The purpose of this study was to examine the sequence of changes in the gross morphology and toxicity of the raphidophyte alga Heterosigma akashiwo in the context of blooms of this species in the Strait of Georgia, British Columbia. Field work focused on this alga’s 1989 fish-killing bloom. That bloom was extensive, with discolouration of the water extending from Jervis Inlet through Malaspina Strait into the Strait of Georgia, and south to Cypress Island in Washington State. Excystment events on Spanish Banks in Vancouver harbour preceded population development in the Strait of Georgia during July and August but toxicity was only noted in the last two days of August and through September. Fish kills occurred near Cypress Island, and in Jervis Inlet and the contiguous waters of Agamemnon channel. These locations represented the geographic extremes of the discoloured waters. In Malaspina Strait and Jervis Inlet, information was collected on water column structure, macronutrient concentrations, and the distribution of algae and fish mortalities. Fish mortalities were coincident with the first sighting of waters discoloured with Heterosigma akashiwo in Agamemnon Channel and Jervis Inlet. The alga appeared to be transported to the areas by currents. Algal concentrations were higher at the Malaspina Strait end of a transect into Jervis Inlet and during flood rather than ebb tides. The water column in Malaspina Strait and Jervis Inlet was stratified and both inorganic nitrogen and phosphorus in surfece waters were low enough to limit growth of H. akashiwo. Though this alga can migrate vertically to obtain nutrients at depth, there was no evidence of migration during this toxic event. Termination of the bloom was associated with a weakening of the water column stratification and the reappearance of non-limiting concentrations of nitrogen in the surface waters. Work in culture demonstrated that there was a sequence of reproducible changes in cell size and shape that improved uptake when nutrients were at the concentrations seen in the Strait at the start of the toxic bloom. These changes involved reduction in cell volume by a factor of between 2- and 4-fold and cells changing from rounded, almost football-shaped cells (oblate spheroids), to plate-like (prolate spheroids). Mathematical modeling suggests that the volume changes could improve nutrient uptake by a factor of 21 to 38%. The changes in shape could improve nutrient uptake dynamics by a further 7.5%. Depending on the nutrient history of the population, changes in cell shape could continue beyond the plate-like form with significant portions of the algal population developing surface protuberances when adequate nutrients and energy were available to the population. The elaboration of surface processes could further improve uptake dynamics. A numerical model to describe these shapes was not available so the degree of improvement could not be quantified. As cells reach the end of their life cycle in culture, they revert to the oblate spheroid form and, if no new nutrients are added, will form resting cysts. However, cyst formation can also be triggered earlier in the life cycle by the addition of nutrients. This may benefit the species by ensuring that cells form cysts in shallow waters where spring temperatures are adequate to fecilitate excystment of cells. In addition to changes in shape. Heterosigma akashiwo cells produce a toxic agent which can suppress growth of nutrient competitors and kill predators, or make the algae unpalatable. Production of those toxins begins and declines immediately prior to decline in population numbers. Toxic effects of the alga can be caused to disappear at any time by the addition of nutrients. Similar to the differentiation of cell shape, the level of toxicity expressed by the cells appears to be correlated with the nutrient history of the population. Cells grown in higher nutrient concentrations appear to be more toxic; however, the population need not have high numbers of cells with processes to be toxic. Heterosigma akashiwo would appear to have adaptations which enhance its ability to compete and survive in the nutrient-limited waters of late summer. The adaptions include both changes in gross morphology of the cells and in the production of toxins which reduce the effects of competition and predation. Population growth and formation of concentrations of the alga capable of discolouring the water can be independent of the occurrence of toxicity. Lack of vertical migration and a protracted period of a stable, stratified water column with depleted nutrients appear to be critical to the genesis of toxicity in wild populations. / Graduate

No description available.

Thesis (M.S.)--University of North Carolina at Wilmington, 2006. / Includes bibliographical references (leaves: 61-66)

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [88]-96).

Thesis (doctoral)--Rijksuniversiteit Groningen, 1996. / Includes bibliographical references (p. [109]-119).

