Karenia brevis dinoflagellate blooms off the west coast of Florida can create devastating effects on marine communities when they release a neurotoxin known as a brevetoxin. These blooms, informally referred to as red tides, can cause massive fish kills, necessitate closures of shellfish fisheries, and can even leave lingering toxins that impact shelf communities long after the bloom has dissipated. As a result, much effort has been put into studying K. brevis bloom initiation and dynamics. However, how K. brevis blooms impact Florida's fisheries is not fully understood because the relationship between K. brevis cell counts and fish mortality is poorly described. To study this relationship and the ecosystem response to K. brevis blooms, Ecopath with Ecosim (EwE) modeling is used to force K. brevis bloom mortality on the shelf ecosystems by using a recently developed time series that indexes K. brevis bloom severity. This index dynamically drives K. brevis bloom mortality in EwE in a historical reconstruction scenario from 1980 to 2009. Three hypotheses on ecosystem response are explored using Gag grouper as a case study. We postulate a) that K. brevis blooms impose bottom-up and top-down effects on the food web, b) that episodic perturbations by these blooms shape the community structure and c) that fishing pressure exacerbates those effects. Results support the hypothesis that K. brevis blooms pose top-down food web pressures, which is seen by evidence of trophic cascading. Changes in community structure with bloom mortality are also evidenced by changes seen in biodiversity and richness. An exacerbation of those effects as a result of heavy fishing pressure is evident, however, is only seen during severe bloom events. Little to no changes were found in the mortality from K.brevis blooms during blooms of average severity, and less mortality was imposed on the system during blooms of particularly low severity. However, this may be an artefact of the mode of action of K. brevis in EwE. Investigation of bloom effects on Gag showed that natural mortality rates of Gag appear to be largely influenced by mortality incurred during K. brevis blooms relative to the low rate of predation on Gag. Moreover, consumption rates of Gag on its prey were found to increase under a realistic schedule of these blooms. This may be due to a combination of effects, including increased mortality on competitors (making more prey available for Gag) and a lowering of the mean age of the Gag stock, which increases population productivity.

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.

Karenia brevis, a toxic dinoflagellate species that blooms regularly in the Gulf of Mexico, frequently causes widespread ecological and economic damage and can pose a serious threat to human health. Satellite-based ocean color imagery may provide a means for detecting and monitoring blooms, providing early alerts to coastal communities. However, a technique for discriminating K. brevis from other chlorophyll-containing algae is required. Between 1999 and 2001, a large bio-optical data set consisting of spectral measurements of remote-sensing reflectance (Rrs(lambda)), absorption (a(lambda)), and backscattering (bb(lambda)) along with chlorophyll a concentrations was collected on the central west Florida shelf (WFS) as part of the Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) and Hyperspectral Coastal Ocean Dynamics Experiment (HyCODE) programs. Reflectance model simulations indicate that cellular pigmentation is not responsible for the factor of 3 to 4 decrease in Rrs(lambda) observed in waters containing greater than 104 cells 1-1 of K. brevis. Instead, particulate backscattering coefficients measured inside K. brevis blooms are responsible for this decreased reflectivity as they were significantly lower than values measured in high-chlorophyll (>1 mg m-3), diatom-dominated waters containing fewer than 104 cells 1-1 of K. brevis. A paucity of high-backscattering detritus present in K. brevis blooms caused by decreased grazing pressure perhaps due to cellular toxicity along with a general inability of K. brevis to out compete diatoms and bloom in high-nutrient, high-backscattering estuarine waters may explain this low backscattering. A classification technique for detecting high-chlorophyll, low-backscattering K. brevis blooms is developed. In addition, a method for quantifying chlorophyll concentrations in positively flagged pixels using fluorescence line height (FLH) data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is introduced. Both techniques are successfully applied to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and MODIS data acquired in late August 2001 and validated using in situ K. brevis cell concentrations.

