Microbial dynamics during the decline of a spring diatom bloom in the Northeast Atlantic (original) (raw)
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The Plymouth Student Scientist, 2009
Phytoplankton is the main driver of ocean net primary production (Falkowski et al., 1998) and a dominant force behind biogeochemical cycling in the ocean. It is a component of one of the oldest and best described virus-host relationships (e.g. Suttle et al., 1990). Viruses have typically been viewed as pathogens of marine organisms but it has become clear that they also play a critical role in biogeochemical processes in marine systems, themselves falling into the category of dissolved organic matter (DOM) (Wilhelm & Suttle, 1999). Viruses play a large part in carbon (Middelboe & Lyck, 2002), sulphur (Hill et al., 1998) and iron cycling (Poorvin et al., 2004) in the world‟s oceans. Earth‟s climate has warmed by approximately 0.6°C during the last 100 years. The rate of warming has doubled in the second half of the century (Houghton, 2001). This rapid change has been attributed to the impact of anthropogenic activities on the atmosphere. Climate change is already affecting marine eco...
Deep Sea Research Part II: Topical Studies in Oceanography, 1993
Bacterial biomass increased five-fold in the euphotic zone (from 450 to 2250 mgC m 2 ) in response to the spring phytoplankton bloom in the eastern North Atlantic Ocean (Lat. 47°N, Long. 20°W) in 1989. Bacterial biomass accounted for about 20-30% of the particulate organic carbon (POC) above 50 m and a somewhat larger fraction in the layer below. Bacterial production averaged about 30% of primary production and remained rather constant while the primary production varied from 600 to 1500 mgC m -2 day -1 in response to event-scale changes in irradiance. Thus bacterial production varied from 15 to 80% of the concurrent primary production, with peaks occurring on overcast days when photosynthesis was low. Bacterial production in both the euphotic zone and the layer immediately below appeared to respond to the meteorologicallydriven variations in photosynthesis with a time lag of 3--4 days, consistent with estimates of turnover rates of 0.2 day t. In the upper layer incorporation of dissolved free amino acids supported about 20% of the production. The bacterial carbon demand at peak production required subsidies of carbon from the bulk POC and/or DOC pools. In the lower layer, decomposition of the vertical flux of sinking POC may have supported about half the mean production. Our bacterial production estimates for the 50-150 m layer are consistent with vertical flux estimates from drifting sediment traps and support other observations in suggesting that very large amounts of primary production pass through the DOC pool on short time-scales.
Uncoupling of bacteria and phytoplankton during a spring diatom bloom in the mouth of the Yellow Sea
Marine Ecology Progress Series, 1994
Bacterial abundance, production, and environmental parameters were investigated to study the distribution of bacterial variables and interrelationships between bacteria and phytoplankton along a transect from the southwestern tip of the Korean Peninsula to the axis of the Yellow Sea in April 1991 The study area showed a tidally induced turbidity maximum in the middle region of the transect. The turbidity maximum had lower phytoplankton abundance, primary production, and bacterial production than the adjacent waters. Diatom blooms were observed in the inner bay and in waters outside of the turbidity maximum. Bacterial abundance and production showed relatively large variations along the transect from 3 to 32 X 10' I-' and from undetectable to 11.9 pg C 1" d-l, respectively. Bacterial and phytoplankton variables did not correlate significantly (p z 0.12). Further, depth-integrated bacterial production over the euphotic zone comprised less than 4 O/o of primary production, suggesting that bacteria and phytoplankton were not closely coupled during the study period. The uncoupling seemed to be unrelated to phytoplankton community structure. Strong tidal mixing, which would mix the organic matter produced in the euphotic zone into the deeper water column, possibly coupled with mass sinking of phytoplankton to the bottom seemed to cause low substrates level and unbalanced growth for bacteria in the euphotic zone and thereby the observed uncoupling of bacteria from phytoplankton. Further, strong tidal mixing seemed to facilitate the bacterial use of sinking carbon in the aphotic zone.
