Cell cycle behavior of laboratory and field populations of the Florida red tide dinoflagellate, Karenia brevis

As a component of the ECOHAB Florida Regional Field Program, this study addresses cell cycle behavior and its importance to bloom formation of the Florida red tide dinoflagellate, Karenia brevis. The cell cycle of K. brevis was first studied by flow cytometry in laboratory batch cultures, and a laboratory mesocosm column, followed by field populations over the 5-year course of the ECOHAB program. Under all conditions studied, K. brevis displayed diel phased cell division with S-phase beginning a minimum of 6 h after the onset of light and continuing for 12–14 h. Mitosis occurred during the dark, and was generally completed by the start of the next day. The timing of cell cycle phases relative to the diel cycle did not differ substantially in bloom populations displaying radically different growth rates (μ_min 0.17–0.55) under different day lengths and temperature conditions. The rhythm of cell cycle progression is independent from the rhythm controlling vertical migration, as similar cell cycle distributions are found at all depths of the water column in field samples. The implications of these findings are discussed in light of our current understanding of the dinoflagellate cell cycle and the development of improved models for K. brevis bloom growth.     

The growth dynamics of Karenia brevis within discrete blooms on the West Florida Shelf

As part of the ECOHAB: Florida Program, we studied three large blooms of the harmful bloom forming dinoflagellate Karenia brevis. These blooms formed on the West Florida Shelf during Fall of 2000 off Panama City, and during Fall 2001 and Fall 2002 off the coastline between Tampa Bay and Charlotte Harbor. We suggest that these blooms represent two different stages of development, with the 2000 and 2001 blooms in an active growth or maintenance phase and the 2002 bloom in the early bloom initiation phase. Each bloom was highly productive with vertically integrated primary production values of 0.47–0.61, 0.39–1.33 and 0.65 g C m⁻² d⁻¹ for the 2000, 2001 and 2002 K. brevis blooms, respectively. Carbon specific growth rates were low during each of these blooms with values remaining fairly uniform with depth corresponding to generation times of 3–5 days. Nitrogen assimilation by K. brevis was highest during 2001 with values ranging from 0.15 to 2.14 μmol N L⁻¹ d⁻¹ and lower generally for 2000 and 2002 (0.01–0.64 and 0.66–0.76 μmol N L⁻¹ d⁻¹ for 2000 and 2002, respectively). The highest K. brevis cell densities occurred during the 2001 bloom and ranged from 400 to 800 cells mL⁻¹. Cell densities were lower for each of the 2000 and 2002 blooms relative to those for 2001 with densities ranging from 100 to 500 cells mL⁻¹. The 2000 and 2001 blooms were dominated by K. brevis in terms of its contribution to the total chlorophyll a (chl a) pool with K. brevis accounting generally for >70% of the observed chl a. For those populations that were dominated by K. brevis (e.g. 2000 and 2001), phytoplankton C biomass (C_p,0) constituted <30% of the total particulate organic carbon (POC). However, in 2002 when diatoms and K. brevis each contributed about the same to the total chl a, C_p,0 was >72% of the POC. The fraction of the total chl a that could be attributed to K. brevis was most highly correlated with POC, chl a and salinity. Nitrogen assimilation rate and primary production were highly correlated with a greater correlation coefficient than all other comparisons.     

The use of the National Research Council of Canada's Falcon 20 research aircraft as a terrestrial analogue space environment (TASE) for space surgery research: Challenges and suggested solutions

Emergency surgery will be needed to prevent death if humans are used to explore beyond low earth's orbit. Laparoscopic surgery (LS) is envisioned as a less invasive option for space, but will induce further stresses and complicate logistical requirements. Thus, further study into the technology and physiology of LS in weightlessness is required. We recently utilized the National Research Council of Canada's Flight Research Laboratory's Falcon 20 aircraft as a terrestrial analogue space environment (TASE) for space surgery research. The Falcon 20 had never been used for this purpose nor had the involved teams collaborated previously. There were many process challenges including the lack of antecedent surgical studies on this aircraft, a requirement for multiple disciplines who were unfamiliar and geographically distant from each other, flight performance limitations with the Falcon 20, complex animal care requirements, requirements for prototypical in-flight life-support surgical suites, financial limitations, and a need to use non-flight hardened technologies. Stepwise suggested solutions to these challenges are outlined as guidelines for future investigators intending similar research. Overall, the Falcon 20 TASE, backed by the flight resources, especially the design and fabrication capabilities of the NRC-FRL, provide investigators with a versatile and responsive opportunity to pursue research into advanced medical techniques that will be needed to save lives during space exploration.     

