Matching Items (4)
Description
The phytoplankton communities in the open oceans are dominated by picophytoplankton (0.7-2µm) and nanophytoplankton (3-5µm). Studying the community dynamics of these phytoplankton is important to learn about their role in the carbon cycle and food web of the oceans. Dilution experiments were used, along with microscopy and molecular techniques, to determine abundance, biomass and phytoplankton growth and grazing rates in the oligotrophic Sargasso Sea (western North Atlantic subtropical gyre) around the Bermuda Atlantic Time Series Station (BATS) in the summer of 2012. With low biomass and chlorophyll a, the Sargasso Sea appears to be unproductive at first glance, but I found that pico- and nanophytoplankton have high instantaneous growth rates that are balanced by the high grazing rates of microzooplankton.
Mesoscale eddies are important features in the Sargasso Sea that can increase or decrease the available nutrients in the euphotic zone. Two different mesoscale eddies were sampled: an anti-cyclonic eddy and the BATS station which was located at the edge of a cyclonic eddy. The results indicated that BATS had overall higher instantaneous growth (µ between 0.1 d-1 and 3.7 d-1) and grazing rates on pico- and nanophytoplankton, as well as diatoms, compared to the anti-cyclonic eddy (µ between 0.2 d-1 and 3 d-1). I also determined taxon-specific rates using quantitative polymerase chain reaction (qPCR) for the order Mamiellales, one of the smallest representatives of the abundant prasinophytes. This method yielded surprisingly high growth (9.7 d-1 ) and grazing rates (-8.2 d-1) at 80m for BATS. The euphotic zone (~100m) integrated biomass of all phytoplankton did not vary significantly between BATS (379 mg C m-2) and the anti-cyclonic eddy (408 mg C m-2) and the net growth rates at both locations were very close to zero for most of the groups. Although the biomass and net growth rates did not vary greatly between the two locations, the high instantaneous growth and grazing rates of pico- and nano-eukaryotic phytoplankton indicate an increase in the rate of the marine microbial food web, or microbial loop, compared to the anti-cyclonic eddy. This could have been due to the input of new nutrients in the edge of the cyclonic eddy at BATS. Thus, my study suggests that mesoscale variability is of considerable importance for the dynamics of the phytoplankton community and their role in the microbial loop. Much can be learned when using DNA based taxon-specific rates, especially to understand the relative importance and contribution of specific taxa.
More taxon-specific molecular studies will have to be carried out to quantify specific rates of more phytoplankton groups, which will supply a more complete knowledge of phytoplankton community dynamics in the Sargasso Sea. This will increase our understanding of the role of specific groups to the biological carbon dynamics in the euphotic zone into the deep ocean.
Mesoscale eddies are important features in the Sargasso Sea that can increase or decrease the available nutrients in the euphotic zone. Two different mesoscale eddies were sampled: an anti-cyclonic eddy and the BATS station which was located at the edge of a cyclonic eddy. The results indicated that BATS had overall higher instantaneous growth (µ between 0.1 d-1 and 3.7 d-1) and grazing rates on pico- and nanophytoplankton, as well as diatoms, compared to the anti-cyclonic eddy (µ between 0.2 d-1 and 3 d-1). I also determined taxon-specific rates using quantitative polymerase chain reaction (qPCR) for the order Mamiellales, one of the smallest representatives of the abundant prasinophytes. This method yielded surprisingly high growth (9.7 d-1 ) and grazing rates (-8.2 d-1) at 80m for BATS. The euphotic zone (~100m) integrated biomass of all phytoplankton did not vary significantly between BATS (379 mg C m-2) and the anti-cyclonic eddy (408 mg C m-2) and the net growth rates at both locations were very close to zero for most of the groups. Although the biomass and net growth rates did not vary greatly between the two locations, the high instantaneous growth and grazing rates of pico- and nano-eukaryotic phytoplankton indicate an increase in the rate of the marine microbial food web, or microbial loop, compared to the anti-cyclonic eddy. This could have been due to the input of new nutrients in the edge of the cyclonic eddy at BATS. Thus, my study suggests that mesoscale variability is of considerable importance for the dynamics of the phytoplankton community and their role in the microbial loop. Much can be learned when using DNA based taxon-specific rates, especially to understand the relative importance and contribution of specific taxa.
More taxon-specific molecular studies will have to be carried out to quantify specific rates of more phytoplankton groups, which will supply a more complete knowledge of phytoplankton community dynamics in the Sargasso Sea. This will increase our understanding of the role of specific groups to the biological carbon dynamics in the euphotic zone into the deep ocean.
