A associação simbiótica entre a diatomácea cêntrica Chaetoceros coarctatus e o ciliado peritríquio Vorticella oceanica é amplamente conhecida e registrada em diversos estudos, porém nunca havia sido analisada sob o ponto de vista de suas implicações para o movimento destes organismos. A fim de contribuir com novos dados acerca desta associação simbiótica, o presente trabalho analisou a relevância ecológica da simbiose entre Chaetoceros e Vorticella, por meio de um estudo comportamental do deslocamento destes organismos na coluna de água. As associações foram coletadas em águas costeiras de Ubatuba, São Paulo, onde sua ocorrência foi observada em elevada abundância, particularmente durante o verão. Utilizando técnicas de imagem de alta frequência em um sistema óptico tridimensional foi possível descrever os padrões de deslocamento desta associação e avaliar as implicações ecológicas deste comportamento. De acordo com as análises realizadas neste trabalho, pode-se sugerir que o comportamento de deslocamento realizado pela associação Chaetoceros-Vorticella na coluna de água resulta em vantagens tanto para o epibionte quanto para o hospedeiro. Em termos de submesoescala, este estudo sugere que o deslocamento realizado pela associação Chaetoceros-Vorticella pode contribuir para a formação de camadas finas, levando à formação de hotspots de atividade biogeoquímica e interações tróficas no ecossistema pelágico. / The symbiotic association between the centric diatom Chaetoceros coarctatus and the peritrich ciliate Vorticella oceanica is widely known and reported in several studies, but its implications for the movement of these organisms have never been analyzed. In order to contribute with new data about this symbiotic association, the present study investigated the ecological relevance of the Chaetoceros-Vorticella association by recording displacement parameters of these organisms in the water column. The associations were collected in coastal waters of Ubatuba, São Paulo, where their occurrence was observed in high abundance, particularly during the summer. Using high-resolution imaging techniques in a three dimensional optical system it was possible to describe the displacement patterns of this association and to provide initial insights about the ecological implications of this behavior. It is suggested that the displacement behavior performed by the Chaetoceros-Vorticella association in the water column is beneficial for both the epibiont and the host. In terms of submesoscale processes, this study indicates that the displacement carried out by the Chaetoceros-Vorticella association may contribute to the formation of thin layers, leading to the formation of hotspots of biogeochemical activity and trophic interactions in the pelagic ecosystem.

A associação simbiótica entre a diatomácea cêntrica Chaetoceros coarctatus e o ciliado peritríquio Vorticella oceanica é amplamente conhecida e registrada em diversos estudos, porém nunca havia sido analisada sob o ponto de vista de suas implicações para o movimento destes organismos. A fim de contribuir com novos dados acerca desta associação simbiótica, o presente trabalho analisou a relevância ecológica da simbiose entre Chaetoceros e Vorticella, por meio de um estudo comportamental do deslocamento destes organismos na coluna de água. As associações foram coletadas em águas costeiras de Ubatuba, São Paulo, onde sua ocorrência foi observada em elevada abundância, particularmente durante o verão. Utilizando técnicas de imagem de alta frequência em um sistema óptico tridimensional foi possível descrever os padrões de deslocamento desta associação e avaliar as implicações ecológicas deste comportamento. De acordo com as análises realizadas neste trabalho, pode-se sugerir que o comportamento de deslocamento realizado pela associação Chaetoceros-Vorticella na coluna de água resulta em vantagens tanto para o epibionte quanto para o hospedeiro. Em termos de submesoescala, este estudo sugere que o deslocamento realizado pela associação Chaetoceros-Vorticella pode contribuir para a formação de camadas finas, levando à formação de hotspots de atividade biogeoquímica e interações tróficas no ecossistema pelágico. / The symbiotic association between the centric diatom Chaetoceros coarctatus and the peritrich ciliate Vorticella oceanica is widely known and reported in several studies, but its implications for the movement of these organisms have never been analyzed. In order to contribute with new data about this symbiotic association, the present study investigated the ecological relevance of the Chaetoceros-Vorticella association by recording displacement parameters of these organisms in the water column. The associations were collected in coastal waters of Ubatuba, São Paulo, where their occurrence was observed in high abundance, particularly during the summer. Using high-resolution imaging techniques in a three dimensional optical system it was possible to describe the displacement patterns of this association and to provide initial insights about the ecological implications of this behavior. It is suggested that the displacement behavior performed by the Chaetoceros-Vorticella association in the water column is beneficial for both the epibiont and the host. In terms of submesoscale processes, this study indicates that the displacement carried out by the Chaetoceros-Vorticella association may contribute to the formation of thin layers, leading to the formation of hotspots of biogeochemical activity and trophic interactions in the pelagic ecosystem.