Marine Ecology Progress Series, 1989
Recently upwelled water from the southern Benguela upwelling system was incubated in a 60 l microcosm for 43 d under simulated in situ conditions, to follow the development and activity of the heterotrophic microplanktonic community associated with phytoplankton growth and decay. The initial bacterial population (40 pg C 1-l), dominated by small rods (V = 0.198 pm3) and large cocci (P = 0.142 l~n73), with Vibrionaceae as the domlnant plateable strain, exhibited slow turnover times for added I4C-labelled substrates (R = 5.7 h 10%ells-l). Net bacterial growth was exponential (0 016 h-') during phytoplankton growth (12 pg C I-' h-', Days 0 to 4). At maximum phytoplankton and bacterial biomass (1330 and 136 pg C 1-' respectively, Day 4) Pseudomonadaceae dominated the plateable isolates; bacterial turnover times for 14C-substrates were rapid (glucose: 1.5 h 106 cells-', alanine: 0.49 h 106 cells-', glutamate: 0.29 h 106 cells-'), suggesting a close coupling between phytoplankton growth and the ab~lity of bacteria to utilise dissolved organic carbon (PDOC) substrates. Bacterial biomass was reduced to < l 5 pg C 1-' by Day 9, due to diminished availability of PDOC during phytoplankton senescence and predation by microflagellates which developed in the microcosm (<5 pg C 1-' up to Day 4, 96 pg C 1-' on Day 8). After phytoplankton senescence (Day 10) detrital carbon stimulated exponential growth (0.021 h-') of a second bacterial community (max. biomass: 231 pg C 1-' on Day 25) dominated by small cocci (P = 0.009 pm3) and large rods (V = 0.672 with Flavobactenaceae as the dominant plateable bacteria. As this community exhibited no uptake of added I4C-labelled substrates, we surmise that it was exploiting POC which dominated carbon resources at this time. Estimates of bacterial production calculated from net growth rates were ca 50 to 97 % higher than values based on ~m e t h~l-~~] thymidine incorporation (TTI). These differences may be due to inadequate DNA extraction procedures, large numbers of bacteria without thymidine transport systems, or isotope dilution. Empirically determined conversion factors to correct for these differences fell within the range of 1.6 to 46 X 106 cells mol-' TTI.
Environmental Microbiology, 2000
As agents of mortality, viruses and nanoflagellates impact on picoplankton populations. We examined the differences in interactions between these compartments in two French Atlantic bays. Microbes, considered here as central actors of the planktonic food web, were first monitored seasonally in Arcachon (2005) and Marennes-Oléron (2006) bays. Their dynamics were evaluated to categorize trophic periods using the models of Legendre and Rassoulzadegan (1995) as a reference framework. Microbial interactions were then compared through 48h-batch-culture experiments performed during the phytoplankton spring bloom, identified as herbivorous in Marennes and multivorous in Arcachon. Marennes was spatially homogeneous compared to Arcachon. The former was potentially more productive, featuring a large number of heterotrophic pathways, while autotrophic mechanisms dominated in Arcachon. A link was found between viruses and phytoplankton in Marennes, suggesting a role of virus in the regulation of autotroph biomass. Moreover, the virus-bacteria relation was weaker in Marennes, with a bacterial lysis potential of 2.6% compared with 39% in Arcachon. The batch experiments (based on sizefractionation and viral enrichment) revealed different microbial interactions that corresponded to the spring-bloom trophic interactions in each bay. In Arcachon, where there is a multivorous web, flagellate predation and viral lysis acted in an opposite way on picophytoplankton. When together they both reduced viral production. Conversely, in Marennes (herbivorous web), flagellates and viruses together increased viral production. Differences in the composition of the bacterial community composition explained the combined flagellate-virus effects on viral production in the two bays.