Blooms of the toxic dinoflagellate Karenia brevis are common on the West Florida Shelf (WFS), yet little is known of the relationships between zooplankton and K. brevis. A comprehensive analysis was undertaken to examine 1) perturbations in zooplankton community composition within K. brevis blooms 2) the contribution of zooplankton ammonium and phosphate excretion to K. brevis bloom nutrient requirements, and 3) the role of zooplankton grazing in K. brevis bloom termination. Prior to undertaking the first portion of the study, an examination of the perturbations in the normal zooplankton assemblage within K. brevis blooms, it was first necessary to define the normal zooplankton assemblage on the WFS. To this end, a seasonal analysis of abundance, biomass and community composition of zooplankton was undertaken at 6 stations on the WFS. Monthly sampling was conducted for one year at the 5, 25 and 50- m isobaths. Two major groups in community composition were observed at the near shore (5-m and 25-m) and offshore (50-m) stations. Considerable overlap was seen in community composition between the 5-m to 25-m and 25-m to 50-m isobaths, but little overlap in community composition was observed between the 5-m and 50-m isobaths. Of the 95 species identified, only 25 proved to be important (>90%) contributors to community composition. Near shore, important contributors were Parvocalanus crassirostris, Penilia avirostris, Paracalanus quasimodo, Oithona colcarva, Oikopleura dioica, Centropages velificatus and Pelecypod larvae. As distance offshore increased, important contributors to community composition were Euchonchoichiea chierchiae, Clausocalanus furcatus, Oithona plumifera, Oithona frigida, Oncaea mediteranea, Calaocalanus pavoninius, Oithona similis, and Gastropod larvae. Variations in abundance and biomass between non-bloom and bloom assemblages were evident, including the reduction in abundance of 3 key species within K. brevis blooms. One potential source of nutrients to support K. brevis blooms may be zooplankton regeneration of nutrients. To test this hypothesis, ammonium and phosphate excretion rates of several West Florida Shelf copepods (Labidocera aestiva, Acartia tonsa, Temora turbinata, and Paracalanus quasimodo) were measured and prorated to a 24-hour day. These excretion rates were then extrapolated to other West Florida Shelf zooplankton, combined with available literature excretion rates for some taxa, and applied to zooplankton abundances found for K. brevis blooms on the West Florida Shelf in 1999 and 2001. Ammonium excretion rates were found to be inadequate to support all but 104 cells l-1 of K. brevis, though phosphate excretion rates were adequate to support even 106 cells l-1 of K. brevis. Grazing assessment was conducted for three common zooplankton species that were found within two K. brevis blooms, A. tonsa, P. quasimodo, and L. aestiva, using 14C labeled K. brevis cells. Grazing rates were then applied to the zooplankton community and grazing assessed. Grazing pressure was occasionally heavy, and was capable of reducing K. brevis to background concentrations at stations in the 1999 bloom and at 1 station in the 2001 bloom. Generally, however, grazing pressure proved to be insufficient to reduce K. brevis to background concentrations during the 1999 and 2001 blooms.

