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Dinoflagellate population growth is inhibited by fluid motion, which is typically characterized by some average flow property, regardless if the flow is steady or unsteady. This study compares the effect of fully characterized steady and unsteady flow on net population growth of the red tide dinoflagellate Lingulodinium polyedrum. The unsteady flow fields were generated using oscillatory laminar Couette flow and characterized analytically to provide complete knowledge of the fluid shear exposure over space and time throughout the chamber. Experimental conditions were selected so all cells experienced a similar shear exposure regardless of their position within the chamber. Unsteady flow with maximum shears of 6.4 [s.sup.-1] and 6.7 [s.sup.-1] and an average absolute shear of 4 [s.sup.-1], comparable with levels found at the ocean surface on a windy day, resulted in higher levels of growth inhibition than for steady Couette flow with shears of 4 and 8 [s.sup.-1]. Over the parameter space studied, growth inhibition increased with increasing treatment duration (5-120 min) but was insensitive to oscillation period (60600 s) or whether the unsteady flow changed in direction. These results indicate that over the parameter space studied, unsteady flow is more inhibitory to net growth than steady flow, for the same average flow conditions, and demonstrate that flow characterization on the basis only of average flow properties is inadequate for comparing population growth in unsteady and steady flows.

Spatial abundance patterns of the heterotrophic dinoflagellate, Noctiluca scintillans, were investigated along the southeast coast of Australia to address the hypothesis that population growth of Noctiluca is driven by anthropogenic eutrophication. Abundance patterns were related to the immediate physical flow field and not the conditions conducive to growth. Noctiluca cells were advected southward with the East Australian Current, which was the dominant, transport vector for the cells in this region. Areas of population growth of Noctiluca were identified by variations in cell-size distributions. Small cells (600 [micro]m), senescent, and the end result of a long series of biological and physical processes occurring in temporally and spatially distant water masses. Small cells were therefore considered to be located closer to the region in which growth was stimulated. The proportion of small cells in the samples was significantly correlated with relatively high concentrations of chlorophyll a. Consequently, this relationship was used to show that population growth of Noctiluca may be stimulated by an increase in chlorophyll a due to sewage discharge, although the prevailing hydrological conditions determine the likelihood of such impacts. High chlorophyll a concentrations within estuaries were also found to sustain a stable but low standing stock of Noctiluca, which may seed oceanic stocks. Thus, by examining cell size rather than abundance distributions, we identified and interpreted the variance in the spatial abundance patterns of Noctiluca within a dynamic hydrological environment.

Results demonstrate that axenic cultures of Alexandrium catenella dinoflagellate although show normal growth they exhibit lower toxicity. The axenic cultures production of toxin is about one-fifth of that in nonaxenic cultures.

Results document the isolation of cDNA fragment of mitogen-activated protein kinase from the dinoflagellate Pfiesteria piscicida and its encoded product containing 428 amino acid residues matching 30 to 40% of residues of the mitogen-activated protein kinase from other organisms. Growth analysis indicates that the cDNA gene expression is correlated with growth rate and perhaps regulates cell proliferation.

The genus Alexandrium has an abnormal amino acid physiology as compared to other dinoflagellates. Three of its species, A. affini, A. minutum, and A. tamarense, were grown in batch culture of a low-nitrogen or a low-phosphate medium. The cells became smaller during the nitrogen-limiting stationary phase and increased during the long phosphate deprivation. The toxic A. minutum had the highest concentrations of free amino acids, arginine and proline and A. affini the lowest. Carbon to nitrogen ratio was the lowest in A. minutum and highest in A. tamarense.

Research has been conducted on Heterocapsa circularisquama virus. The authors have examined the growth characteristics and intraspecies host specificity of this virus via the study of interactions between the virus and H. circularisquama, and have described the results.

The potential for in situ turbulence to inhibit dinoflagellate population growth has been demonstrated by experimentally exposing dinoflagellate cultures to quantified shear flow. However, despite interest in understanding environmental factors that affect the growth of toxic dinoflagellates, little is known of the effect of shear on the growth of toxin-producing dinoflagellate species. Cultures of the dinoflagellate, Alexandrium fundyense, a producer of toxins responsible for paralytic shellfish poisoning, were exposed to quantified laminar shear generated in Couette flow for 1-24 h [d.sup.-1] over 6-8 d. Shear stress in all experiments was 0.003 N [m.sup.-2], similar to levels expected in near-surface waters on a windy day. Net population growth decreased with shear exposures [is greater than] 1 h [d.sup.-1] and became negative with exposures [is greater than] 12 h [d.sup.-1]. Cellular toxin content at the end of each experiment was measured by a receptorbinding assay that used [[sup.3]H]saxitoxin. Toxin [cell.sup.-1] of cultures sheared for [is greater than] 1 h [d.sup.-1] increased up to three times that of control cultures. Cellular toxin content increased significantly as growth rate of sheared cultures decreased. However, varying culture growth rate using irradiance had no significant effect on toxin [cell.sup.-1]. Because shear stress levels used in this study were plausible for near-surface turbulent flows, oceanic turbulence may inhibit population growth and increase cellular toxin content of A. fundyense. However, in natural populations it would be difficult to distinguish the effect of turbulence on toxin content from other influences on toxin variability, particularly if volume- or mass-specific, rather than cell-specific, measures of toxin are used.

The inhibition of NH4+ by NO3- uptake was investigated in estuarine diatoms and dinoflagellates. This was done by growing four species of phytoplankton on NO3- at several different temperatures. The impact of NH4+ additions were then assessed for all species. Results showed that in both diatoms and flagellates, NO3- uptake was reduced with increasing NH4+ concentrations. It was also shown that estimated half-inhibition concentrations were higher in diatoms than in dinoflagellates. Analysis indicates that the mechanism for NO3- inhibition may be similar across species.