Over the past two decades, Lake Winnipeg has been experiencing increasingly rapid eutrophication, and large cyanobacterial blooms now form in the North Basin in most years in late summer or fall. Cyanobacteria are considered a relatively poor food source compared with other phytoplankton, but the impacts of these blooms upon the primary consumers in the lake have not previously been researched. A microscopic analysis of whole water samples found cyanobacteria to be scarcely present in summer 2012, with nitrogen-fixing and non-fixing cyanobacteria comprising 11.2% and 8.4% of the basin-wide biovolume, respectively, and all but absent in fall. Gut content analysis of chironomids found that cyanobacteria made up an almost negligible part of their diet. Stable isotope analysis revealed that nitrogen-fixing cyanobacteria reduced phytoplankton δ15N values, and that this same reduction could be traced through the zooplankton, but not down to the sediments or chironomids.

Over the past two decades, Lake Winnipeg has been experiencing increasingly rapid eutrophication, and large cyanobacterial blooms now form in the North Basin in most years in late summer or fall. Cyanobacteria are considered a relatively poor food source compared with other phytoplankton, but the impacts of these blooms upon the primary consumers in the lake have not previously been researched. A microscopic analysis of whole water samples found cyanobacteria to be scarcely present in summer 2012, with nitrogen-fixing and non-fixing cyanobacteria comprising 11.2% and 8.4% of the basin-wide biovolume, respectively, and all but absent in fall. Gut content analysis of chironomids found that cyanobacteria made up an almost negligible part of their diet. Stable isotope analysis revealed that nitrogen-fixing cyanobacteria reduced phytoplankton δ15N values, and that this same reduction could be traced through the zooplankton, but not down to the sediments or chironomids.

Excess nutrients from human activity trigger toxic cyanobacterial and algal blooms, creating expansive hypoxic dead zones in lakes, damaging ecosystems, hurting local economies, undermining food and water security, and directly harming human health. To identify when and where nutrients limit phytoplankton and cyanobacterial growth, and cyanotoxin concentrations across Utah Lake, USA we conducted four in-situ bioassay studies (563 cubitainers or experimental units) that experimentally added N, P or N+P over the spring, early summer, summer, late summer, and fall in lake water from the top 20 cm of the water column. For our purpose, we defined total phytoplankton as all prokaryotic or eukaryotic organisms containing chlorophyll-a. We evaluated changes in chlorophyll-a and phycocyanin concentrations; the abundance of cyanobacterial species and total phytoplankton species or divisions; cyanotoxin concentrations of the microcystin, anatoxin-a, and cylindrospermopsin; DIN, SRP, TP, and TN concentrations; and other water chemistry parameters. We found that the nutrient limitation of cyanobacteria, and to a lesser extent phytoplankton, was influenced by season and space. Cyanobacteria were often co-limited in the spring or early summer, limited by a single nutrient in the summer, and not limited by N or P in the late summer and fall. Alternatively, phytoplankton were co-limited from the summer into the fall in the main body of the lake and either N limited or co-limited continually in Provo Bay. Microcystis, Aphanocapsa, Dolichospermum, Merismopedia, and Aphanizomenon spp., and Aulacoseira and Desmodesmus spp. and two taxonomical categories of algae (i.e., unicellular and colonial green algae) were primarily associated with cyanobacteria and phytoplankton nutrient limitations. Concentrations of the three cyanotoxins demonstrated a seasonal signal and loosely followed the growth of specific cyanobacteria but was not dependent on total cyanobacterial cell density. The DIN and SRP were biologically available in all water and nutrient treatments with nutrient concentrations declining over the incubation period, suggesting that nutrient levels were not oversaturated. Our results offer insights into specific nutrient targets, species, and, and cyanotoxins to consider in the future to manage Utah Lake.

