Robert E. Reed

Comparison of sinking velocity, swimming velocity, rotation and path characteristics among six marine dinoflagellate species

Six marine dinoflagellate species representing a range of equivalent spherical diameters between 12 and 36 μm were examined for several characteristics that influence their translation velocity. Sinking velocities estimated by three independent techniques and applied to swimming and narcotized cells generally agreed, and followed the cell-size relationships previously reported for diatoms. Dinokont sinking and swimming velocities both decreased with increasing surface area: volume ratio, but a small desmokont deviated from the dinokont relationships. Sinking velocities influenced the relative ascent/descent capabilities of a species. The swim:sink ratio decreased as equivalent spherical diameter increased to 25 μm and then remained constant at 7.6, despite further increases in cell size. This relationship suggests a minimum required swimming capability relative to cell size. The swim:sink ratio increased with increasing surface area:volume ratio for all the surveyed species. Out observations of decreasing cell rotation:translation ratio and increasing cell drag with increasing cell size supported the hypothesis that the dinoflagellate flagellar apparatus generates maximum swimming velocity at intermediate cell sizes. However, an alternate analysis supported the hypothesis that swimming velocity increases with cell size and that variations among genera are due to subtle differences in the basic dinoflagellate propulsion system. A three-dimensional helical path index provided a more realistic estimate of the actual translation velocity (along the helix axis) during diel vertical migration when applied as a correction factor to the more typically measured helix velocity (along the helix) of a given dinoflagellate.

GEOTAXIS/PHOTOTAXIS AND BIOCHEMICAL PATTERNS IN HETEROCAPSA (=CACHONINA) ILLDEFINA (DINOPHYCEAE) DURING DIEL VERTICAL MIGRATIONS

Two separate experiments with Heterocapsa (=Cachonina) illdefina Herman et Sweeney, one with and the other without water volume replacement, were performed in a 250‐L laboratory mesocosm (45‐cm diameter × 150‐cm height) to examine how diel vertical migration (DVM) relates to taxis sign and strength and to cellular biochemical state. Although only the cell population grown with water volume replacement maintained a division per day over the course of the experiment, periodic measurements during both experiments demonstrated that cells aggregating at the surface during the light period generally were deficient in all measured biochemical constituents compared to cells obtained from a midcolumn depth. More specifically, H. illdefina cells that aggregated at the surface during the light period in both experiments exhibited weakened positive geotaxis but strengthened positive phototaxis and were very deficient in lipid and free amino acid compared to midcolumn cells. Cells sampled at midcolumn during the light period exhibited similar but weaker taxes changes compared to surface samples, and geotaxis strength was inversely correlated with cell diameter, cellular DNA and protein content, and RNA/DNA ratio. In comparison, published data on Gymnodinium breve Davis, a harmful algal bloom species, showed that cells aggregating at the surface during the light period generally exhibited weakened negative geotaxis and strengthened positive phototaxis and were very deficient in lipid and chl a compared to midcolumn cells. Although the persistent tendency toward negative geotaxis was weaker in midcolumn subpopulations throughout the day, its strength was inversely correlated with cell diameter and cellular lipid content. The combined results for both species support a revised conceptual model of optimized DVM in autotrophic marine dinoflagellates incorporating generalized expressions of taxis and biochemical state of individual cells.