Thesis (M.S.)--University of North Carolina Wilmington, 2009. / Title from PDF title page (January 19, 2010) Includes bibliographical references (p. 32-33)

Coral reefs worldwide are threatened by many environmental disturbances including harmful algal blooms (HABs) which have been increasing on Florida coasts over the past decade. Research has mainly focused on HAB identification, percent cover and other effects on the benthos but the relationship of HABs with upper trophic levels has received less attention. To study this relationship, a two-year investigation on a 10-m deep reef off of Hallandale Beach, was conducted. Stationary fish census coupled with benthic transect videos were conducted quarterly between April 2005-July 2007. A significant correlation between Lyngbya sp. blooms and alterations in fish assemblages was observed. Lyngbya had a negative interaction with fish species and abundance; additionally, HAB sample periods were significantly different from low algal abundance periods. Blooms of Dictyota sp. had no measurable relationship with the fish assemblage indicating HABs may have variable impacts on fishes depending on family, species and chemistry of the algae. / by Rex E. Baumberger, Jr. / Thesis (M.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.

Dumbliai – mikroskopiniai planktono organizmai – vienas iš pagrindinių hidroekosistemų komponentų, pirminiai organinės medžiagos producentai. Didėjant vandens telkinių trofiškumui, mažėja dumblių rūšių įvairovė, keičiasi vyraujančių rūšių kompleksas. Dažnai eutrofikuotuose vandens telkiniuose ima dominuoti prokariotiniai autotrofiniai mikroorganizmai – melsvabakterės, kurios sukelia intensyvius vandens „žydėjimo“ procesus ežeruose, jūrinėse lagūnose, jūrose bei vandenynuose. Dėl šios priežasties blogėja vandens kokybė. Pastaraisiais dešimtmečiais išsamių tyrimų objektu visame pasaulyje tampa toksiniai fitoplanktono dumbliai ir melsvabakterės. Tyrimais yra nustatyta, kad pusė iš visų vandens „žydėjimo“ atvejų yra toksiški (RAPALA, LAHTI, 2002). Pasaulyje atliekami monitoringiniai tyrimai, siekiant įvertinti toksinių dumblių ir melsvabakterių vystymosi tendencijas, priklausomybę nuo aplinkos sąlygų, toksinio vandens „žydėjimo“ priežastis. Pasitelkiant cheminius bei genetinius metodus, nustatoma toksinių medžiagų cheminė sudėtis, vertinamas jų poveikis gyviems organizmams. Šiaurinės Kuršių marių dalies vasariniame planktone 2004-2006 m. aptiktos 223 dumblių rūšys, priklausančios 5 klasėms. 97 rūšys (43 %), priklauso Chlorophyceae klasei, 71 rūšis (32 %) – Cyanophyceae, 40 rūšių (18 %) – Bacillariophyceae, 9 rūšys (4 %) – Euglenophyceae ir 6 rūšys (3 %) – Dinophyceae klasei, iš jų aptiktos 26 potencialiai toksinės dumblių ir melsvabakterių rūšys, priklausančios 3 klasėms, 14... [toliau žr. visą tekstą] / Curonian Lagoon is a shallow transitional water basin located in the south-eastern part of the Baltic Sea. The southern and central parts of the lagoon contain freshwater due to discharge from the Nemunas River, while the salinity in the northern part varies from 0 to 8 PSU, depending on winds activity affecting brackish water inflow from the Baltic Sea. The investigation was carried out in the fresh-brackish water mixing zone (Influence zone of Baltic Sea), in the central part and Nemunas River influence zone in July-August 2004 - 2006. Changes in physico-chemical parameters, chlorophyll a concentration, phytoplankton and toxic algae cell density were monitored. Totally 223 species and varieties mainly belonging to Chlorophyceae (43 %) and Cyanophyceae (32 %) were found. 26 algae species from 3 algae classes (Cyanophyceae, Chlorophyceae and Dinophyceae) were identified as potential toxic species in the northern part of Curonian Lagoon during 2004 and 2006 summer time. Dominated toxic species Ahpanizomenon flos-aquae, Microcystis aeruginosa, M. viridis, M. wesenbergii, Woronichinia compacta. Phytoplankton biomass in Curonian Lagoon surface ranged from 12,27 to 50,22 mg/l. The peak of phytoplankton (33,11 mg/l) and potential toxic algae (28,67 mg/l) biomass in 2004 summer time was observed near by Klaipeda Strait, were Aphanizomenon flos-aquae contain 36 % from total biomass. In 2005 summer time the highest phytoplankton (50,22 mg/l) and toxic algae (21.46 mg//l) biomass were... [to full text]

