Master of Science (MS), Bowling Green State University, 2011, Biological Sciences

Dreissena bugensis, a freshwater mussel from the Ponto-Caspian region, was discovered in Lake Erie in 1989. Though similar to Dreissena polymorpha, a previous invader to the Great Lakes, it was initially thought that Dreissena bugensis is regulated to colder, deeper portions of the lake were they were thought to be competitively dominant. However, recent evidence indicates that quagga mussels (Dreissena bugensis) have replaced zebra mussels (Dreissena polymorpha) throughout the shallow warm water of Lake Erie's western basin. Many studies have looked at the physiological and biochemical differences between the two dreissenid species, but no definitive explanation has been given for the slow but overwhelming displacement of Dreissena polymorpha by Dreissena bugensis. In this study, I look specifically at the hypoxia tolerance of post-veliger dreissenids, and determine if mortality rates vary between species over a range of dissolved oxygen concentrations (0.0 – 2.0 mg/l) in a 12-hour period. From August 2007 to September 2007 over 900 dreissenids were collected and tested in 48 trials. Based on a binary logistic regression analysis there was a direct correlation between dreissenid survivorship and dissolved oxygen concentrations (p<0.001), but there was no difference between D. polymorpha and D. bugensis mortality over the dissolved oxygen levels tested (z=-0.069, p=0.484). For the size class tested, visual identification was not possible and some D. polymorpha may have been present in the D. bugensis trials. In order to determine the effect of misclassifying our dreissenids from Lake Erie, I reanalyzed the data assuming that as many as 10% of the D. bugensis were actually D. polymorpha and found a significant species iii effect (z=-2.40, p=0.016). My hypothesis that D. bugensis are more tolerant of lower dissolved oxygen than D. polymorpha as settling post-veligers was not supported by the data I was able to generate. However, the data is limited because it is possi (open full item for complete abstract)

Committee: Jeffrey G. Miner PhD (Advisor); Christine Mayer PhD (Committee Member); R. Michael McKay PhD (Other) Subjects: Biology; Ecology; Freshwater Ecology

Doctor of Philosophy (PhD), Wright State University, 2021, Environmental Sciences PhD

Attached algae are ubiquitous components of lake benthic habitats wherever sufficient light reaches submerged surfaces. Attached algae interact with heterotrophic bacteria and fungi to form complex biofilms (“periphyton”) that provide a nutritious food source for consumers and influence biogeochemical cycling by regulating redox potential at the sediment-water interface. Despite their ecological importance, there are limited data on the role of periphyton in the Laurentian Great Lakes. I quantified wave exposure and light availability in rocky nearshore habitats in Lake Erie and Lake Huron. Periphyton biomass and productivity in nearshore Lake Erie was very high while algal biomass and productivity in Lake Huron were uniformly low irrespective of depth. Regression modeling demonstrated that wave disturbance and light availability control periphyton biomass and productivity in nearshore areas of the Great Lakes. To better understand how attached algal diversity and abundance vary with depth and substrate, I measured the biomass and composition of sediment algae and periphyton growing on Dreissena across broad depth gradients in Lake Ontario and Lake Erie. Sediment and mussel shell algal biomass were greatest around 20 m and declined with depth. Algal photosynthesis on sediments and mussels declined with depth down to approximately 40 m in both lakes. I found that sediments from both lakes were dominated by benthic diatoms and settled phytoplankton. In contrast, mussel shells harbored diverse filamentous algal assemblages. I analyzed the stable isotope signatures of Dreissena tissue and biofilms collected in Lake Ontario and Lake Erie, discovering enrichment of nitrogen isotopic signatures in both organisms with depth. DNA metabarcoding data from Lake Erie revealed that Dreissena biofilms harbor greater abundances of putative nitrifying and denitrifying bacteria than surrounding sediments, suggesting that Dreissena may be hotspots for nitrogen cycling in the Great Lak (open full item for complete abstract)

Committee: Yvonne Vadeboncoeur Ph.D. (Advisor); Volker Bahn Ph.D. (Committee Member); Soren Brothers Ph.D. (Committee Member); Katie Hossler Ph.D. (Committee Member); Silvia E. Newell Ph.D. (Committee Member) Subjects: Ecology; Environmental Science; Limnology

Doctor of Philosophy, University of Toledo, 2011, Biology (Ecology)

