-time PCR technique constitutes a quick and accurate method. Another useful tool is microsatellite markers, and the characterisation and development of primers enabled the study of population genetics of S. marinoi. Resting stages from undisturbed and dated sediment cores from a fjord with anoxic bottom conditions, were germinated and cultures established. The fjord has during a few decades been hypereutrophicated and populations found during this time were significantly different from populations found before and after. The postand pre-eutrophication populations showed no significant genetic difference. Environmental changes may favour only some populations from a pool of several different populations at a specific location, and maybe other changes would favour different populations.
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- Härnström, Karolina, 1980, et al.
(författare)
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Tropical phytoplankton community development in mesocosms inoculated with different life stages
- 2007
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 346, s. 75-88
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Tidskriftsartikel (refereegranskat)abstract
- Many diatom species have the ability to form benthic resting stages, but the importance of these stages as a supply for planktonic blooms is uncertain. A mesocosm study was carried out in December 2005 to January 2006 in Mangalore, India. Mesocosms were inoculated with various combinations of benthic and/or planktonic cells, sampled from the coastal SE Arabian Sea, and the development of the planktonic community was followed. Diatoms dominated the phytoplankton community in all mesocosms, irrespective of inoculum. The most significant differences among inoculum types were altered species composition, and the timings of the maximum cell abundances, which lagged behind in the sediment mesocosms. Populations of Thalassiosira were initiated by both plankton and benthic propagules. Taxa known from temperate coastal areas to seed bloom by benthic propagules, such as Chaetoceros and Skeletonema, were predominantly seeded by planktonic cells in this experiment; this implies differential seeding strategy within the same species at different latitudes. The species assemblage encountered in the plankton and sediment was similar, which indicates that the benthic resting stages seed an autochthonous phytoplankton flora in the area. High species diversity in all inoculated mesocosms was maintained throughout the experimental period, although the actual number of species was fewer at the end. The hydrographic conditions and timing of formation, survival, and germination of diatom resting stages in SE Arabian Sea are discussed.
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| 10. |
- Rehnstam-Holm, Ann-Sofi, 1959-, et al.
(författare)
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Association between phytoplankton and Vibrio spp. along the southwest coast of India : a mesocosm experiment
- 2010
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Ingår i: Aquatic Microbial Ecology. - 0948-3055 .- 1616-1564. ; 58:2, s. 127-139
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Tidskriftsartikel (refereegranskat)abstract
- We report the results from a mesocosm study investigating the interrelationship between microalgae and vibrios. The mesocosms were inoculated with plankton, plankton + sediment, or sediment. We followed the diatom bloom and increases in the abundance of Vibrio spp. and V parahaemolyticus in conjunction with several environmental variables in all mesocosms and at a reference site. The dominating diatom genera were also identified. Temperature, salinity, and pH were nearly invariant in the mesocosms and did not contribute to the results. The principal environmental variables that correlated to vibrio abundance were total bacterial plate counts, phosphorus and ammonia (positive relationship), and oxygen and silica (negative). Nitrate, total bacterial counts and chlorophyll a (chl a) did not correlate with vibrio growth. The highest diatom abundances were followed by increases in vibrios in all mesocosms. This was also observed in field sampling. Together, these results suggest that diatom blooms could support Vibrio spp. growth. V parahaemolyticus was initially favoured by sediment. The contribution of V parahaemolyticus to the total bacterial population was low, on average 0.5 %, but constituted a rather high proportion of the vibrio population in the mesocosm systems, i.e. on average 18 %. Some of the identified diatom genera, e.g. Chaetoceros and Skeletonema, were negatively correlated to vibrios, while Coscinodiscus was positively correlated. The results indicate that phytoplankton blooms, when recorded as high levels of chl a, should be used with caution as predictors for future vibrio epidemics, since the origin of the chl a might have a significant effect on vibrio abundance.
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