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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigations into temporal and spatial variability of zooplankton at the Svalbard archipelago

Rabindranath, Ananda January 2013 (has links)
Plankton are generally considered good indicators for ocean climate variability, but plankton data from the Arctic are still comparatively scarce. Due to this scarcity of information, the prevalence of vertical migration behaviour at high latitude is still debated. Atlantic inflow is a key process governing biological diversity in the Arctic Ocean, and the location of the Svalbard archipelago makes it an ideal study area to monitor this inflow. Comparing the zooplankton community within the fjords of Svalbard at various latitudes allowed us to assess the influence of Atlantic inflow and any subsequent changes in zooplankton composition that may have implications for higher trophic levels. Using sediment traps deployed on oceanic moorings, Chapter 3 of this thesis analysed long term observations from sea-ice dominated Rijpfjorden for the first time, and compared the zooplankton to Atlantic Water influenced Kongsfjorden. Chapters 4 and 5 investigated the spatial relevance of our moored observations using shipboard observations, and chapters 6 and 7 present observations of vertical migration across a range of conditions. Kongsfjorden was dominated by Calanus copepods associated with Arctic and Atlantic water, and strongly influenced by Atlantic Water advection. Rijpfjorden was largely influenced by sea-ice formation with higher proportional abundances of macrozooplankton species. Advection brought Atlantic associated species into Rijpfjorden during warmer years. Prevailing hydrology and bathymetry were highlighted as factors forcing zooplankton distribution, while advection was identified as responsible for much of the observed small scale spatial variation amongst weaker swimmers. At an aggregation scale of 0.5 nautical miles, zooplankton distribution was highly patchy and moored observations could only be reliably expanded outwards to a maximum of 1 nautical mile. Low amplitude diel vertical migration (especially by younger copepodids) was identified in surface waters when a food source was available. These observations must be considered within the dynamic framework of advection highlighted by this thesis.
2

Sobrevivência e migração vertical de larvas infectantes de Trichostrongylus colubriformis em gramíneas, nas diferentes estações do ano

Rocha, Raquel Abdallah da [UNESP] 24 April 2006 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:32:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-04-24Bitstream added on 2014-06-13T19:43:51Z : No. of bitstreams: 1 rocha_ra_dr_botfmvz.pdf: 361805 bytes, checksum: 5c55d3f7c6f6c5d5c1f2a2ed98259327 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / O experimento teve como objetivo avaliar a sobrevivência de larvas infectantes (L3) de Trichostrongylus colubriformis em três espécies forrageiras. Para tal, foram utilizados módulos experimentais constituídos por seis canteiros de 32,4 m2 cada, estabelecidos com as seguintes gramíneas forrageiras: Brachiaria decumbens cv. Australiana, Cynodon dactilon cv. Coast-cross e Panicum maximum cv. Aruana, perfazendo dois canteiros por espécie. Cada canteiro foi dividido em 36 parcelas, de 30 x 30 cm, de forma a permitir seis repetições por espécie e por altura em cada semana de colheita de material. A sobrevivência larval foi avaliada nas quatro estações do ano, sob o efeito de duas alturas de poda das forragens (baixa, 5 cm e alta, 30 cm). A poda foi realizada imediatamente antes da deposição das fezes. Ocorreram quatro deposições de fezes, uma a cada estação do ano. A colheita das fezes e da forragem foi realizada uma, duas, quatro, oito, 12 e 16 semanas após cada deposição de fezes nos canteiros experimentais. A altura da forragem foi medida em cada uma das subdivisões imediatamente antes das colheitas. A forragem foi cortada com uma tesoura de poda, rente ao solo, de uma área delimitada com o auxílio de um círculo de 10 cm de raio. As fezes foram recolhidas manualmente dos canteiros. A recuperação de L3 das amostras fecais foi maior quando as fezes foram depositadas em meio ao capim alto (com 30 cm - P<0,05). Porém, a recuperação de L3 nas forragens foi similar em ambos os cortes. Em relação à concentração de L3, o corte baixo propiciou maior quantidade de L3 por quilo de matéria seca (P<0,05). As maiores recuperações de L3, nas fezes e nas forragens, ocorreram quando as fezes foram depositadas no outono e na primavera. Dentre as espécies forrageiras, o capim aruana foi o que no geral apresentou maiores concentrações de larvas infectantes de T. colubriformis. / The purpose of the experiment was to evaluate infective Trichostrongylus colubriformis larvae (L3) survival in three forage species. Experimental modules formed by six 32.4-m2 plot, established with the following forage grass species, were used in the study: Australian Brachiaria decumbens cv., Cynodon dactilon cv. Coast-cross, and Panicum maximum cv. Aruana, totaling two plots for each species. Each plot was divided into 36 30 x 30 cm parts in order to allow six replicates per species and per height in each week of material collection. Larval survival was evaluated in the four seasons of the year under the effect of two forage paring heights (low, 5 cm, and high, 30 cm). The paring was carried out immediately before the feces were deposited. Four feces deposits were made, one in each season of the year. Feces and forage collection was performed one, two, four, eight, 12 and 16 weeks after each feces deposition in the experimental plots. Forage grass height was measured in each subdivision immediately before the collections. The forage was cut using pairing scissors, close to the soil, from an area delimited with a circle with a 10-cm radius. The feces were collected manually from the plots. L3 recovery rates from fecal samples were bigger when the feces were deposited in high grass (measuring 30 cm - P<0,05). However, L3 recovery in the forages was similar for both cuts. So far as the L3 concentration is concerned, the low cut resulted in a bigger number of L3 per kilogram of dry matter (P<0,05). The higher L3 recovery in the feces and in the forage grass occurred when the feces were deposited in the autumn and in the spring. Among the forage species, the aruana grass was the one that, in general, harbored the biggest concentrations of infecting T. colubriformis larvae.
3

