David F. Millie

RAIN FOREST CANOPY COVER, RESOURCE AVAILABILITY, AND LIFE HISTORY EVOLUTION IN GUPPIES

Life history traits in guppies (Poecilia reticulata) vary geographically along a predator assemblage gradient, and field experiments have indicated that the association may be causal; guppies introduced from high predation sites to low predation sites have evolved the phenotype associated with low predation in as few as seven generations. It has long been recognized, however, that low predation sites tend to have greater forest canopy cover than high predation sites. Stream differences in canopy cover could translate into stream differences in resource availability, another theoretically potent agent of selection on life history traits. Moreover, new computer simulations indicate that the high predation phenotype would outcompete the low predation phenotype under both mortality regimes. Thus, predation alone may not be sufficient to explain the observed life history patterns. Here we show that food availability for guppies decreases as forest canopy cover increases, among six low predation streams in the ...

Optical Monitoring and Forecasting Systems for Harmful Algal Blooms: Possibility or Pipe Dream?

Monitoring programs for harmful algal blooms (HABs) are currently reactive and provide little or no means for advance warning. Given this, the development of algal forecasting systems would be of great use because they could guide traditional monitoring programs and provide a proactive means for responding to HABs. Forecasting systems will require near real‐time observational capabilities and hydrodynamic/biological models designed to run in the forecast mode. These observational networks must detect and forecast over ecologically relevant spatial/ temporal scales. One solution is to incorporate a multiplatform optical approach utilizing remote sensing and in situ moored technologies. Recent advances in instrumentation and data‐assimilative modeling may provide the components necessary for building an algal forecasting system. This review will outline the utility and hurdles of optical approaches in HAB detection and monitoring. In all the approaches, the desired HAB information must be isolated and extracted from the measured bulk optical signals. Examples of strengths and weaknesses of the current approaches to deconvolve the bulk optical properties are illustrated. After the phytoplankton signal has been isolated, species‐recognition algorithms will be required, and we demonstrate one approach developed for Gymnodinium breve Davis. Pattern‐recognition algorithms will be species‐specific, reflecting the acclimation state of the HAB species of interest.Field data will provide inputs to optically based ecosystem models, which are fused to the observational networks through data‐assimilation methods. Potential model structure and data‐assimilation methods are reviewed.

Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates

Abstract In estuarine waters, phytoplankton are exposed to rapidly changing conditions that may affect community structure and function. In this study we determined the effects of mixing, turbidity, and limiting nutrient (N) additions on natural phytoplankton growth rates and algal group-specific biomass changes. Mesocosm bioassays were used to quantify the short-term (2–3 day) responses of phytoplankton from the Neuse river estuary, NC. Growth rates were higher under static conditions in N-amended tanks, while biomass of most algal groups was higher under mixed, turbid conditions with N additions. Shifts in community composition did not follow any consistent pattern but each factor influenced phytoplankton growth, biomass, and community composition. Differing growth responses to nutrient additions, mixing, and turbidity resulted in taxonomically-distinct communities. These results highlight the complexity of phytoplankton community structuring processes in estuarine waters. The combination of biomarker quantifications and the radiolabeling method is a useful tool for assessing phytoplankton responses and offers insights into the mechanisms driving blooms and bloom species in estuarine waters.

Using absorbance and fluorescence spectra to discriminate microalgae

The utility of absorbance and fluorescence-emission spectra for discriminating among microalgal phylogenetic groups, selected species, and phycobilin- and non-phycobilin-containing algae was examined using laboratory cultures. A similarity index algorithm, in conjunction with fourth-derivative transformation of absorbance spectra, provided discrimination among the chlorophyll [Chl] a/phycobilin (cyanobacteria), Chl a/Chl c/phycobilin (cryptophytes), Chl a/Chl b (chlorophytes, euglenophytes, prasinophytes), Chl a/Chl c/fucoxanthin (diatoms, chrysophytes, raphidophytes) and Chl a/Chl c/peridinin (dinoflagellates) spectral classes, and often between}among closely related phylogenetic groups within a class. Spectra for phylogenetic groups within the Chl a/Chl c/fucoxanthin, Chl a/Chl c/peridinin, Chl a/phycobilins and Chl a/Chl c/phycobilin classes were most distinguishable from spectra for groups within the Chl a/Chl b spectral class. Chrysophytes/diatoms/raphidophytes and dinoflagellates (groups within the comparable spectral classes, Chl a/Chl c/fucoxanthin and Chl a/Chl c/peridinin, respectively) displayed the greatest similarity between/among groups. Spectra for phylogenetic groups within the Chl a/Chl c classes displayed limited similarity with spectra for groups within the Chl/phycobilin classes. Among the cyanobacteria and chlorophytes surveyed, absorbance spectra of species possessing dissimilar cell morphologies were discriminated, with the greatest range of differentiation occurring among cyanobacteria. Among the cyanobacteria, spectra for selected problematic species were easily discriminated from spectra from each other and from other cyanobacteria. Fluorescence-emission spectra were distinct among spectral classes and the similarity comparisons involving fourth-derivative transformation of spectra discriminated the increasing contribution of distinct cyanobacterial species and between phycobilin- and non-phycobilin-containing species within a hypothetical mixed assemblage. These results were used to elucidate the application for in situ moored instrumentation incorporating such approaches in water quality monitoring programmes, particularly those targeting problematic cyanobacterial blooms.

