Populations of the toxic dinoflagellate Karenia brevis that remain near the benthos in deep shelf water in the Gulf of Mexico could be the source for toxic bloom occurrences near shore. A biophysical dynamic simulation model and migrating drifters were used to assess whether such 'seed populations' could persist in nature. The vertical migration responses of plankton to an exclusively benthic nutrient source and light limitation would result in near-benthic behavioral trapping of a slowly growing population in conditions found on the West Florida Shelf (WFS). The model in- dicated that for a 50 m deep bottom, a 2-m-thick layer of ≥2 µmol NO3 - /NO2 - fluxing from the benthos was the minimum needed to permit growth for dark- adapted K. brevis in an oligotrophic water column. Growth rates depended more on the duration of expo- sure to nutrients than on concentration; a 1-m-thick nutrient layer sustained minimum growth levels inde- pendently of the nutrient distri bution at depths ≤40 m. Field experiments using Autonomous Behaving La- grangian Explorer drifters (ABLEs) that exhibited bio- mimetic vertical migration responses to the external environment demonstrated a benthically-oriented movement pattern in response to natural light and cues correlated with elevated near-benthic nutrients. Aver- age measurements of nutrients and light from the bot- tom 2 m of the water column in a potential bloom- forming region of the WFS were higher than the model-generated requirements for growth, suggesting that coastal nutrient distributions could support a ben- thic population offshore. Under upwelling conditions, such populations could be advected inshore to frontal convergence zones and form toxic 'red tide' blooms.

Zooplankton and their phytoplankton prey form the basis of the marine food web, yet historically it has been difficult to discern species-specific trophic interactions. Molecular techniques provide opportunities to obtain taxonomic data where the traditional methodologies for gut content analysis lack resolution. The large subunit gene of RubisC/O, rbcL , was utilized as a molecular marker for the identification of prey species in calanoid copepods. Clone libraries were generated from DNA extracted from seawater and whole copepods during a transect cruise on the northern Gulf of Mexico shelf. Sequence data analysis provided evidence of diatoms, nanoplankton-sized chlorophytes, and cyanobacteria in DNA extracted from whole copepods. These data demonstrate that rbcL can be a useful marker for the identification of copepod phytoplankton prey. Combining the described approach with quantitative techniques such as quantitative PCR will provide opportunities for the assessment of species-specific predator–prey interactions.

Observations of near-bottom populations of Karenia brevis suggest that these cells may derive nutrients from the sediment–water interface. Cells undergoing a metabolic-mediated migration may be in close proximity to enhanced concentrations of nutrients associated with the sediment during at least a fraction of their diel cycle. In this study, the growth, uptake and assimilation rates of ammonium, nitrate, and urea by K. brevis were examined on a diel basis to better understand the potential role of these nutrients in the near-bottom ecology of this species. Three strains of K. brevis, C6, C3, and CCMP 2229, were grown under 12:12 light dark cycle under 30μmol photonsm−2s−1 delivered to the surface plain of batch cultures. Nitrogen uptake was evaluated using 15N tracer techniques and trichloroacetic acid extraction was used to evaluate the quantity of nitrogen (N) assimilated into cell protein. Growth rates ranged from a low of 0.12 divisionsday−1 for C6 and C3 grown on nitrate to a high of 0.18 divisionsday−1 for C3 grown on urea. Diurnal maximum uptake rates, ρmax, varied from 0.41pmol-N cell−1h−1 for CCMP 2229 grown on nitrate, to 1.29pmol-N cell−1h−1 for CCMP 2229 grown on urea. Average nocturnal uptake rates were 29% of diurnal rates for nitrate, 103% of diurnal uptake rates for ammonium and 56% of diurnal uptake rates for urea. Uptake kinetic parameters varied between substrates, between strains and between day and night measurements. Highest maximum uptake rates were found for urea for strains CCMP2229 and C3 and for ammonium for strain C6. Rates of asmilation into protein also varied day and night, but overall were highest for urea. The comparison of maximal uptake rates as well as assimilation efficiencies indicate that ammonium and urea are utilized (taken up and assimilated) more than twice was fast as nitrate on a diel basis.

Light and nutrient availability change throughout dinoflagellate diel vertical migration (DVM) and/or with sub-population location in the water column along the west Florida shelf. Typically, the vertical depth of the shelf is greater than the distance a sub-population can vertically migrate during a diel cycle, limiting the ability of a sub-population to photosynthetically fix carbon toward the surface and access nutrients sub-surface. This project investigated changes of Karenia brevis (C.C. Davis) G. Hansen et Moestrup intracellular carbon, nitrogen, internal nitrate (iNO3), free amino acid (FAA), and total lipid concentrations in high-light, nitrate-replete (960μmolquantam−2s−1, 80μM NO3), and high-light, nitrate-reduced (960μmolquantam−2s−1, <5μM NO3) mesocosms. The nitrate-reduced mesocosm had a slowed cell division rate when compared to the nitrate-replete mesocosm. Minimum intracellular carbon, nitrogen, iNO3, FAA, and total lipid concentrations during the largest surface sub-population aggregations led to the conclusion that daughter cells resulting from cell division received unequal shares of the parental resources and that this inequality influenced migration behavior. Nutrient reduced daughter cells were more strongly influenced by light and phototaxis for carbon production than their replete same cell division sister cells during vertical migration thus rapidly increasing the fulfillment of constituents through photosynthesis. Vertical migration was consistent with an optimization scheme based on threshold limits through utilization or formation of photosynthate. We propose a simplified conceptual model describing how K. brevis is transported along the benthos of the west Florida shelf from off-shore to on-shore. Dynamic carbon thresholds are also suggested for future DVM modeling efforts on K. brevis populations transported between nitrogen replete and nitrogen reduced environmental conditions.

