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Kim N.,York University | Yan N.D.,Dorset Environmental Science Center
Limnology and Oceanography: Methods | Year: 2010

The invasive spiny water flea's (Bythotrephes longimanus) current North American distribution encompasses the Laurentian Great Lakes as well as a number of inland lakes, particularly on the Canadian Shield. In the past, poor survival in the laboratory has precluded controlled long-term studies on Bythotrephes. Here we investigated field collection techniques and choices of culture media, temperature, and diet that led to the successful maintenance of Bythotrephes from birth to reproduction. Gravid parthenogenic females were collected from invaded lakes. Resulting offspring were reared in source lake water filtered through 20 or 80 μm, or a fully defined artificial culture medium, FLAMES. Individuals raised in FLAMES produced significantly larger broods than those in lake water, indicating that it is an appropriate culture medium. We next conducted a 96-h temperature bioassay on juvenile Bythotrephes. Survival was comparable at 16°C, 20°C, and 24°C but decreased after 48 h at 28°C, and most animals died after 24 h at 32°C. We also reared Bythotrephes at 16°C, 19°C, 22°C, and 25°C. Corresponding intrinsic rates of natural increase (r) for animals maintained to first brood release were 0.02, 0.05, 0.06, and 0.03 d-1, suggesting that Bythotrephes should be reared at ~22°C to benefit from maximum population increases. Feeding trials confirmed that young Bythotrephes prefer small, slow-moving prey. Finally, we devised a protocol for rearing Bythotrephes that yielded 100% survival to reproduction and r = 0.10 d-1 (for animals maintained to first brood release). Given these results, it is now possible to conduct long-term laboratory studies on this invader. © 2010, by the American Society of Limnology and Oceanography, Inc.

Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center | Leung B.,McGill University | Lewis M.A.,University of Alberta | Peacor S.D.,Michigan State University
Biological Invasions | Year: 2011

More than most sub-disciplines of ecology, the study of biological invasions is characterized by breadth rather than by depth. Studies of expanding ranges of invaders are common, as are post-invasion case studies, but we rarely have a deep understanding of the dynamics and regulators of the processes of invasion and resultant ecological transformations. This is unfortunate because such depth may well be needed to develop targeted, knowledge-based, management plans. In this collection we provide this needed depth of study of the key aspects of the invasion process for the spiny water flea, Bythotrephes longimanus. We do so by presenting the results of the work conducted by researchers in the Canadian Aquatic Invasive Species Network (CAISN), and several of their American and European collaborators over the past half decade. Given its rapid spread in the Great Lakes basin in North America, and the decreases in pelagic biodiversity that have ensued, the last decade has witnessed a surge of research on Bythotrephes. In this collection we learn much about mechanisms and dynamics of its spread, about the key role of humans in that spread, about the importance of Allee effects to establishment and persistence, about choices and parameterization of risk assessment models, about the value of comparing "effects" in native and invaded regions, about complex probable interactions of the invasion with impending changes in the climate, and about the regulators of the invader's abundance and impacts. There should be much of interest in the collection for aquatic ecologists and invading species biologists alike. © 2011 Springer Science+Business Media B.V.

Piscia R.,National Research Council Italy | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center | Manca M.M.,National Research Council Italy
Journal of Limnology | Year: 2016

The goal of this study was to improve the understanding of the large-scale mechanisms underlying the recovery of the zooplankton of Lake Orta from historical contamination, following reduced input of ammonia and metals and the subsequent 1989/90 liming intervention. The industrial pollution had been severe and long-lasting (1929-1990). Zooplankton biodiversity has improved, but most of the new taxa appearing in our counts are rotifers, while many calanoids and the large cladoceran predators (Bythotrephes and Leptodora) that are common in the nearby Lake Maggiore, were still absent from Lake Orta 17 years after liming. To aid understanding of the large-scale mechanisms controlling changes in annual richness, we assessed the annual persistence (P) of Crustacea and Rotifera taxa as an estimator of whether propagules that survived introduction, as result of the natural recolonization process, also thrived. We found that the rate of introduction of zooplankton colonists and their persistence in the water column of Lake Orta changed from 1971 to 2007. New rotifer taxa appeared in the lake after the mid-1980s, when discharge of toxic substances decreased, but their annual persistence was low (P<0.5) until the turn of the century. The numerical values of rotifer and crustacean persistence in Lake Orta were unexpectedly high in 2001 and 2007 (0.55 and 0.72 for rotifers, 0.85 and 0.86 for crustacean, respectively), much higher than in limed lakes in Sudbury, Canada, and in adjacent Lake Maggiore. We hypothesize this could be related to the lack of Cladoceran predators and zooplanktivorous fish in the pelagic waters of Lake Orta. © 2016, Page Press Publications. All rights reserved.