Microcystin Concentrations and Genetic Diversity of Microcystis in the Lower Great Lakes

The resurgence of Microcystis blooms in the lower Great Lakes region is of great concern to public and ecosystem health due to the potential for these colonial cyanobacteria to produce hepatotoxic microcystins. A survey of Microcystis cell densities and microcystin concentrations during August 2004 showed particularly high concentrations of both cells and toxin in the nearshore regions of Saginaw Bay (Lake Huron) and western Lake Erie, often exceeding the World Health Organizations recommended drinking water limit of 1 μg L−1. The dominant congener of microcystin in both basins was microcystin‐LR (MC‐LR), whereas the second most abundant congeners, accounting for up to 20–25% of the total microcystin concentrations, were MC‐LA in Saginaw Bay and MC‐RR in western Lake Erie. Multiplex PCR assays of Microcystis colonies isolated from these two regions showed that a much greater percentage of the Microcystis colonies from Saginaw Bay carried the mcyB gene necessary for microcystin production, in comparison with those from western Lake Erie. The mcyB genotypes sequenced separated into two distinct phylogenetic clusters, with Microcystis originating from Lake Erie predominantly in one branch and from Saginaw Bay present in both branches. These results indicate that the genetic composition of the bloom could impact the concentrations and congeners of microcystin produced and that the cell count methods currently being used to gauge public health threats posed by Microcystis blooms may not sufficiently assess actual bloom toxicity.

EVALUATING THE RELATIONSHIP BETWEEN PHOTOPIGMENT SYNTHESIS AND 2-METHYLISOBORNEOL ACCUMULATION IN CYANOBACTERIA

 The relationship between photopigments and the terpene‐derived secondary metabolite, 2‐methylisoborneol (MIB), was analyzed in photoacclimated cultures of Pseudanabaena articulata Skuja throughout growth, during the diel cycle, and following chemical‐induced inhibition of the isoprenoid pathway. Accumulation of MIB coincided with the accumulation of lipophilic and phycobilin pigments during the early to mid‐exponential portion of the growth cycle with the greatest accumulation of MIB during the late‐exponential phase. Cellular release of MIB occurred as culture populations entered mid‐ to late‐logarithmic phase of growth and was greatest in irradiance‐stressed cultures. The greater correspondence of MIB accumulation with photopigments was seen in cultures transferred from a 12:12 h LD photoperiod alone and the consistent relationship between MIB and photopigment accumulation under varying irradiance suggested a photopigment‐dependent regulation for MIB synthesis. However, the consistent allocation of carbon into MIB during instances of phytofluene and tetrapyrrole biosynthetic inhibition within P. articulata and Oscillatoria perornata Skuja indicated that MIB accumulation is not limited by isopreniod‐carbon availability and does not appear to serve as an “overflow” product. Rather, MIB accumulation simply appears to reflect overall carbon accumulation resulting from increased cell metabolism.

PHOTOSYSTEM II QUANTUM YIELDS AND XANTHOPHYLL-CYCLE PIGMENTS OF THE MACROALGA SARGASSUM NATANS (PHAEOPHYCEAE) : RESPONSES UNDER NATURAL SUNLIGHT

Our understanding of the physiological mechanisms that allow marine photoautotrophs to thrive in a high light environment is limited. The pelagic phaeophyte, Sargassum natans (L.) Gaillon, exists at the air–sea interface and often is exposed to high irradiances. During a cruise in the Gulf of Mexico, aggregates of S. natans were collected and maintained in a shipboard incubator under natural sunlight. In vivo fluorescence and pigmentation dynamics were assessed over two daily cycles to characterize the photophysiological responses of this taxon to varying irradiance (i.e. overcast and sunny conditions). The relative proportion of the photosynthetic carotenoid, violaxanthin, to the photoprotective carotenoid, zeaxanthin, decreased during daylight hours. This mirrored the dynamics in the maximum quantum yield for stable charge separation at photosystem II (FV/FM[variable fluorescence/maximum fluorescence]), which decreased (relative to predawn levels) by 50%–60% during periods of sustained bright light and recovered to predawn values 3 h after sunset. The ratio of de‐epoxidized to epoxidized components of the xanthophyll‐cycle pigment pool (violaxanthin, zeaxanthin) was associated with energy dissipation activity within the pigment bed. The operational quantum yield for photosystem II activity (φIIe) was substantially lower than FV/FM due to both a decreased probability that absorbed photons reached open reaction centers and to the induction of nonphotochemical fluorescence quenching (which was rapidly reversible). Bright light also affected the rate of electron flow from the reaction center chlorophyll through to the secondary electron acceptor, quinone B (QB); specifically, single turnover decay curves indicated that the proportion of QB bound to the D1–D2 complex in photosystem II decreased during the protracted periods of bright light. Kautsky curves suggested that the relative proportion of inactive light‐harvesting complexes also increased during periods of bright light. Taken together, these findings suggest that S. natans can tolerate high irradiances by down‐regulating its quantum yield during the day, decreasing its functional absorption coefficient through the uncoupling of light‐harvesting complexes, and decreasing the efficiency with which absorbed light is utilized. These cellular responses appear to be driven by the absolute flux of light and not by an endogenous rhythm, which is phased to a particular time of day.