Re-evaluation of the relationship between Pfiesteria and estuarine fish kills

In recent years, fish kills along the mid-Atlantic US coast have become an increasing problem, with important economic, environmental, and public health implications (Glasgow and others 1995; Burkholder 1998; Grattan and others 1998; Haselow and others 2001; Shoemaker and Hudnell 2001). Research into the causes of these fish kills is ongoing, and monitoring and surveillance programs have been instituted to investigate (among other factors) the role of actively toxic forms of two known species within the dinoflagellate genus Pfiesteria (Burkholder and others 1995, 2001a; Steidinger and others 1996; Burkholder and Glasgow 1997; Glasgow and others 2001b). In their recent analyses of the relationship between Pfiesteria and fish kills, Burkholder and others (1999) and Stow (1999) stated, as others have noted previously (Meyer and Barclay 1990), that it is difficult to establish the causes of estuarine fish kills at the ecosystem level. The evaluation of Burkholder and others (1999) was based on the biology and toxic behavior of Pfiesteria, as well as empirical sampling of field fish kill events then in progress, as supported by laboratory analyses of samples collected from each fish kill. In contrast, Stow (1999) conducted theoretical probability calculations and argued that information demonstrating the presence of toxic Pfiesteria during fish kills was insufficient to prove that there was a cause-and-effect

Examining Material Transport in Dynamic Coastal Environments: An Integrated Approach Using Field Data, Remote Sensing and Numerical Modeling

Coastal environments are critical ecological systems and offer vital resources and functions to societies worldwide. As a major interface between terrestrial and ocean environments, coastal water bodies (rivers, estuaries, bays and coastal margins) provide key ecological services and are the major conduit and processors of terrestrially derived particulate and dissolved material as they are transported to the ocean. Consequently, coastal environments have been shown to play a major role in global bio-geochemical cycles and provide critical habitat for a host of marine species. Globally, these important environments are under considerable pressure from high population densities, increasing growth rates and are particularly vulnerable from the effects of projected climate change such as sea level rise and increased storm events. Despite their importance, significant gaps remain in our understanding of how these environments will respond to climate change, increasing human population, land use changes, and over exploitation of natural resources. This lack of understanding is due in part to the difficulties in developing effective monitoring and analysis programs using only a single measurement approach that is limited in its spatial and temporal coverage.

Phytoplankton quantum yield measured on minute time scales in situ

We measure simultaneously, on sub-minute time scales, the downwelling irradiance spectra and the vertical attenuation spectra for downwelling irradiance of a contained phytoplankton culture while the culture is exposed to the full spectrum of an in situ light treatment. This technique incorporates miniature, fiber optical spectrometers and twin self-contained, underwater photosynthesis apparatus (SUPA). One SUPA serves as the reference, with filtered culture media in the exposure chamber. The other SUPA contains the phytoplankton sample in the exposure chamber. Using the assumptions that irradiance reflectance is small in the SUPA and that upwelling vertical attenuation equals downwelling vertical attenuation in the culture, it is possible to approximate the flux absorbed by the phytoplankton by the product of downwelling irradiance and downwelling vertical attenuation. The concurrent measurements of net carbon uptake and net oxygen production in SUPA, each minute, support calculations of net quantum yield of the phytoplankton in situ. Results from a field study using the red tide organism Gymnodinium breve illustrate the ability to quantify the effects high, fluctuating irradiance exposure near the surface.

Short-period photophysiological responses of Thalassiosira pseudonana during photoacclimation to near-surface irradiance

A two-day deployment of the self-contained underwater photosynthetic apparatus (SUPS) was conducted to examine the effects of high and variable natural irradiance on the optical properties and primary productivity of the diatom Thalassiosira pseudonana. Study objectives included the determination of short time response in the cycling of diadinoxanthin (DD) and diatoxanthin (DT), and associated changes in the rates of primary production, and quantum yield, and in cell absorption characteristics over a tow day period. A nutrient replete, lowlight acclimated diatom culture was placed in SUPA and in a collocated culture reservoir fitted with a quartz top. The instrument was deployed in shallow water in Sarasota Bay under fluctuating, high irradiance typical for June. A pigment sampling series reveals a correlation of DD to DT cycling with exposure to high irradiance. Net quantum yields, determined by cell absorption spectra and minute-to-minute SUPA net primary productivity values, exhibit high values initially which decay to lower values upon exposure to high light. Short time scale changes in quantum yield are observed due to changes in DD/DT cycling and fluctuating irradiance.