Berit R. Heimdal

Blooms of phytoplankton including Emiliania huxleyi (Haptophyta). Effects of nutrient supply in different N : P ratios

Abstract Enclosures containing natural phytoplankton communities were fertilized with nitrate and phosphate in duplicates in three different ratios (16 : 5, 16 : 1, 16 : 0.2) in order to initiate blooms of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler under controlled environmental conditions. The development of the phytoplankton community was in addition followed in two unfertilized enclosures and in the surrounding sea water. The phytoplankton succession during the experiment (22 April - 29 May 1992) was mainly dinoflagellates-diatoms-E. huxleyil Phaeocystis sp. in all fertilized enclosures, but the importance of the different species/groups were different in enclosures with different N : P ratio. Diatom numbers decreased when the N : P ratio increased in the nutrient supply. From an initial concentration of 0.09 109 cells m−3 E. huxleyi increased to concentrations between 20 109 cells m−3 and 37 109 cells m−3 in the enclosures supplied with nitrate and phosphate in aN: P ratio of 16 : ...

Production of DMSP and DMS during a mesocosm study of an Emiliania huxleyi bloom: influence of bacteria and Calanus finmarchicus grazing

We investigated the influence of bacteria and metazooplankton on the production of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) during blooms of Emiliania huxleyi (Lohmann) Hay and Mohler in seawater mesocosms. The phytoplankton succession was marked by the rapid collapse of an initial Skeletonema costatum (Greville) Cleve bloom followed by a small E. huxleyi bloom. The collapse of the diatom bloom was accompanied by an increase in concentrations of dissolved DMSP (DMSPd) and bacterial abundance and activity (as determined by the thymidine incorporation technique). The increase in bacterial activity was followed by a rapid decrease in DMSPd concentrations which remained low for the rest of the experiment, even during the subsequent collapse of the E. huxleyi blooms. The absence of DMSPd and DMS peaks during the declining phase of the E. huxleyi blooms was attributed to the high bacterial activity prevailing at that time. The influence of metazooplankton grazing on DMSP and DMS production was investigated by adding moderate (24 mg dry weight m-3) and high (520 mg dry weight m-3) concentrations of Copepodite Stage V and adults of Calanus finmarchicus to two of four filtered (200 μm mesh net) enclosures during the E. huxleyi blooms. The addition of C. finmarchicus, even in high concentrations, had no apparent effect on the dynamics of E. huxleyi, suggesting that the copepods were not grazing significantly on nanophytoplankton. The addition of copepods in high concentrations favored an accumulation of chlorophyll a and particulate DMSP. These results suggest that copepods were preying on the herbivorous microzooplankton which, in turn, was controlling the biomass of nanophytoplankton. DMS production was also enhanced in the enclosure with maximum metazooplankton biomass, suggesting that the grazing of C. finmarchicus on microzooplankton containing DMSP may contribute to DMS production. These results provide strong support to the emerging idea that bacteria and metazooplankton grazing play a dominant role in determining the timing and magnitude of DMS pulses following phytoplankton blooms.

Seasonal development of phytoplankton at a high latitude oceanic site

A three-year time series of hydrography, nutrients, chlorophyll, a, Secchi depth and phytoplankton composition taken at the Ocean Weather Station Mike (OWSM)(66°N, 2°E) was investigated. The pattern in the seasonal development of phytoplankton biomass was very similar in all three years, despite some differences in the magnitude of the spring bloom. From January to March typical winter conditions prevailed with low water mass stability, high and homogeneously depth distributed nutrient concentrations, and phytoplankton biomass below 0.05 mg m−3 chlorophyll a. During April a pre-bloom situation still prevailed, characterised by still low, but now steadily increasing biomass. The spring bloom started in May concurrent with incipient thermal stratification. Maximum phytoplankton biomass was observed between mid May and mid June, but the Chl a concentrations never exceeded 2.8 mg m−3. By July the biomass had decreased to pre-bloom levels. Generally nutrients were not depleted at this time. The decrease in phy...

Effects of increased concentration of nitrate and phosphate during a springbloom experiment in mesocosm

A mesocosm experiment was carried out in the early spring of 1991 (19 February to 20 March) in Raunefjorden, Norway. The experiment consisted of four enclosures of which two were initially supplied with nitrate and phosphate corresponding to an increase in concentration of 6 and 0.2 μM, respectively. Effects of an increased concentration of nitrate and phosphate on the development of the annual phytoplankton springbloom was investigated. Measurement of light, temperature, salinity, nutrients, chlorophyll (chl) a, primary production, phytoplankton enumeration and identification were performed daily or every other day. Average daily irradiance during the experiment was low (4.8 mol · m−2 · d−1). Maximum concentrations of biomass (chl a) and primary production were 11.5 μg chl a · 1−1 and 109 μg C ·1−1 · d−1. The initial phytoplankton community in all enclosures were dominated by diatoms, mainly Skeletonema costatum (Grev.) Cleve, and maximum cell number of this species was 11.2 · 106 1−1. After 1 wk, the diatoms were replaced by flagellates, due to silicate deficiency (< 2 μM). The fertilized enclosures were dominated by the haptophyte Phaeocystis cf. pouchetii (18 · 106 cells 1−1), and the non-fertilized enclosures were dominated by unidentified flagellates, together with cryptophytes and prasinophytes. High abundance of choanoflagellates and microzooplankton were also registered in the fertilized enclosures (3.3 · 106 1−1 and 11 · 106 1−1, respectively). This indicates that the microzooplankton may have controlled the growth of flagellates by grazing in the fertilized enclosures. The effect of an increased concentration of nitrate and phosphate was not an increase in biomass (chl a) or primary production, but a change in the species composition. The species composition changed from a diatom community dominated by S. costatum to a flagellate community dominated by P. cf. pouchetii. These results also suggest that major limiting factors for the biomass and primary production have been silicate deficiency, low irradiance and temperature.

