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Phytoplankton are the oceans' principal source of polyunsaturated fatty acids that support the growth and reproduction of consumers such as copepods. Previous studies have demonstrated ocean acidification (OA) can change the availability of polyunsaturated fatty acids to consumer diets which may affect consumer reproduction. Two laboratory experiments were conducted to examine the effects of feeding high-pCO2-reared phytoplankton on copepod egg production, hatching success, and naupliar survival. Marine phytoplankton Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans, and Isochrysis galbana were exponentially grown in semi-continuous cultures at present (control) (400 ppm CO2, pH~8.1) and future (1,000 ppm CO2, pH~7.8) conditions and provided to Acartia tonsa copepods over 4 consecutive days as either nitrogen-limited (Exp. I) or nitrogen-depleted (Exp. II) mixed assemblage of phytoplankton. The composition of FAs in the phytoplankton diet was affected by pCO2 concentration and nitrogen deficiency; the ratio of essential fatty acids to total polyunsaturated fatty acids decreased in phytoplankton grown under high pCO2 and the mass of total fatty acids increased under nitrogen depletion. Additionally, total concentrations of essential fatty acids and polyunsaturated fatty acids in the diet mixtures were less under the high-pCO2 compared to the control-pCO2 treatments. Median egg production, hatching success, and naupliar survival were 48-52%, 4-87%, and 9-100% lower, respectively, in females fed high-pCO2 than females fed low-pCO2 phytoplankton, but this decrease in reproductive success was less severe when fed N-depleted, but fatty acid-rich cells. This study demonstrates that the effects of OA on the nutritional quality of phytoplankton (i.e., their cellular fatty acid composition and quota) were modified by the level of nitrogen deficiency and the resulting negative reproductive response of marine primary consumers., Competing Interests: The authors have declared that no competing interests exist.

The Redfield ratio of 106 carbon:16 nitrogen:1 phosphorus in marine phytoplankton is one of the foundations of ocean biogeochemistry, with applications in algal physiology, palaeoclimatology and global climate change. However, this ratio varies substantially in response to changes in algal nutrient status and taxonomic affiliation. Here we report that Redfield ratios are also strongly affected by partitioning into surface-adsorbed and intracellular phosphorus pools. The C:N:surface-adsorbed P (80-105 C:15-18 N:1 P) and total (71-80 C:13-14 N:1 P) ratios in natural populations and cultures of Trichodesmium were close to Redfield values and not significantly different from each other. In contrast, intracellular ratios consistently exceeded the Redfield ratio (316-434 C:59-83 N:1 intracellular P). These high intracellular ratios were associated with reduced N2 fixation rates, suggestive of phosphorus deficiency. Other algal species also have substantial surface-adsorbed phosphorus pools, suggesting that our Trichodesmium results are generally applicable to all phytoplankton. Measurements of the distinct phytoplankton phosphorus pools may be required to assess nutrient limitation accurately from elemental composition. Deviations from Redfield stoichiometry may be attributable to surface adsorption of phosphorus rather than to biological processes, and this scavenging could affect the interpretation of marine nutrient inventories and ecosystem models.

Pelagic primary production ( 14 C uptake) was measured 81 times between 1990 and 2013 at sites spanning the broad, shallow Northern Australian Shelf (NAS; 120−145°E) which borders the Australian continent. The mean of all areal production measurements was 1048±109 mg C m −2 d −1 (mean±95% CI). Estimates of areal primary production were correlated with integral upper-euphotic zone chlorophyll stocks (above the 50% and 20% light penetration depths) accessible to ocean color remote sensing and total water column chlorophyll standing crop, but not surface (0–2 m) chlorophyll concentrations. While the NAS is subject to a well characterized monsoonal climate regime (austral summer-NW monsoon -wet: austral winter- SE monsoon -dry), most seasonal differences in means of regional-scale chlorophyll standing crop (11–33 mg Chl m −2 for 12 of 15 season-region combinations) and areal primary production (700–1850 mg C m − day −1 for 12 of 15 season-region combinations) fell within a 3−fold range. Apart from the shallow waters of the Torres Strait and northern Great Barrier Reef, picoplankton (<2 µm size fraction) dominated chlorophyll standing crop and primary production with regional means of picoplankton contributions ranging from 45 to >80%. While the range of our post-1990 areal production estimates overlaps the range of production estimates made in NAS waters during 1960–62, the mean of post-1990 estimates is over 2-fold greater. We regard the difference to be due to improvements in production measurement techniques, particularly regarding the reduction of potential metal toxicity and incubations in more realistic light regimes. [ABSTRACT FROM AUTHOR]