Marine Ecology Progress Series, 2003
The possible influence of viral infection on respiration rates in marine microbial pelagic communities was assessed by means of 3 experiments on respiration rate with viral concentrate addition on single-species cultures of Mantoniella sp. and Micromonas pusilla and another 3 on natural microplankton communities (organisms < 200 µm) from the Kattegat Sea (Åstol) and the Baltic Sea. Coastal surface seawater samples were taken during cruises of the RVs 'Ancylus' and 'Argos' during winter and spring 2000. Approximately 50 to 70 l of seawater were concentrated by ultrafiltration. The experiments were started by adding a viral particle concentrate to a container with algae or a natural microplankton community; a control container was kept free of the viral concentrate addition. Oxygen concentration determinations were carried out on each treatment and control to measure respiration rates throughout the incubation period. The in vivo chlorophyll a fluorescence was also monitored as an indication of algal infection. The rates of respiration indicated that the addition of the viral particle concentrate affected the respective metabolisms of the Mantoniella sp. and Micromonas pusilla cultures as well as natural microplankton communities. Viral infection decreased the Mantoniella sp. respiration rate (by 96%) and increased the Micromonas pusilla respiration rate (by 235%). Hence, if our results can be extrapolated to nature, then, at least in a bloom situation, the fate of primary production and carbon fluxes could be strongly modulated by viral infection. The addition of a viral particle concentrate to the microplankton community generated complex responses in terms of respiration rates, which increased (by 84%) or remained similar to the controls. Our results suggest that viral infection of microplanktonic organisms could be one of the factors significantly modifying pelagic carbon fluxes.
Microbial Ecology, 2002
We analyzed the strength of phytoplankton±bacterioplankton coupling by comparing the rate of particulate (PPP) and dissolved primary production (DPP) with bacterial carbon demand (BCD) in four contrasting marine regions: offshore and coastal waters of the Southern Ocean, a coastal area of the NE Atlantic, and a coastal±offshore transect in the NW Mediterranean. We measured bacterial heterotrophic production (BHP) and estimated BCD from a literature model. Average phytoplanktonic percent extracellular release [PER = DPP/(DPP + PPP)] was 18±20% in the Antarctic (offshore and coastal, respectively), 16% in the NW Mediterranean, and 7% in the NE Atlantic. A signi®cant inverse relationship was found between PER and total system productivity with pooled data. On average BHP amounted to <5% of total primary production in all regions.
Biogeochemical controls on bacteria in the Atlantic Ocean
Little is known about bacterial dynamics in the oligotrophic ocean, particularly about cultivable bacteria. We examined the abundance of total and cultivable bacteria in relation to changes in biogeochemical conditions in the eastern Atlantic Ocean with special regard to Vibrio spp., a group of bacteria that can cause diseases in human and aquatic organisms. Surface, deep water and plankton (<20 µm, 20-55 µm and >55 µm) samples were collected between 50 • N and 24 • S. Chlorophyll-a was very low (<0.3 µg l −1 ) in most areas of the nutrient-poor Atlantic, except at a few locations near upwelling regions. In surface water, dissolved organic carbon (DOC) and nitrogen (DON) concentrations were 64-95 µM C and 2-10 µM N accounting for ≥90 % and ≥76 % of total organic C and N, respectively. DOC and DON gradually decreased to ∼45 µM C and <5 µM N in the bottom water. In the surface layer, culture independent total bacteria and other prokaryotes represented by 4 -6-diamidino-2-phenylindole (DAPI) counts, ranged mostly between 10 7 and 10 8 cells l −1 , while cultivable bacterial counts (CBC) and Vibrio spp. were found at concentrations of 10 4 -10 7 and 10 2 -10 5 colony forming units (CFU) l −1 , respectively. Most bacteria (>99 %) were found in the nanoplankton fraction (<20 µm), however, bacterial abundance did not correlate with suspended particulates (chlorophyll-a, particulate