Density data for Lake Ontario benthic invertebrate assemblages from 1964 to 2018

Benthic invertebrates are important trophic links in aquatic food webs and serve as useful bioindicators of environmental conditions because their responses integrate the effects of both water and sediment qualities. However, long-term data sets for benthic invertebrate assemblages across broad geographic areas are rare and, even if collected, historic data sets are often not readily accessible. This data set provides densities of benthic macroinvertebrates for all taxa collected during lake-wide surveys in Lake Ontario, a Laurentian Great Lake, from 1964 to 2018. This information resulted from surveys funded by the governments of the United States and Canada to investigate the status and changes of Lake Ontario benthic community. Of the 13 lake-wide benthic surveys conducted in Lake Ontario over the course of 54 yr, we were able to acquire taxonomic data to the species level for 11 of the surveys and data to the group level for the other two surveys. Density data are provided for taxa representing the Annelida, Arthropoda, Mollusca, Cnidaria, Nemertea, and Platyhelminthes phyla. Univariate and multivariate analyses revealed that the compositional structure of Lake Ontario invertebrate assemblages differed markedly by depth and were also significantly altered by the Dreissena spp. invasion in early 1990s. The introduction of invasive dreissenids has changed the community historically dominated by Diporeia, Oligochaeta, and Sphaeriidae, to a community dominated by quagga mussels and Oligochaeta. Considering the rarity of long-term benthic data of high taxonomic resolution in lake ecosystems, this data set could be useful to explore broader aspects of ecological theory, including effects of different environmental factors and invasive species on community organization, functional and phylogenetic diversity, and spatial scale of variation in community structure. The data set could also be useful for studies on individual species including abundance and distribution, species co-occurrence, and how the patterns of dominance and rarity change over space and time. Use of this data set for academic or educational purposes is encouraged as long as the data source is properly cited using the title of this Data Paper, the names of the authors, the year of publication, the journal name, and the article number

Spatio-temporal diet variation and movement decisions of Lake Erie yellow perch

Yellow perch, Perca flavescens, are a native species to the Laurentian Great Lakes with high economic and ecological value, making them a useful model species to study ecosystem dynamics and species interactions. Here, we examined trophic connections and movement decisions of yellow perch in the Lake Erie’s Central Basin (LECB) at multiple spatial and temporal scales. We first examined stomach contents, fatty acids, and stable isotopes to determine spatio-temporal variability in diets and underlying production pathways across a sampling season at three distinct sites within LECB. Biochemical markers such as fatty acids and stable isotopes, quantified in conjunction with stomach contents analyses, provide information about not only prey consumption, but also underlying production pathways, which may change with seasonal succession of primary producer communities or spatio-temporal variation in riverine input or autochthonous production. Specifically, we demonstrated high temporal variation in biochemical trophic indicators and limited spatial variation. This high temporal variation in biochemical trophic indicators occurred despite relatively consistent stomach contents, demonstrating the importance of lake-wide seasonal effects on the underlying energy pathways that support yellow perch production. We then examined movement decisions by adult Lake Erie yellow perch at fine spatial and temporal scales using a spatially-explicit individual-based eco-genetic model with movement preferences set as heritable traits. Choice of appropriate movement rules is a central challenge in spatially-explicit ecological modeling due to the difficulty of understanding the relative influence of multiple proximate cues that result in movement and ultimate cues that influence fitness. Our framework allowed selection for appropriate combinations of movement rules in response to light, temperature, dissolved oxygen, predation risk, and prey availability that influenced individual growth and subsequent reproductive output. We found that yellow perch fitness was greatest when individuals weighted light and predation risk highly in conjunction with reduced weighting of temperature and prey availability. Additionally, we found little evidence of strong selection for dissolved oxygen preference. This high importance of light and predation risk evidently reflected their influence on survival, and therefore, fitness. Our selection-based modeling framework is applicable in a diversity of contexts with dynamic environmental resource gradients and interactive effects of proximate cues on individuals