Understanding what factors drive an organism's population fluctuations in time and space can be very difficult in complex ecosystems due to changing environmental conditions and issues with spatial scale. In this dissertation, I examined the effect of soft-sediment Dreissena (D. polymorpha and D. rostriformis bugensis) clusters, an invasive ecosystem engineer, on a native burrowing mayfly (Hexagenia limbata and H. rigida). Specifically, at the small-scale, I examined the effect of Dreissena clusters on Hexagenia: 1) habitat preference, 2) availability as prey, and 3) behavior during changing abiotic (low oxygen) and biotic (presence of a predator) conditions. At the large scale I examined: 1) the spatial association of Hexagenia and Dreissena and 2) the abiotic and biotic factors influencing Hexagenia spatial distribution and temporal fluctuations. I conducted experiments, spatial mapping and statistics, and generalized additive models to examine these objectives. Hexagenia were found to prefer sediment covered with both live and artificial clusters over bare sediment, likely due to decreased fish predation when under Dreissena clusters in turbid conditions. Hexagenia also received benefit from Dreissena clusters during hypoxic conditions; Hexagenia were able to exit anoxic burrows to seek well-oxygenated waters while staying within the Dreissena cluster as refuge from predation. At the large scale, Hexagenia density was not related to Dreissena density, however Hexagenia were more likely to occur where Dreissena were also present. Similarly, Dreissena density was not a good predictor of Hexagenia density in western Lake Erie, but abiotic factors, such as percent silt, organic carbon, depth, and distance from western shore did significantly influence Hexagenia distribution. Sites with high average Hexagenia density were clustered near the western shoreline of Lake Erie and exhibited a two-year density cycle, likely a density-dependent regulation. Overall, abiotic fa (open full item for complete abstract)

Committee: Christine Mayer PhD (Advisor); Jonathan Bossenbroek PhD (Committee Member); Thomas Bridgeman PhD (Committee Member); Lynda Corkum PhD (Committee Member); Kenneth Krieger PhD (Committee Member) Subjects: Aquatic Sciences; Ecology; Environmental Studies; Limnology

Master of Science, University of Toledo, 2011, Biology (Ecology)

Dreissena spp. (zebra and quagga mussels) have greatly altered aquatic ecosystems since their invasion of the Great Lakes. Dreissena increase light to the benthos, provide hard structure for algal attachment, and may contribute a limiting nutrient to benthic algae, thereby facilitating blooms. The benthic cyanobacterium Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck has recently become abundant in western Lake Erie and reaches nuisance levels. Cladophora glomerata (L.) Kutz., a green alga, has also been resurging in the Great Lakes and studies link this increase to Dreissena. Manipulative experiments showed that L. wollei had a significantly higher concentration of carbon, nitrogen, phosphorus, potassium, and sulfur in tanks with live Dreissena. C. glomerata had greater biomass in tanks with live Dreissena, but did not have significant increases in nutrient concentration as did L. wollei. Dreissena decreased calcium concentrations, a nutrient important for cell walls, in both algal species; although concentrations were still above the limiting level for growth. Neither algal species responded to structure as a resource for growth. These results suggest that Dreissena are giving several nutrients to benthic algae and these added resources can promote their growth and productivity, aiding in blooms.

Committee: Christine Mayer PhD (Advisor); Scott Heckathorn PhD (Committee Member); Thomas Bridgeman PhD (Committee Member); Rex Lowe PhD (Committee Member) Subjects: Biology; Ecology; Freshwater Ecology

Master of Science, University of Toledo, 2007, Biology (Ecology)

Stream flow is a major vector for zebra mussel spread among inland lakes. I hypothesized that vegetated waterways, i.e. wetland streams, would hinder downstream dispersal of zebra mussels in connected inland lake systems. To test this hypothesis, veliger (larva) abundance, recruitment, and adult mussels were surveyed in four lake-wetland systems in southeastern Michigan, USA from May through August 2006. Sampling was conducted downstream of the zebra mussel invaded lakes, beginning at the upstream edge of aquatic vegetation and continuing downstream through the wetland streams. Results showed that veliger abundance decreased rapidly in vegetated waterways compared to their previously reported rates of decrease in non-vegetated streams. Veligers were rarely found more than 1 km downstream from where vegetation began. Newly recruited individuals and adults were extremely rare beyond open water in the study systems. These results suggest that densely vegetated aquatic ecosystems limit the dispersal of zebra mussels downstream from invaded sources. Natural, remediated and constructed wetlands may therefore serve as a protective barrier to help prevent the spread of zebra mussels and other aquatic invasive species to other lakes and ecosystems.