High-temperature 29Si MAS NMR spectroscopy of anorthite (CaAl2Si2O8) and its P\bar 1-I\bar 1structural phase transition

We present ²⁹Si MAS NMR data for a well-ordered natural anorthite, obtained in situ at temperatures of from 25 to 500° C, which follow the changes in the aluminosilicate framework through the P $\bar 1$ -I $\bar 1$ structural phase transition. Pairs of peaks due to sites offset by approximately 1/2 [111] converge through the P $\bar 1$ phase and only four peaks are present above about 241° C. The variation of the peak positions with temperature and correlations based on structural data for the P $\bar 1$ and I $\bar 1$ phases allow assignment of all the MAS-NMR peaks to crystallographic sites. A Landau-type analysis gives an expression that relates the separation of pairs of con verging peaks to the local order parameter for the P $\bar 1$ -I $\bar 1$ transition, from which we determine its temperature dependence. Data for the best-constrained set of peak positions give for the order parameter critical exponent β = 0.27±0.04, consistent with previous results indicating that the P $\bar 1$ -I $\bar 1$ transition in pure anorthite is tricritical. No significant change in the ²⁹Si spin-lattice relaxation rate occurs across the P $\bar 1$ -I $\bar 1$ transition.     

BRI 0021-0214: Another Surprise at the Bottom of the Main Sequence

We report the detection of an Halpha flare on the low-luminosity M9.5 dwarf BRI 0021-0214. This star has rapid rotation, vsin&parl0;i&parr0; approximately 40 km s-1, but generally shows no significant chromospheric emission. Our detection of the flare shows that a magnetic field is present, although the level of activity at maximum is 3 times lower than the mean quiescent level in early- and mid-type M dwarfs. Based on data available in the literature, we estimate that the star is in outburst for no more than 7% of the time.     

The origin and persistence of alpine vernal ponds in mineral soils

Little is known of the processes that create and maintain vernal ponds in mineral soils in alpine environments. On the Central Plateau, Tasmania, we tested the hypotheses that vernal pond complexes on mineral soils formed in response to the underlying topography of a glacio-fluvial plain; relate to present day topography; resulted from past damming by organic accumulation; are moulded by wind. The underlying topography did not relate to the surface ponds, nor were they on steeper slopes than adjacent areas without ponds. The morphology of the ponds and the morphological and edaphic characteristics of the pond complexes and adjacent areas are consistent with an origin by organic material damming. The strongest winds orientate most ponds, rather than the aspect of the slope. Sediments were preferentially caught on sticky traps to the northeast of the ponds, away from fierce prevailing southwesterly winds. Temperature measurements and fortnightly observation showed non-concordant patterns of variation in water levels in the ponds. We deduce that the complexes of vernal ponds may have formed in previous moister conditions more favourable to organic matter accumulation, possibly in the early Holocene, and are maintained by a faster rate of accumulation of mineral and organic particles in the tussock grassland adjacent to the ponds than in the ponds themselves. © 2019 John Wiley & Sons, Ltd.     

Bearing capacity of a strip foundation on a sand layer overlying a smooth rigid stratum

The effect of a smooth rigid stratum, located beneath a dense sand layer, on the bearing capacity and settlement of surface and shallow strip footings is investigated using an advanced experimental model. A theoretical analysis is presented for the bearing capacity of surface footings. The results indicate that the bearing capacity reaches a minimum value at a specific sand-layer thickness. Any increase in the layer thickness above this value causes an increase in the bearing capacity up to that corresponding to a continuous media.Notation H= thickness of the sand layer - B= foundation width - N _q and N = bearing capacity factors for a semi-infinite layer - N _qs and N _s= bearing capacity factors for a finite layer - H _o /B= limiting depth - D _r= relative density - = angle of soil internal friction - M= model width - D= depth of surcharge - q= bearing stress, pressure applied on the footing - q _u= bearing capacity - = unit weight of sand     

Throughfall and its spatial variability in a temperate rainforest of simple structure

