Comparing Climate Change and Species Invasions as Drivers of Coldwater Fish Population Extirpations

Species are influenced by multiple environmental stressors acting simultaneously. Our objective was to compare the expected effects of climate change and invasion of non-indigenous rainbow smelt (Osmerus mordax) on cisco (Coregonus artedii) population extirpations at a regional level. We assembled a database of over 13,000 lakes in Wisconsin, USA, summarising fish occurrence, lake morphology, water chemistry, and climate. We used A1, A2, and B1 scenarios from the Intergovernmental Panel on Climate Change (IPCC) of future temperature conditions for 15 general circulation models in 2046–2065 and 2081–2100 totalling 78 projections. Logistic regression indicated that cisco tended to occur in cooler, larger, and deeper lakes. Depending upon the amount of warming, 25–70% of cisco populations are predicted to be extirpated by 2100. In addition, cisco are influenced by the invasion of rainbow smelt, which prey on young cisco. Projecting current estimates of rainbow smelt spread and impact into the future will result in the extirpation of about 1% of cisco populations by 2100 in Wisconsin. Overall, the effect of climate change is expected to overshadow that of species invasion as a driver of coldwater fish population extirpations. Our results highlight the potentially dominant role of climate change as a driver of biotic change

Life After Death in Lake Erie: Nutrient Controls Drive Fish Species Richness, Rehabilitation

We explored the recent (1969–1996) dynamics of fish communities within Lake Erie, a system formerly degraded by eutrophication and now undergoing oligotrophication owing to phosphorus abatement programs. By merging bottom trawl data from two lake basins of contrasting productivity with life-history information (i.e., tolerances to environmental degradation, diet and temperature preferences), we examined (1) the relationship between system productivity and species richness, (2) whether fish communities are resilient to eutrophication, and (3) whether oligotrophication necessarily leads to reduced sport and commercial fish production. Reduced phosphorus loading has led to fish community rehabilitation. In the productive west basin, six species tolerant of eutrophy (i.e., anoxia, turbidity) declined in abundance, whereas the abundance of three intolerant species increased through time. In the less productive central basin, although only one tolerant species declined, four species intolerant of eutrophic conditions recovered with oligotrophication. These differential responses appear to derive from dissimilar mechanisms by which reduced productivity alters habitat and resource availability for fishes. Specifically, enhanced bottom oxygen, combined with reduced biogenic turbidity and sedimentation, likely drove the loss of tolerant species in the west basin by reducing detrital mass or the ability of these species to compete with intolerant species under conditions of improved water clarity. In contrast, reduced bottom anoxia, which enhanced availability of cool- and cold-water habitat and benthic macroinvertebrate communities, appears important to the recovery of intolerant species in the central basin. Ultimately, these productivity-induced shifts caused species richness to decline in Lake Erie’s west basin and to increase in its central basin. Beyond confirming that unimodal models of productivity and species diversity can describe fish community change in a recovering system, our results provide optimism in an otherwise dismal state of affairs in fisheries management (e.g., overexploitation), given that many recovering intolerant species are desired sport or commercial fishes.Support for this work was provided by (1) Federal Aid in Sport Fish Restoration F-69-P (to R. A. Stein), administered jointly by the U.S. Fish and Wildlife Service and ODNR-ODW, (2) the Department of Evolution, Ecology, and Organismal Biology at The Ohio State University, and (3) a Presidential Fellowship awarded to S. A. Ludsin by The Ohio State University

Ecological Consequences of Hypoxia for Yellow Perch (Perca Flavescens) in Lake Erie.