Behavioral Strategies of Lanternfishes (Family Myctophidae) in a High-Latitude Fjord and the Tropical Red Sea

Dypvik, Eivind 12 1900 (has links)
The diel vertical migration (DVM) and feeding periodicity of myctophids (lanternfishes) were studied in the high-latitude Masfjorden, Norway, and the tropical Red Sea. In Masfjorden, a bottom-mounted echo sounder permitted continuous studies throughout the year, and revealed a diverse seasonal DVM behavior. During spring and summer, when zooplankton peaks in the epipelagic zone, migrating glacier lanternfish performed normal DVM (NDVM), ascending to the epipelagic zone during night and residing below ~200m during daytime. During autumn and winter, when Calanus overwinters between ~150–300 m, migrating glacier lanternfish mainly performed inverse DVM (IDVM), ascending to feed on Calanus in mid-waters during daytime. Non migrating (NoDVM) individuals were present all year below ~300 m in Masfjorden. In the Red Sea, where zooplankton has an epipelagic distribution, the whole population of skinnycheek lanternfish performed NDVM, feeding in the epipelagic zone at night, while residing at ~500–750 m during daytime. The warm waters of the Red Sea were hypothesized to limit the time individuals can stay in the mesopelagic zone without migrating to feed in the epipelagic layers. The DVM behavior of myctophids largely seemed to relate to the distribution of zooplankton, and it was hypothesized that NDVM will prevail with epipelagic distribution of prey, while IDVM and NoDVM are common in areas where zooplankton migrate seasonally to mesopelagic depths. Potential predators were continuously present, found to apparently attack glacier lanternfish, at mesopelagic depth in Masfjorden. Thus, myctophids are under threat of predation even at mesopelagic depth.
4

Sezónní vývoj a vertikální distribuce korýšů v hluboké stratifikované nádrži Josefův Důl v Jizerských horách / Seasonal dynamics and vertical distribution of Crustacea in the deep stratified reservoir Josefův Důl (the Jizera Mountains, Czech Republic)

Adámek, Radek January 2015 (has links)
The zooplankton of Josefův Důl, a large and deep drinking water reservoir recovering from acidification, develop in relation to the improving water chemistry but also predation by salmonid fish re-stocked at the end of the 1990s. Crustacea are represented by small numbers of several species only, and nothing is known about their distribution in the water column. Recently, picocyanobacteria Merismopedia sp. became dominant in the phytoplankton, which hampers substantially the treatability of the raw water. The aim of the thesis is to describe the seasonal dynamics and vertical distribution of Crustacea in the Josefův Důl reservoir, together with parameters of the environment, and to study their possible diurnal vertical migrations in the summer period.
5

Filamentous cyanobacteria in the Baltic Sea - spatiotemporal patterns and nitrogen fixation

