Matching Items (37)

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Response of Daphnia feeding rate to food C:P ratio: a test for the ""stoichiometric knife edge"" mechanism

Description

It is well known that deficiencies in key chemical elements (such as phosphorus, P) can reduce animal growth; however, recent empirical data have shown that high levels of dietary nutrients

It is well known that deficiencies in key chemical elements (such as phosphorus, P) can reduce animal growth; however, recent empirical data have shown that high levels of dietary nutrients can also reduce animal growth. In ecological stoichiometry, this phenomenon is known as the "stoichiometric knife edge," but its underlying mechanisms are not well-known. Previous work has suggested that the crustacean zooplankter Daphnia reduces its feeding rates on phosphorus-rich food, causing low growth due to insufficient C (energy) intake. To test for this mechanism, feeding rates of Daphnia magna on algae (Scenedesmus acutus) differing in C:P ratio (P content) were determined. Overall, there was a significant difference among all treatments for feeding rate (p < 0.05) with generally higher feeding rates on P-rich algae. These data indicate that both high and low food C:P ratio do affect Daphnia feeding rate but are in contradiction with previous work that showed that P-rich food led to strong reductions in feeding rate. Additional experiments are needed to gain further insights.

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  • 2014-05

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Symbiotic state & reproduction in the giant green sea anemone Anthopleura xanthogrammica

Description

The giant green sea anemone, Anthopleura xanthogrammica, hosts two different endosymbiotic algae. One is a unicellular chlorophyte, Elliptochloris marina; the other is Symbiodinium muscatinei, a dinoflagellate. Hosting these different symbionts

The giant green sea anemone, Anthopleura xanthogrammica, hosts two different endosymbiotic algae. One is a unicellular chlorophyte, Elliptochloris marina; the other is Symbiodinium muscatinei, a dinoflagellate. Hosting these different symbionts influences the life history strategy of A. xanthogrammica's congener A. elegantissima, directly impacting its reproductive strategy (asexual vs. sexual). My study sought to examine whether the type and density of symbiont also affects the reproductive condition of A. xanthogrammica, which reproduces only sexually. Gonad development was measured in anemones from Slip Point, Clallam Bay, WA and Tongue Point, WA along with symbiont type and density per mg of anemone protein. The results indicate a trend towards brown anemones having more developed gonads, especially in males. This may mean that A. xanthogrammica anemones that host zooxanthellae are more reproductively fit than zoochlorellate anemones. Thus, it may be favorable for anemones to host zooxanthellae. This is especially true in summer months when the high temperatures and mid-day low tides coincide with the period of most rapid gonad development.

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Date Created
  • 2015-05

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Studying Plankton Community Dynamics in the Sargasso Sea Using Microscopy and Molecular Techniques

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

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.

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Date Created
  • 2013-05

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Prochlorococcus Marinus Cell Growth, Aggregate Formation and TEP Production under Nutrient Limited Conditions

Description

Prochlorococcus marinus (MED4), a genus of marine picocyanobacteria that proliferates in open oligotrophic ocean, is one of the most abundant photosynthetic microbes in the world, estimated to contribute up to

Prochlorococcus marinus (MED4), a genus of marine picocyanobacteria that proliferates in open oligotrophic ocean, is one of the most abundant photosynthetic microbes in the world, estimated to contribute up to 10% of the ocean’s primary production. The productivity of these microorganisms is controlled by macronutrient availability in the surface waters. The ratio of macronutrients in the ocean was defined, by Alfred Redfield, as an elemental ratio of 106C:16N:1P. However, the C:N:P ratio varies based on region, season, temperature and irradiance, as well as the composition of the primary producers. In oligotrophic gyres, these nutrient ratios are elevated from the Redfield stoichiometry, but whether this ratio exerts influence on the growth rate of the organism has not been investigated. Elemental stoichiometry of available nutrients can affect the aggregation of organic carbon and exportation of the particles to the ocean depths. The purpose of this study was to investigate the effects of nutrient limitation on aggregation and transparent exopolymeric particle (TEP) production which aids in aggregation. My findings suggested that nutrient limitation reduces TEP production and does not increase aggregate volume concentration. With continued warming, certain regions of the ocean will become more oligotrophic, which further decreases the nutrient supply available for Prochlorococcus. My research shows that this could lead to decreased exportation of organic carbon matter to the depths of the sea.

