Ecological stoichiometry is the study of the balance of chemical substances in ecosystems. In freshwaters, research has focused on how the ratios of carbon, nitrogen and phosphorus in organisms and their environment affect ecosystem processes. Because autotrophs have variable stoichiometry, particulate C:N:P ratios are used to assess nutrient availability in lakes. Zooplankton have relatively fixed stoichiometry and so differences between their body stoichiometry and the stoichiometry of their food can constrain their growth. Ecological stoichiometry predicts that zooplankton with low C:P body ratios (e.g., Daphnia) will be limited by the P content of their food in lakes where seston C:P is high. The stoichiometric theory of consumer-driven nutrient recycling (CNR) predicts that the stoichiometry of a consumer will influence the stoichiometry of the nutrients they regenerate through such processes as egestion and excretion. In lakes, zooplankton with a low body N:P are expected to regenerate nutrients in a high N:P ratio, potentially shifting nutrient limitation of the food web from N to P limitation. I used data from 99 Canadian lakes to test the following: a. Are particulate C:P and N:P ratios consistent with other P deficiency indicators? b. Do seston C:P and N:P ratios affect zooplankton community composition? c. Does zooplankton community composition affect plankton P limitation as predicted by CNR? Particulate C:P and N:P ratios generally agreed with other P deficiency indicators, except dissolved phosphate turnover times (TTPO4). C:P and N:P suggested P sufficiency more often than TTPO4, possibly because these two indicators respond to P deficiency over different time scales. Most zooplankton biomass parameters were negatively related to seston C:P ratios consistent with improved food quality at lower seston C:P. There was, however, no evidence that Daphnia were more strongly affected than any other zooplankton. Turnover times of particulate P in the whole plankton assemblage were not related to zooplankton community structure parameters. However, particulate P turnover in the >200 µm size fraction increased with increasing zooplankton biomass. There was no evidence for a particular effect of Daphnia on particulate P turnover. Phosphorus deficiency indicators showed a trend of relaxing P deficiency as zooplankton biomass and the proportion of Daphnia increased. This contradicts the predictions of CNR which suggest that Daphnia should cause greater P deficiency in lakes.

Plankton samples were taken at fortnightly intervals from January 1986 to June 1987 at six stations 20-50 km north of Jeddah, Saudia Arabia: three in a mangrove area ( Zahban village) , two outside the mangrove area ( Thuwal village) and one off Obhor Creek. Larvae of decapod Crustacea ( excluding the Brachyura ) were identified as far as possible and descriptions are given of the anomuran larvae encountered . Studies were made on seasonal variations in the numbers of larvae and on differences in occurrence and abundance between the stations. Eighty nine species of A/pileus larvae were distinguished , largely using differences in chromatophore pattern. Only two species of adult A/pfJeus are recorded from the central Red Sea. Thirty seven unnamed species of Anomura were distinguished on morphological characters and these are described and figured. The anomuran larvae belong to the fo1lowing families : Upogebi1dae ( 4 species ) , Callianassidae ( 7 species) , Laomedi1dae ( 2 species) , Galatheidae (7 species) , Porcellanidae ( 6 species) , Paguridae ( 4 species) , Diogenidae ( 7 species ) , and the Dlogenidae are made up of the fo1lowing genera: Oiogenes ( 2 species), Ca/cinus ( 2 species) , Dardanus ( 2 species ) , Clioanari(Js ( 1 species ) . Ten genera of Macrura, belonging to seven families, are also listed.Descriptions are g1ven of the complete larval development of Coenobita sceevole ( Forskal ) ( Coenob1tidae ) and Dardanus ttoctor ( Forskal ) ( Diogenidae ) I based on laboratory rearing. Comparisons are made with the larvae of related species . The presence of a central telson sptne in zoea III and all subsequent zoeal stages 1s a feature of all known coenootttd larvae, although 1t does not occur 1nother larvae of the Anomura ( sensu stricto) ( i. e. excluding the tnatasstntoae ) . The concentration of decapod larvae over the 18 months at the d1fferent stations was fairly strnttar I averaging about 1190/1000 m3 . The most common anomuran larvae were those of the Dtoqentdae , w1th Diogenes avarus Heller the most common 1n the mangrove area and the unnamed spec1es Ca/ein(Js A the most common off Obhor Creek. Larvae of A/pneus spp. and Harpil/us spp. made up a large percentage of the decapod larvae I especially at the stations outside the mangrove area and off Obhor Creek . Larvae of Galatheldae I Paguridae and Callianassidae were conspicuously more abundant 1n the night samples than 1nthe day samples. During the e1ghteen months of sampling at the six stations I decapod larvae tended to be more common 1n summer, particularly in June. More sampl1ng would be reoutrec to establ1sh whether th1s 1s a regular annual feature.