Almesjö, Lisa January 2007 (has links)
<p>Summer blooms of filamentous, diazotrophic cyanobacteria are typical of the Baltic Sea Proper, and are dominated by <i>Aphanizomenon </i>sp<i>.</i> and the toxic <i>Nodularia spumigena.</i> Although occurring every summer, the blooms vary greatly in timing and spatial distribution, making monitoring difficult and imprecise. This thesis studies how the spatial variability of Baltic cyanobacterial blooms influences estimates of abundance, vertical and horizontal distribution and N<sub>2</sub>-fixation. Implications for sampling and monitoring of cyanobacterial blooms are also discussed.</p><p>The results of the thesis confirm the importance of diazotrophic cyanobacteria in providing N for summer production in the Baltic Proper. It also highlights the large spatial and temporal variation in these blooms and argues that improved spatial coverage and replication could make monitoring data more useful for demonstrating time trends, and for identifying the factors regulating the blooms. The vertical distribution of <i>Aphanizomenon</i> and <i>Nodularia</i> was found to be spatially variable, probably as a combination of species-specific adaptations and ambient weather conditions. Vertical migration in <i>Aphanizomenon</i> was more important towards the end of summer, and is probably regulated by a trade-off between P-availability and light and temperature.</p>
6

Filamentous cyanobacteria in the Baltic Sea - spatiotemporal patterns and nitrogen fixation

Almesjö, Lisa January 2007 (has links)
Summer blooms of filamentous, diazotrophic cyanobacteria are typical of the Baltic Sea Proper, and are dominated by Aphanizomenon sp. and the toxic Nodularia spumigena. Although occurring every summer, the blooms vary greatly in timing and spatial distribution, making monitoring difficult and imprecise. This thesis studies how the spatial variability of Baltic cyanobacterial blooms influences estimates of abundance, vertical and horizontal distribution and N2-fixation. Implications for sampling and monitoring of cyanobacterial blooms are also discussed. The results of the thesis confirm the importance of diazotrophic cyanobacteria in providing N for summer production in the Baltic Proper. It also highlights the large spatial and temporal variation in these blooms and argues that improved spatial coverage and replication could make monitoring data more useful for demonstrating time trends, and for identifying the factors regulating the blooms. The vertical distribution of Aphanizomenon and Nodularia was found to be spatially variable, probably as a combination of species-specific adaptations and ambient weather conditions. Vertical migration in Aphanizomenon was more important towards the end of summer, and is probably regulated by a trade-off between P-availability and light and temperature.
7

Larval Release Rhythms and Larval Behavior of Palinurid Lobsters: a Comparative Study

Ziegler, Tracy Ann 28 November 2007 (has links)
This dissertation investigated larval release and larval behavior of the Caribbean spiny lobster Panulirus argus and the spotted spiny lobster P. guttatus. These species were examined under laboratory conditions to determine the phase relationship between larval release and natural environmental cycles. P. argus displayed a nocturnal tidal rhythm, while P. guttatus displayed a circadian rhythm in larval release. P. argus releases larvae near the time of nocturnal high slack water, while P. guttatus released larvae near the time of sunrise. The role of 'pumping pheromones' in controlling larval release behaviors was tested by measuring the pumping response of ovigerous P. argus to (1) hatch water, (2) homogenized-embryo water, (3) embryo-conditioned water, and (4) water containing homogenized-egg cases. Lobsters with late-stage embryos displayed increased pleopod pumping with increased concentration of hatch water. Water individually conditioned with homogenized late-stage embryos, intact late-stage embryos, and homogenized egg-cases induced pumping activity in females with late-stage embryos, indicating the presence of a chemical cue. I quantified pumping responses upon exposure to synthetic peptides to determine if they mimicked pheromones that induce larval release behaviors. Pumping behavior was evoked by oligopeptides with a basic amino acid at the carboxy-terminus, preceded by several neutral amino acids. Carboxyl-terminal arginine peptides serve as pheromone mimics. I investigated whether these peptides originate from the action of trypsin-like enzymes by conducting a bioassay measuring pumping activity of ovigerous P. argus subjected to increasing concentrations of trypsin, trypsin inhibitor, and a combination of the two. Pumping activity increased with increasing concentrations of trypsin and trypsin inhibitor, while behaviors ceased when ovigerous females were subjected to a complex of the two. Pheromones are generated by trypsin-like enzymes assisting in the degradation of the egg membranes at the time of hatching. Vertical swimming behaviors of stage-I phyllosoma larvae of P. argus and P. guttatus were observed under laboratory conditions. P. argus larvae displayed a pattern of twilight vertical migration, while P. guttatus larvae displayed nocturnal diel vertical migration (DVM). Rhythms persisted for 5-6 cycles under constant conditions, indicating that an endogenous rhythm in activity plays a proximate role in DVM for both species. / Dissertation
8