Comprendre les facteurs favorables à l’établissement et au maintien de proliférations d’algues toxiques et nuisibles est essentiel afin de mieux les prévoir. L’allélopathie, c’est-à-dire la libération de composés qui inhibent les compétiteurs, favorise l’espèce allélopathique et contribue ainsi à modifier la communauté planctonique. Les dinoflagellés toxiques du genre Alexandrium produisent des composés allélopathiques, cependant les interactions allélopathiques sont encore mal comprises. L'objectif de cette thèse était de contribuer à la compréhension des mécanismes d’allélopathie en étudiant l'interaction allélopathique entre A. minutum et la diatomée Chaetoceros muelleri. Les résultats de ces travaux ont mis en évidence que les composés allélopathiques d'A.minutum perturbaient le fonctionnement des membranes des diatomées en quelques minutes. La cascade d'événements physiologiques suivant l'interaction allélopathique comprend des effets tels que la perméabilisation de membranes, l'inhibition de la photosynthèse, la production d'espèces réactives de l'oxygène et la modification de la composition des membranes. Ce projet a mis en évidence le fait que l’allélopathie d’A. minutum est sous contrôle environnemental, son activité s’est accrue d’un facteur 4 en présence de concentrations toxiques de Cu. Enfin, le développement d’un bioessai a facilité la purification des composés allélopathiques par fractionnement guidé. Nous avons isolé un groupe de candidats hydrophobes dont l’activité doit être testée après isolement. Cette thèse propose de nouveaux outils et ouvre de nouvelles perspectives pour étudier les conséquences de ces interactions dans les écosystèmes marins. / Understanding the factors that favor the establishment and the persistance of harmful algal blooms is essential for predicting them. Allelochemical potency, i.e. the release of compounds that inhibit competitors, is hypothesized to favor the organisms that produce them and shape plankton community. The toxic dinoflagellates from the genus Alexandrium produce allelochemicals, however, associated interactions are poorly understood. The objective of this thesis is to contribute to our understanding by studying the mechanisms behind the allelochemical interactions between the A. minutum and the diatom Chaetoceros muelleri. The results of this work have highlighted that A. minutum allelochemicals disrupted membrane functioning of the diatoms within minutes. The cascade of physiological events following the allelochemical interaction that was described here, included permeabilisation of membranes, inhibition of photosynthesis, production of reactive oxygen species and modifications of the biochemical composition of membranes. This project has also highlighted that the allelochemical potency of A. minutum can be significantly modulated by environmental parameters, as allelochemical potency increased 4 times when exposed to toxic concentrations of Cu. Finally, a bioassay developed during this PhD eased the partial isolation of the allelochemicals through fractionation. We isolated a hydrophobic candidates whose activity have to be investigated following their isolation. This PhD provides a better understanding of the cellular mechanisms underlying allelochemical interactions and offers new tools and raises new perspectives to study the consequences of these interactions on marine ecosystems.

Diatoms are estimated to contribute 25 percent of the primary production on Earth and therefore they play a significant role in the global carbon cycle. Diatom blooms often terminate with the formation of aggregates that sink rapidly from surface waters, affecting the flux of organic carbon from the surface to deep waters and the sea floor. The role of carbon-rich transparent exopolymeric particles (TEP) in aggregate formation as ocean temperature increases has yet to investigated in continuous cultures. I hypothesize that temperature increase can influence the production of TEP, a fraction of total suspended exopolymers. To test the hypothesis, a laser in situ scattering and transmissometry instrument (LISST-100X, Sequoia Instruments) successfully counted and sized six individual diatom species in batch culture: Chaetoceros muelleri, Coscinodiscus wailesii, Thalassiosira weissflogii, Phaeodactylum tricornutum, Skeletonema costatum, and Skeletonema marinoi and successfully demonstrated its efficacy in detecting diatom aggregates using S. costatum. Four replicate continuous cultures were sampled for particle size distribution (PSD), nutrients, chlorophyll a, total carbohydrates, prokaryote concentration, and TEP at temperatures of 22.5, 27 and then 20 degrees C. While TEP particles were scarce, acid polysaccharide (APS)-coated C. muelleri cells were observed, forming dense webs on the filters. Both carbohydrate per cell and APS area per cell were found to significantly correlate with temperature (p<0.05) while significant difference between APS concentration at each temperature was only found between 27 and 22.5 or 20 degrees C (p<0.05). Net changes in PSDs with increasing temperature showed that distributions of relative volume concentration decreased in the smallest size bins and increased in the largest size bins. Our results show that increasing the temperatures of nitrogen-limited C. muelleri cultures did not cause increased TEP formation but instead resulted in increased cell-surface coating. Increasing concentration of cell coatings and TEP particles will cause diatoms to aggregate more readily, enhancing their sinking rate away from the ocean surface. Increased ocean temperature has great implications for diatom blooms and other microorganisms, causing greater export of carbon out of the surface waters and potentially altering the microbial loop.