Hypoxia (<2 mg O2•L-1) is a widespread phenomenon in marine and freshwater systems worldwide, yet the ecological consequences of hypoxia are generally unknown, especially for mobile species such as fish. Areas of hypoxic conditions or “dead zones”, due primarily to eutrophication (i.e. nutrient enrichment), are viewed as a major threat to aquatic ecosystem function worldwide. Areas of bottom water (hypolimnetic) hypoxia have long been documented and are increasing in the Lake Erie ecosystem, an economically and ecologically important water body within the Laurentian Great Lakes. Quantifying the ecological consequences of hypoxia for highly mobile organisms (e.g., yellow perch Perca flavescens) is a complex task. Such organisms are capable of avoiding direct lethal effects of hypolimnetic hypoxia, but may be indirectly affected as they are forced to occupy inferior habitats (i.e., novel prey, predators, competitors and physical conditions). I used field, and laboratory techniques to address the overall hypothesis that hypolimnetic hypoxia in Lake Erie negatively affects yellow perch. Laboratory results suggest yellow perch growth and consumption are negatively affected by low oxygen conditions. However, my field results suggest yellow perch attempt to mitigate these potential consequences by altering their distribution and foraging patterns in the presence of hypoxic conditions. My results also suggest a change in the sub-daily behaviors of yellow perch. This behavioral change involves short-term forays to forage within hypoxic habitats. The largest consequence of hypoxia for yellow perch in LECB is altered distribution patterns due to vertical or horizontal migrations in avoidance of low oxygen conditions. Overall, it appears hypoxia has the potential to negatively affect yellow perch however, behavioral modifications allow yellow perch to mitigate the extent of these consequences in Lake Erie. These results will have management implications for Lake Erie resource agencies and provide important conclusions concerning the ecological consequences of hypoxia for freshwater fishes.Ph.D.Natural Resources and EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75890/1/jjrobert_1.pd

Effects of Hypoxia on Consumption, Growth, and RNA:DNA Ratios of Young Yellow Perch

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie’s central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA : DNA ratios (an index of short‐term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie’s central basin by collecting individuals in hypoxicand normoxic regions of the lake and quantifying their RNA : DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (≤2 mg O2/L). While yellow perch RNA : DNA ratios responded strongly to experimental temperature, nucleic acid ratios were not significantly affected by dissolved oxygen or feeding ration. We did, however, observe a positive correlation between yellow perch growth and RNA : DNA ratios at low temperatures (11°C). The nucleic acid ratios of yellow perch collected in Lake Erie varied spatiotemporally, but their patterns were not consistent with hypoxia. In short, while yellow perch consumption and growth rates respond directly and negatively to low oxygen conditions, these responses are not necessarily reflected in RNA : DNA ratios. Moreover, in central Lake Erie, where yellow perch can behaviorally avoid hypoxic areas, the RNA : DNA ratios of yellow perch do not respond strongly to bottom hypoxia. Thus, this study suggests that there is no strong negative effect of bottom hypoxia on the growth of young yellow perch in Lake Erie.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141858/1/tafs1574.pd

Evidence of hypoxic foraging forays by yellow perch ( Perca flavescens ) and potential consequences for prey consumption

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91146/1/FWB_2753_sm_fS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91146/2/j.1365-2427.2012.02753.x.pd

Effects of Hypoxia on Consumption, Growth, and RNA:DNA Ratios of Young Yellow Perch

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie's central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA: DNA ratios (an index of short-term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie's central basin by collecting individuals in hypoxic and normoxic regions of the lake and quantifying their RNA: DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (<= 2 mg O-2/L). While yellow perch RNA: DNA ratios responded strongly to experimental temperature, nucleic acid ratios were not significantly affected by dissolved oxygen or feeding ration. We did, however, observe a positive correlation between yellow perch growth and RNA: DNA ratios at low temperatures (11 degrees C). The nucleic acid ratios of yellow perch collected in Lake Erie varied spatiotemporally, but their patterns were not consistent with hypoxia. In short, while yellow perch consumption and growth rates respond directly and negatively to low oxygen conditions, these responses are not necessarily reflected in RNA: DNA ratios. Moreover, in central Lake Erie, where yellow perch can behaviorally avoid hypoxic areas, the RNA: DNA ratios of yellow perch do not respond strongly to bottom hypoxia. Thus, this study suggests that there is no strong negative effect of bottom hypoxia on the growth of young yellow perch in Lake Erie.Keywords: Hypolimnetic oxygenation, Vertical distribution, Cisco Coregonus-artedi, Nucleic acid, Aquaculture ponds, Lake Erie, RNA-DNA ratios, Dissolved oxygen, Winter flounder, Fish bioenergetic

Interactive Effects of Hypoxia and Temperature on Coastal Pelagic Zooplankton and Fish