ContributorsHamill, Demetra Scott (Author) / Neuer, Susanne (Thesis director) / Elser, Jim (Committee member) / De Martini, Francesca (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2013-05
Description
Lower termites are classified as termites that require a symbiotic relationship with their hindgut community of single-celled protozoa in order to gather nutrients to survive. The class Spirotrichonymphea is one of the six classes of protists that make up the Phylum Parabasalia. Within the class Spirotrichonymphea, there are 3 families and 11 genera. In this study, the Spirotrichonympha, Spironympha, and Microjoenia genera (family Spirotrichonymphidae), Holomastigotes genus (family Holomastigotidae), along with a new genus Brugerollea were targeted for molecular analysis. Protist cells were collected from Reticulitermes tibialis (Rhinotermitidae), Hodotermopsis sjostedti (Archotermopsidae), and Paraneotermes simplicornis (Kalotermidiae). Most molecular phylogenetic studies of termite-associated protists have used the 18S rRNA gene, however, there have been some ambiguities in the phylogeny of this gene. EF1-α, also known as EF1A, is a protein whose sequence can additionally be used to study the evolution of protists. EF1-α gene sequences were obtained from isolated protist cells by reverse transcription PCR (RT-PCR). Additionally, the 18S rRNA gene was amplified to confirm the isolated cells’ identity and compare the two phylogenetic methods, to see which would better resolve phylogenetic ambiguities. Sequences were compiled into an alignment for each target gene, and then a maximum likelihood tree was created for each using RAxML. Results from both trees supports the monophyly of Spirotrichonymphea and the polyphyly of genus Spirotrichonympha. However, neither gene fully resolves the phylogeny of Spirotrichonymphea.
ContributorsNguyen, Keana (Author) / Gile, Gillian (Thesis director) / De Martini, Francesca (Committee member) / Taerum, Stephen Joshua (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Trichonympha is a Parabasalian symbiont of lower termites. They are characterized by their spindle-shape, length ranging from 75-150 micrometers, longitudinal flagella, as well as their true rostral tube composed of two plates of parabasal fibers. Ealy analysis through microscopy has revealed that the same species of Trichonympha could be found across multiple species of termites. However, with recent phylogenetic analysis of the 18S region, it has been found that the species is actually genetically distinct and that Trichonympha have coevolved with their termite hosts. In this study, Trichonympha cells from Reticulitermes tibialis, R. flavipes, and R. lucifugus were isolated. DNA from the single cell samples were purified and amplified through a series of polymerase chain reactions (PCR) and gel electrophoresis. The amplified DNA was extracted from the gel and cloning was performed using competent E. coli. The colonies that formed from each sample were collected and those that amplified after a PCR reaction were sent to the ASU Genomics Core for sanger sequencing. The sequences were assembled, cleaned, and aligned and the maximum likelihood and Bayesian phylogenetic trees were constructed. It was found that there is evidence of multiple species of Trichonympha in R. flavipes and that there were multiple species found in R. lucifugus. However, the Trichonympha sequences from R. lucifugus branch in different clades which indicates that they are more distant species than those of R. flavipes. Additionally, Trichonympha cells from R. tibialis branched in the same clade as those from R. flavipes which provides evidence that the same Trichonympha species can be found in multiples species of Reticulitermes. With these pieces of evidence, we can see multiple patterns of diversity of Trichonympha in their termite hosts.
ContributorsGaylor, Maya (Author) / Gile, Gillian (Thesis director) / De Martini, Francesca (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2022-05
Description
The ocean sequesters more than 25% of the carbon released by anthropogenic action every year, and oligotrophic oceans, such as the Sargasso Sea, are responsible for about 50% of the global carbon export. Pico- and nano-phytoplankton (cells < 5 µm), mostly unicellular eukaryotes (protists) and cyanobacteria, dominate the primary production in the Sargasso Sea; however, little is known about their contribution to the export of carbon into the deep ocean via sinking particles. The overall goal of this study is to examine the link between growth and grazing rates of pico- and nano-phytoplankton and the carbon export in the Sargasso Sea. I investigate three aspects: 1) how microzooplankton grazing and physical forcing affect taxon-specific primary productivity in this region, 2) how these microbial trophic dynamics impact their contribution to the export of particulate matter, and 3) how much pico-phytoplankton, specifically the pico-cyanobacteria Synechococcus and Prochlorococcus, contribute to the carbon export. I collected seawater samples within the sunlit (euphotic) zone, and sinking particles at 150 m depth using particle traps in the Sargasso Sea during the winter and summer seasons of 2011 and 2012. I conducted dilution experiments to determine the growth and grazing rates of the pico- and nano-phytoplankton community, and used 454 pyrosequencing and quantitative Polymerase Chain Reaction to measure the relative and absolute contribution of these primary producers to the plankton community within the euphotic zone and in the sinking particles. I found that micrograzing controls taxon-specific primary production, and that microbial trophic dynamics impact directly the taxonomical composition of the sinking particles. For the first time, I was able to quantify clade-specific carbon export of pico-cyanobacteria and found that, despite their small size, these tiny primary producers are capable of sinking from the surface to the deeper oceans. However, their contribution to the carbon flux is often less than one tenth of their biomass contribution in the euphotic zone. Our study provides a comprehensive approach to better understand the role of pico- and nano-phytoplankton in the carbon cycle of oligotrophic oceans, and a baseline to study changes in the carbon export in future warmer oceans.
ContributorsDe Martini, Francesca (Author) / Neuer, Susanne (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Hartnett, Hilairy (Committee member) / Lomas, Michael (Committee member) / Arizona State University (Publisher)
Created2016