Assessing climatic and spatial variables influencing zooplankton richness for space-for-time predictions

1. The macroecological drivers of freshwater diversity are accredited geographical, spatial and climatic variables, but also to productivity, ecosystem age and landscape history. Locally diversity is also influenced by the dispersal ability of species. Here we evaluated how spatial and climatic variables influence species richness and macroecological patterns in Cladocera and Copepoda. We also discuss whether a space-for-time approach is suitable to predict the community's response to the current rapid warming of lakes. 2. We use the presence-absence of pelagic and littoral microcrustaceans in 1465 Norwegian lakes with a wide range of latitudinal, longitudinal, and altitudinal gradients, as well as a wide span in lake areas, to evaluate how spatial and climatic factors influence zooplankton diversity in two major groups: Cladocera and Copepoda. 3. Longitude and latitude per se were poor predictors of zooplankton richness, but a combination of spatial and ecological predictors gave a good spatial prediction of cladoceran and copepod richness. These two groups did, however, not differ in their spatial distribution, with a strikingly fixed proportion of copepods close to 0.3, suggesting no obvious Allee- effects regarding the mode of reproduction (asexual vs sexual). 4. Since temperature alone was a poor predictor of species richness for both groups and dispersal constraints can make it very difficult to estimate a new richness equilibrium under a future climate, space-for-time predictions may have limited value for assessing future patterns of microcrustacean diversity. 5. Based on a quite unique dataset in terms of the sheer number of sites, spatial gradients, and inclusion of littoral species, our study demonstrates that assessments on how changing climate will shape and modulate zooplankton communities in the future are problematic. biogeography, dispersal, diversity, lakes, micro-crustaceanspublishedVersio

Water Browning Influences the Behavioral Effects of Ultraviolet Radiation on Zooplankton

In the last decades, limnic water bodies in the Northern hemisphere have experienced a noticeable browning, i.e., increasing levels of dissolved organic matter (DOM). While the effects on primary producers is usually considered negative (light attenuation), zooplankton is thought to benefit from increased DOM, which absorbs harmful ultraviolet radiation (UVR). However, behavioral alterations due to browning in zooplankton have not yet been studied. We investigated the effects of a DOM gradient, alone and in combination with UVR, on the swimming behavior of Daphnia magna. Making use of a computer-controlled imaging system, we repeatedly filmed individuals over 6 h and analyzed the video material to unravel effects on exploration behavior and other motility patterns. The results show that increasing DOM buffers the detrimental effects of UVR on swimming behavior. This is likely due to attenuation of UVR by DOM. Interestingly, DOM also raised the overall swimming activity independent of UVR exposure. Our findings highlight the importance of DOM in freshwater systems, not only because of its physico-chemical properties, but also due to its higher-level effects on zooplankton communities

Eavesdropping on plankton—can zooplankton monitoring improve forecasting of biotoxins from harmful algae blooms?

Harmful algae bloom (HAB) forecasting has developed rapidly over recent decades, but predicting harmful levels of marine biotoxins in shellfish is still a challenge. New discoveries suggest that predator-prey interactions may be an important driver in the formation of HABs. Key species of harmful algae respond to copepod infochemicals with increased toxin production. In addition, copepods feed selectively on less defended prey, which may further promote harmful taxa. Here we explore if eavesdropping on predator-prey dynamics by monitoring zooplankton can improve HAB forecasting. We first examine an 8-yr time series including copepod biomass, harmful algae cells (Dinophysis spp.), and diarrhetic shellfish toxins in blue mussels (Mytilus edulis) using generalized additive models. Models including copepod biomass more accurately predicted okadaic acid in mussels than phytoplankton alone. We then apply this connection more narrowly by analyzing the specific copepod exudates known to induce toxin production, copepodamides, from the mussels sampled in biotoxin monitoring. Adding copepodamide data from shellfish extracts increased model performance compared to copepod biomass. Results suggest that including grazing effects through copepodamide measurements may provide a cost-efficient way to improve accuracy and lead time for predicting the accumulation of microalgal toxins in shellfish

The Hidden Dimension: Context‐Dependent Expression of Repeatable Behavior in Copepods

In ecotoxicology and aquatic ecology, we often ignore responses of individuals and focus on average responses. However, both terrestrial and aquatic animals display consistent behavioral differences between individuals. The distribution of behavioral differences within a population contains vital information for predicting population responses to novel environmental challenges. Currently, individual data for behavioral and physiological traits of small marine invertebrates are few, partly because such variation is lost within published group means and assumed normality. We tested the combined effects of an inorganic contaminant (copper) and a biological stressor (i.e., chemical cues of a fish predator) on activity in a marine copepod. Although direct stress effects were weak, individuals behaved consistently differently, depending on the context. Individual differences in behavior were only expressed under the influence of kairomones, but not by copper exposure alone. This finding indicates that copepods express repeatable and context‐dependent behavior. We also demonstrate how large variations in behavioral data can hide consistent differences between individuals. Environ Toxicol Chem 2020;39:1017–1026. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC

Analysing individual growth curves for the copepod Tigriopus brevicornis, while considering changes in shape

