Blue Lake, Jefferson County, Oregon, has high summer surface phosphorus concentrations (ca. 30 ug/l) yet is oligotrophic (summer Secchi depth is 11 to 16 meters). Nutrient enrichment experiments done with 1000 1 polyethylene enclosures indicate nitrate limitation of phytoplankton growth. Basin morphology may be an important factor in nutrient cycling in this lake. The lake has a maximum depth of 95.7 meters with an average depth of 42.7 meters. The lake basin has steep sides with only 4% of the lake bottom less than 3.3 meters deep. of recent volcanic origin. In contrast, Suttle Lake, which is immediately downstream from Blue Lake, is moderately eutrophic (Secchi depth 1.7 meters) and supports much larger populations of phytoplankton, including nitrogen fixing cyanophytes. Suttle Lake is shallower and more subject to wind mixing.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 143-154). / The physical environment in the oceans dictates not only how phytoplankton cells are dispersed and their populations intermingled, but also mediates the supply of nutrients to the surface mixed layer. In this thesis I explore both of these aspects of the interaction between phytoplankton ecology and ocean physics, and have approached this topic in two distinct but complementary ways, working with a global ocean ecosystem model, and collecting data at sea. In the first half of the thesis, I examine the role of mesoscale physical features in shaping phytoplankton community structure and influencing rates of primary production. I compare the output of a complex marine ecosystem model coupled to coarse resolution and eddy-permitting physical models. Explicitly resolving eddies resulted in marked regional variations in primary production, zooplankton and phytoplankton biomass. The same phytoplankton phenotypes persisted in both cases, and were dominant in the same regions. Global phytoplankton diversity was unchanged. However, levels of local phytoplankton diversity were markedly different, with a large increase in local diversity in the higher resolution model. Increased diversity could be attributed to a combination of enhanced dispersal, environmental variability and nutrient supply in the higher resolution model. Diversity "hotspots" associated with western boundary currents and coastal upwelling zones are sustained through a combination of all of these factors. In the second half of the thesis I describe the results of a fine scale ecological and biogeochemical survey of the Kuroshio Extension Front. I found fine scale patterns in physical, chemical and biological properties that can be linked back to both the large scale horizontal and smaller scale vertical physical dynamics of the study region. A targeted genomic analysis of samples focused on the ecology of the picoeukaryote Ostreococcus clade distributions strongly supports the model derived hypotheses about the mechanisms supporting diversity hotspots. Strikingly, two distinct clades of Ostreococcus co-occur in more than half of the samples. A "hotspot" of Ostreococcus diversity appears to be supported by a confluence of water masses containing either clade, as well as a local nutrient supply at the front and the mesoscale variability of the region. / by Sophie Anne Clayton. / Ph.D.

Thesis: Ph. D., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 124-131). / Dinoflagellates are a diverse group of single-celled eukaryotic phytoplankton that are important for their unique genetics and molecular biology, the multitude of ecological roles they play, and the ability of multiple species to produce toxins that affect human and ecosystems health. Two dinoflagellate genera, Alexandrium and Gambierdiscus each contain species that can cause human poisoning syndromes, although the methods of toxin transfer, accumulation, and exposure are very different. Gambierdiscus is a benthic organism that produces lipophilic ciguatoxins that can bioaccumulate in coral reef fish and cause ciguatera fish poisoning (CFP) in human consumers. Alexandrium is a planktonic species that produces saxitoxins that can directly accumulate in shellfish and cause paralytic shellfish poisoning (PSP) in humans. Both genera contain multiple species that vary dramatically in toxicity and physiology. Through transcriptomic analysis, this thesis describes the genetic diversity present across dinoflagellates that produce saxitoxin, elaborating on differences in their complement of genes within the saxitoxin biosynthesis pathway. This study demonstrated retention and expression of some of these saxitoxin genes by non-toxic species within Alexandrium, as well as in Gambierdiscus, which does not produce saxitoxins. Furthermore it confirmed the presence of certain transcripts only in toxin-producing species. This thesis then developed novel fluorescence in situ hybridization (FISH) probes that can be used to identify and enumerate six Gambierdiscus species, thereby enabling the community composition of Gambierdiscus to be examined in a quantifiable manner. The probes were tested in the laboratory on cultures, and then successfully applied to field samples from Florida Keys and Hawai'i. Gambierdiscus species are diverse in both their toxicity and optimal temperature ranges for growth. Analysis of Gambierdiscus community composition in an area of variable temperature allowed the characterization of species shifts that were driven both by a seasonal increase in mean seawater temperatures and spatial variability of temperature experienced between tidal pools. Overall this thesis advances the knowledge of dinoflagellate genetics and ecology, aids in the characterization of species harmful to public health, and provides tools and approaches to help monitor and manage harmful effects from these species, including some that are projected to increase with climate change. / by Kathleen Johnson Pitz. / Ph. D.

