Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)

Coccolithophores are key components of phytoplankton communities, exerting a critical impact on the global carbon cycle and the Earth’s climate through the production of coccoliths made of calcium carbonate (calcite) and bioactive gases. Microzooplankton grazing is an important mortality factor in coccolithophore blooms, however little is currently known regarding the mortality (or growth) rates within non-bloom populations. Measurements of coccolithophore calcite production (CP) and dilution experiments to determine microzooplankton (≤63 µm) grazing rates were made during a spring cruise (April 2015) at the Central Celtic Sea (CCS), shelf edge (CS2), and within an adjacent April bloom of the coccolithophore Emiliania huxleyi at station J2. CP at CCS ranged from 10.4 to 40.4 µmol C m−3 d−1 and peaked at the height of the spring phytoplankton bloom (peak chlorophyll-a concentrations ∼6 mg m−3). Cell normalised calcification rates declined from ∼1.7 to ∼0.2 pmol C cell−1 d−1, accompanied by a shift from a mixed coccolithophore species community to one dominated by the more lightly calcified species E. huxleyi and Calciopappus caudatus. At the CCS, coccolithophore abundance increased from 6 to 94 cells mL−1, with net growth rates ranging from 0.06 to 0.21 d−1 from the 4th to the 28th April. Estimates of intrinsic growth and grazing rates from dilution experiments, at the CCS ranged from 0.01 to 0.86 d−1 and from 0.01 to 1.32 d−1, respectively, which resulted in variable net growth rates during April. Microzooplankton grazers consumed 59 to >100% of daily calcite production at the CCS. Within the E. huxleyi bloom a maximum density of 1986 cells mL−1 was recorded, along with CP rates of 6000 µmol C m−3 d−1 and an intrinsic growth rate of 0.29 d−1, with ∼80% of daily calcite production being consumed. Our results show that microzooplankton can exert strong top-down control on both bloom and non-bloom coccolithophore populations, grazing over 60% of daily growth (and calcite production). The fate of consumed calcite is unclear, but may be lost either through dissolution in acidic food vacuoles, and subsequent release as CO2, or export to the seabed after incorporation into small faecal pellets. With such high microzooplankton-mediated mortality losses, the fate of grazed calcite is clearly a high priority research direction

Amino acid uptake of Prochlorococcus spp. in surface waters across the South Atlantic Subtropical Front

To test the hypothesis that surface-living Prochlorococcus spp. (Pro) cyanobacteria metabolism declines towards the boundaries of its natural habitat, a latitudinal transect of surface waters was sampled from the centre of the Southern Atlantic Gyre (SAG, 20 to 35° S) to the South Subtropical Frontal Zone (SSFZ, 35 to 45° S). Along this transect, amino acid uptake rates of Pro, Synechococcus spp. (Syn) and an average bacterioplankton cell were determined using 35S-methionine precursor and flow-cytometry sorting, with methionine uptake rate as an index of cellular metabolic activity. Methionine and possibly other amino acids were a very minor nutrient source for Syn, while their contribution to Pro production was significant. Contrary to expectations, the mean methionine uptake rate per Pro cell in the SSFZ was about 3 times higher than in the SAG. The uptake rates per unit Pro biomass were equal to or higher than that of an average bacterioplankton cell in both the SAG and SSFZ. About 20 and 5% of total bacterioplankton consumption of amino acids could be assigned to Pro in the SAG and SSFZ, respectively. Methionine and leucine turnover rates were 3.5 and 3 times higher in the SSFZ than in the SAG, respectively. These results suggest that Pro remained highly metabolically active and acquired more methionine at its habitat boundaries, despite higher rates of bacterioplankton activity and therefore greater competition, as well as exposure to deep water mixing, low light and low temperature conditions

Aspects of grazing behaviour of the marine dinoflagellate Oxyrrhis marina, Dujardin

SIGLEAvailable from British Library Document Supply Centre- DSC:DX180744 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Bacterioplankton of low and high DNA content in the suboxic waters of the Arabian Sea and the Gulf of Oman: abundance and amino acid uptake