There are few throughfall data from southern hemisphere closed-forest, and none from Tasmanian callidendrous cool-temperate rainforest, which has a simpler structure than most primary rainforests. We determined throughfall, measured its local spatial variation, and tested its relationships with rainfall, rainfall intensity, wind speed, canopy dryness, canopy cover, and other structural variables in a cool-temperate callidendrous rainforest in Tasmania. Eighty-two percent of the precipitation was measured as throughfall, which occurred after 2.3 mm of rain fell on dry canopies. The cumulative rainfall in 25 randomly located funnel rain gauges on the forest floor varied from 160 to 567 mm. Canopy cover and other structural variables did not predict the spatial pattern of throughfall. While throughfall in rainfall events was related to rainfall amount and intensity, wind speed did not affect throughfall as a percentage of rainfall. Percentages of throughfall to rainfall over 100 for many low rainfall events may indicate a contribution of fog drip to precipitation on the forest floor. The high local spatial variability in throughfall indicates the mean moisture conditions on the forest floor may not be a good indicator of the potential for localised fire damage.     

Structural studies of imogolite and allophanes by aluminum-27 and silicon-29 nuclear magnetic resonance spectroscopy

High-resolution aluminum-27 and silicon-29 nuclear magnetic resonance spectra of natural and synthetic imogolites and allophanes obtained using high-field“magic-angle” sample-spinning (MASS) techniques indicate that the imogolite and protoimogolite components of allophanes are characterized by sharp (≈3 ppm) silicon-29 resonances at ?78±1 ppm from tetramethylsilane (in accord with Barron et al. 1982), and quite narrow (≈10 ppm at 11.7 Tesla) aluminum-27 resonances, at 5.2±1 ppm from Al(H₂O) ₆ ³⁺ (in accord with Wilson et al. 1984). However, the spectra of natural allophanes usually contain significant intensity arising from a less well defined material, characterized by a broad (≈20 ppm) silicon-29 resonance centered at ?90±2 ppm from tetramethylsilane, and a second relatively narrow (≈15 ppm at 11.7 Tesla) aluminum-27 resonance at 58.5±2 ppm from Al(H₂O) ₆ ³⁺ . Similar characteristic spectral features are exhibited by a synthetic amorphous Si:Al (1:1) gel, and presumably indicate the presence of framework aluminosilicate materials in the gel, and in most allophanes.     

A three-dimensional biophysical model of Karenia brevis dynamics on the west Florida shelf: A look at physical transport and potential zooplankton grazing controls

The development of accurate predictive models of toxic dinoflagellate blooms is of great ecological importance, particularly in regions that are most susceptible to their detrimental effects. This is especially true along the west Florida shelf (WFS) and coast, where episodic bloom events of the toxic dinoflagellate Karenia brevis often wreak havoc on the valuable commercial fisheries and tourism industries of west Florida. In an effort to explain the dynamics at work within the maintenance and termination phases of a red tide, a simple three-dimensional coupled biophysical model was used in the analysis of the October 1999 red tide offshore Sarasota, Florida. Results of the numerical experiments indicate that: (1) measured and modeled flowfields were capable of transporting the observed offshore inoculum of K. brevis to within 16 km of the coastal boundary; (2) background concentrations (1000 cells L⁻¹) of K. brevis could grow to a red tide of over 2×10⁶ cells L⁻¹ in little more than a month, assuming an estuarine initiation site with negligible offshore advection, no grazing losses, negligible competition from other phytoplankton groups, and no nutrient limitation; (3) maximal grazing pressure could not prevent the initiation of a red tide or cause its termination, assuming no other losses to algal biomass and a zooplankton community ingestion rate similar to that of Acartia tonsa; and (4) the light-cued ascent behavior of K. brevis served as an aggregational mechanism, concentrating K. brevis at the 55 μE m⁻² s⁻¹ isolume when mean concentrations of K. brevis exceeded 100,000 cells L⁻¹. Further improvements in model fidelity will be accomplished by the future inclusion of phytoplankton competitors, disparate nutrient availability and limitation schemes, a more realistic rendering of the spectral light field and the attendant effects of photo-inhibition and compensation, and a mixed community of vertically-migrating proto- and metazoan grazers. These model refinements are currently under development and shall be used to aid progress toward an operational model of red tide forecasting along the WFS.