No description available.

Climate change predictions include increasing precipitation and runoff events that expose phytoplankton communities to colored dissolved organic matter (cDOM) and nutrient pulses of varying intensity and frequency. The consequence of different nutrient/cDOM pulse regimes on phytoplankton communities and the role of legacy effects related to the characteristics of previous exposure regimes remain largely unresolved. To investigate this, we implemented add-on bottle experiments with water collected from a mesocosm experiment conducted in Lake Erken (Sweden) with four nutrient regime treatments with varying intensity and frequency. The nutrient additions of the mesocosm experiment lasted for three weeks and were followed by a two-week recovery period. At the end of both periods, water from three mesocosm treatments was filled into microcosms and either exposed to a second single nutrient pulse or left as control. The microcosms were incubated for 8 days in the lab and changes in phytoplankton biomass and composition were analyzed to determine the legacy effect of antecedent nutrient regimes on the community response to a second nutrient addition. The results showed that past nutrient regimes created legacy effects on the community, dampening further changes in response to a second nutrient addition. However, the effects were transient, since they were not detected in the second microcosm experiment. Further, the lack of legacy effects in the second microcosm experiment suggests that the communities from the mesocosm treatments in fact recovered from the nutrient regimes they were exposed to in the two-week period. Consequently, the results of the thesis suggest that legacy effects may be important in predicting phytoplankton community response to extreme nutrient and cDOM pulses but they might be temporary.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24454号 / 理博第4953号 / 新制||理||1707(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 中野 伸一, 教授 木庭 啓介, 教授 中務 真人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Deer Creek Reservoir in Utah has a history of high algae concentrations. Despite recent nutrient reduction efforts, seasonal algae continue to present problems. Cost effective, accurate, and comprehensive monitoring is important to understand the reservoir processes driving this problem and characterizing the algae spatial and temporal distributions are an important part of this effort. Current laboratory methods for accurately measuring algae are expensive and time consuming and are based on water samples taken in the field and transported to the laboratory. This approach only provides data for relatively few point samples because of the time and expense of sample collection and analysis. These relatively few samples do not describe the complex spatial and temporal trends in the algal data. Algae exhibit non-uniform distributions, especially in the vertical direction. In situ probes are able to measure chlorophyll-a and provide a less expensive measuring alternative than laboratory methods. These probes provide relatively quick, high resolution vertical profile measurements, which allows for more comprehensive horizontal and temporal sampling. To have confidence in the probe data, good correlations between in situ chlorophyll-a measurements and laboratory algae or chlorophyll measurements are important, but these correlations can be reservoir and time dependant as reservoir conditions change. Therefore, they must be developed for each study site. This study reports on efforts at Deer Creek Reservoir to develop these correlations and provide a general description of the dynamic reservoir algal processes. I found that chlorophyll-a is weakly correlated to most algae species in the reservoir. However, it correlated well with total phytoplankton biovolume and the dominant algal species, which for this study was the diatom. Variations in correlation strength among the several algae species was assumed to most likely be affected by environmental factors, sample methods, algae species diversity, and the accuracy of the optical chlorophyll-a sensor. The data analysis indicate that the field methods used to obtain laboratory samples may have been a significant source of error because of the difficulty of matching the location of a probe measurement to the location of a sample. Field samples were not taken at the same depths as probe measurements and field samples from two locations were either mixed before laboratory analysis or the sample was a composite over a 2-meter range. Based on my observations, I have made several recommendations to improve the accuracy of the correlation between algae and chlorophyll-a.