Made available in DSpace on 2014-06-12T23:02:30Z (GMT). No. of bitstreams: 2 arquivo8258_1.pdf: 1570642 bytes, checksum: 2b0c8c62eb728b6a2ff6cca67f0a17bb (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2007 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho teve por objetivo determinar a composição bioquímica de Chaetoceros muelleri Lemmerman, uma importante espécie para atividades na aqüicultura, em diferentes meios de cultivo. Os bioensaios foram realizados em duas etapas e mantidos nas mesmas condições (iluminação constante; 22±1°C; pH de 8 a 9 e salinidade 33 ups). O meio controle utilizado foi F/2 Guillard (F/2) e os meios alternativos de cultivo foram extrato de esterco de gado (EEG) e de minhoca (EEM). Na primeira etapa, a diatomácea C. muelleri foi cultivada em 500 mL dos meios de cultivo, em triplicatas, e determinou-se a densidade celular, taxa diária de crescimento, clorofila a e biovolume. A fase exponencial foi definida através da curva de crescimento. A segunda etapa dos bioensaios foi iniciada em garrafão plástico até o volume final de 20 litros, para cada meio. A cada aumento do volume foram determinadas a densidade celular e a concentração de clorofila a. As análises bioquímicas foram realizadas com o material precipitado dos garrafões (20 L), através de centrifugação (4000 rpm, 15 min). Esse precipitado foi seco em estufa até peso constante, à temperatura de 40ºC. Foram analisados nitrogênio total, carboidrato total, proteína total e lipídeo total, em triplicatas. Na primeira etapa dos bioensaio, as maiores densidades celulares foram de 11,05±1,32 x106 céls.mL-1, F/2; no 60 dia; de 8,33±0,83 x106 céls.mL-1, EEG, no 40 dia e de 6,86±0,38 x106 céls.mL-1, EEM, 80 dia. O valor médio da taxa diária de crescimento celular de C. muelleri, na fase log, para o meio F/2 foi de 0,65±0,70, enquanto que, para os meios EEG e EEM foi de 0,97±0,43 e 0,36±0,31, respectivamente. Os teores máximos de clorofila a foram de 0,34±0,03 pg.cél.-1, no 70 dia, meio F/2; de 0,74±0,90 pg.cél.-1, no 90 dia; meio EEG e de 2,26±1,70 pg.cél.-1, no 120 dia, meio EEM. Os maiores valores de biovolume celular foram de 528,55±321,06 &#956;m3, para o meio F/2 e de 515,28±351,87 &#956;m3, para o meio EEG, no 50 dia, em ambos meios; e, de 534,17±454,13 &#956;m3, para o meio EEM, no 110 dia. Na segunda etapa dos bioensaios, para o volume final de 20 L, as concentrações médias da densidade celular para o meio F/2 foi de 21,61±0,24 x106 céls.mL-1, para o meio EEG de 18,53±0,43 x106 céls.mL-1 e para o meio EEM de 23,07±0,44 x106 céls.mL-1. Os teores médios de clorofila a foram de 0,90±0,01 x10-7 pg.cél.-1, para o meio EEG, seguida de 0,79±0,05 x10-7 pg.cél.-1, para o meio EEM e de 0,73±0,02 x10-7 pg.cél.-1, para o meio F/2. Quanto ao nitrogênio total, os valores médios foram 3,35±0.06% de matéria seca, para o meio EEM; 2,30±0,05% de matéria seca, para o meio F/2 e 1,80±0.05% de matéria seca, para o meio EEG. Em relação ao valor médio de lipídio total, no meio EEM foi de 0,112±0,001 pg.cél.-1; e para os meios F/2, de 0,104±0,001 pg.cél.-1 e EEG, 0,100±0,001 pg.cél.-1. Para a proteína total, o valor médio no meio EEM, foi de 0,226±0,012 pg.cél.-1 e nos meios F/2, de 0,140±0,014 pg.cél.-1 e EEG, 0,125±0,001 pg.cél.-1. Para o carboidrato total, o valor médio no meio EEM, foi de 36,22±1,53 pg.cél.-1, seguido dos meios EEG, 29,16±0,81 pg.cél.-1 e F/2, 19,76±0,85 pg.cél.-1. Entre as médias dos dados analisados para os bioensaios (F/2, EEG e EEM), foram encontradas diferenças significativas (p<0,05). Estatisticamente, em relação aos parâmetros analisados para a espécie C. muelleri, o meio extrato de esterco de minhoca demonstrou que pode ser utilizado como fonte nutritiva para o desenvolvimento algal, podendo substituir meios convencionais como o meio F/2 Guillard