38-kHz ADCP investigation of deep scattering layers in sperm whale habitat in the northern Gulf of Mexico

Kaltenberg, Amanda May 17 February 2005 (has links)
A hull-mounted 38-kHz phased-array acoustic Doppler current profiler (ADCP) was used to acoustically survey the continental margin of the northern Gulf of Mexico (GOM) during 6 cruises in 2002-2003. This is the first backscatter survey with a 38-kHz ADCP in the Gulf of Mexico. ADCPs have been used as a proxy to measure the volume backscatter return from plankton in the water column, however previous studies were restricted to the upper 200 to 300 meters due to the relatively high frequency of operation (150-300 kHz) of the transducers. In addition to measuring deep water current velocities, the 38-kHz phased-array ADCP can measure Relative Acoustic Backscatter Intensity (RABI) as deep as 1000 meters. The daytime depth of the main deep scattering layer at 400 to 500 meters was resolved, and locally high backscatter intensity can be seen down to 800 meters. The objectives were to determine how to analyze RABI from the instrument to resolve scattering layers, and then to seek secondary deep scattering layers of potential prey species below the main deep scattering layer, from 600 to 800 meters in the feeding range for Gulf of Mexico sperm whales. Based on RABI from the 38-kHz ADCP, secondary DSLs in sperm whale diving range were more commonly recorded over the continental shelf than in the deep basin region of the Gulf of Mexico. The daytime depths of migrating plankton showed variation depending on physical circulation features (cyclone, anticyclone, proximity to Mississippi river, and Loop Current) present. Vertical migrations compared between concurrently running 38 and 153-kHz ADCPs showed an overlap of acoustic scatterers recorded by the two instruments, however the 153-kHz instrument has much finer vertical resolution. Vertical migration rates were calculated and simultaneous net tow samples from one of the cruises was used to compare abundance estimates by the two methods.
9

The influence of the Loop Current on the diversity, abundance, and distribution of zooplankton in the Gulf of Mexico

Rathmell, Katie 01 June 2007 (has links)
Physical processes in the Gulf of Mexico (GOM) and mesoscale (10-300 km) processes associated with the Loop Current are fairly well known. However, little is known about the physical/ biological interactions of the frontal boundary system of the Loop Current. Zooplankton abundance and distribution was determined at 28 stations in the vicinity of the Loop Current. Species richness was high at all stations. Copepods comprised 60% of the total zooplankton collected. Oithona plumifera, Nannocalanus minor and Euchaeta marina were the most abundant copepods. Chaetognaths and ostracods were also very abundant and made up 11 and 5 % respectively of the zooplankton total. Total zooplankton abundance was higher at the boundary of the LC than it was inside the LC but not significantly different from abundances outside of the LC. Stations in the western Gulf of Mexico and on the western boundary had the highest abundances of zooplankton overall. The chlorophyll concentrations at the chlorophyll maximum were higher at the boundary of the LC than inside the LC. Physical-biological processes associated with the frontal boundary of the LC appear to influence the abundance and distribution of zooplankton in the GOM.
10

Influence of swimming marine organisms on turbulence in the ocean from in-situ measurements

Rousseau, Shani 23 July 2009 (has links)
Microstructure and acoustic data were collected in Saanich Inlet, British Columbia, and at Ocean Station P in the eastern subarctic North Pacific Ocean with the objective of observing krill-generated turbulence. At Ocean Station P, although a number of species composing the zooplankton community are large enough to generate turbulent flow (Re > 10e3), no turbulence events could be correlated with presence of swimming marine organisms and measurements indicated turbulence generated by shear. Zooplankton densities were likely too low to produce turbulence at the scale of an aggregation and the O(10e-2 m) scattered turbulent signals generated by individuals are difficult to detect in the natural environment. In Saanich Inlet, higher dissipation rates were observed in regions of high acoustic backscattering, suggesting that zooplankton-generated turbulence was occurring. Although presence of zooplankton was often correlated with high dissipation rates, high dissipation rates were frequently observed in the absence of zooplankton, suggesting multiple sources of turbulence. High dissipation rates were observed in the presence of non-migrating zooplankton as much as in the migrating layer. These turbulence events occurred at a scale of more than 1 m as they were positively detected by our dissipation rate estimation technique. This suggests that marine organisms can act together to generate turbulence at scales that can produce diapycnal mixing. Over all time-series collected, dissipation rates in the presence of zooplankton averaged 1.4 x 10e-8 W/kg whereas the average in the absence of zooplankton was 0.7 x 10e-8 W/kg.

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