Consumption Data

Data used in a meta-analysis of the effects of low dissolved oxygen on fish consumption

Data from: Sub-lethal effects on fish provide insight into a biologically-relevant threshold of hypoxia

Hypoxia (low dissolved oxygen) is a mounting concern for aquatic ecosystems as its prevalence increases with rising anthropogenic nutrient inputs. Hypoxia is most commonly defined as 2.0 mg l–1 of dissolved oxygen, although this level varies widely across studies and agency regulations. Such definitions may be too conservative, as ecologically-relevant non-lethal effects (e.g. consumption and growth) of hypoxia on important aquatic species, such as fish, often occur at oxygen levels much higher than 2.0 mg l–1. In addition, many mechanisms that regulate hypoxia tolerance in fish have been proposed, including temperature, habitat, location in the water column, and body size, but there is ongoing debate over which mechanisms are most important. Using a structured meta-analysis of published studies, we showed consistent, significant negative effects on fish growth and consumption below 4.5 mg l–1. While the total amount of variation explained was generally low, below 4.5 mg l–1 of dissolved oxygen, phylogenetic relationships accounted for most of the explained variation in fish growth. Ecological factors including body size, location in the water column (pelagic, demersal, or benthopelagic), habitat (freshwater, marine, or diadromous), and temperature explained very little of the effect of hypoxia on fish growth and explained only a moderate level of variation in consumption. Our results suggest a dramatically higher threshold for sub-lethal effects of hypoxia on fish than oxygen levels generally set for regulation purposes, and provide little support for accepted ecological mechanisms thought to influence hypoxia tolerance

Growth Data

Data used in a meta-analysis of the effects of low dissolved oxygen on fish growth

Earlier winter/spring runoff and snowmelt during warmer winters lead to lower summer chlorophyll-a in north temperate lakes

Winter conditions, such as ice cover and snow accumulation, are changing rapidly at northern latitudes and can have important implications for lake processes. For example, snowmelt in the watershed—a defining feature of lake hydrology because it delivers a large portion of annual nutrient inputs—is becoming earlier. Consequently, earlier and a shorter duration of snowmelt are expected to affect annual phytoplankton biomass. To test this hypothesis, we developed an index of runoff timing based on the date when 50% of cumulative runoff between January 1 and May 31 had occurred. The runoff index was computed using stream discharge for inflows, outflows, or for flows from nearby streams for 41 lakes in Europe and North America. The runoff index was then compared with summer chlorophyll-a (Chl-a) concentration (a proxy for phytoplankton biomass) across 5–53 years for each lake. Earlier runoff generally corresponded to lower summer Chl-a. Furthermore, years with earlier runoff also had lower winter/spring runoff magnitude, more protracted runoff, and earlier ice-out. We examined several lake characteristics that may regulate the strength of the relationship between runoff timing and summer Chl-a concentrations; however, our tested covariates had little effect on the relationship. Date of ice-out was not clearly related to summer Chl-a concentrations. Our results indicate that ongoing changes in winter conditions may have important consequences for summer phytoplankton biomass and production

A New Thermal Categorization of Ice-Covered Lakes

Lakes are traditionally classified based on their thermal regime and trophic status. While this classification adequately captures many lakes, it is not sufficient to understand seasonally ice‐covered lakes, the most common lake type on Earth. We describe the inverse thermal stratification in 19 highly varying lakes and derive a model that predicts the temperature profile as a function of wind stress, area, and depth. The results suggest an additional subdivision of seasonally ice‐covered lakes to differentiate underice stratification. When ice forms in smaller and deeper lakes, inverse stratification will form with a thin buoyant layer of cold water (near 0°C) below the ice, which remains above a deeper 4°C layer. In contrast, the entire water column can cool to ∼0°C in larger and shallower lakes. We suggest these alternative conditions for dimictic lakes be termed “cryostratified” and “cryomictic.