Understanding growth and development over ontogeny, and the effects of stressors on life history, requires bioenergetic analysis, for example using models based on dynamic energy budget theory. Such analyses require precise and accurate determination of the animal's biomass or biovolume over time. Automated imaging offers great advantages by allowing size measurements at a high temporal resolution and the possibility to follow individual animals, thus providing detailed growth trajectories as well as handles on inter-individual variation in growth. Here we report on a re-analysis of images from a life-cycle experiment with the coastal harpacticoid copepod Tigriopus brevicornis. Biovolume was estimated by approximating the organism's shape by a generalised ellipsoid. This analysis confirmed, rather unsurprisingly, that the moult from the last naupliar to the first copepodite stage is accompanied by a major change in shape. However, within the naupliar and copepodite stages, more gradual elongation was observed. These changes in shape imply that total body length is a poor proxy for body size throughout the developmental stages, and is therefore not suitable for bioenergetic analysis. Volumetric length (cubic root of estimated body volume) is far more appropriate. Interestingly, growth ceases for some 1.5 days around the moult to the first copepodite stage. Such a growth stop was not observed in earlier studies of several other copepod species. Furthermore, the growth rate of the copepodites exceeded that of the nauplii. These complexities in the life history of T. brevicornis pose challenges for bioenergetic analysis that will require determination of additional traits (e.g., feeding and respiration rates) to unravel

Coordinated gas release among the physostomous fish sprat (Sprattus sprattus)

Abstract Previous experimental studies suggest that the production of sound associated with expelling gas from an open swimbladder may play a role in communication. This would suggest non-random gas release. We used deployed echosounders to study patterns of gas release among a fjord population of sprat ( Sprattus sprattus ). The echosounder records concurrently revealed individual fish and their release of gas. The gas release primarily occurred at night, partly following recurrent temporal patterns, but also varying between nights. In testing for non-randomness, we formulated a data-driven simulation approach. Non-random gas release scaled with the length of the analyzed time intervals from 1 min to 6 h, and above 30 min the release events in more than 50% of the intervals were significantly connected

Density-Dependent Metabolic Costs of Copper Exposure in a Coastal Copepod

Traditional ecotoxicology methods involving copepods have focused on exposure of pooled individuals and averaged responses, but there is increasing awareness of the importance of individual variation. Many biological traits are density dependent, and decisions to use single-individual or pooled exposure may affect responses to anthropogenic stressors. We investigated how conspecific density as a biotic stressor affects behavioral and respiratory responses to copper (Cu) exposure in the coastal copepod Tigriopus brevicornis. Adults were incubated at densities of 1, 2, or 4 individuals per replicate in 3.2 mL of exposure medium (23 µg Cu L–1 or control). Our results show an interaction of Cu exposure and density on respiration. The Cu exposure increased respiration, but this effect diminished with increasing density. We also found reduced swimming activity with increasing density. We propose 2 nonexclusive alternative explanations for the density-dependent respiratory increase of Cu exposure: 1) a behavioral stress response to low conspecific density, or 2) increased Cu exposure due to increased swimming activity. We emphasize the importance of considering density-dependency in responses when designing and interpreting ecotoxicology studies

Contrasting Effects of Predation Risk and Copper on Copepod Respiration Rates

Natural biotic and anthropogenic stressors can interact to alter contaminant toxicity. Energetic restrictions are potential mechanisms causing this pattern. To identify processes underlying observed effects of predation risk and copper (Cu) on delayed copepod age at maturity, we examined how these 2 stressors affect respiration rates. We tested 2 very different copepod species: the large, pelagic calanoid Calanus finmarchicus and the small, semibenthic harpacticoid Tigriopus brevicornis. Adult individuals were exposed for 12 h to the treatments: predation risk, Cu (23 µg L−1), combined predation risk and Cu (23 µg L−1), or control. Oxygen concentrations were monitored continuously. The 2 species differed in their responses. We found no clear effects of either stressor in C. finmarchicus. In T. brevicornis, predation risk increased respiration rates, whereas Cu alone had little impact. In contrast, combined exposure to predation risk and Cu interacted to reduce respiration rates to less than expected. We further observed an effect of sex because female‐biased T. brevicornis replicates were more sensitive to both predation risk (increased respiration rates) and Cu exposure (reduced respiration rates). The present study provides further evidence that predation risk can interact with copepod responses toward Cu exposure. Interactive effects of biotic stressors ought to be considered to improve future marine environmental monitoring. Environ Toxicol Chem 2020;39:1765–1773. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC

Catchment properties as predictors of greenhouse gas concentrations across a gradient of boreal lakes

Boreal lakes are the most abundant lakes on Earth. Changes in acid rain deposition, climate, and catchment land use have increased lateral fluxes of terrestrial dissolved organic matter (DOM), resulting in a widespread browning of boreal freshwaters. This browning affects the aqueous communities and ecosystem processes, and boost emissions of the greenhouse gases (GHG) CH 4 , CO 2 , and N 2 O. In this study, we predicted biotic saturation of GHGs in boreal lakes by using a set of chemical, hydrological, climate, and land use parameters. For this purpose, concentrations of GHGs and nutrients (organic C, -P, and -N) were determined in surface water samples from 73 lakes in south-eastern Norway covering wide ranges in DOM and nutrient concentrations, as well as catchment properties and land use. The spatial variation in saturation of each GHG is related to explanatory variables. Catchment characteristics (hydrological and climate parameters) such as lake size and summer precipitation, as well as NDVI, were key determinants when fitting GAM models for CH 4 and CO 2 saturation (explaining 71 and 54%, respectively), while summer precipitation and land use data were the best predictors for the N 2 O saturation, explaining almost 50% of deviance. Our results suggest that lake size, precipitation, and terrestrial primary production in the watershed control the saturation of GHG in boreal lakes. These predictions based on the 73-lake dataset was validated against an independent dataset from 46 lakes in the same region. Together, this provides an improved understanding of drivers and spatial variation in GHG saturation in boreal lakes across wide gradients of lake and catchment properties. The assessment highlights the need to incorporate multiple explanatory parameters in prediction models of GHGs for extrapolation across the boreal biome

Catchment properties as predictors of greenhouse gas concentrations across a gradient of boreal lakes

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