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Date Created
  • 2019-05

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Assessing Light Use Efficiencies (LUEs) Of Benthic Reef Communities For Spectral Modeling Applications

Description

Coral reefs are diverse marine ecosystems, where reef building corals provide both the structure of the habitat as well as the primary production through their symbiotic algae, and alongside algae

Coral reefs are diverse marine ecosystems, where reef building corals provide both the structure of the habitat as well as the primary production through their symbiotic algae, and alongside algae living on the reef itself, are the basis of the food web of the reef. In this way, coral reefs are the ocean's "forests" and are estimated to support 25% of all marine species. However, due to the large size of a coral reef, the relative inaccessibility and the reliance on in situ surveying methods, our current understanding of reefs is spatially limited. Understanding coral reefs from a more spatially complete perspective will offer insight into the ecological factors that contribute to coral reef vitality. This has become a priority in recent years due to the rapid decline of coral reefs caused by mass bleaching. Despite this urgency, being able to assess the entirety of a coral reef is physically difficult and this obstacle has not yet been overcome. However, similar difficulties have been addressed in terrestrial ecosystems by using remote sensing methods, which apply hyperspectral imaging to assess large areas of primary producers at high spatial resolutions. Adapting this method of remote spectral sensing to assess coral reefs has been suggested, but in order to quantify primary production via hyper spectral imaging, light-use efficiencies (LUEs) of coral reef communities need to be known. LUEs are estimations of the rate of carbon fixation compared to incident absorbed light. Here, I experimentally determine LUEs and report on several parameters related to LUE, namely net productivity, respiration, and light absorbance for the main primary producers in coral reefs surrounding Bermuda, which consist of algae and coral communities. The derived LUE values fall within typical ranges for LUEs of terrestrial ecosystems, with LUE values for coral averaging 0.022 ± 0.002 mol O2 mol photons-1 day-1 at a water flow rate of 17.5 ± 2 cm s^(-1) and 0.049 ± 0.011 mol O2 mol photons-1 day-1 at a flow rate of 32 ± 4 cm s^(-1) LUE values for algae averaged 0.0335 ± 0.0048 mol O2 mol photons-1 day-1 at a flow rate of 17.5 ± 2 cm s^(-1). These values allow insight into coral reef productivity and opens the door for future remote sensing applications.

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Date Created
  • 2019-05

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Marine Aggregation interactions of Prochlorococcus and Marinobacter adhaerens

Description

The changes in marine ecological conditions brought on by warming and stratification of the oceans have radically shifted many marine environments around the globe. This project aimed to better characterize

The changes in marine ecological conditions brought on by warming and stratification of the oceans have radically shifted many marine environments around the globe. This project aimed to better characterize the aggregation behavior of the abundant picocyanobacterium Prochlorococcus marinus, which is hypothesized to dominate over other phytoplankton as the primary autotroph in increasingly warmer and nutrient poor oceans. This aggregation, believed to be mediated through the secretion of sticky Transparent Exopolymeric Substances (TEP), might be key for Prochlorococcus to sink throughout the ocean and serve as a source of carbon to other communities within its environment. Considering the relatively low concentration of TEP secreted by Prochlorococcus when on its own, this study explored the synergistic effect that heterotrophic bacteria and inorganic minerals in the surrounding seawater may have on the aggregation of P. marinus. This was done by inoculating P. marinus and the model heterotroph Marinobacter adhaerens HP15 individually and mixed in cylindrical roller tanks with the addition of ballasting clay minerals into roller tanks to simulate constant sinking for 7 days. The aggregates which formed after rolling were quantified and their sinking velocities and excess densities were measured. Our results indicate that the most numerous and densest aggregates formed when Prochlorococcus was in the presence of both M. adhaerens and kaolinite clay particles. I will discuss how methodology, particularly cell number, may play a role in the enhanced aggregation that I found when Prochlorococcus was cultured together with the Marinobacter.