Amino acid uptakes by bacterioplankton of low DNA (LNA) and high DNA (HNA) content, populating the oxygen minimum zone (OMZ: <5 µM O2) and adjacent oxygen-depleted waters (5 to 50 µM O2), were determined using a 35S-methionine precursor and flow cytometric sorting. The HNA cells were further differentiated into low light scatter (HNA-ls) and high cell light scatter (HNA-hs) groups. Total bacterioplankton methionine uptake strongly correlated (r > 0.998, p < 0.0001) with leucine incorporation into protein and with microbial glucose uptake, suggesting that bacterioplankton growth was controlled by dissolved organic matter, and that methionine uptake could be used as a general estimate for the metabolic activity of bacterioplankton. The variation in methionine uptake depended on the prokaryote group rather than on ambient oxygen concentration, e.g. the numerically dominant LNA cells took 3 to 5 times less precursor than the HNA cells. A percentage of the LNA cells with double the amount of DNA was proposed as an incubation-independent index of growth of the cells in the G2 stage of the cell cycle. The vertical profiles of the percentage of LNA cells in G2 showed pronounced peaks at 300 to 600 m in the OMZ that did not correlate with peaks of either total bacterioplankton abundance or productivity. The present paper underlines the importance of bacterioplankton group studies in the OMZ since high microbial cell abundance does not necessarily mean high metabolic activity and other mechanisms, such as resilience to mortality pressure, have to be investigated

Latitudinal changes in the standing stocks of nano- and picophytoplankton in the Atlantic Ocean

The latitudinal distributions of picoeukaryote phytoplankton (PEUK), coccolithophores (COCCO), cryptophytes (CRYPTO) and other nanoeukaryote phytoplankton (NEUK) were studied in the Atlantic Ocean between 49°N and 46°S in September–October 2003 and April–June 2004 by flow cytometry. Phytoplankton abundance and carbon (C) biomass varied considerably with latitude and down through the water column. Abundance and C biomass of all eukaryotic groups studied were highest in North and South Atlantic temperate waters and in the Mauritanian Upwelling off the west coast of Africa, where the total C biomass of eukaryotic phytoplankton smaller than 10 μm reached almost 150 mg C m−3. Phytoplankton in the Equatorial Upwelling region was concentrated well below the surface at 50–80 m, with total C biomass in this layer being approximately 4 times that in the mixed layer. The North and South Atlantic Gyres supported much lower eukaryotic phytoplankton C biomass, with total eukaryote C biomass only reaching 2–3 mg C m−3, peaking below 100 m. Of the four eukaryote groups studied, the PEUK were the most abundant, reaching densities of up to 40,000 cells cm−3. They often contributed between 25% and 60% of total C biomass, particularly in the deep chlorophyll maxima of the different oceanic regions and also in the South Atlantic temperate waters, both in austral spring and autumn. NEUK also contributed significantly to C biomass. They generally dominated in the mixed layer, where they contributed 65–85% of total C biomass in the subtropical gyres and in North Atlantic temperate waters. CRYPTO and COCCO were generally less abundant. CRYPTO attained highest abundance in the Southern Temperate waters of over 500 cells cm−3 on both cruises. COCCO were often undetectable but on the European continental shelf abundance reached up to 2600 cells cm−3 during AMT 14. The C biomass standing stock of eukaryotic phytoplankton (<10 μm) for the Atlantic Ocean as a whole was estimated to be 80 million tonnes C during AMT 13, approximately one-third of total phytoplankton C biomass in the Atlantic Ocean

Differential microbial uptake of dissolved amino acids and amino sugars in surface waters of the Atlantic Ocean

Nitrogen bioavailability is considered to limit the productivity of oceanic oligotrophic gyres, the largest biomes on Earth. In order to assess the microbial requirement for small organic nitrogen molecules in these and other waters, the microbial uptake rates of amino acids (leucine, methionine and tyrosine) and amino sugars (glucosamine and N-acetyl-glucosamine) as well as glucose were compared using a bioassay technique of radiotracer dilution. The bioassays were carried out on four mid-Atlantic meridional transects spanning a latitudinal range from 60°N to 42°S. The mean concentrations of both bioavailable N-acetyl-glucosamine and glucose in the gyres were 1 nM, four times higher than the mean leucine concentration. Despite its lower concentration, the mean turnover time of leucine in the gyres of 15 h was 90 and 9 times shorter than the turnover time of N-acetyl-glucosamine and glucose, respectively. In addition, among amino acids, leucine was taken up in the gyres at a rate of 1.5 times faster than methionine and 2.5 times faster than tyrosine. Hence, oceanic bacterioplankton as a community showed a clear preference for amino acids, particularly leucine, compared with amino sugars. The preferential uptake of amino acids to sugars challenges the concept of microbial nitrogen or carbon limitation in the open ocean

High rate of uptake of organic nitrogen compounds by Prochlorococcus cyanobacteria as a key to dominance in oligotrophic oceanic waters