With the global rise in frequency of harmful algal blooms in estuarine environments comes an increase in prevalence of toxic metabolites, such as microcystin (MC), that some of the cyanobacteria involved will produce. At high concentrations, MC may accumulate in consumer tissues and have deleterious effects on organisms; however impacts of the toxin on aquatic living resources at ecologically relevant concentrations have not been widely documented. We analyzed the effects of MC on juveniles of five fish species from the James River, Virginia to determine if MC has the potential to impede growth. Using three separate experimental approaches, it was shown that exposure to concentrations of the toxin currently observed in the James River estuary do not appear to significantly impact the growth or survivorship of tested fish species. Extraneous factors in parts of the study led to an inability to draw clear conclusions on mortality or growth impacts; however it is evident from the experiments that at least some of the fish species have biological mechanisms in place that allow them to effectively eliminate the toxin from their systems. An ability to extricate the toxin suggests the possibility for fishes to withstand MC exposures and sustain few negative health impacts at low MC concentrations.

Karenia brevis is a toxic marine dinoflagellate species that blooms almost every year in the Gulf of Mexico. These blooms have had devastating effects on local economies, as well as on the fauna of the area. The ECOHAB:Florida project was founded to study the population dynamics and trophic impacts of K. brevis. The project included a series of monthly hydrographic offshore research cruises, as well as monthly surveys of a transect along the 10-meter isobath of the West Florida Shelf. This study focused on data from the alongshore transect over a three-year period (1999-2001). Physical parameters (temperature, salinity, and density) and chemical parameters (particulate carbon, nitrogen, and phosphorus; dissolved inorganic nitrogen and phosphorus) of the West Florida Shelf were analyzed. The amount of chlorophll a and the location and amount of K. brevis cells present were also examined. Clear spatial, seasonal, and interannual patterns in the hydrographic parameters, particulate matter (C, N, P), dissolved inorganic nutrient (nitrite, nitrate, and phosphate), and chlorophyll a concentrations were found. At various times throughout the study, the location of K. brevis blooms was influenced by all of these factors except for the amount of dissolved inorganic nutrients. There were differences in particulate matter ratios present in bloom and non-bloom periods. No clear-cut differences in dissolved inorganic nutrients between bloom and non-bloom periods were found. Finally, relationships between the biological indicators of blooms (i.e., chlorophyll a) and the aforementioned physical and chemical parameters were found.

Optical research has shown that Karenia brevis has distinct spectral characteristics, yet most studies have focused exclusively on absorption and chemical properties, ignoring the size, shape, internal structure, and orientation, and their effect on scattering properties. The application of a new spectral interpretation model to K. brevis is shown to provide characterization of unique spectral information, not previously reported, through the use of scattering and absorption properties. The spectroscopy models are based on light scattering and absorption theories, and the approximation of the frequency-dependent optical properties of the basic constituents of living organisms. The model uses the process of mathematically separating the cell into four components, while combining their respective scattering and absorption properties, and appropriately weighted physical and chemical characteristics. The parameters for the model are based upon both reported literature values, and experimental values obtained from laboratory grown cultures and pigment standards. Measured and mathematically derived spectra are compared to determine the adequacy of the model, contribute new spectral information, and to establish the proposed spectral interpretation approach as a new detection method for K. brevis. Absorption and scattering properties of K. brevis, such as cell size/shape, internal structure, and chemical composition, are shown to predict the spectral features observed in the measured spectra. This research documents for the first time the exploitation of every spectral feature produced by the interaction of light with the cellular components and their contribution to the total spectrum of a larger (20-40 µm) photosynthetic eukaryote, K. brevis. Overall, this approach could eventually address the detection deficiencies of current optical detection applications and facilitate the understanding of K. brevis bloom ecology.