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Date Created
  • 2020-05

The Intertidal Ecosystems of Puerto Peñasco: A Collaboration with CEDO and the Clean Beaches Committee of Puerto Peñasco to Educate Beach Visitors on Local Biodiversity

Description

The Northern Gulf of California is characterized by an extreme tidal range and temperature fluctuations between seasons, as well as a large variation in microhabitats along its shoreline. As a

The Northern Gulf of California is characterized by an extreme tidal range and temperature fluctuations between seasons, as well as a large variation in microhabitats along its shoreline. As a result, the intertidal regions exhibit a diverse and distinct collection of species that have adapted to these environmental conditions, with roughly 4.6 percent being endemic. Minimal knowledge of these ecosystems existed until the 1940’s, when the renowned author John Steinbeck accompanied marine biologist Edward Ricketts on an expedition with the purpose of documenting the biodiversity of the Sea of Cortez. Today, the majority of research in the Northern Gulf of California is directed by CEDO, the Intercultural Center for the Study of Deserts and Oceans. The purpose of this project is to compile a literature review of research on the intertidal areas of the Northern Gulf and produce an illustrated brochure that educates beach visitors on local biodiversity as a collaboration with CEDO and the Clean Beaches Committee of Puerto Peñasco. This brochure aims to increase respect and appreciation for these species, as increased tourism over the past few decades has led to detrimental effects on the ecosystem. Additionally, it serves to promote the success of the Blue Flag certification of El Mirador beach in front of Manny’s Beach Club.

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Date Created
  • 2021-05

How cyanobacteria bore

Description

Some cyanobacteria, referred to as boring or euendolithic, are capable of excavating tunnels into calcareous substrates, both mineral and biogenic. The erosive activity of these cyanobacteria results in the destruction

Some cyanobacteria, referred to as boring or euendolithic, are capable of excavating tunnels into calcareous substrates, both mineral and biogenic. The erosive activity of these cyanobacteria results in the destruction of coastal limestones and dead corals, the reworking of carbonate sands, and the cementation of microbialites. They thus link the biological and mineral parts of the global carbon cycle directly. They are also relevant for marine aquaculture as pests of mollusk populations. In spite of their importance, the mechanism by which these cyanobacteria bore remains unknown. In fact, boring by phototrophs is geochemically paradoxical, in that they should promote precipitation of carbonates, not dissolution. To approach this paradox experimentally, I developed an empirical model based on a newly isolated euendolith, which I characterized physiologically, ultrastructurally and phylogenetically (Mastigocoleus testarum BC008); it bores on pure calcite in the laboratory under controlled conditions. Mechanistic hypotheses suggesting the aid of accompanying heterotrophic bacteria, or the spatial/temporal separation of photosynthesis and boring could be readily rejected. Real-time Ca2+ mapping by laser scanning confocal microscopy of boring BC008 cells showed that boring resulted in undersaturation at the boring front and supersaturation in and around boreholes. This is consistent with a process of uptake of Ca2+ from the boring front, trans-cellular mobilization, and extrusion at the distal end of the filaments (borehole entrance). Ca2+ disequilibrium could be inhibited by ceasing illumination, preventing ATP generation, and, more specifically, by blocking P-type Ca2+ ATPase transporters. This demonstrates that BC008 bores by promoting calcite dissolution locally at the boring front through Ca2+ uptake, an unprecedented capacity among living organisms. Parallel studies using mixed microbial assemblages of euendoliths boring into Caribbean, Mediterranean, North and South Pacific marine carbonates, demonstrate that the mechanism operating in BC008 is widespread, but perhaps not universal.