Committee: Jonathan Bossenbroek (Advisor) Subjects:

Master of Science, University of Toledo, 2006, Biology (Ecology)

It is well known that invasive species, such as the dreissenid mussels in the Great Lakes, play significant roles in changing the substrate, community species composition, and habitat. This study examined the role of Dreissena, (zebra mussel, D. polymorpha and quagga mussel, D. bugensis) as an invasive “paver”, which compacts the sediment, and its effects on two native bioturbators, Hexagenia (burrowing mayflies; H. limbata and H. rigida) and unionid bivalve mollusks. Resulting consequences on sediment properties, infaunal invertebrates, and microbial community composition were analyzed. I further examined the spatial relationship between Dreissena and Hexagenia. Experiments showed that Hexagenia density increased in the presence of Dreissena, nematodes decreased, and oligochaetes and microbes were unaltered. In the absence of Dreissena, bioturbating species altered sediment water content and increased infaunal invertebrate densities, microbial activity, and microbial functional diversity. In further exploration of the relationship between Dreissena and Hexagenia, Hexagenia preferred habitat with 50-100% spatial coverage of live Dreissena clusters. These experiments thus revealed habitat facilitation by an invasive ecosystem engineer on a native ecosystem engineer, Hexagenia, with opposite effects on invertebrates, microbes, and sediment properties.

Committee: Christine Mayer (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2006, Evolution, Ecology, and Organismal Biology

Lake Erie is facing many perturbations. This study focuses on two issues, the external phosphorus loading and dreissenids' invasion, and investigates the interactions of the responses of the lower trophic levels to these two stressors. I construct an ecological model, EcoLE, based on a USEPA two-dimensional hydrodynamic and water quality model, CE-QUAL-W2. Data from the field year 1997 are used to calibrate the model, while data from 1998 and 1999 are used for verification. There is a good agreement between the modeled and field-measured state variables, and EcoLE catches the major characteristics of the physical, chemical and biological processes found in Lake Erie. We are confident in using this model for qualitative analysis, but one should be cautious in using it for quantitative predictions of Lake Erie processes. When I turn off the turbulent mixing processes, total dissolved phosphorus (TP-F) becomes concentrated in the lower water strata and diatom biomass decreases dramatically. When I turn on the mixing processes again, there is more TP-F in the upper water strata but less TP-F accumulated in the whole water column, because non-diatom edible algae (NDEA) and diatoms become more abundant in the water column. Blue-green algae are less affected by hydrodynamics but depend on the amount of available phosphorus in the whole water column. When I turn off the chemical and biological processes, external TP loads are distributed throughout the western basin and the west central basin as a result of physical mixing. External TP loads have minor direct effects on the east central and the eastern basins, where up to 60% of the daily algal P-demands come from SRP released by organic matter decomposition and by algal and crustacean P excretion. Dreissenid mussel daily grazing impact is less than 10% of the NDEA and diatom biomass in the western basin, and only 1-2% in the central and eastern basins. Impacts of dreissenid nutrient excretion become more important than the (open full item for complete abstract)

Committee: David Culver (Advisor) Subjects: Biology, Limnology

Master of Science, University of Toledo, 2013, Biology (Ecology)

Native unionids are endangered in the Laurentian Great Lakes due to habitat degradation and biofouling by dreissenids. However, a robust community was discovered living within the thermal discharge of a power plant at Oregon, Ohio, on the south shore of Lake Erie. Chapter 1 describes comparisons of the characteristics of this community to nearby communities outside the thermal plume, and examines habitat characteristics that may affect unionids. Unionids were sampled from the exposed lake bed at three sites during a seiche in 2011: (1) within the thermal plume, (2) at Bayshore Park (2.0km east of the plant), and (3) at the University of Toledo's Lake Erie Center (4.0km east). In 2010, sediment samples were collected along a 2km transect extending east from the plant discharge roughly parallel to the south shore of Lake Erie. Data from other studies done in proximity to the power plant were also analyzed. Results indicated that the community within the thermal plume had higher densities, higher diversity (H'), more small individuals, and overall larger sizes than communities outside the plume (all p<0.05). Both the rate and intensity of fouling by dreissenids were lower within the plume (p<0.05). Both dry mass of coarse surface sediment and lakebed sediment organic matter content were negatively correlated with distance from the plant (both p<0.05; R2 = 0.497, and 0.479, respectively). An unexpected discovery was that the bulk of the coarse sediment was comprised of shell material from Asian clams and dreissenid mussels, suggesting a contribution of these exotic species to sediment accumulation. In total, these results suggest that several habitat characteristics close to the power plant are favorable to unionids. Chapter 2 outlines work completed in the summer of 2012, examining habitat characteristics within the thermal plume for insights to why it is favorable to unionids: I expected warmer water temperatures, higher POM concentrations, higher organic matter in (open full item for complete abstract)

Committee: Daryl Moorhead PhD (Committee Co-Chair); Todd Crail PhD (Committee Co-Chair); Jonathan Bossenbroek PhD (Committee Member); Christine Mayer PhD (Committee Member) Subjects: Conservation; Ecology; Environmental Science; Natural Resource Management; Organismal Biology; Wildlife Conservation; Wildlife Management