The distinctive karstic, freshwater wetlands of the northern Caribbean and Central American region support the prolific growth of calcite-rich periphyton mats. Aside from the Everglades, very little research has been conducted in these karstic wetlands, which are increasingly threatened by eutrophication. This study sought to (i) test the hypothesis that water depth and periphyton total phosphorus (TP) content are both drivers of periphyton biomass in karstic wetland habitats in Belize, Mexico and Jamaica, (ii) provide a taxonomic inventory of the periphytic diatom species in these wetlands and (iii) examine the relationship between periphyton mat TP concentration and diatom assemblage at Everglades and Caribbean locations. Periphyton biomass, nutrient and diatom assemblage data were generated from periphyton mat samples collected from shallow, marl-based wetlands in Belize, Mexico and Jamaica. These data were compared to a larger dataset collected from comparable sites within Everglades National Park. A diatom taxonomic inventory was conducted on the Caribbean samples and a combination of ordination and weighted-averaging modeling techniques were used to compare relationships between periphyton TP concentration, periphyton biomass and diatom assemblage composition among the locations. Within the Everglades, periphyton biomass showed a negative correlation with water depth and mat TP, while periphyton mat percent organic content was positively correlated with these two variables. These patterns were also exhibited within the Belize, Mexico and Jamaica locations, suggesting that water depth and periphyton TP content are both drivers of periphyton biomass in karstic wetland systems within the northern Caribbean region. A total of 146 diatom species representing 39 genera were recorded from the three Caribbean locations, including a distinct core group of species that may be endemic to this habitat type. Weighted averaging models were produced that effectively predicted mat TP concentration from diatom assemblages for both Everglades (R2=0.56) and Caribbean (R2=0.85) locations. There were, however, significant differences among Everglades and Caribbean locations with respect to species TP optima and indicator species. This suggests that although diatoms are effective indicators of water quality in these wetlands, differences in species response to water quality changes can reduce the predictive power of these indices when applied across systems.

Estuaries are dynamic on many spatial and temporal scales. Distinguishing effects of unpredictable events from cyclical patterns can be challenging but important to predict the influence of press and pulse drivers in the face of climate change. Diatom assemblages respond rapidly to changing environmental conditions and characterize change on multiple time scales. The goals of this research were to 1) characterize diatom assemblages in the Charlotte Harbor watershed, their relationships with water quality parameters, and how they change in response to climate; and 2) use assemblages in sediment cores to interpret past climate changes and tropical cyclone activity. Diatom assemblages had strong relationships with salinity and nutrient concentrations, and a quantitative tool was developed to reconstruct past values of these parameters. Assemblages were stable between the wet and dry seasons, and were more similar to each other than to assemblages found following a tropical cyclone. Diatom assemblages following the storm showed a decrease in dispersion among sites, a pattern that was consistent on different spatial scales but may depend on hydrological management regimes. Analysis of sediment cores from two southwest Florida estuaries showed that locally-developed diatom inference models can be applied with caution on regional scales. Large-scale climate changes were suggested by environmental reconstructions in both estuaries, but with slightly different temporal pacing. Estimates of salinity and nutrient concentrations suggested that major hydrological patterns changed at approximately 5.5 and 3 kyrs BP. A highly temporally-resolved sediment core from Charlotte Harbor provided evidence for past changes that correspond with known climate records. Diatom assemblages had significant relationships with the three-year average index values of the Atlantic Multidecadal Oscillation and the El Niño Southern Oscillation. Assemblages that predicted low salinity and high total phosphorus also had the lowest dispersion and corresponded with some major storms in the known record, which together may provide a proxy for evidence of severe storms in the paleoecological record.

Benthic diatoms are often used as indicators of water quality and past environmental conditions. This depends entirely on a reliable taxonomic system. With the advent of DNA techniques, genetic analyses can now be used in tandem with traditional microscopy in order to improve taxonomy and determine evolutionary relationships. This thesis examined a speciose genus of diatoms Neidium (> 300 species) and, using sequence data from molecular markers as well as traditional morphological analyses, investigated phylogenetic relationships. Fresh benthic samples from aquatic ecosystems in Eastern North America were collected; Neidium taxa were examined using light and scanning electron microscopy then compared to the original specimen types. A total of 124 individual cells were retrieved, amplified, and sequenced for four molecular markers (rbcL, 18S, psbA, and psbC). Phylogenetic reconstructions were completed using Maximum likelihood and Bayesian analyses; when compared with morphological analyses this led to the delineation of several novel Neidium species.

In this study, I examined water chemistry of 31 Canadian Shield lakes in relation to catchment characteristics to test the hypothesis that Shield lakes with more marble may exhibit iron (Fe) deficiency and, hence, be more vulnerable to eutrophication. I performed a diatom-based paleolimnological reconstruction of one of these lakes (Heney Lake), which was subjected to anthropogenic stresses including a fish farm. Results suggest that the presence of marble influenced lake chemistry, including lowering the ratio of Fe: P. The reconstruction of historical P concentrations was not statistically possible but past Fe could be inferred, which no previous study has attempted. Certain eutrophication-associated diatom species suggest that logging and European settlement beginning in the early XXth century led to a slight increase in nutrient concentrations. However, a more important diatom species shift was likely related to climate change, as observed in other temperate lakes worldwide.