Harmful Algal Blooms (HABs) in the Gulf of Mexico (GOM) are natural phenomena that can have negative impacts on marine ecosystems on which human health and the economy of some Gulf States depends. Many of the HABs in the GOM are dominated by the toxic dinoflagellate Karenia brevis. Non-toxic phytoplankton taxa such as Scrippsiella sp. also form intense blooms off the Mexican coast that result in massive fish mortality and economic losses, particularly as they may lead to anoxia. The main objectives of this dissertation were to (1) evaluate and improve the techniques developed for detection of Karenia spp. blooms on the West Florida Shelf (WFS) using satellite remote sensing methods, (2) test the use of these methods for waters in the GOM, and (3) use the output of these techniques to better understand the dynamics and evolution of Karenia spp. blooms in the WFS and off Mexico. The first chapter of this dissertation examines the performance of several Karenia HABs detection techniques using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images and historical ground truth observations collected on the WFS from August 2002 to December 2011. A total of 2323 in situ samples collected by the Florida Fish and Wildlife Research Institute to test for Karenia spp. matched pixels with valid ocean color satellite observations over this period. This dataset was used to systematically optimize variables and coefficients used in five published HAB detection methods. Each technique was tested using a set of metrics that included the F-Measure (FM). Before optimization, the average FM for all techniques was 0.47. After optimization, the average FM increased to 0.59, and false positives decreased ~50%. The addition of a Fluorescence Line Height (FLH) criterion improved the performance of every method. A new practical method was developed using a combination of FLH and Remote Sensing Reflectance at 555 nm (Rrs555-FLH). The new method resulted in an FM of 0.62 and 3% false negatives, similar to those from more complex techniques. The first chapter concludes with a series of recommendations on how to improve the detection techniques and how to take these results a step further into a Gulf wide observing systems for HABs. In chapter two, ocean color techniques were used to examine the extension, evolution and displacement of four Karenia spp. events that occurred in the WFS between 2004 and 2011. Blooms were identified in the imagery using the new Rrs-FLH method and validated using in situ phytoplankton cell counts. The spatial extension of each event was followed in time by delineating the blooms. In 2004 and 2005, the WFS was affected by a series of hurricanes that led to high river discharge and intense sediment resuspension events. Both processes had an impact on HAB occurrence. For example, I tracked a Karenia spp. bloom found in late December 2004 approximately 40-80 km offshore Saint Petersburg, which then expanded reaching an extension of >8000 km2 in February 2005. The bloom weakened in spring 2005 and intensified again in summer reaching >42,000 km2 after the passage of hurricane Katrina in August 2005. This bloom covered the WFS from Charlotte Harbor to the Florida Panhandle. Two other cases were studied in the WFS. The results of the Hybrid Coordinate Ocean Model from the U.S. Navy aid understanding the dispersal of the blooms. During fall 2011, three field campaigns to study HABs in Mexico were conducted to do an analysis of optical properties and explore the possibility of using ocean color techniques to distinguish between the main phytoplankton blooms in that region. Three main bloom scenarios were observed in the Campeche Bank region: massive diatom blooms, blooms dominated by Scrippsiella spp., and Karenia spp. blooms. The normalized specific phytoplankton absorption spectra were found to be different for Karenia spp. and Scrippsiella sp. blooms. A new technique that combines phytoplankton absorption derived from MODIS data and the new technique developed in Chapter One showed potential for a detection technique that can distinguish between Karenia and Scrippsiella blooms. Additional work is needed to improve the new technique developed for Mexican waters, but results show potential for detection techniques that can be used Gulf-wide. This will help better understand the dynamic and possible connectivity of phytoplankton blooms in the GOM.

Harmful algal blooms, commonly referred to as red tides, occur yearly with dramatic impacts on marine ecology, coastal economies, and human health. As a consequence, research into the zooplankton grazers that consume HABs is highly important. However, changes in ocean temperature may increase the range of many HABs, exposing historically naive copepods to new species and their associated chemicals. Little research into the impact of allopatric verses sympatric species, particularly on the immediate behavioral impact, has been performed, leaving the indirect fitness effects of HAB exposure and consumption relatively unknown. We measured alterations in the swimming behavior of the calanoid copepod Temora longicornis following exposure to sympatric Alexandrium fundyense and allopatric Karenia brevis treatments. After a 15-16 hours depuration period postA. fundyense exposure, T. longicornis exhibited increased average swimming speed and an elevated net to gross displacement ratio (NGDR). During exposure toK. brevis, copepods exhibited an immediate decrease in swimming speed and NGDR, as well as an increased frequency of jump behavior. However, these effects faded after an one-hour depuration period, and disappeared after a 15-16 hour depuration period. The alterations in swimming behavior demonstrated by the copepods treated A. fundyense may increase encounter rate with predators, while copepods treated with K. brevis remain in bloom conditions for longer periods of time, negatively affecting survivorship. Temora longicornis individuals also may be made more visible to predators due to the increase in jumps seen during treatment with K. brevis. These behavioral changes suggest how HABs escape from zooplankton grazer control by altering copepod swimming behavior, and the pattern of predator-prey evolution that occurs over time.