The effect of the invasive macrophyte Myriophyllum spicatum L. on native macrophyte diversity was studied across 21 lakes at small (1 quadrat) and large (18 quadrats) scales and in mesocosms. No relationship was observed between M. spicatum and native richness at either spatial scale, or native evenness at small scales; however, at large scales native evenness was negatively correlated with the cover of M. spicatum in lakes. This suggests that M. spicatum can grow in lakes with other dominant species, contrary to predictions that invasive species will outcompete other dominant species. While macrophyte communities were mainly distinguished by environmental and spatial variables, M. spicatum was a significant predictor of the remaining variation in community composition. Within lakes M. spicatum occurred in deep water apart from other species; however, competition studies in mesocosms did not find sufficient evidence that this isolation was due to superior competitiveness.

The effect of the invasive macrophyte Myriophyllum spicatum L. on native macrophyte diversity was studied across 21 lakes at small (1 quadrat) and large (18 quadrats) scales and in mesocosms. No relationship was observed between M. spicatum and native richness at either spatial scale, or native evenness at small scales; however, at large scales native evenness was negatively correlated with the cover of M. spicatum in lakes. This suggests that M. spicatum can grow in lakes with other dominant species, contrary to predictions that invasive species will outcompete other dominant species. While macrophyte communities were mainly distinguished by environmental and spatial variables, M. spicatum was a significant predictor of the remaining variation in community composition. Within lakes M. spicatum occurred in deep water apart from other species; however, competition studies in mesocosms did not find sufficient evidence that this isolation was due to superior competitiveness.

Degradation of water quality, introduction of dreissenid mussels (notably <i>Dreissena polymorpha</i>) and depletion of oxygen concentrations in the hypolimnion in Lake Simcoe, Ontario prompted a study of phytoplankton primary production to inform efforts to improve the lake conditions. The characterization of algal production is critical since, as primary producers, their biomass is positively correlated with production at higher trophic levels in pelagic food webs and oxygen levels. This study was conducted from August 2010 to August 2011, including the winter season (Dec-Mar). Temporally, the lake displayed a unimodal pattern with late summer to fall production maxima. For all seasons considered, the pelagic daily areal primary production (P_int) was lower in the nearshore than offshore, consistent with the nearshore shunt hypothesis that mussels should be able to deplete phytoplankton more effectively in the nearshore. The sensitivity analysis revealed that chl a and the photosynthetic parameter P^B_max were the most influential variables for explaining such spatial differences. The size distribution of chl a and production varied where both netplankton (>20µm) and nanoplankton (2-20µm) were greatest in fall and picoplankton (<2µm) was highest in summer and early fall. A large chl a peak of nanoplankton was also found in late-winter (Mar) at offshore stations. The seasonal areal primary production (SAPP; May-Oct) and chl a:TP were significantly lower nearshore than offshore, consistent with grazing impacts from the large nearshore dreissenid mussel community. The lake as a whole is quite productive comparable to other large lakes with comparable total P concentrations and dreissenid mussel populations. The latter part of the study showed that the deep chlorophyll layer (DCL) was not as frequent as expected and was detected only 28% of time during late-spring to summer when the lake was thermally stratified (Aug-Sept 2010 and May-Aug 2011). The percent dissolved oxygen (%) did not show any indications of elevated primary production in the DCL although the production estimates suggested that there is a substantial (an average of 55%) amount of primary production occurring below thermocline when a DCL exists. Whether or not the DCL has potential to nourish the benthic filterers (dreissenids) and has ecological significance in the lake remains unclear. Overall, the factors that control phytoplankton primary production in Lake Simcoe seem to operate somewhat differently from other large lakes and further investigation is needed to elucidate them. The analysis of primary production and biomass has improved knowledge of non-summer production and can provide guidance to site-specific P and oxygen remediation.

Degradation of water quality, introduction of dreissenid mussels (notably <i>Dreissena polymorpha</i>) and depletion of oxygen concentrations in the hypolimnion in Lake Simcoe, Ontario prompted a study of phytoplankton primary production to inform efforts to improve the lake conditions. The characterization of algal production is critical since, as primary producers, their biomass is positively correlated with production at higher trophic levels in pelagic food webs and oxygen levels. This study was conducted from August 2010 to August 2011, including the winter season (Dec-Mar). Temporally, the lake displayed a unimodal pattern with late summer to fall production maxima. For all seasons considered, the pelagic daily areal primary production (P_int) was lower in the nearshore than offshore, consistent with the nearshore shunt hypothesis that mussels should be able to deplete phytoplankton more effectively in the nearshore. The sensitivity analysis revealed that chl a and the photosynthetic parameter P^B_max were the most influential variables for explaining such spatial differences. The size distribution of chl a and production varied where both netplankton (>20µm) and nanoplankton (2-20µm) were greatest in fall and picoplankton (<2µm) was highest in summer and early fall. A large chl a peak of nanoplankton was also found in late-winter (Mar) at offshore stations. The seasonal areal primary production (SAPP; May-Oct) and chl a:TP were significantly lower nearshore than offshore, consistent with grazing impacts from the large nearshore dreissenid mussel community. The lake as a whole is quite productive comparable to other large lakes with comparable total P concentrations and dreissenid mussel populations. The latter part of the study showed that the deep chlorophyll layer (DCL) was not as frequent as expected and was detected only 28% of time during late-spring to summer when the lake was thermally stratified (Aug-Sept 2010 and May-Aug 2011). The percent dissolved oxygen (%) did not show any indications of elevated primary production in the DCL although the production estimates suggested that there is a substantial (an average of 55%) amount of primary production occurring below thermocline when a DCL exists. Whether or not the DCL has potential to nourish the benthic filterers (dreissenids) and has ecological significance in the lake remains unclear. Overall, the factors that control phytoplankton primary production in Lake Simcoe seem to operate somewhat differently from other large lakes and further investigation is needed to elucidate them. The analysis of primary production and biomass has improved knowledge of non-summer production and can provide guidance to site-specific P and oxygen remediation.