The Amazon River has the largest discharge of all rivers on Earth, and its complex plume system fuels a wide array of biogeochemical processes, across a large area of the western tropical North Atlantic. The plume thus stimulates microbial processes affecting carbon sequestration and nutrient cycles at a global scale. Chromosomal gene expression patterns of the 2.0 to 156 μm size-fraction eukaryotic microbial community were investigated in the Amazon River Plume, generating a robust dataset (more than 100 million mRNA sequences) that depicts the metabolic capabilities and interactions among the eukaryotic microbes. Combining classical oceanographic field measurements with metatranscriptomics yielded characterization of the hydrographic conditions simultaneous with a quantification of transcriptional activity and identity of the community. We highlight the patterns of eukaryotic gene expression for 31 biogeochemically significant gene targets hypothesized to be valuable within forecasting models. An advantage to this targeted approach is that the database of reference sequences used to identify the target genes was selectively constructed and highly curated optimizing taxonomic coverage, throughput, and the accuracy of annotations. A coastal diatom bloom highly expressed nitrate transporters and carbonic anhydrase presumably to support high growth rates and enhance uptake of low levels of dissolved nitrate and CO2. Diatom-diazotroph association (DDA: diatoms with nitrogen fixing symbionts) blooms were common when surface salinity was mesohaline and dissolved nitrate concentrations were below detection, and hence did not show evidence of nitrate utilization, suggesting they relied on ammonium transporters to aquire recently fixed nitrogen. These DDA blooms in the outer plume had rapid turnover of the photosystem D1 protein presumably caused by photodegradation under increased light penetration in clearer waters, and increased expression of silicon transporters as silicon became limiting. Expression of these genes, including carbonic anhydrase and transporters for nitrate and phosphate, were found to reflect the physiological status and biogeochemistry of river plume environments. These relatively stable patterns of eukaryotic transcript abundance occurred over modest spatiotemporal scales, with similarity observed in sample duplicates collected up to 2.45 km in space and 120 minutes in time. These results confirm the use of metatranscriptomics as a valuable tool to understand and predict microbial community function. [ABSTRACT FROM AUTHOR]

Coccolithophores are unicellular phytoplankton that produce calcium carbonate coccoliths as an exoskeleton. E miliania huxleyi, the most abundant coccolithophore in the world's ocean, plays a major role in the global carbon cycle by regulating the exchange of CO2 across the ocean-atmosphere interface through photosynthesis and calcium carbonate precipitation. As CO2 concentration is rising in the atmosphere, the ocean is acidifying and ammonium ( NH4+) concentration of future ocean water is expected to rise. The latter is attributed to increasing anthropogenic nitrogen ( N) deposition, increasing rates of cyanobacterial N2 fixation due to warmer and more stratified oceans, and decreased rates of nitrification due to ocean acidification. Thus, future global climate change will cause oceanic phytoplankton to experience changes in multiple environmental parameters including CO2, pH, temperature and nitrogen source. This study reports on the combined effect of elevated p CO2 and increased NH4+ to nitrate ( NO3−) ratio ( NH4+/ NO3−) on E . huxleyi, maintained in continuous cultures for more than 200 generations under two p CO2 levels and two different N sources. Herein, we show that NH4+ assimilation under N-replete conditions depresses calcification at both low and high p CO2, alters coccolith morphology, and increases primary production. We observed that N source and p CO2 synergistically drive growth rates, cell size, and the ratio of inorganic to organic carbon. These responses to N source suggest that, compared to increasing CO2 alone, a greater disruption of the organic carbon pump could be expected in response to the combined effect of increased NH4+/ NO3− ratio and CO2 level in the future acidified ocean. Additional experiments conducted under lower nutrient conditions are needed prior to extrapolating our findings to the global oceans. Nonetheless, our results emphasize the need to assess combined effects of multiple environmental parameters on phytoplankton biology to develop accurate predictions of phytoplankton responses to ocean acidification. [ABSTRACT FROM AUTHOR]

Rodeo Lagoon, a low-salinity coastal lagoon in the Golden Gate National Recreation Area, California, United States, has been identified as an important ecosystem due to the presence of the endangered goby ( Eucyclogobius newberri). Despite low anthropogenic impacts, the lagoon exhibits eutrophic conditions and supports annual episodes of very high phytoplankton biomass. Weekly assessments (February–December 2007) of phytoplankton indicated diatoms, Nodularia spumigena, Chaetoceros muelleri var. muelleri, flagellated protozoa, a mixed assemblage, and Microcystis aeruginosa dominated the algal community in successive waves. Phytoplankton succession was significantly correlated ( r = 0.37, p < 0.001) with averaged daily irradiance (max = 29.7 kW m d), water column light attenuation (max = 14 m), and orthophosphate and dissolved inorganic carbon concentrations (max = 1.5 and 2920 μM, respectively). Negative effects of phytoplankton growth and decay included excessive ammonia concentrations (exceeded EPA guidelines on 77% of sampling days), hypoxia (<3 mg l dissolved oxygen), and introduction of several microcystins, all in the latter half of the year. Our one-year study suggests that this coastal lagoon is a highly seasonal system with strong feedbacks between phytoplankton and geochemical processes. [ABSTRACT FROM AUTHOR]