As human populations increase along coastal watersheds, the understanding and monitoring of Harmful Algal Blooms (or red tides) is an increasingly important issue. A consistent method for accurately detecting red tides using satellite measurements would bring tremendous societal benefits to resource managers, the scientific community and to the public as well. In the West Florida Shelf, blooms of the toxic dinoflagelate Karenia brevis are responsible for massive red tides causing fish kills, massive die-offs of marine mammals, shellfish poisoning, and acute respiratory irritation in humans. In this work, for the first time a long-term dataset (2002~2006) the MODerate Resolution Imaging Spectroradiometer (MODIS) is compared (i.e., matched-up) to an extensive data set of in situ cell counts of K. brevis; provided by the Florida Fish and Wildlife Conservation Commission's Fish and Wildlife Research Institute. The pairing of remote sensing data with near-coincident field measurements of cell abundance was successfully used to derive the basis for the development of an alternative ocean color based algorithm for detecting the optical signatures associated with blooms of K. brevis in waters of the West coast of Florida. Conclusions are geographically limited to the Central West Florida Shelf during the boreal Summer-Fall (i.e., the K. brevis blooming season). The new simpler Empirical approach is compared with other two more complicated published techniques. Their potential is verified and uncertainties involved in the identification of blooms of K. brevis are presented. The results shown here indicate that the operational NOAA method for detecting red tides in the Gulf of Mexico (Stumpf et al., 2003; Tomlinson et al., 2004) performs less accurately than the other two algorithms at identifying K. brevis blooms. The sensitivity and specificity of the Bio-optical (Cannizzaro, 2004; Cannizzaro et al., 2008) and Empirical algorithms are simultaneously maximized with an optimization procedure. The combined use of these two optimized algorithms in sequence provides another new monitoring tool with improved accuracy at detecting K. brevis of blooms. The ability of this Hybrid scheme ranges about 80% for both sensitivity and specificity; and the capability at predicting a correct red tides is 70%, and ~85% for non-blooms conditions. The spatial and temporal knowledge of K. brevis blooms can improve the direction of field monitoring to areas that should receive special attention, allowing better understanding of the red tide phenomenon by the scientific community. The relevant agencies can also develop more appropriate mitigation action plans, and public health guidance can be improved with the enhancement of sustainable costal management strategies.

The focus of my thesis research is on the interplay between individual behavior, population dynamics and community-level processes within zooplankton communities in coastal Maine. The target organisms of my thesis work are marine copepods. Copepods are small (1-10 mm) crustaceans that perform the essential ecosystem function of consuming and assimilating primary production (phytoplankton) making it available to higher trophic levels such as commercially important fishes. Therefore, copepod population growth is of critical importance to marine food webs. Fertilization limitation has been suggested as a constraint on copepod population growth but field surveys describing the prevalence of fertilization limitation are lacking. During my doctoral research, I explored the in situ fertilization success of two marine copepod species, Temora longicornis and Eurytemora herdmani in coastal Maine. I collected monthly zooplankton samples and analyzed clutches from field-caught females using an egg-staining technique. My results indicate that both species exhibit fertilization limitation in nature and the factors correlated with their fertilization span population, community and ecosystem level factors. To determine a causal relationship between predator density and copepod mating success, I conducted laboratory experiments to assess the effects of a common mysid shrimp predator, Neomysis americana on Eurytemora herdmani mating success. I subjected males and females to predators or predator cues. I found that the presence of a mysid predator, or only a predator cue, reduced copulation frequency and spermatophore transfer leading to a 38-61% decrease in E. herdmani nauplii production. These results suggest that mysid predators can constrain copepod population growth through non-consumptive processes. To determine the effects that resources can impose on copepod behavior, I explored the behavioral and fitness consequences of Temora longicornis ingesting Alexandrium fundyense, a phytoplankton species that forms harmful algal blooms in coastal Maine. My results suggest that ingesting A. fundyense causes copepods to swim faster and with more directional persistence compared to control algae. Temora longicornis increased their average swimming velocity by 24%, which leads to a 24-54% increase in their theoretical encounter rate with predators. Therefore, these findings suggest behaviorally mediated copepod-algal interactions may have significant impacts on harmful algal bloom dynamics and the fate of toxins in marine food webs.