The occurrence of phytoplankton taxa, with special focus on harmful algal bloom (HAB) taxa, was monitored for one year off the central coast of California to examine both their co-occurrence and physical and chemical variables influencing their temporal patterns. Bi-weekly samples were taken from October 6, 2008 to October 5, 2009 in San Luis Obispo Bay, CA. Canonical correspondence analysis (CCA) of weekly samples indicated that 46.1% of the variability in species abundance was explained by the variables in the model, higher than previous reports. Cluster analysis divided phytoplankton communities into HAB and non-HAB groups of species, while shared distribution analysis identified specific co-occurring species of HABs. The HAB dinoflagellate group consisted exclusively of HAB taxa, including Cochlodinium polykrikoides Margalef, Dinophysis acuminata Claparède & Lachmann, and Alexandrium spp., and was correlated with a homogeneous water column and high nitrate concentration during the fall and winter seasons. The domoic acid producing diatoms Pseudo-nitzschia seriata (Cleve) H. Peragallo complex and Pseudo-nitzschia delicatissima (Cleve) Heiden complex grouped with several other non-HAB diatoms, and were correlated with warm, thermally stratified waters of the summer season. These results contradict the classic diatom / dinoflagellate succession theory and suggest that event-scale processes influencing water column stability within seasons may influence the distribution of HAB species in near shore upwelling dominated regions.

Understanding and explaining spatio-temporal dynamics of ecological communities and their interaction with the environment is a central goal in ecology, but at the same time a very challenging task. Functional traits are a promising concept to achieve a better mechanistic understanding of variations in community structure. Traits are characteristics of organisms that directly or indirectly influence fitness and vary largely between different species. As traits functionally link communities with their bio-geochemical environment, they are well suited for explaining how community structure changes in response to changing environmental conditions, and how in turn communities shape their surrounding environment. Despite the potential of trait-based approaches to mechanistically explain the relationship between communities and their environment, they have rarely been applied in freshwater ecology. Therefore, this thesis explores spatio-temporal dynamics in functional traits of freshwater phytoplankton communities and their interaction with the environment, using the Rappbode Reservoir in Germany as a case study. Phytoplankton community data from a seasonally resolved dataset with 50 years of observation from the Rappbode Reservoir were used to translate taxonomic composition into ecologically meaningful functional trait values. The studied functional traits showed consistent, reoccurring seasonal developments that clearly mirrored environmental pressures over the year. From late autumn to spring nutrients and turbulence were high. Hence small celled, fast growing species that are able to rapidly incorporate existing nutrients and tolerate poor light conditions dominated (dominant traits: maximum growth rate, light affinity). In contrast, when turbulence and nutrients were low in summer, large cell size and more complex mechanisms to efficiently exploit mineral nutrients or acquire previously unexploited nutrient pools were key ecological strategies (dominant traits: phosphate affinity, mixotrophy, motility, nitrogen fixation). The similarity in observed trait patterns over several years indicates that despite the diversity and complexity of phytoplankton species dynamics, the seasonal succession is a highly ordered, predictable process, driven by trade-offs between different ecological strategies. During the 50 years of observation, nutrient concentrations in the Rappbode Reservoir decreased strongly (oligotrophication). A comparison between nutrient-rich and nutrient-deficient years revealed that the general intra-annual succession patterns of phytoplankton functional traits remained the same. However, the intra-annual succession patterns were more pronounced in nutrient-rich years. While functional community composition in summer changed little after oligotrophication, spring communities were largely affected by nutrient reductions and functional traits in spring became more similar to the ones in summer. Based on the quantitative analysis of functional traits, the thesis could generalize the existing patterns to provide a quantitative, functional template for seasonal succession patterns in lake ecosystems under nutrient-rich and nutrient-deficient conditions. Over the entire observation period, phytoplankton biomass did not respond to reduced phosphorus concentrations. This unexpected resistance of algal biomass against reductions in the limiting resource phosphorus was caused by changes in internal processes and functional