Palmer M.E.,York University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Freshwater Biology | Year: 2013

Ecological integrity is increasingly threatened by multiple anthropogenic stressors, but the cumulative impact of stressors is poorly understood because they can interact in unexpected ways. Knowledge of these interactions and their associated impacts is needed to support the conservation of valued ecosystems. We used a large-scale, replicated field survey and multiple regression analysis to investigate the cumulative impacts of multiple physical, chemical and biological stressors on the crustacean zooplankton assemblages of 34 Canadian Shield lakes between 1980s and 2004-2005. Zooplankton total abundance, species richness, diversity and community structure, as well as the relative abundances of prominent taxonomic orders of zooplankton, changed at a regional scale. These changes occurred in response to changes in water quality and lake thermal regime, and invasion by an exotic predator. Interactions between stressors were common and represented an important determinant of zooplankton assemblage changes over time. We provide the first evidence that the individual and combined impacts of multiple stressors cause regional ecological change over decades. Our results demonstrate the prevalence of stressor interactions in natural environments and highlight the complexity of ecosystem responses to multiple stressors. Zooplankton changes recorded here may be widespread because climate change, acidification, development and the spread of invasive species are globally pervasive. These changes could have cascading impacts because zooplankton is an essential link in aquatic food webs. Our findings highlight the need to consider the interactive effect of stressors when assessing anthropogenic impacts and will inform management and conservation of ecosystems threatened by multiple stressors. © 2013 John Wiley & Sons Ltd.

Celis-Salgado M.P.,York University | Keller W.B.,Laurentian University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Journal of Limnology | Year: 2016

Smelting of sulphur-rich metallic ores in Sudbury, Ontario, Canada, has caused acidification and metal contamination of thousands of lakes in the region. Recent reductions in smelter emissions have resulted in much ecological recovery, but the recovery of Daphnia species has been poor. To determine if Cu and Ni toxicity could explain differences in daphniid recovery among lakes, we compared results of 14 d static with renewal bioassays in waters from Blue Chalk Lake, an uncontaminated reference lake 200 km from Sudbury, and from five Sudbury lakes ranging in distance from the smelters and varying in metal and cation concentrations. We spiked Blue Chalk Lake water with Cu and Ni to levels resembling those of the Sudbury lakes and also tested the lake waters for toxicity. Survival of Daphnia pulex, D. pulicaria and D. mendotae decreased monotonically with increasing metal concentrations in the spiked Blue Chalk Lake treatments, falling from 90% in the controls to 0% at the two highest Cu and Ni levels, reflecting levels of Middle and Hannah lakes. In contrast, survival in waters collected from the actual Sudbury lakes did not monotonically track their total metal concentrations. Rather, survival fell to 0% in Clearwater Lake water, a lake with intermediate metal contamination (8.9 and 79.9 µg L–1 of Cu and Ni, respectively) vs 70-100% in the other lakes. We performed an additional assay with Clearwater Lake waters increasing its Ca and Na concentrations, singly and in combination to levels that reflected the levels in Middle Lake. The survival of the four daphniid species increased from 0% up to 80-100% with added Ca and from 0% to 60-90% with added Na. Lipid-ovarian indices had a similar trend to survival for D. mendotae and D. pulicaria in Bioassay 1, varying with the cation concentrations in the lakes for the daphniids in Bioassay 2. The bioassays results imply that regional recovery patterns of daphniids in Sudbury lakes cannot be understood without as a minimum considering both metal and base cation concentration differences among lakes, and give an indication of differences among Daphnia species to cope with metal stress. © 2016, Page Press Publications. All rights reserved.

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