Hypoxia, triggered in large part by eutrophication, exerts widespread and expanding stress on coastal ecosystems. Hypoxia is often specifically defined as water having dissolved oxygen (DO) concentrations &lt; 2 mg L−1. However, DO concentration alone is insufficient to categorize hypoxic stress or predict impacts of hypoxia on zooplankton and fish. Hypoxic stress depends on the oxygen supply relative to metabolic demand. Water temperature controls both oxygen solubility and the metabolic demand of aquatic ectotherms. Accordingly, to assess impacts of hypoxia requires consideration of effects of temperature on both oxygen availability and animal metabolism. Temperature differences across ecosystems or across seasons or years within an ecosystem can dramatically impact the severity of hypoxia even at similar DO concentrations. Living under sub-optimum DO can reduce temperature-dependent metabolic efficiencies, prey capture efficiency, growth and reproductive potential, thus impacting production and individual zooplankton and fish fitness. Avoidance of hypoxic bottom water can reduce or eliminate low-temperature thermal refuges for organisms and increase energy demands and respiration rates, and potentially reduce overall fitness if alternative habitats are sub-optimal. Moreover, differential habitat shifts among species can shift predator-prey abundance ratios or interactions and thus modify food webs. For example, more tolerant zooplankton prey may use hypoxic waters as a refuge from fish predation. In contrast, zooplankton avoidance of hypoxic bottom waters can result in prey aggregations at oxyclines sought out by fish predators. Hypoxic conditions that affect spatial ecology can drive taxonomic and size shifts in the zooplankton community, affecting foraging, consumption and growth of fish. Advances in understanding the ecological effects of low DO waters on pelagic zooplankton and fish and comparisons among ecosystems will require development of generic models that estimate the oxygen demand of organisms in relation to oxygen supply which depends on both DO and temperature. We provide preliminary analysis of a metric (Oxygen Stress Level) which integrates oxygen demand in relation to oxygen availability for a coastal copepod and compare the prediction of oxygen stress to actual copepod distributions in areas with hypoxic bottom waters

Global Stressors, Regional Impacts: How Will Climate Change Influence Future Cisco (Coregonus Artedii) Distributions in Ontario? Are Sport Fish Mercury Levels Affected By Climate?

As global air temperatures rise and precipitation events fluctuate as a result of climate change, environmental conditions for many freshwater fish are expected to change. Fish are particularly sensitive to climate change as their distributions and contaminant loads are influenced by water temperatures. My study focuses on two main objectives: (1) how the distributions of cisco (Coregonus artedii) may be altered by future climate change and (2) the role of climate and industrial emissions on fish mercury trends in Ontario. Data were obtained from multiple government and open sources. Future cisco occurrence models demonstrated a decline of 7-47% by 2070. Trend analysis and models of mercury levels in sport fish revealed increasing rates (0.2-0.4 ug/g/decade) within recent years, particularly influenced by changes in local climate. This period of rapid environmental change demands further investigation, to better inform fisheries management decisions and consumption advisories at various spatial and temporal scales

Analysis of Stressors Contributing to Hypoxia in Lake Erie Using Deterministic Models.

Lake Erie continues to experience hypoxia (dissolved oxygen concentrations < 2 mg/L), despite basin-wide reductions in total phosphorus loads intended to limit or eliminate hypoxia, as outlined in the Great Lakes Water Quality Agreement (GLWQA) in 1978. Despite initial success, periodic hypoxia in the central basin of Lake Erie persisted, and more recently, hypoxic area has enlarged and reemerged as a potential hazard to ecosystem health. The consequences of hypoxic conditions (e.g., loss of suitable fish habitat and decrease in fish abundance and growth rates) have therefore led to a renewal in interest in understanding the relative contributions to the stressors contributing to hypoxia in Lake Erie. This dissertation focuses on the impacts of nutrients and hydro-meteorological forcings To analyze these stressors, a group of models was developed and applied in multiple management frameworks. First, a simple dissolved oxygen model was applied in a 1-dimensional, vertically stratified domain. Meteorological forcings determined temperature and mixing conditions, while the oxygen depletion rate within the water column was adjusted to match observed spatial and temporal dissolved oxygen concentrations, therefore determining if the water column oxygen demand has varied inter-annually. The model required an annually varying water column oxygen demand, suggesting that hypoxia is a function of variations in biological activity within the water column, and not strictly a meteorological phenomenon. Second, a more robust lower-food web model was developed, using the same 1-dimensional temperature and mixing conditions, but including nutrient loads and internal cycling to assess the effects of inter-annual variation in loading magnitude. The analysis suggests that a 46% reduction from the 2003-2011 average total phosphorus load and a 56% reduction from the current GLWQA target would be required to reduce hypoxic area to 2,000 km2. Finally, several hypothetical scenarios were explored with the lower-food web model, representing variations in load seasonality and meteorological conditions; including two climate warming scenarios. This work suggests that while there has been significant variation in seasonal patterns of nutrient loads, meteorological conditions play an important role due to the impact on stratification.PHDNatural Resources and EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102411/1/dkrucins_1.pd