Representation of Emiliania huxleyi in phytoplankton simulation models. A first approach

Abstract Emiliania huxleyi (Lohmann) Hay et Mohler is represented as a state variable in a general phytoplankton model that also includes one diatom group and one phytoplankton group encompassing the ‘other flagellates’ than E. huxleyi. Furthermore, three nutrient variables (nitrogen-, phosphorus-, and silicon-nutrients) are included. The main features of the model are that E. huxleyi has been given a higher growth affinity for orthophosphate than the two other groups, and that diatoms, besides being dependent on silicon, have been given a higher maximal growth rate than the two flagellate groups. The output from the simulation model is compared with observations made in mesocosm experiments loaded with different amounts of nitrate and orthophosphate. The simulated E. huxleyi is not able to grow as well as the real E. huxleyi, and this applies especially to the experiments low in orthophosphate. It is difficult to account for the high observed numbers of E. huxleyi in terms of the available inorganic otho...

The 1992 Norwegian Emiliania huxleyi experiment. An overview

Abstract Todays rapid increase in the worlds population density and industrial activity raises public anxiety for imminent climate change. Predictions based on General Circulation Models of the ocean/atmosphere system play a key role in this debate. Lack of quantitative and qualitative data on the biogeochemical fluxes limits, however, the value of such models.

Emiliania huxleyi. Chemical composition and size of coccoliths from enclosure experiments and a Norwegian fjord

Abstract Single Emiliania huxleyi (Lohmann) Hay et Mohler, type A, coccoliths harvested from mesocosm enclosures (June 1991) with different nutrient regimes, and the Norwegian fjord, Samnangerfjorden (October 1992), were analyzed with- X-ray microanalysis in a Transmission Electron Microscope (TEM). The average molar Ca : C ratios of the free coccoliths varied within a range of 0.65–1.0, dependent on growth condition of E. huxleyi. Free coccoliths sampled from enclosures with high production or density of E. huxleyi, had Ca : C ratios near 1. Coccoliths sampled from Samnangerfjorden, and enclosures with low production or cell density the Ca : C ratios were close to 0.7. The excess of carbon in the coccoliths compared to CaC03 is probably due to organic matter, mainly carbohydrates. It is concluded that the amount of organic matter associated with coccoliths of E. huxleyi, is dependent on the growth conditions, and carbohydrate may protect the coccoliths from dissolution. A higher Ca : C ratio (0.8 versus ...

Effects of unbalanced nutrient regime on coccolith morphology and size in Emiliania huxleyi (Prymnesiophyceae)

Single coccoliths of Emiliania huxleyi grown in mesocosm enclosures (60°16′N, 05°14′E, May–June 1991) under different N:P regimes were analysed in a scanning electron microscope. The results indicate that only E. huxleyi with Type A coccoliths was present in the enclosures. Approximately 80–90% of the total coccolith assemblages had developed normally, whilst the remainder were malformed, incompletely grown or dissolved. Severely under-calcified specimens were rare and dissolution and breakage less than 5%. The coccoliths were of larger size than normal, as has been found previously in fjords of southwestern Norway, supporting the conclusion that a local population of E. huxleyi has developed, specific to these waters. Both phosphorus and nitrogen stress caused significant changes in coccolith size and evidence of malformation was clear, particularly in the low-phosphate enclosure. Although the observations presented here concern only Type A coccoliths and it is not known how nutrient stress may affect th...

Calcifying phytoplankton in Bjørnafjorden, Norway. The prebloom situation

Abstract Various physical, chemical and biological parameters were followed over a two week period prior to the blooming of the coccolithophorid Emiliania huxleyi (Lohmann) Hay et Mohler in Bj0rnafjorden (western Norway). Total inorganic carbon concentrations and pCO2 profiles showed low values at the surface, due to freshwater influence. Such low values may be of competitive advantage for phytoplankton like coccolithophorids capable of utilising bicarbonate besides CO2 as an inorganic carbon source for growth. Low nutrient concentrations in the surface limited dense bloom formation here. Subsurface bloom formation was restricted because of the poor incident irradiance conditions. The assimilation number was low (varying between 3.16 and 15.88 mg C mg chi a −1 day−1, mean 7.82 mg C mg chi a −1 day−1). Calcification rate of E. huxleyi increased gradually over the sampling period, but did not exceed 11 % of total inorganic carbon assimilation by the end of the survey. In general the phytoplankton population...

Hydrography and hydro chemistry from March to July 1976 in Fauskangerpollen, western Norway

Abstract Hydrography and nutrients (phosphate/total P, nitrate/nitrite, and silicate) were studied at a station in Fauskangerpollen near Bergen on three days in 1976, one in March, one in May, and one in July. The surface layers were highly stable, while there were only small density gradients in deeper layers. While oxygen conditions were good in the upper layers, the bottom layers were stagnant with H2 S being produced. An inflow took place in the middle layers between March and May. Nutrient concentrations were high throughout the water column in March, but decreased in the top layers during spring due to consumption in primary production. The stagnant bottom layers acted as a ‘nutrient trap’ and had extremely high nutrient concentrations. Variations coinciding with the tidal cycle were observed, a result of change in surface level due to tidal movement, such that samples were taken relatively nearer the bottom at low tide than at high tide. This means that when samples were taken at a level with large...