The sediment Core SWERUS-L2-2-PC1 (2PC) retrieved from the Chukchi Sea, Arctic Ocean sits in an oceanographically dynamic location at the Arctic-Pacific Ocean gateway. The 8.3 m-long core was retrieved in Herald Canyon at the marginal ice zone at 57 m depth. Core 2PC is well-positioned to record variability in inflow of Bering Sea Water (BSW) and Pacific Water (PW) in Herald Canyon. With the 2PC high sedimentation rate (200 cm/kyr), two independent age models (radiocarbon and palaeomagnetism) based on tephra age markers, and a richness in well-preserved siliceous sediment, validate 2PC as an outstanding sequence for applying diatom assemblage analysis as a proxy for ocean-climate change back to 4250 years BP, including the past few hundred years where global warming and sea ice decline is recorded by instrumental records. These characteristics make Core-2PC a useful record for investigating the role of PW on sea ice variability in the Chukchi Sea, both in the past and predicting the future. To investigate the impact of PW on ocean and sea ice conditions in the Chukchi Sea, diatom assemblage analysis was performed on 49 samples through the Late Holocene. The over-arching goal was to test the hypothesis, suggested by existing research on 2PC using benthic foraminifera Mg/Ca palaeothermometry, that the strength of PW inflow into the Chukchi Sea via Herald Canyon has varied on a time scales of ~500-1000 years in the past 4000 years. PW is slightly warmer than resident Arctic surface waters and is known to be an important control on Arctic sea-ice. The diatom assemblage approach assumes that there are recognizable differences between end-member diatom assemblages that are characteristic of PW versus Arctic Ocean type environments associated with extensive sea-ice conditions. The mapping of species in the Herald Canyon was used to test the idea of variability of sea-ice extent and the role of the Pacific Ocean forcings into the western Chukchi Sea. The results reveal diverse diatom assemblages throughout the past 4000 years in Herald Canyon, showing this core to be very useful for diatom palaeoclimate reconstructions. A total of 126 species with abundance &gt;1% are recognized. Several generalist species typically dominate assemblages especially Chaetoceros, ice-algae, marine-neritic and near ice or cold-water planktic centric diatoms. Distinct changes in stratigraphy are illustrated by changes in identified diatom assemblage zones. The 2PC diatom assemblages were contrasted with records from Chukchi-, Laptev-, East Siberian- and Bering Sea and North Pacific Ocean. At 2PC, sympagic (sea-ice related), planktic and neritic species abundance varies on time scales of ~500-1000 years. Importantly, there is a clear similarity between the timing of diatom assemblage changes and the 2PC benthic foraminifera Mg/Ca bottom water temperature (BWT) reconstruction. In particular, abundance changes in the warm water species Thalassionema nitzschioides, Shionodiscus oestrupii and Thalassionema simonsenii, tychoplanktic Paralia sulcata, Ice algae- and sympagic assemblages and cold-water indicators correspond best to BWT fluctuations shown by the Mg/Ca reconstruction. These oscillations are suggestive of changes in warmer PW inflow. Other aspects of the diatom data appear to correlate with colder and warmer climate events and suggest that changes in PW inflow amplified the effects of these events in the Chukchi Sea region through the Late Holocene in the Northern Hemisphere. It can thus, be concluded that diatoms from 2PC, support the palaeoceanographic reconstruction suggested by the benthic foraminifera Mg/Ca palaeothermometry and that variations in PW inflow through Herald Canyon is an important driver of sea ice variability on thousand-year time scales.