Direct evidence that marine cyanobacteria take up organic nitrogen compounds in situ at high rates is reported. About 33% of the total bacterioplankton turnover of amino acids, determined with a representative [35S]methionine precursor and flow sorting, can be assigned to Prochlorococcus spp. and 3% can be assigned to Synechococcus spp. in the oligotrophic and mesotrophic parts of the Arabian Sea, respectively. This finding may provide a mechanism for Prochlorococcus' competitive dominance over both strictly autotrophic algae and other bacteria in oligotrophic regions sustained by nutrient remineralization via a microbial loop

Dynamics of ribulose 1,5-bisphosphate carboxylase/xxygenase gene expression in the coccolithophorid Coccolithus pelagicus during a tracer release experiment in the northeast Atlantic

We report a pronounced diel rhythm in ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) gene expression in a natural population of the coccolithophorid Coccolithus pelagicus sampled during a Lagrangian experiment in the Northeast Atlantic. Our observations show that there is greater heterogeneity in the temporal regulation of RubisCO expression among planktonic chromophytes than has been reported hitherto

Mesoscale distribution of dominant bacterioplankton groups in the northern North Sea in early summer

A case study was performed to evaluate the potential of a combination of flow cytometry, cell sorting and fluorescence in situ hybridisation (FISH) for mesoscale monitoring of dominant bacterioplankton groups. In June 1999, the spatial distribution of phylogenetically characterised bacterioplankton groups in an area of 150 x 350 km in the northern North Sea was studied in conjunction with blooms of phytoplankton including coccolithophores. The bacterial cells were enumerated using flow cytometry and 3 groups were defined on the basis of cellular light scatter, nucleic acid and protein content. The phylogenetic composition of cells sorted from those 3 groups was analysed using FISH with a restricted set of rRNA targeted oligonucleotide probes. Cells with high nucleic acid and high protein content were mainly affiliated to the alpha- proteobacterial genus Roseobacter. Members of the Cytophaga- Flavobacterium cluster consistently accounted for the majority of cells in the high nucleic acid and low protein group; and members of the gamma-proteobacterial SAR86 cluster were always present in significant amounts among the cells with low nucleic acid and low protein content. The composition of bacteria within the groups was remarkably conservative in 13 randomly selected samples, while the concentration of the groups varied considerably on the 10 to 100 km scale. The bacterial groups formed patches of high abundance; these were spatially separated and could remain traceable for 2 to 3 d. The distribution of bacterioplankton groups did not correlate with distribution of either chlorophyll a (chl a), or phytoplankton groups (small coccolithophores and picoeukaryotic algae) or physical parameters such as temperature and salinity. It seems unlikely therefore that currently used remotely sensed parameters may be used as proxies of bacterioplankton group concentration at basin scales. However, this case study proves that a shipboard survey conducted over 4 to 6 d is effective for identifying and monitoring patches of certain bacterioplankton groups

Prokaryoplankton standing stocks in oligotrophic gyre and equatorial provinces of the Atlantic Ocean: evaluation of inter-annual variability

Temporal changes of prokaryoplankton in three different provinces of the Atlantic Ocean were examined between 1996 and 2004. The abundance and integrated biomass of three prokaryote groups (Prochlorococcus spp., Synechococcus spp. and other prokaryoplankton) were used to detect standing stock changes in the northern and southern oligotrophic gyres and in the equatorial region. Mean cell concentrations (±standard error of the mean) of Prochlorococcus spp., Synechococcus spp. and other prokaryoplankton above the nitracline in the northern oligotrophic gyre were 1.2×105 (±0.08), 5.0×103 (±1.22) and 0.9×106 (±0.03) cells mL-1, respectively. Similar concentrations of 1.2×105 (±0.06) Prochlorococcus mL-1, 1.9×103 (±0.29) Synechococcus mL?1 and 0.7×106 (±0.03) other prokaryoplankton mL-1 were measured in the southern oligotrophic gyre, with higher concentrations of all prokaryote groups in equatorial waters. Integrated biomass (±standard error of the mean) of Prochlorococcus spp. above the nitracline was 173 (±21) mg C m-2 in the northern oligotrophic gyre, 190 (±14) mg C m-2 in the southern oligotrophic gyre and 141 (±15) mg C m-2 in the equatorial region. Synechococcus spp. biomass was lower in each of the three provinces (18 (±2), 17 (±4) and 32 (±5) mg C m-2, respectively). The data showed no statistically significant inter-annual variability in Prochlorococcus or Synechococcus abundance or integrated biomass above the nitracline in any of the provinces. The abundance and biomass of the remaining prokaryoplankton were variable, but these variations could not be ascribed to seasonal differences and did not follow a clear inter-annual trend. In light of results presented here, recommendations on the frequency and spatial resolution of sampling needed to characterise province-scale temporal variability of prokaryoplankton communities have been suggested. <br/