An immunofluorescence protocol for intracellular antigens of phytoplankton was developed empirically. Paraformaldehyde (4%) was used to fix samples of 6 h at 4° C; fixed samples can be stored in cold (-20°C) methanol for at least 1 month. We used Triton X-100, Nonidet P-40, and dimethyl sulfoxide to permeabilize the cells for antibody penetration across the cell wall and plasma membrane. After immunolabeling at room temperature, the samples were mounted on slides and could be stored at 4° C for up to 6 month without significant decay of the fluorescence. The staining was examined with an epifluorescence microscope; semiquantitative (percentage of cells with positive staining) and quantitative (staining intensity measured with an imaging system) analyses were performed. Reproducible staining was achieved for nuclear, chloroplastic, cytoplasmic, and cell surface antigens in species of Chlorophyceae, Prymnesiophyceae, Bacillariophyceae, and Dinophyceae including some field-collected samples. This protocol is advantageous to previously published protocols in that it allows relatively simple and long-term storage of fixed samples and allows staining of multiple antigens for the same sample. Although improvement on cell permeabilization is required for some species, the present protocol could prove useful for physiological or ecological studies when frequent sampling is required and immediate processing of the samples is not possible. [ABSTRACT FROM AUTHOR]

Ethmodiscus spp. is an important contributor to oceanic tropical-ooze sediments and thus might be an important transport vehicle of carbon from the ocean surface to sediments. The knowledge of its cell cycle and growth rate, which is still lacking, is necessary to evaluate the importance of Ethmodiscus in nutrient cycling and to solve the discrepancy between its high sedimentary abundance and rarity in the plankton. We used immunofluorescence of a cell cycle protein, proliferating cell nuclear antigen (PCNA), and DNA-specific staining to study the progression of the cell cycle and roughly estimate the growth rate for E. rex (Rattray) Wiseman and Hendey in the southwestern North Atlantic Ocean and Caribbean Sea in June 1994 and January 1995. During the cell division cycle, the chloroplasts appeared to synthesize DNA before the nucleus (S phase). Following the S phase, the nucleus moved from one end of the cell toward the center underneath the midline of the girdle band (G2 phase) where it divided (34 phase). During a very brief period, the parent cell split and moved apart from the girdle midline, and two new valves were produced (late M phase). The two daughter nuclei apparently remained attached at the joint of the two newly produced valves, where they appeared to be responsible for coordinating the symmetrical formation of the new valves. The morphologically complete daughter cells remained joined for a short period of time before separating into solitary cells whose nucleus was located at one end of the cell. Derived from the phase fraction curves, the duration of the cell cycle phases decreased in the order from G I, S, G2, to M. A conservative estimate of the growth rate in the study area obtained by using PCNA immunostaining was 0.39-0.46 d[SUP-1] in June and 0.15 d[SUP-1] in January. The validity and implication of the growth rate estimates are discussed. [ABSTRACT FROM AUTHOR]

Physiological rate measurements were made with Oscillatoria thiebautii (Gom.) Geitler in the subtropical north Atlantic Ocean between Spain and Bermuda during May and June of 1975. The near surface C:N fixation ratios averaged 6.5, and the cellular composition ratio was 6.2, suggesting that N[sub2] fixation is the major path of nitrogenous nutrition for this alga. Compared to other oceanic phytoplankters, it has a low affinity for orthophosphate at oceanic concentrations (K[subs] = 9.0); however, it has a high potential for utilizing phosphomonoesters (170-300 ng atoms P·μg chl a[sup-1]·h[sup-1]). Maximal photosynthesis occurred at 450-700 μ Einstein · m[sup-2]·s[sup-1], and was inhibited by full sunlight. Calculated cell division rates (ca. 180 days) suggest that relative to other phytoplankters in this oceanic region. O. thiebautii must be subjected to negligible grazing pressure. No major differences in C, N, chl a or ATP were observed between the tuft (fusiform) and puff (spherical) colonies. ATP concentrations relative to other cellular constituents varied greatly between colonies, suggesting a general inter-colony physiological variability in the open Atlantic. With increasing depth in the euphotic zane, there was no evidence for chromatic adaption. The observations that O. thiebautii represents only a small fraction of total phytoplankton biomass and that its growth rate is 10-100 times slower than that of the other indigenous phytoplankton, strongly suggest that N[sub2] fixation by this alga is a virtually insignificant component of the nitrogenous nutrition for the phytoplankton of the North Atlantic central gyre in late Spring. [ABSTRACT FROM AUTHOR]