The meta-ecosystem concept is an attempt to combine metacommunity, ecosystem and landscape ecology. In meta-ecosystems, both organismal dispersal and material movement between patches can have important effects on communities. This concept provides a more realistic framework of natural systems by considering both processes jointly. My dissertation presents a case-study of natural metaecosystems by studying the role of waterfowl in structuring zooplankton communities in prairie pothole wetlands in South Dakota. I use observations of natural wetlands, microcosm and mesocosm experiments to show how dispersal of materials and organisms by waterfowl can affect zooplankton abundance and community composition. Waterfowl are conspicuous, behaviorally adaptable, highly mobile and economically important members of wetland habitats. They are thought to have possible effects on zooplankton communities either by dispersing zooplankton propagules among wetlands or by moving nutrients into (via defecation) or out of (via consumption of macrophytes and invertebrates) wetlands. In this dissertation, I show evidence that waterfowl disperse a limited subset of locally rare zooplankton species between wetlands. I also provide experimental evidence that these dispersed species may have impacts on zooplankton community assembly. I also show how input of waterfowl excreta may sometimes have strong impacts on the local community. Very large inputs of goose excreta promote abundance and diversity of zooplankton. However, inputs at more modest levels, such as those routinely found in nature, are rarely detectible. Additions of excreta at levels five-times that typically found in nature produce a possible shift in zooplankton community structure away from both no-excreta communities and communities fertilized with comparable amounts of nitrogen and phosphorus. I postulate that most excreta quickly sinks to the benthos and only a small fraction becomes available for use by zooplankton. On the time scales used in my dissertation, it is only with very large additions of excreta that shifts in the zooplankton community become apparent. My dissertation is one of the first to apply the meta-ecosystem concept to a natural system. It also shows that waterfowl impacts on the zooplankton community may be most important in small wetlands or early in community assembly. / text

Estuarine phytoplankton growth is often controlled by nitrogen availability. In addition to overall nitrogen loads, nitrogen form (organic vs. inorganic) is an important factor affecting estuarine phytoplankton growth and community composition. Recent studies have shown that in addition to nitrogen availability, trophic cascades and relaxation of grazing pressure may also be important for phytoplankton bloom formation in estuaries. With a goal of better understanding how nitrogen availability and grazing pressure interact to control estuarine phytoplankton growth and community composition, we examined the individualistic as well as the combined effects of nitrogen (varying availability and form) and grazing pressure on estuarine phytoplankton growth and community composition in the Neuse River Estuary, North Carolina, USA. During each of three sampling events (June 2011, August 2011, March 2012) natural phytoplankton assemblages were manipulated with added nitrogen (as urea or nitrate) and reduced grazing pressure (by filtering out zooplankton grazers). Treatments were incubated for 48 hours in an experimental pond, and subsamples taken daily to assess phytoplankton growth responses to treatments through chlorophyll a, diagnostic photopigments and cell enumerations. The effects of nitrogen additions and reduced grazing pressure varied throughout the events. In June, only nitrogen addition stimulated phytoplankton community growth (chlorophyll a), while in August, only grazing reduction had a significant impact on community growth. Neither treatment had a significant effect on community growth in March, as the phytoplankton community faced phosphorus-limitation and decreased grazing pressure associated with cooler winter/spring temperatures. While both treatments did not continuously effect overall phytoplankton growth throughout all experiments, there were always effects seen in some diagnostic photopigments, indicating varying taxa-specific responses to treatments throughout the year, which can be explained by shifts in phytoplankton community composition and environmental factors. These results demonstrate the importance of both bottom-up (nutrient availability and form) and top-down (grazing) controls in a temperate, eutrophic estuary. Results also hint at the potential for other factors (i.e. light and phosphorus-limitation) to play a role in phytoplankton growth as well. Phytoplankton growth, biomass and community dynamics are relevant indicators of environmental change and this study highlights the need to consider the potential interactive effects of controlling factors for proper management of estuarine ecosystems.

The influence of regional processes, such as dispersal, on ecological communities has been the focal point of considerable ecological research. Evidence has shown that dispersal can impact community composition through interactions with predation, the introduction of keystone species, and maintenance of species lost due to competitive exclusion. Ecological communities can be characterized by several metrics including species richness, diversity, evenness, abundance and species co-occurrence patterns. Negative species co-occurrence patterns have historically been attributed to competitive interactions between species causing pairs of species to never co-occur. However, little attention has been paid to the contribution of dispersal on species co-occurrence patterns. I have experimentally investigated the influence of dispersal on species co-occurrence patterns in addition to local species richness, total species abundance, evenness, and Simpson’s diversity. Local species richness significantly increased with dispersal, with variation in total local richness being mainly attributed to differences in the rotifer community. Local diversity, total abundance, and evenness were not significantly influenced by changes in the level of dispersal. Species co-occurrence patterns were greatly affected by changes in dispersal, with negative species co-occurrence patterns peaking at intermediate levels of dispersal. The potential for dispersal to increase the number of rare species within a community suggested that the presence of rare species could be behind the changes in the co-occurrence patterns between dispersal treatments. The effect size of the co-occurrence tests increased with the removal of rare species in the intermediate dispersal treatment and decreased in the remaining dispersal treatments. Likely, through mass effects, the presence of rare species, and the establishment of keystone predators changes in the level of dispersal strongly influenced species co-occurrence patterns. I conclude that external processes, like dispersal, can influence species co-occurrence patterns and that caution should be taken when interpreting the mechanisms driving species co-occurrence patterns across landscapes. / Thesis (Master, Biology) -- Queen's University, 2011-09-28 15:00:40.972

