The relative contribution of allochthonous and autochthonous production in zooplankton nutrition has been of interest since the net heterotrophy of lakes was recognised to be common. I measured the 13C signature of epilimnetic CO2, particulate organic carbon (POC), and zooplankton in 27 north-temperate lakes in late summer and used the relationships between the POC and zooplankton 13C signatures and the CO2 signature to estimate the autochthonous contribution to these fractions of the plankton. My hypothesis was that POC and zooplankton signature would reflect the 13CO2 signature if they were autochthonous. Conversely, increasing allochthonous C would result in a 13C signature of POC or zooplankton that is increasingly influenced by the allochthonous 13C signature (δ-28‰) and decreasingly dependent on the CO2 signature. The average autochthonous contribution to epilimnetic POC was estimated to be between 62 and 75%. Epilimnetic zooplankton were, on average, between 77 and 91% autochthonous, indicating that zooplankton bias their feeding towards the autochthonous fraction of POC. On average, zooplankton were 1.2‰ enriched in 13C relative to POC, but their biased feeding on phytoplankton means that they can be depleted relative to POC in lakes where POC is highly depleted in 13C. The relationship between 13C POC and 13CO2 allowed us to estimate average photosynthetic fraction as -15.9‰. This estimate is independent of how much allochthonous C contributes to POC. Variation in photosynthetic fractionation was not a major contributor to differences among lakes in POC and zooplankton 13C signature. Allochthonous C is an important, although clearly secondary, source of C to zooplankton of these lakes in late summer. I expanded the above analysis by culling the literature for 13C stable isotope data of lake CO2, POC, and zooplankton. I found that, similar to the lakes that I had sampled, POC signature showed a strong influence of allochthonous C, and inferred that it was close to 50% allochthonous on average. I calculated an autochthonous fractionation of -14.1‰ for the metadata, which was similar to that of the lakes I sampled. While POC had a considerable allochthonous contribution, zooplankton signatures were strongly related to the CO2 signatures, suggesting that their carbon was mostly autochthonous. Therefore, while terrestrial inputs form a major portion of POC, zooplankton C, on average, was largely autochthonous. I also examined the differences in 13C/15N among zooplankton taxa, and differences in 13CO2, 13C/15N of POM, and 13C/15N of zooplankton with depth. There were small differences among the 15N of various taxa, and I did not detect differences in 13C amongst taxa. I found vertical heterogeneity was most marked in 13CO2 signatures, which generally depleted appreciably with increasing lake depth. The signatures of 13C POM and 13C zooplankton also generally depleted with depth, but much less so than did 13CO2. I interpret this as indicating that a large portion of POM and zooplankton C in the metalimnia and hypolimnia of these lakes is derived from C fixed in the epilimnia.

The relative contribution of allochthonous and autochthonous production in zooplankton nutrition has been of interest since the net heterotrophy of lakes was recognised to be common. I measured the 13C signature of epilimnetic CO2, particulate organic carbon (POC), and zooplankton in 27 north-temperate lakes in late summer and used the relationships between the POC and zooplankton 13C signatures and the CO2 signature to estimate the autochthonous contribution to these fractions of the plankton. My hypothesis was that POC and zooplankton signature would reflect the 13CO2 signature if they were autochthonous. Conversely, increasing allochthonous C would result in a 13C signature of POC or zooplankton that is increasingly influenced by the allochthonous 13C signature (δ-28‰) and decreasingly dependent on the CO2 signature. The average autochthonous contribution to epilimnetic POC was estimated to be between 62 and 75%. Epilimnetic zooplankton were, on average, between 77 and 91% autochthonous, indicating that zooplankton bias their feeding towards the autochthonous fraction of POC. On average, zooplankton were 1.2‰ enriched in 13C relative to POC, but their biased feeding on phytoplankton means that they can be depleted relative to POC in lakes where POC is highly depleted in 13C. The relationship between 13C POC and 13CO2 allowed us to estimate average photosynthetic fraction as -15.9‰. This estimate is independent of how much allochthonous C contributes to POC. Variation in photosynthetic fractionation was not a major contributor to differences among lakes in POC and zooplankton 13C signature. Allochthonous C is an important, although clearly secondary, source of C to zooplankton of these lakes in late summer. I expanded the above analysis by culling the literature for 13C stable isotope data of lake CO2, POC, and zooplankton. I found that, similar to the lakes that I had sampled, POC signature showed a strong influence of allochthonous C, and inferred that it was close to 50% allochthonous on average. I calculated an autochthonous fractionation of -14.1‰ for the metadata, which was similar to that of the lakes I sampled. While POC had a considerable allochthonous contribution, zooplankton signatures were strongly related to the CO2 signatures, suggesting that their carbon was mostly autochthonous. Therefore, while terrestrial inputs form a major portion of POC, zooplankton C, on average, was largely autochthonous. I also examined the differences in 13C/15N among zooplankton taxa, and differences in 13CO2, 13C/15N of POM, and 13C/15N of zooplankton with depth. There were small differences among the 15N of various taxa, and I did not detect differences in 13C amongst taxa. I found vertical heterogeneity was most marked in 13CO2 signatures, which generally depleted appreciably with increasing lake depth. The signatures of 13C POM and 13C zooplankton also generally depleted with depth, but much less so than did 13CO2. I interpret this as indicating that a large portion of POM and zooplankton C in the metalimnia and hypolimnia of these lakes is derived from C fixed in the epilimnia.