The internal lipid, carotenoid, and toxin concentrations of Karenia brevis (C. C. Davis) Gert Hansen and Moestrup are influenced by its ability to use ambient light and nutrients for growth and reproduction. This study investigated changes in K. brevis toxicity, lipid class, and carotenoid concentrations in low‐light, nitrate‐replete (250 μmol quanta · m−2 · s−1, 80 μM NO3); high‐light, nitrate‐replete (960 μmol quanta · m−2 · s−1, 80 μM NO3); and high‐light, nitrate‐reduced (960 μmol quanta · m−2 · s−1, <5 μM NO3) mesocosms. Reverse‐phase HPLC quantified the epoxidation state (EPS) of the xanthophyll‐cycle pigments diadinoxanthin and diatoxanthin, and a Chromarod Iatroscan thin layer chromatography/flame ionization detection (TLC/FID) system quantified changes in lipid class concentrations. EPS did not exceed 0.20 in the low‐light mesocosm, but increased to 0.65 in the high‐light mesocosms. Triacylglycerol and monogalactosyldiacylglycerol (MGDG) were the largest lipid classes consisting of 9.3% to 48.7% and 37.3% to 69.7% of total lipid, respectively. Both lipid classes also experienced the greatest concentration changes in high‐light experiments. K. brevis increased EPS and toxin concentrations while decreasing its lipid concentrations under high light. K. brevis may mobilize its toxins into the surrounding environment by reducing lipid concentrations, such as sterols, limiting competition, or toxins are released because lipids are decreased in high light, reducing any protective mechanism against their own toxins.

Many laboratories have solely used the Wilson isolate to physiologically characterize the harmful algal bloom (HAB) dinoflagellate Karenia brevis (C. C. Davis) G. Hansen et Moestrup. However, analysis of one isolate may lead to misinterpretations when extrapolating measurements to field populations. In this study, pulse‐amplitude‐modulated chlorophyll fluorometer (PAM‐FL) relative electron transport rate (ETR), Fv/Fm, and chl were compared with traditional techniques, such as 14C photosynthesis versus irradiance (P–E) curves, DCMU [3‐(3′,4′‐dichlorophenyl)‐1,1‐dimethyl urea] Fv/Fm, and extracted chl. The DCMU and PAM‐FL values of Fv/Fm (r2 = 0.51) and chl (r2 = 0.58) were in good agreement. There was no correlation between 14C and PAM‐FL α, Pmax, and β parameters because PAM‐FL ETR was only a relative measurement. The PAM‐FL techniques were then used to investigate P–E curves, quantum yield of PSII (Fv/Fm), and chl from 10 K. brevis isolates to determine whether one or all isolates would better represent the species. Comparisons were made with a radial photosynthetron, which allowed for controlled conditions of light and temperature. Isolate α, Pmax, and β varied between 0.097 and 0.204 μmol e− · m−2 · s−1 · (μmol quanta · m−2 · s−1)−1, 80.41 and 241 μmol e− · m−2 · s−1, and 0.005 and 0.160 μmol e− · m−2 · s−1 · (μmol quanta · m−2 · s−1)−1, respectively. Either carbon limitation and/or bacterial negative feedback were implicated as the cause of the P–E parameter variability. Furthermore, these results directly contradicted some literature suggestions that K. brevis is a low‐light‐adapted dinoflagellate. Results showed that K. brevis was more than capable of utilizing and surviving in light conditions that may be present on cloudless days off Florida.

Behavior, growth, and production are integral in the life history of Karenia brevis, an autotrophic, dinoflagellate HAB species, and are important variables in modeling blooms in the Gulf of Mexico. This study compares swimming speeds, growth rates, and photosynthetic responses of recent isolates of K. brevis (specifically the Apalachicola – APA, Manasota – MAN, and Jacksonville – JAX strains) over a range of light intensities and temperatures. Strain swimming speeds were similar and remained fairly constant from 17 to 30°C, but decreased markedly at 13°C. Photosynthetic responses of the strains to different acclimated temperatures had opposite trends with APA exhibiting higher electron transport rates (ETR) at higher temperatures and MAN exhibiting higher ETR at lower temperatures. In the light experiments, the cells’ internal physiological state (represented by photosynthetic yield, ETR, and neutral lipid reserves) and swimming capabilities were examined in the dark after 6h incubations in the radial photosynthetron. For all strains, at initial incubation light intensities swimming speed decreased and ETR increased. As incubation light intensities increased, ETR decreased and swimming speed increased. At the highest incubation light intensities, ETR and swimming speed decreased. Neutral lipids followed a pattern similar to ETR, only lipids peaked after ETR at a light intensity that corresponded to the increase in swimming speed. The results suggest that cells may partition energy selectively depending on the needs of the cell. Information was combined to characterize a generalized species response to light and temperature ranges.

This paper considers evidence on whether deregulation of single-buyer Producer Boards is likely to yield net benefits to producers, relevant industries and the New Zealand economy. It assumes some familiarity with industry structures and the ongoing debate. The discussion focuses on the static and dynamic effects of the statutory single buyer powers of the Dairy, Apple & Pear and Kiwifruit Boards, and concludes that on balance, the benefits of deregulation are expected to significantly outweigh the risks posed. The paper also considers the implications of the cooperative industry structures inherent in the producer boards for dairy, apples and pears, and kiwifruit, noting evidence that the cooperative payment systems of Producer Boards impose an economic cost.