We analyzed the cellular content of C, N, P, S, K, Mg, Ca, Sr, Fe, Mn, Zn, Cu, Co, Cd, and Mo in 15 marine eukaryotic phytoplankton species in culture representing the major marine phyla. All the organisms were grown under identical culture conditions, in a medium designed to allow rapid growth while minimizing precipitation of iron hydroxide. The cellular concentrations of all metals, phosphorus, and sulfur were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and those of carbon and nitrogen by a carbon hydrogen nitrogen analyzer. Accuracy of the HR-ICPMS method was validated by comparison with data obtained with 55 Fe radioactive tracer and by a planktonic reference material. The cellular quotas (normalized to P) of trace metals and major cations in the biomass varied by a factor of about 20 among species (except for Cd, which varied over two orders of magnitude) compared with factors of 5 to 10 for major nutrients. Green algae had generally higher C, N, Fe, Zn, and Cu quotas and lower S, K, Ca, Sr, Mn, Co, and Cd quotas than coccolithophores and diatoms. Co and Cd quotas were also lower in diatoms than in coccolithophores. Although trace element quotas are influenced by a variety of growth conditions, a comparison of our results with published data suggests that the measured compositions reflect chiefly the intrinsic (i.e. genetically encoded) trace element physiology of the individual species. Published field data on the composition of the planktonic biomass fall within the range of laboratory values and are generally close to the approximate extended Redfield formula given by the average stoichiometry of our model species (excluding the hard parts):While clearly this elemental stoichiometry varies between species and, potentially, in response to changes in the chemistry of seawater, it provides a basis for examining how phytoplankton influence the relative distributions of the ensemble of major and trace elements in the ocean.Abbreviation: HR-ICPMS, high-resolution inductively coupled plasma mass spectrometry Over the past two decades, both culture and field studies have revealed that trace metals can be important in controlling primary production and regulating the community structure of marine phytoplankton. For 1

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The steady state growth rates of three species of marine phytoplankton, Thalassiosira weisflogii, Isochrysis galbana, and Prorocentrum micans, were followed in turbidostat culture. At each growth irradiance, photosynthesis and respiration were measured by following changes in oxygen. Together with measurements of optical absorption cross sections, cellular chlorophyll, carbon and nitrogen, and excretion rates as well as knowledge of the quantum flux, the quantum requirement for growth (l/&J and photosynthesis (l/&J were calculated. Our results suggest that variations in growth rate caused by changes in irradiance may be related to changes in respiration rates relative to growth as well as changes in optical absorption cross sections for a given species. Interspecific differences in growth rate at a given irradiance are not related to changes in respiration however, but are primarily attributable to differences in optical absorption cross sections normalized to chlorophyll a and differences in chlorophyll : carbon-ratios.A basic problem in phytoplankton physiological ecology has been that of defining relationships between irradiance, photosynthesis, and growth (e.g. Eppley 1972). Although the relationship between growth and photosynthesis is fixed for a given species under nutrient-saturated, steady state growth conditions (Laws and Bannister 1980), the relationships between irradiance and photosynthesis and between photosynthesis and growth may vary between species. At least five hypotheses can be advanced to account for interspecific variations in the relationship between irradiance and growth: differences in the light-harvesting properties of different species; variations in photosynthetic machinery which result in changes in the quantum requirement of photosynthesis; differences in photosynthesis : respiration ratios; varying proportions of photosynthetically fixed carbon which is excreted or secreted; and the *chemical composition of different species influencing photosynthetic quotients.These hypotheses are not mutually exclusive, but some factors may be more impor-' This research was performed under the auspices the U.S. DOE Contract DE-AC02-76CHOOO 16. of tant in influencing the relationship between irradiance and growth than others. Here we use a simple model (Kiefer and Mitchell 1983) relating growth to irradiance in photoautotrophic organisms. The model explicitly or implicitly includes each of the aforementioned factors. Our goal here is to investigate the relative importance of these variables on growth-irradiance relationships.We compared the photosynthetic performance and growth-irradiance relationships in three species of marine phytoplankton, the diatom Thalassiosira weisflogii, the chrysophyte Isochrysis galbana, and the dinoflagellate Prorocentrum micans. All species were grown in a turbidostat under identical growth conditions in continuous irradiance to avoid any variations in photosynthetic activities and growth responses arising from nutrient limitation or photoperiodicity.We thank ...

In the marine unicellular chlorophyte, Dunaliella tertiolecta Butcher, the spectrally averaged m vivo absorption cross section, normalized to chlorophyll a (so‐called a* values), vary two‐fold in response to changes in growth irradiance. We used a kinetic approach to examine the specific factors which account for these changes in optical properties as cells photoadapt. Using Triton X‐100 to solubilize membranes, we were able to differentiate between “package” effects and pigmentation effects. Our analyses suggest that 43–49% of the variability in a* is due to changes in pigmentation, whereas 51–57% is due to the “package” effect. Further analyses revealed that changes in cell sue did not significantly affect packaging, while thylakoid stacking and the transparency of thylakoid membranes were important factors. Our results suggest that thylakoid membrane protein/lipid ratios change during photoadaptation, and these changes influence the effective rate of light harvesting per unit chlorophyll a.

There has been a widespread increase in the reporting of harmful and ‘nuisance’ algal blooms in the coastal ocean over the past few decades. On the global scale this is suspected to be a consequence of coastal eutrophication, however, on a case‐by‐case basis there is usually insufficient evidence to discriminate between the effects of human and natural causal factors. Intense blooms of the ‘Brown Tide’ unicellular algae (Aureococcus anophagefferens) have occurred sporadically since 1985 in coastal waters of Eastern Long Island and have devastated the local commercial scallop fishery. Analysis of an 11‐year time‐series dataset from this region indicates that bloom intensity is correlated with higher salinities and inversely correlated with the discharge of groundwater. Laboratory and field studies suggest that whereas salinity is unlikely to represent a direct physiological control on Brown Tide blooms, the addition of inorganic nitrogen tends to inhibit Brown Tide blooms. Budget calculations indicate that the inorganic nitrogen supply from groundwater is 1–2 orders of magnitude higher than any other external source of nitrogen for this ecosystem. Biweekly time series data collected in 1995 demonstrate that Brown Tide blooms utilize dissolved organic nitrogen (DON) for growth, as evidenced by a large decrease in DON parallel with an increase in cell abundance. On an interannual basis, bloom intensity was also positively correlated with mean DON concentrations. We hypothesize that bloom initiation is regulated by the relative supply of inorganic and organic nitrogen, determined to a large extent by temporal variability in groundwater flow. The 1980s and 1990s were characterized by exceptionally high and interannually variable groundwater discharge, associated with a large‐scale climate shift over the North Atlantic. This, coupled with the time‐lagged discharge of groundwater with high nitrate concentrations resulting from increased fertilizer use and population increase during the 1960s and 1970s, may have been a key factor in the initiation of Brown Tide blooms in 1985.