Plankton communities are important members of the food web in coastal systems and are regulated by top-down and bottom-up controls. This study examined the influence of bottom-up controls, such as physicochemical factors, and top-down controls, such as predation, on the plankton communities in South Bay, Texas. Microalgal photopigments were ascertained by high-performance liquid chromatography (HPLC) to determine the relative abundances of major algal classes. Zooplankters were identified to the lowest possible taxon and enumerated. No spatial trends were observed for the physicochemical factors. The northern bay sections exhibited significantly higher phytoplankton and microphytobenthic diatom biomass, probably due to their proximity to the bay inlet. Copepod, gastropod veliger and brachyuran zoea abundances were also higher in this area, albeit insignificantly. The southern bay sections experienced significantly higher cyanobacterial, euglenophyte and chlorophyte biomass, and polychaete larval abundances. Total zooplankton and nauplii abundances were also higher in the southern areas, albeit insignificantly. Sampling the inaccessible areas of the bay in the future may reveal spatial variability among the physicochemical factors which could be influencing the distribution of plankton. Temporal variation for the physicochemical factors followed a typical trend for subtropical climates and influenced the seasonality of the plankton communities. Phytoplankton biomass peaked in February, August and October but these maximums were not significantly different from the other months sampled. Microphytobenthic biomass peaked during the summer months, while diatom biomass also peaked in February. Zooplankton abundances peaked in October, while nauplii and polychaete larvae also peaked in February. Relationships between wind speed, turbidity and the microalgal pigments were assessed to determine if wind-induced resuspension influenced the location of the major algal classes within the water column compared to the sediments. Wind speed and turbidity were directly related to each other, albeit insignificantly. Some phytoplankton and microphytobenthos were considered tychopelagic because wind-induced resuspension increased their biomass in the water column compared to the sediments. The physicochemical factors exerted bottom-up control of plankton community dynamics in this study, while top-down controls, such as predation, require further investigation. Future studies should focus on which of these controls have more influence on plankton community dynamics in South Bay.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 154-166). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 60-75, 135-143, 161-163). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ66384.

Thesis (Ph. D.)--York University, 2000. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ56267.

Increasing temperatures are expected to cause secondary salinisation in freshwater systems, such as the zooplankton community of Churchill, Manitoba. Salinity is a key environmental factor structuring these communities, thus, increasing salinity should cause these communities to change; however, previous research has shown that they are resilient. In order to ascertain how changing salinity will affect these communities I conducted toxicity tests for five crustacean species, individually and in a community setting. I sampled several pools throughout the season to ascertain the salinity level at which those same species were most abundant in the field. While the species had significantly different field distributions along the salinity gradient, the salinity levels associated with maximum densities did not correlate with the lab tolerances. However, lab tolerances were outside the field salinity range, thus providing an unexpected result. Local interactions appear to be very important in determining final community composition along this salinity gradient. / Northern Scientific Training Program, Northern Research Fund

Ecologists studying acid-damaged zooplankton communities have often documented a time lag in recovery following pH increases. While previous work has provided a solid understanding of the local factors that may delay recovery (e.g. competition), less is known about the role of dispersal. The work in this thesis was conducted to test the hypothesis that dispersal limitation contributes to delays in the recovery of acid-damaged zooplankton communities. To assess the role of dispersal during recovery I pursued three objectives: 1) To measure dispersal in the field and determine the relative importance of various dispersal vectors for contributing acid-sensitive colonists to lakes; 2) to determine if spatial structure in recovering zooplankton communities exists across the landscape independent of environmental gradients; and 3) to determine if an interaction between dispersal and local environmental variables could influence recovery. Data collected for Objective 1 demonstrated that overland dispersal rates for acid-sensitive species in Killarney Park were relatively low, but some species were found emerging from the diapausing egg bank or dispersing through streams to recovering lakes. Spatial modeling and variation partitioning analyses for Objective 2 revealed spatial patterns indicative of dispersal limitation in recovering Killarney Park zooplankton communities. Enclosure experiments conducted for Objective 3 suggested that the colonization of the acid-sensitive copepod Epischura lacustris may be influenced by an interaction between dispersal levels and pH, such that higher dispersal levels may be required for establishment in lakes that are early in the process of pH recovery. Enclosure experiments also indicated that community resistance and low dispersal levels might hinder the reestablishment of the acid-sensitive copepod Skistodiaptomus oregonensis. Taken together, my results strongly suggest that dispersal limitation could contribute to delays in zooplankton community recovery. The recovery of acid-sensitive copepod species may be particularly difficult, as their reestablishment in recovering lakes appears to be influenced by Allee effects, community resistance, and an interaction between pH and dispersal levels. While dispersal rates could be artificially increased by human intervention, this would carry the risk of introducing invasive species. As a result, patience and continued monitoring of recovering lakes may be the best management approaches at this time. / Thesis (Ph.D, Biology) -- Queen's University, 2011-12-20 22:49:05.193

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