Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea

Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20–23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles

Quantitative ultrastructural changes associated with lead-coupled luxury phosphate uptake and polyphosphate utilization

Quantitative electron microscopy (stereology) was used to assess the ultrastructural response of three algae representative of the classes Chlorophyceae, Cyanophyceae, and Bacillariophyceae to lead-coupled polyphosphate degradation. The organisms were exposed to a culture medium concentration of 20 ppb Pb for 3 hr at the time of luxury phosphate uptake and subsequently transferred to phosphorus and lead-free medium. A differential sensitivity was observed as follows: Plectonema > Scenedesmus > Cyclotella . In Plectonema and Scenedesmus , detrimental cytological changes were observed when the polyphosphate relative volume dropped below 0.5%, which was approximately the P-starvation level of polyphosphate. Few significant ultrastructural changes were observed in Cyclotella after one week in P-deficient medium. At this time, the relative volume of polyphosphate was still 1.5%. Although a few significant ultrastructural changes occurred with phosphate deprivation, the greatest numbers of changes occurred in cells that had been exposed to a short-term (3 hr) low level of Pb. Changes in the relative volume of polyphosphate in all three organisms suggest that Plectonema and Scenedesmus have higher phosphate nutrient requirements than Cyclotella . The ecological implications of metal sequestering by polyphosphate are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48065/1/244_2005_Article_BF01054908.pd

Bulk sediment and diatom silica carbon isotope composition from coastal marine sediments off East Antarctica

Organic carbon occluded in diatom silica is assumed to be protected from degradation in the sediment. δ13C from diatom carbon (δ13C(diatom)) therefore potentially provides a signal of conditions during diatom growth. However, there have been few studies based on δ13C(diatom). Numerous variables can influence δ13C of organic matter in the marine environment (e.g., salinity, light, nutrient and CO2 availability). Here we compare δ13C(diatom) and δ13C(TOC) from three sediment records from individual marine inlets (Rauer Group, East Antarctica) to (i) investigate deviations between δ13C(diatom) and δ13C(TOC), to (ii) identify biological and environmental controls on δ13C(diatom) and δ13C(TOC), and to (iii) discuss δ13C(diatom) as a proxy for environmental and climate reconstructions. The records show individual δ13C(diatom) and δ13C(TOC) characteristics, which indicates that δ13C is not primarily controlled by regional climate or atmospheric CO2 concentration. Since the inlets vary in water depths offsets in δ13C are probably related to differences in water column stratification and mixing, which influences redistribution of nutrients and carbon within each inlet. In our dataset changes in δ13C(diatom) and δ13C(TOC) could not unequivocally be ascribed to changes in diatom species composition, either because the variation in δ13C(diatom) between the observed species is too small or because other environmental controls are more dominant. Records from the Southern Ocean show depleted δ13C(diatom) values (1–4 ‰) during glacial times compared to the Holocene. Although climate variability throughout the Holocene is low compared to glacial/interglacial variability, we find variability in δ13C(diatom), which is in the same order of magnitude. δ13C of organic matter produced in the costal marine environment seems to be much more sensitive to environmental changes than open ocean sites and δ13C is of strongly local nature

Diatoms, dissolved silica and biogenic silica dynamics in the Scheldt estuary

info:eu-repo/semantics/publishe