With steady growth in global commerce and intensified ship traffic worldwide, comes the increased risk of invasion by non-indigenous organisms. Annually, >7000 vessels traveled across Galveston Bay, Texas from 2005-2010. These vessels discharged ~106 million metric tons of ballast water, equivalent to ~3.4% of the total volume of the Bay. A majority of these discharging vessels originated from around the Gulf of Mexico and the Caribbean Sea. By evaluating the source and frequency of inoculations from various locations, we are striving to assess the invasibility risk to Galveston Bay by way of ballast water. We identified organisms from Galveston Bay, ballast water samples and growout experiments using molecular methods. To our knowledge, this is the first utilization of molecular methods to identify the phytoplankton community within Galveston Bay. Within Galveston Bay, we identified 15 genera of dinoflagellates, 2 of which have previously gone undetected including Takayama and Woloszynskia. Thirteen ballast water samples yielded twenty genera of Protists, Fungi or Animalia from at least ten different phyla. With more than seven genera identified, dinoflagellates were the most diverse group: including the known toxin producer Pfiesteria and Scrippsiella which has not previously been detected in Galveston Bay. The most common diatoms in the ballast water samples were Actinocyclus, Ditylum, Nitzschia, Stephanopyxis and Thalassiosirales. At the termination of the growout experiments eight genera of phytoplankton were identified including: Dinophysis, Gymnodinium, Gyrodinium, Heterocapsa, Peridinium, Scrippsiella, Chaetoceros and Nitzschia. With these findings, Galveston Bay has the potential to be both a recipient and donor region of dinoflagellates. Dinoflagellates, capable of forming harmful algal blooms leading to fish and shellfish kills, are being transported to Galveston Bay via ballast water. Our results suggest that Galveston Bay is at risk for invasive species introductions via ballast water and support the idea that a monitoring system within the ports as well as the bay should be put in place. The actions would help to maintain the current health of this ecosystem and aide in preventing a negative impact in the event of successful establishment of a non-indigenous species of phytoplankton transported to Galveston Bay via ballast water.

Harmful algal blooms (HABs) are increasing in frequency and duration worldwide. Karenia brevis, the major toxic dinoflagellate in the Gulf of Mexico, produces potent neurotoxins, known as brevetoxins. For K. brevis, only minor concentrations of brevetoxins are needed to induce toxicity and environmental conditions appear to have the most direct impact on the cellular content of these toxins. A better understanding of K. brevis biology is essential to understand the mechanisms underlying toxin production and the ecology of such HABs, as well as to better anticipate and respond to such blooms. Here we present findings on the effect of salinity and availability of carbon on cellular physiology and brevetoxin and brevenal production by K. brevis. When grown at salinities of 35 and 27, but otherwise identical conditions, total brevetoxin cellular concentration varied between 0 to 18.5 pg cell-1 and brevenal varied between 0 and 1 pg cell-1. In response to hypoosmotic stress brevetoxin production was triggered, as a result, brevetoxin production increased up to 53%, while growth rates remained unchanged. A significant hypoosmotic event of >11%, was needed to trigger the response in brevetoxin production. To determine if K. brevis was sensing changes in specific ions within seawater (K+, Cl- or Ca2+), we systematically removed one ion while keeping the remaining ions at equivalent molar concentration for salinity of 35. Dilution in seawater K+ concentrations triggered the production of brevetoxins, increasing production ≥44%. Ecosystem changes due to climate change have increased the production of toxins in other HAB species; here we examined the impact on K. brevis. We have shown that modification of pCO2 level and temperature did not influence brevetoxin production; however, predicted climate change scenarios (increased temperature and pCO2) did significantly increase the growth rate of K. brevis, by 60% at 25°C and 55% at 30°C. We suggest that K. brevis blooms could benefit from predicted increase in pCO2 over the next 100 years. Overall, our findings close a critical gap in knowledge regarding the function of brevetoxin in K. brevis by identifying a connection between brevetoxin production and osmoacclimation.