ALBERT

Notes: Abstract The growth rate and maximum yield of Skeletonema costatum (Grev.) Cleve in batch culture were inhibited by dissolved lead at concentrations of 0.05 to 10.0 μg Pb l-1. Growth rate, maximum yield, and respiration cell-1 decreased and photosynthesis cell-1 and cell volume increased in response to increased lead concentration in the medium. At 0.1 and 1.0 μg Pb l-1, the chlorophyll a:carbon and protein:carbon ratios did not significantly differ from the control and the increased cellular chlorophyll a, carbon and protein observed at these concentrations reflect an increased cell volume. However, at 10.0 μg Pb l-1, associated with an increase in cell volume, the chlorophyll a:carbon ratio was significantly lower and the protein:carbon ratio was significantly higher than in the control, reflecting a changed cellular chemical composition. The rates of cell division and dark respiration decreased relative to photosynthesis and to carbon and protein production, resulting in an alteration of the cellular chemical composition.

Notes: Abstract The phosphorus metabolism of Pyrocystis noctiluca Murray (Schuett) 1886 has characteristics which may enhance its potential for success in orthophosphate impoverished waters. The steady-state phosphate uptake rates were equal in the light and dark, and were directly proportional to both the phosphorus cell quota and the cell division rate. In contrast, nutrient-saturated uptake rates were multiphasic, faster in the light than the dark, 2 to 4 orders of magnitude greater than steady-state rates, and were inversely proportional to both the phosphorus cell quota and the cell division rate. These uptake characteristics suggest that P. noctiluca may take up phosphate coincidently at their typically low ambient concentrations as well as to exploit episodic nutrient events in nature. Cell division rates were a hyperbolic function of the ambient orthophosphate concentration. The shortest doubling time was 8.7 d, the phosphate concentration at half the maximum division rate was 0.15 μM and the threshold, concentration for cell division was ca 0.05 μM PO 4 3- . Division rates of P. noctiluca in the ocean are much faster than predicted from the measured ambient orthophosphate concentrations. Since this dinoflagellate has high naturally occurring alkaline phosphatase activities, and can utilize organic-P compounds, we suggest that organic-P can be as important as orthophosphate in supporting the observed division rates of P. noctiluca in the sea.

Notes: Abstract Phosphate depleted Pyrocystis noctiluca (Murray) Schuett 1895 has at least one phosphomonoesterase (EC 3:1:3:1) which is triphasic between 0.1 and 222 μmol P. The enzyme has a broad temperature range with maximum activity at 50 °C and a Q10 of 1.4 to 1.5. A break in the Arrhenius plot at 35 °C implies the enzyme is membrane-bound. Cytological staining of whole cells and cell fractionation studies (showing 26 times higher specific activity in the particulate compared with the cytoplasmic fraction) suggest the enzyme is plasmalemma-bound. The enzyme has an absolute metal requirement which would be satisfied by Mg++ but not Mn++, Zn++, Fe++, or Co++ at seawater concentrations. Alkaline phosphatase is a stable enzyme whose activity is not altered by inhibitors of protein synthesis. Orthophosphate inhibition of enzyme activity was largely eliminated in the presence of these inhibitors. Apparently, a protein induced by PO4 3-, rather than PO4 3- itself, inhibits alkaline phosphatase. Cell-free alkaline phosphatase can hydrolyze a variety of phosphate esters and linear polymers of inorganic phosphorus as well as disolved organic phosphorus from tropical oceanic waters. These same hydrolysable organic and inorganic phosphorus compounds support the axenic culture growth of P. noctiluca, suggesting that naturally occurring hydrolysable organic phosphorus compounds may also support the growth of this alga.

Notes: Abstract In the Chesapeake Bay estuary there are persistent seasonal frontal and interfrontal regions that serve to deliver and retain different phytoplankton populations. The “patchiness” of phytoplankton, both in total chlorophyll a concentrations and in species compositions and abundances, is shown to be causally related to density flow forcing which results in these frontal and interfrontal regions. The delineation of these regions by on-line, two-dimensional profiling of density isopleths serves to identify stations within these regions for biological and chemical sampling as opposed to sampling on an arbitrary geographical grid. It is possible, by superposition of nutrient and organism concentration isopleths upon salinity isopleths, to infer conservative and non-conservative features of the system.

Notes: Abstract Photosynthate incorporation into lipids, low molecular weight compounds, polysaccharides and proteins by individual phytoplankton species isolated from natural populations is described. This sensitive method uses serial solvent extraction and liquid scintillation counting and gives results indentical to those obtained from filtering large numbers of cells from suspension. The time course of incorporation of 14C into these polymers for algae isolated from estuarine and coastal populations shows (i) considerable differences in the carbon metabolism among species, (ii) the pattern of incorporation by any individual species may not reflect that of the phytoplankton community and (iii) significant reallocation of cell carbon among carbon pools and net protein synthesis at night. This technique permits the in-situ carbon metabolism of individual species to be examined.