PIGMENT AND PHOTOSYNTHETIC RESPONSES OF OSCILLATORIA AGARDHII (CYANOPHYTA) TO PHOTON FLUX DENSITY AND SPECTRAL QUALITY1

The effects of photon flux density (PFD) and spectral quality on biomass, pigment content and composition, and the photosynthetic activity of Oscillatoria agardhii Gomont were investigated in steady‐state populations. For alterations of PFD, chemostat populations were exposed to 50, 130 and 230 μmol photons·m−2·s−1 of photosynthetic active radiation (PAR). Decreases in biomass, chlorophyll a (Chl a) and c‐phycocyanin (CPC) contents, and CPC: Chl a and CPC: carotenoid content was not altered. Increases in the relative abundances of myxoxanthophyll and zeaxanthin and deceases in the relative abundances of echinenone and β‐carotene within the carotenoid pigments coincided with increasing PFD. Increases in Chl a‐specific photosynthetic rates and maxima and decreases in biomass‐specific photosynthetic rates and maxima with increasing PFD were attributed to increased light harvesting by carotenoids per unit Chl a and reduction in total pigment content, respectively.

HIGH-RESOLUTION AIRBORNE REMOTE SENSING OF BLOOM-FORMING PHYTOPLANKTON1

Remote sensing of highly turbid finfish aquaculture impoundments using the Calibrated Airborne Multispectral Scanner (CAMS) mounted on a Lear jet flown at 900 m was conducted in central Mississippi on 16 May 1990. Concurrent in situ data consisted of phytoplankton pigment concentrations and standing crop, water color, turbidity, and surface‐water temperature. Surface and near‐surface assemblages of cyanophytes and chlorophytes varied dramatically among impoundments; total chlorophyll concentrations and standing crop values ranged from 8 to 483 mg·m−3 and 8.0 × 102 to 2.2 × 106 cells‐mL−1, respectively. Regression models fit to CAMS data provided reliable estimates for and produced accurate digital cartographs of total chlorophyll and carotenoid concentrations, phytoplankton standing crop, and turbidity. Although a model to effectively estimate in situ c‐phycocyanin concentrations was not identified, the lack of a suitable model may have resulted from variability of pigment extraction during quantification rather than failure of remotely sensed imagery to detect c‐phycocyanin. Models derived from imagery of impoundments directly beneath the aircraft sufficiently described in situ parameters in imagery of adjacent series of impoundments not directly below the aircraft. High‐resolution airborne remote sensing provides a means for monitoring local phytoplankton dynamics in temporal and spatial scales analogous to biotic and abiotic processes affecting such dynamics and necessary for applications to ecological research and fisheries or aquacultural management.

Aquatic Macrophytes and Algae at Old Woman Creek Estuary and Other Great Lakes Coastal Wetlands

Abstract Studies on aquatic macrophyte and algal floras of Old Woman Creek estuary (OWC) are examined in light of work conducted in other Great Lakes coastal wetlands. Since the last detailed inventory of aquatic macrophytes at OWC in 1973, many emergent and floating leaved species have become very restricted in their distribution, or have disappeared altogether. Possible causes for this vegetation shift are discussed. The algal flora of OWC is distinct from that in adjacent Lake Erie. Storm events are proposed to be a major factor in regulating phytoplankton species composition and dynamics in OWC. Primary productivity in OWC appears to be dominated by the algal communities rather than by macrophytes. The botanical research on Great Lakes coastal wetlands conducted to date has provided only cursory insights into these complex and dynamic communities. Knowledge of factors regulating these communities along with the roles these communities play in coastal wetland dynamics is needed. The impact of changing watershed use patterns on these wetland communities has not yet been determined. Finally, symbiotic and competitive interactions between the macrophyte and algal communities need to be elucidated.