traits of the phytoplankton community, allowing them to adapt to lower nutrient levels without a loss in total biomass. The main casual mechanism for the decoupling of inorganic nutrients from phytoplankton biomasses was an increase in phagotrophic mixotrophs and their ability to make bacterial phosphorus available for the entire phytoplankton community. Further, in nutrient-deficient years biomass losses in spring were compensated by high biomasses in summer. Higher summer biomasses compared to spring biomasses in nutrient-deficient years were probably also linked to a decrease in diatoms in spring. Diatoms are characterized by high sinking velocities. This trait in combination with phosphorus uptake by diatom cells leads to high downward nutrient exports from the pelagic zone. The decrease of diatoms in nutrient-poor years was related to less phosphorus losses over the season, leaving more nutrients for summer phytoplankton. The effect of species with high sinking velocities on seasonal phosphorus processing illustrates the importance of functional trait composition on biogeochemical cycling. A one-year monitoring campaign with a high temporal and depth resolution at Rappbode Reservoir allowed to investigate the impact of vertical phytoplankton trait distributions on the geochemical environment. During summer, a phytoplankton mass development occurred at the depth of the metalimnion, mainly represented by the cyanobacterium Planktothrix rubescens. The positive net growth at larger depth of this metalimnetic species is enabled through the possession of specific traits, e.g. buoyancy regulation and the ability for efficient light harvesting. The data indicated that the occurrence of metalimnetic species was connected to the formation of a metalimnetic oxygen minimum. The oxygen minimum occurred after the metalimnetic algae peak disappeared from the thermocline. Metalimnetic phytoplankton induced oxygen depletion probably through one of the following processes: Oxygen consumption by bacteria related to the degradation of dead organic material from metalimnetic algae or internal respiration of metalimnetic algae towards the end of the growing season leading to net oxygen losses due to the continuation of algal respiration. This constitutes a previously undiscovered mechanism for the development of metalimnetic oxygen minima. In conclusion, the thesis illustrates how trait-based approaches enhance ecological understanding of phytoplankton community dynamics. The trait-based approaches shed light on how phytoplankton communities respond to environmental gradients and how communities can affect their geochemical environment. The thesis also shows that functional traits can be used to reduce the complexity of communities through converting species information into ecologically meaningful functions and that they allow to link changes in community composition to corresponding features in the biogeochemical environment. The quantitative, trait-based approaches used in this study therefore improve our mechanistic understanding of community dynamics and are a step forward to higher predictability and generality in limnology.

Long-term ecological research in deep lakes offers valuable insights into understanding changes in trophic states and organization of phytoplankton assemblages. Utilizing five decades of phytoplankton taxonomic trait data from pre-alpine Lake Constance, a confirmed negative relationship was found between phosphate and light affinity at the annual community trait level. Drawing inspiration from the stronger community-level tradeoff observed between the affinity for phosphate and light among phytoplankton species in Lake Constance, I hypothesized that resource acquisition traits, characterized by the half-saturation constants for nutrient-limited growth (Mi) and light-limited growth (Hi), should exhibit a negative trade-off mechanism at the community mean trait level, derived from the traits of the species in Lake Constance. The developed model was parametrized using empirical data from the lake. Intra- and inter-annual variation in environmental conditions were incorporated in the model by considering seasonal changes in temperature, light intensity, temperature-influenced exchange rates of the vertical water column, and decadal changes in nutrients in Lake Constance. Simulations reflected observed seasonal dominance patterns of phytoplankton species and predicted differences in relative abundance under varying nutrient supplies, aligning with resource limitation trends. Consistent with empirical observations, a negative relationship between light and phosphorous affinity is observed in the 60-year simulation of Lake Constance. The elucidation of such a trade-off mechanism is expected to facilitate the understanding of the coexistence of phytoplankton species in Lake Constance amidst the decadal changes in phosphorus loading by selecting for higher light affinity during eutrophic phases and higher phosphorus affinity during oligotrophic phases.