This project evaluated the feasibility of salvaging zebra mussel-infested freshwater mussels from their native habitat by determining 1) how zebra mussel infestation affects unionid feeding and body condition, 2) how starvation in quarantine affects body condition of unionids, and 3) what feeding regime maintain unionid condition in quarantine. The effects of zebra mussel infestation on two mussel species were evaluated through glycogen analyses of mantle tissue and gut content analysis. Specimens of Amblema p. plicata (Say, 1817) and Quadrula p. pustulosa (I. Lea, 1831), collected from a heavily infested reach of the Ohio River in 1996, had significantly lower (p<0.05) glycogen levels than specimens collected from a low-infestation reach upstream. In 1996 and 1997, heavily infested Amblema p. plicata and Quadrula p. pustulosa had significantly less (p<0.01) organic matter and fewer algal cells in their guts than lightly infested specimens. In addition, gut contents of individual A. p. plicata contained significantly less (p<0.05) organic matter and fewer algal cells than the combined gut contents of all zebra mussels (18-33 mm in length) attached to their shells. Gut analyses also revealed significant diet overlap between native unionids and infesting zebra mussels. Thus, competitive interactions or interference by zebra mussels likely reduced unionid ingestion and consequently reduced glycogen stores. During quarantine, unionids salvaged from a lightly infested area and starved for 30 days had glycogen levels that declined dramatically. After 30 days without supplemental feeding, mean glycogen levels of A. p. plicata declined 85%, and mean glycogen levels of Q. p. pustulosa declined 70%. Thus, feeding of unionids is necessary to maintain their condition during lengthy quarantine. To determine the best feeding regime for unionids in quarantine, assimilation efficiencies and carbon budgets were established for the rainbow mussel, Villosa iris (Lea, 1829), using radio-labelled cultures of Neochloris oleoabundans (Chantanachat and Bold 1962) at three cell concentrations. Assimilation efficiencies for Villosa iris at 100,000cells/ml, 10,000 cells/ml, and 1,000 cells/ml were similar (45-56%); however, regardless of these similarities, assimilation efficiencies from this study indicate that Neochloris oleoabundans is readily assimilated (~50% AE) by Villosa iris . In addition, total assimilation was maximized at 100,000cells/ml, which indicates that Villosa iris has the greatest amount of energy available for growth, reproduction, and maintenance of condition in captivity at this cell concentration. During a second quarantine experiment, specimens were provided with 100,000cells/ml of N. oleoabundans twice per day. Initial mean glycogen levels for Amblema p. plicata (9.4 + 2.4 mg/g) and Quadrula p. pustulosa collected from ORM 175.5 in July 1997 were not significantly different (p>0.3) than the mean glycogen levels of A. p. plicata and Q. p. pustulosa collected from the same site in July 1996. Glycogen stores of unionids entering quarantine, therefore, were similar in both the starvation and controlled feeding experiments. After 7, 14, and 30 days of controlled feeding in quarantine, mean glycogen levels of A. p. plicata and Q. p. pustulosa did not change significantly (p>0.1). Thus, quarantine protocol for salvaged native mussels should include the feeding of algae to captive specimens to sustain glycogen levels prior to relocation. / Master of Science

Interactions between multiple anthropogenic stressors can have unexpected synergistic or antagonistic effects, making it difficult to predict their combined effect using single stressor studies. The interaction between invasive consumers and nutrient enrichment is particularly important as both of these stressors frequently co-occur and their respective bottom-up and top-down effects have the potential to interact across multiple trophic levels. We conducted a mesocosm experiment that crossed an increasing nutrient addition gradient against an increasing zebra mussel invasion gradient. Native zooplankton communities were added to the mesocosms, and after three months we examined how the single stressor effects on available resources and the zooplankton community were altered by their multiple stressor interaction. Added nutrients had no effect on primary producer abundance, but increased the abundance and dominance of the top consumer, which likely increased predation pressure on the producers and so prevented their response to increased nutrients. Zebra mussels reduced total phytoplankton abundance by ~75%, rotifer abundance by ~80%, and shifted communities towards dominance of cladocerans and adult/juvenile copepods. When combined, the top-down control exerted by the mussels interacted antagonistically to prevent any bottom-up influence of nutrient enrichment on the zooplankton community. These results provide insight into the potential outcomes of nutrient and invasive consumer stressor interactions, and illustrate the need for researchers to consider single stressor problems in a multiple stressor context. / Thesis (Master, Biology) -- Queen's University, 2014-01-31 15:20:15.387

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