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Date Created
  • 2010

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The ecology of the plankton communities of two desert reservoirs

Description

In 2010, a monthly sampling regimen was established to examine ecological differences in Saguaro Lake and Lake Pleasant, two Central Arizona reservoirs. Lake Pleasant is relatively deep and clear, while

In 2010, a monthly sampling regimen was established to examine ecological differences in Saguaro Lake and Lake Pleasant, two Central Arizona reservoirs. Lake Pleasant is relatively deep and clear, while Saguaro Lake is relatively shallow and turbid. Preliminary results indicated that phytoplankton biomass was greater by an order of magnitude in Saguaro Lake, and that community structure differed. The purpose of this investigation was to determine why the reservoirs are different, and focused on physical characteristics of the water column, nutrient concentration, community structure of phytoplankton and zooplankton, and trophic cascades induced by fish populations. I formulated the following hypotheses: 1) Top-down control varies between the two reservoirs. The presence of piscivore fish in Lake Pleasant results in high grazer and low primary producer biomass through trophic cascades. Conversely, Saguaro Lake is controlled from the bottom-up. This hypothesis was tested through monthly analysis of zooplankton and phytoplankton communities in each reservoir. Analyses of the nutritional value of phytoplankton and DNA based molecular prey preference of zooplankton provided insight on trophic interactions between phytoplankton and zooplankton. Data from the Arizona Game and Fish Department (AZGFD) provided information on the fish communities of the two reservoirs. 2) Nutrient loads differ for each reservoir. Greater nutrient concentrations yield greater primary producer biomass; I hypothesize that Saguaro Lake is more eutrophic, while Lake Pleasant is more oligotrophic. Lake Pleasant had a larger zooplankton abundance and biomass, a larger piscivore fish community, and smaller phytoplankton abundance compared to Saguaro Lake. Thus, I conclude that Lake Pleasant was controlled top-down by the large piscivore fish population and Saguaro Lake was controlled from the bottom-up by the nutrient load in the reservoir. Hypothesis 2 stated that Saguaro Lake contains more nutrients than Lake Pleasant. However, Lake Pleasant had higher concentrations of dissolved nitrogen and phosphorus than Saguaro Lake. Additionally, an extended period of low dissolved N:P ratios in Saguaro Lake indicated N limitation, favoring dominance of N-fixing filamentous cyanobacteria in the phytoplankton community in that reservoir.

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Date Created
  • 2011

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El Niño Southern Oscillation influences on precipitation, discharge, and nutrient concentrations in the upper Salt River Watershed in Arizona

Description

Many studies over the past two decades examined the link between climate patterns and discharge, but few have attempted to study the effects of the El Niño Southern Oscillation (ENSO)

Many studies over the past two decades examined the link between climate patterns and discharge, but few have attempted to study the effects of the El Niño Southern Oscillation (ENSO) on localized and watershed specific processes such as nutrient loading in the Southwestern United States. The Multivariate ENSO Index (MEI) is used to describe the state of the ENSO, with positive (negative) values referring to an El Niño condition (La Niña condition). This study examined the connection between the MEI and precipitation, discharge, and total nitrogen (TN) and total phosphorus (TP) concentrations in the Upper Salt River Watershed in Arizona. Unrestricted regression models (UMs) and restricted regression models (RMs) were used to investigate the relationship between the discharges in Tonto Creek and the Salt River as functions of the magnitude of the MEI, precipitation, and season (winter/summer). The results suggest that in addition to precipitation, the MEI/season relationship is an important factor for predicting discharge. Additionally, high discharge events were associated with high magnitude ENSO events, both El Niño and La Niña. An UM including discharge and season, and a RM (restricting the seasonal factor to zero), were applied to TN and TP concentrations in the Salt River. Discharge and seasonality were significant factors describing the variability in TN in the Salt River while discharge alone was the significant factor describing TP. TN and TP in Roosevelt Lake were evaluated as functions of both discharge and MEI. Some significant correlations were found but internal nutrient cycling as well as seasonal stratification of the water column of the lake likely masks the true relationships. Based on these results, the MEI is a useful predictor of discharge, as well as nutrient loading in the Salt River Watershed through the Salt River and Tonto Creek. A predictive model investigating the effect of ENSO on nutrient loading through discharge can illustrate the effects of large scale climate patterns on smaller systems.

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Date Created
  • 2012