The spatial and temporal distribution of modern diatom assemblages in surface sediments, on the most dominant macrophytes, and in the water column at 96 locations in Florida Bay, Biscayne Bay and adjacent regions were examined in order to develop paleoenvironmental prediction models for this region. Analyses of these distributions revealed distinct temporal and spatial differences in assemblages among the locations. The differences among diatom assemblages living on subaquatic vegetation and sediments, and in the water column were significant. Because concentrations of salts, total phosphorus (WTP), total nitrogen (WTN) and total organic carbon (WTOC) are partly controlled by water management in this region, diatom-based models were produced to assess these variables. Discriminant function analyses showed that diatoms can also be successfully used to reconstruct changes in the abundance of diatom assemblages typical for different habitats and life habits. To interpret paleoenvironmental changes, changes in salinity, WTN, WTP and WTOC were inferred from diatoms preserved in sediment cores collected along environmental gradients in Florida Bay (4 cores) and from nearshore and offshore locations in Biscayne Bay (3 cores). The reconstructions showed that water quality conditions in these estuaries have been fluctuating for thousands of years due to natural processes and sea-level changes, but almost synchronized shifts in diatom assemblages occurred in the mid-1960’s at all coring locations (except Ninemile Bank and Bob Allen Bank in Florida Bay). These alterations correspond to the major construction of numerous water management structures on the mainland. Additionally, all the coring sites (except Card Sound Bank, Biscayne Bay and Trout Cove, Florida Bay) showed decreasing salinity and fluctuations in nutrient levels in the last two decades that correspond to increased rainfall in the 1990’s and increased freshwater discharge to the bays, a result of increased freshwater deliveries to the Everglades by South Florida Water Management District in the 1980’s and 1990’s. Reconstructions of the abundance of diatom assemblages typical for different habitats and life habits revealed multiple sources of diatoms to the coring locations and that epiphytic assemblages in both bays increased in abundance since the early 1990’s.

Diatoms are single-celled photosynthetic eukaryotes that substantially contribute to global primary productivity. They are also among the most diverse groups of organisms in Antarctica. Biogeographically, Antarctica is divided into three distinct regions including the Sub-Antarctic, Maritime Antarctic, and Continental Antarctic. Recent taxonomic revisions of diatoms within the Sub-Antarctic and Maritime Antarctic Regions have uncovered a number of endemic taxa initially misidentified as cosmopolitan due to species "force-fitting". Within Continental Antarctica, this taxonomic uncertainty has led to confusion about the environmental drivers of limno-terrestrial diatom communities, although this knowledge is important given the use of diatoms as regional bioindicators for environmental change. The purpose of this dissertation is to reevaluate the diatom flora of Continental Antarctica and determine variables that structure their communities within two historically and biologically important localities within East Antarctica; the Vestfold Hills and Windmill Islands. The erection of the genus Sabbea was performed to accommodate a long-misidentified species, Sabbea adminensis, that occurs within the Vestfold Hills and McMurdo Sound Region where it had been the source of taxonomic confusion since the...

Aquatic microbial food webs are in general size structured. Phytoplankton, which constitute the base of the food web, are grazed by protozoa and mesozooplankton, which in turn are consumed by planktivorous fish. Food web efficiency (FWE) is a measure of how efficiently energy is transported up the food web. FWE is low if the phytoplankton is inedible by the grazers, while FWE is higher if the phytoplankton community is dominated by edible phytoplankton. Recently, the presence of microfungi in aquatic food webs have been suggested to facilitate energy transfer up the food web, via the “mycoloop”. The aim of the study was to set-up a model system of phytoplankton – zooplankton food chains, relevant to the Baltic Sea, and to test FWE in diatom and flagellate-based food webs. Further, I wanted to introduce microfungi in the system and observe their impact on FWE. After many phytoplankton and zooplankton species tests, I decided to perform grazing experiments using one grazer, the ciliate Tetrahymena pyriformis, and two phytoplankton species: a diatom (Skeletonema marinoi) and a flagellate (Rhodomonas baltica). I hypothesized that T. pyriformis would more efficiently feed on flagellates than on diatoms. I performed a grazing experiment where the increase in ciliate abundance was measured, the consumption of the phytoplankton monitored and the FWE estimated. The diatom-based food web led to 14 times higher FWE than the flagellate-based food web. The variation in FWE may be explained by a difference in initial abundances introduced in the experimental treatment, which created unequal grazer:prey ratio between treatments. Further, the swimming behaviour of the flagellate might have reduced the capture efficiency by the ciliate. Microfungi were introduce in an experiment, from a natural seawater sample, but fungal infection was not observed for any of the tested phytoplankton species. Further development is needed to test the effects of microfungi on marine FWE.

京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第21236号 / 地環博第172号 / 新制||地環||35(附属図書館) / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)教授 山下 洋, 教授 柴田 昌三, 教授 宮下 英明 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

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A taxonomic study of the diatoms of the Goshen ponds and adjacent wet meadows, Utah County, Utah, was conducted from April 1974 to March 1975. The diatom flora of these warm spring fed ponds consisted of thirty-five genera containing one hundred twenty-one species, twenty-eight varieties, and two forms. The flora was dominated primarily by the following genera: Achnanthes, Fragilaria, Synedra, Navicula, Cymbella, Terpsinoe, and Nitzschia. Nineteen plates with 150 illustrations accompany the text.