By immunohistochemistry and immunofluorescence methods, we observed that the analog of proliferating cell nuclear antigen (PCNA) in Dunaliella tertiolecta Butcher (Chlorophyceae) was exclusively located in the nucleus. Among positively stained cells, PCNA abundance varied, being highest in S-phase cells, lower in others, and undetectable in early G1- or late M-phase cells. In exponentially growing and partially synchronized cultures, the percentage of PCNA-stained cells (% PCNA-stained cells) oscillated in the photocycle (12:12 h LD). It increased during the light period and reached a peak (75%) before the onset of the dark period when the culture was mainly (71%) in the S phase of the cell cycle. The DNA synthesis inhibitor, hydroxyurea, depressed PCNA abundance, whereas no effect was detected for the mitosis inhibitor colchicine. We conclude that PCNA in D. tertiolecta is associated with the S phase of the cell cycle where it is accumulated and functioning. PCNA was used to characterize the growth pattern of cultures grown in different media, temperatures, and growth stages. The time lag between the PCNA-stained phase and the M phase was very short in a continuous culture grown in reduced f/2 medium at 22°C and was considerably longer in the cultures grown in f/2 at 15°C. When an exponentially growing culture grew older, % PCNA-stained cells decreased. In a late stationary culture where there was no net growth, a small member of cells were still cycling through the PCNA-stained phase and cell division. In the continuous culture grown at 22°C, the duration of the PCNA-stained phase (T) was 13 h. Calculations with this T, and % PCNA-stained cells yielded a growth rate of 0.77 d[SUP-1], which was close to that obtained by cells counts (0.69 d[SUP-1]). Taken together, the results suggest that PCNA is a useful indicator of growth status and a promising cell cycle marker for estimation of species-specific growth rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] The distribution of phytoplankton communities within the Amazon River plume during peak river discharge are described. [•] Three distinct communities of phytoplankton were identified which separated largely on the basis of salinity gradients across the plume. [•] Although salintiy has a substantial influence on phytoplankton communities in the plume, the biomass and composition of each community was controlled by the availability of inorganic nitrate and nitrite. [Copyright &y& Elsevier]

Abstract: Whereas diatoms (class Bacillariophyceae) often dominate phytoplankton taxa in the Amazon estuary and shelf, their contribution to phytoplankton dynamics and impacts on regional biogeochemistry are poorly understood further offshore in the western tropical Atlantic Ocean (WTAO). Thus, relative contribution of diatoms to phytoplankton biomass and primary production rates and associated environmental conditions were quantified during three month-long cruises in January–February 2001, July–August 2001, and April–May 2003. The upper water column was sampled at 6 light depths (100%, 50%, 25%, 10%, 1% and 0.1% of surface irradiance) at 64 stations between 3° and 14°N latitude and 41° and 58°W longitude. Each station was categorized as ‘oceanic’ or ‘plumewater’, based on principal component analysis of eight physical, chemical and biological variables. All stations were within the North Brazil Current, and plumewater stations were characterized by shallower mixed layers with lower surface salinities and higher dissolved silicon (dSi) concentrations than oceanic stations. The major finding was a much greater role of diatoms in phytoplankton biomass and productivity at plumewater stations relative to oceanic stations. Mean depth-integrated bSi concentrations at the plumewater and oceanic stations were 14.2 and 3.7mmolm−2, respectively. Mean depth-integrated SiP rates at the plumewater and oceanic stations were 0.17 and 0.02mmolm−2 h−1, respectively. Based on ratios of SiP and PP rates, and typical Si:C ratios, diatoms contributed on average 29% of primary productivity at plumewater stations and only 3% of primary productivity at oceanic stations. In contrast, phytoplankton biomass (as chlorophyll a concentrations) and primary production (PP) rates (as 14C uptake rates) integrated over the euphotic zone were not significantly different at plumewater and oceanic stations. Chlorophyll a concentrations ranged from 8.5 to 42.4mgm−2 and 4.0 to 38.0mgm−2 and PP rates ranged from 2.2 to 11.2mmolm−2 h−2 and 1.8 to 10.8mmolm−2 h−2 at plumewater and oceanic stations, respectively. A conservative estimate of annual integrated SiP in offshore waters of Amazon plume between April and August is 0.59Tmol Si, based on mean SiP rates in plumewaters and satellite-derived estimates of the area of the Amazon plume. In conclusion, river plumewaters dramatically alter the silicon dynamics of the WTAO, forming extensive diatom-dominated phytoplankton blooms that may contribute significantly to the global Si budget as well as contributing to energy and matter flow off of the continental shelf. [Copyright &y& Elsevier]