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: [70]-74)

Florações de microalgas potencialmente nocivas têm aumentado em termos globais e causado impactos na aquicultura, no turismo, na saúde humana e em vários aspectos do funcionamento dos ecossistemas. No Brasil, uma atenção cada vez maior tem sido dada ao tema, em virtude do elevado potencial de nossas águas para o cultivo de bivalves marinhos, um dos grupos de invertebrados mais afetados. Deste modo, a preocupação com a contaminação de consumidores humanos tem gerado projetos voltados para a detecção de espécies potencialmente nocivas e de suas toxinas, mas ainda há poucos estudos sobre interações alimentares entre as espécies de fitoplâncton e zooplâncton. No presente trabalho interações entre dinoflagelados potencialmente nocivos e organismos pertencentes ao zooplâncton marinho foram investigadas em dois capítulos. Capítulo 1: O presente estudo tem como objetivo avaliar a influência do dinoflagelado potencialmente nocivo Alexandrium tamiyavanichii na alimentação e reprodução do copépode planctônico marinho Temora turbinata. Taxas de produção de ovos e sucesso de eclosão naupliar foram estimadas para fêmeas alimentadas em misturas de A. tamiyavanichii e do dinoflagelado Prorocentrum minimum, tratado aqui como alimento controle. Capítulo 2: O principal objetivo deste estudo foi analisar os efeitos de exsudatos de dinoflagelados e células intactas na sobrevivência e mobilidade de táxons zooplanctônicos de uma região subtropical (Ubatuba, Brasil). Efeitos letais foram observados em cinco dos seis táxons testados, três dos quais (náuplios de copépodes, tintinídeos e larvas de gastrópodes) quando expostos a exsudatos e dois (rotíferos e larvas de braquiúros) quando expostos a células intactas. Em adição, larvas de gastrópodes demonstraram comprometimento da mobilidade após exposição à exsudatos. Apenas larvas de poliquetas não foram aparentemente afetadas no curso dos experimentos. / Harmful algae blooms have increased globally and caused impacts in aquaculture, tourism, and human health and in various aspects of ecosystem functioning. In Brazil, increasing attention has been given to this issue, because of the high potential of our waters for marine bivalve farming. Therefore, there are risks of contamination of the crops, and consequent poisoning of the consumers. This concern has led research projects to mostly focus on the detection of potentially harmful species and their toxins, with few initiatives to understand feeding interactions among species of phytoplankton and zooplankton. In this research interactions between potentially harmful dinoflagellates and marine zooplankton were investigated in two chapters. Chapter 1 - This study aims to evaluate the influence of the potentially harmful dinoflagellate Alexandrium tamiyavanichii on Temora turbinata feeding and reproduction. Egg production rates and hatching success were estimated for females fed on mixtures of A. tamiyavanichii and P. minimum. Chapter 2: The aim of this study was to analyze the effects of dinoflagellate exudates and intact cells on the survivorship and mobility of zooplankton taxa from a subtropical location (Ubatuba, Brazil). Lethal effects were observed in five out of six taxa investigated, three of which (copepod nauplii, tintinnids and gastropod larvae) when exposed to dinoflagellate exudates and two (rotifers and brachyuran zoeae) when exposed to intact cells. In addition, gastropod larvae displayed mobility impairment during exposure to dinoflagellate exudates. Only polychaete larvae were not apparently affected during the course of the experiments.