Notes: Abstract Species-specific rates of photosynthetic carbon uptake (P), chlorophyll a content and P versus irradiance (P-I), have been measured for cells of Pyrocystis noctiluca and P. fusiformis isolated from natural populations collected in the euphotic zone within and below the surface mixed layer in the Sargasso Sea. These same measurements and the assay for ribulose bis-phosphate carboxylase (RuBP-Case), have been made for cultures of P. noctiluca in a 12 h L: 12 h D photoperiod at 9 different constant or at changing light intensities. In nature chl a cell-1 was constant throughout the euphotic zone. The photosynthetic capacity (Pmax), of cells captured below the surface mixed layer was lower by a factor of 10 compared with cells collected from the surface mixed layer. The Pmax for P. noctiluca collected and incubated within the surface mixed layer was the same as for cell cultures grown under high light, non nutrient-limiting conditions, suggesting that photosynthesis in the natural system was not nutrient limited. In laboratory cultures under constant low light intensities, chl a cell-1 increased by a factor of 5 while both Pmax and RuBPCase activity decreased by a factor of ca 4 compared with high light intensities. In changing light intensities both Pmax and RuBPCase activities were decreased by factors of 4 during low light intervals while chl a cell-1 approached a constant intermediate value. The change in chl a cell-1 in response to prolonged exposure to constant low light intensities was first order with a rate constant of 0.33 d-1. For all irradiance conditions in culture, the P-I dependence could be described by the simple Michaelis-Menten formula. The ratio of Pmax to KI, (the light intensity where P=Pmax/2) was a constant with a Coefficient of Variation of 12%: The constancy of this ratio, the parallel changes in RuBPCase activity with Pmax and the constant chl a cell-1 in the Sargasso Sea imply that for P. noctiluca and presumably P. fusiformis in nature, a dark enzymatic step rather than changes in photosynthetic pigment concentrations may regulate the photosynthetic capacity in the changing photic environment.

Notes: Abstract Vertical and horizontal distributions of 3 larval stages of the oyster Crassostrea virginica were measured concurrently with phytoplankton species compositions, phytoplankton size distributions and physical hydrographic parameters in tributaries of the Chesapeake Bay (USA) during the oyster spawning seasons of 1980 and 1981. The superposition of the biological distributions upon the physical hydrographic data provide instantaneous distributions of the entire system which are consistent with the upstream transport of oyster larvae. Oyster larvae distributions in the Choptank River and its Broad Creek and Tred Avon River tributaries can be described in terms of three contiguous regions: (1) a common spawning region, (2) an intermediate, upstream transport region and (3) a seed bed region where major spat set occurs. The phytoplankton species compositions and abundances in the size fraction less than 10 μm in the tributary system during the transport were sufficient to supply optimum growth requirements of developing larvae. The transport proposed can explain the 30 yr record of consistently higher spat set success in one tributary, Broad Creek, relative to an adjoining tributary, the Tred Avon River. This may be a general mechanism whereby oysters maintain reproductive success and emigrate to seed bed regions in the Chesapeake Bay.

Notes: Abstract Algal and bacterial biomass and production were measured in the plankton, platelet ice and congelation ice communities at one station in McMurdo Sound, Antarctica during September and October 1986. Bacterial abundances and particulate organic carbon and nitrogen were 10 to 100 times greater in the plankton than in the sea ice, whereas the chlorophyll a concentrations in the plankton and sea ice microbial communities (SIMCO) were similar Rates of both light-limited and light-saturated photosynthesis and daily primary production were 2 to 6 times greater in the plankton than in the SIMCO. Bacterial growth rates ranges from 0.7 to 1.5 d-1 in all three communities; however, because of the greater bacterial biomass in the plankton, bacterial production was 15 to 20 times higher there than in the SIMCO. These results suggest that during the early austral spring, planktonic production contributes significantly to total production in ice-covered environments.

Notes: Abstract Diel patterns of photosynthesis were measured for two polar diatoms (Coscinodiscus sp. and Porosira pseudodenticulata) collected in September 1985 from McMurdo Sound, Antarctica, and four temperate dinoflagellates (Gonyaulax hyalina, Gymnodinium splendens, Dinophysis caudata, and Glenodinium sp.) collected in July 1985 and January 1986 from the Southern California Bight, California, USA. For phytoplankton incubated under three combinations of photoperiod and irradiance, distinct diel patterns of light-saturated (P max) and light-limited (P L ) photosynthesis were found for (i) different species isolated from the same environment, and (ii) polar diatoms and temperate dinoflagellates. The time of day when the maximum rate of P max occurred was influenced by both irradiance and daylength for the polar diatoms but not by daylength for three out of four temperate dinoflagellates. The range of values of the ratio of maximum to minimum rates of photosynthesis (P max:P min) was similar for polar diatoms and temperate dinoflagellates. The results of this study suggest that changes in irradiance or photoperiod could influence species-specific patterns of photosynthesis in nature. As a consequence, in light-limited environments differential reproductive success could result from these diel patterns, and ultimately be reflected in temporal and spatial differences in community structure.