The Canadian province of Nova Scotia has an abundance of lakes impacted by multiple stressors, including acidification, lakewater calcium (Ca) decline, climate change, and fish introductions. In spite of this, little is known about long-term trends in aquatic biota, especially microfaunal communities that are useful indicators of lake trophy. This thesis helps address this knowledge gap by providing information on the ecological distribution and long-term dynamics of Cladocera in softwater lakes in Nova Scotia using their subfossil remains preserved in lake sediments. Based on a surface sediment survey of 49 lakes, Cladocera in Nova Scotia are mainly structured along gradients of maximum lake depth and dissolved organic carbon (DOC). Daphnia (generally considered sensitive to low pH and [Ca]) were common in the Cape Breton Highlands National Park, but were rare in southwestern Nova Scotia in both modern and pre-industrial sediments, although some lakes exhibited declines in Daphnia since pre-industrial times. The most notable example of this is Lake George (Kings County), where a striking decline in Daphnia, likely a result of declining [Ca], resulted in a marked increase in estimates of past algal production. In Kejimkujik National Park, which has experienced declines in pH and [Ca] since pre-industrial times, significant reductions in chydorid relative abundances were observed, as well as significant increases in the jelly-clad planktonic cladoceran species Holopedium. Cladoceran assemblages in lakes near Yarmouth have also changed significantly since pre-industrial times, but showed no consistent regional trends in the direction of cladoceran species shifts, reflecting the influence of local anthropogenic stressors. An extreme example of this is Trefry Lake, which was treated with copper sulphate in 1938 to remove the native fish community and provide better stocking conditions for brook trout. Copper sulphate treatment resulted in significant and permanent changes to the aquatic food web inferred from a strong decline in the body size of Bosmina. Collectively, these results suggest that many aquatic ecosystems in Nova Scotia are in a state of flux as a result of multiple anthropogenic stressors, and Cladocera subfossils can be effective for inferring the food web implications of these stressors. / Thesis (Ph.D, Biology) -- Queen's University, 2012-08-14 09:39:27.617

Lakes near Sudbury, Ontario, experienced widespread acidification and metal-contamination beginning in the late-19th century. These stressors caused extreme damage to regional aquatic systems and their catchments, with aquatic biota experiencing reduced species richness and, in some cases, extirpations. Emission control measures markedly improved pH, however biotic recovery continues to lag water quality improvements, prompting investigation into mechanisms leading to this phenomenon. Due to the lack of long-term monitoring data, I use paleolimnological approaches to examine temporal trends in cladoceran zooplankton, from pre-impact conditions, through the period of acidification/metal contamination, and following the implementation of emission controls. I assess the degree of biotic recovery that has taken place in these lakes, and review the mechanisms that continue to structure cladoceran assemblages. Lakes closest to Sudbury recorded increases of ~15-65% relative abundance of Chydorus brevilabris, concurrent with the late-1800s industrial development. The relative abundance of C. brevilabris remains elevated above pre-impact levels in two Sudbury lakes; however, in Middle Lake, which was neutralized with calcium carbonate, declines in C. brevilabris (to ~pre-impact levels) occurred following neutralization. Conversely, lakes located ~60 km southwest of Sudbury, in Killarney Provincial Park, experienced muted assemblage change, with minor (< ~5%) increases in grazers (e.g., Daphnia spp., Holopedium glacialis) occurring within the past ~40 years. Lakes in Sudbury and Killarney acidified to pH < ~5, however those in Sudbury additionally received high inputs of nickel and copper, which have toxic effects on aquatic organisms, including some Cladocera. Contamination with these metals may have been a primary driver of cladoceran assemblage change. Elevated metal concentrations likely continue to structure the cladoceran assemblages in the Sudbury lakes. In addition, many of the lakes contain altered food webs (e.g., large populations of yellow perch) as a legacy of the acid and metal contamination, acting as a potential barrier to recovery. Finally, warming air temperatures over the past ~40 years, which I link to increases in primary production, may alter the composition of cladoceran species found in these lakes, and therefore prevent a return to pre-impact conditions. / Thesis (Master, Biology) -- Queen's University, 2014-04-28 12:26:39.903

Bibliography: p. 145-153. / v, 153 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1996?

Thesis (M.S.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 131-138). Also available via Humboldt Digital Scholar.

Thesis (M.S. in environmental science)--Washington State University, August 2008. / Title from PDF title page (viewed on Mar. 11, 2009). "School of Earth and Environmental Science." Includes bibliographical references (p. 42-46).