Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea

It is commonly accepted that summer cyanobacterial blooms cannot be efficiently utilized by grazers due to low nutritional quality and production of toxins; however the evidence for such effects in situ is often contradictory. Using field and experimental observations on Baltic copepods and bloom-forming diazotrophic filamentous cyanobacteria, we show that cyanobacteria may in fact support zooplankton production during summer. To highlight this side of zooplankton-cyanobacteria interactions, we conducted: (1) a field survey investigating linkages between cyanobacteria, reproduction and growth indices in the copepod Acartia tonsa; (2) an experiment testing relationships between ingestion of the cyanobacterium Nodularia spumigena (measured by molecular diet analysis) and organismal responses (oxidative balance, reproduction and development) in the copepod A. bifilosa; and (3) an analysis of long term (1999–2009) data testing relationships between cyanobacteria and growth indices in nauplii of the copepods, Acartia spp. and Eurytemora affinis, in a coastal area of the northern Baltic proper. In the field survey, N. spumigena had positive effects on copepod egg production and egg viability, effectively increasing their viable egg production. By contrast, Aphanizomenon sp. showed a negative relationship with egg viability yet no significant effect on the viable egg production. In the experiment, ingestion of N. spumigena mixed with green algae Brachiomonas submarina had significant positive effects on copepod oxidative balance, egg viability and development of early nauplial stages, whereas egg production was negatively affected. Finally, the long term data analysis identified cyanobacteria as a significant positive predictor for the nauplial growth in Acartia spp. and E. affinis. Taken together, these results suggest that bloom forming diazotrophic cyanobacteria contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii.     

Linking climate change projections for an Alaskan watershed to future coho salmon production

Climate change is predicted to dramatically change hydrologic processes across Alaska, but estimates of how these impacts will influence specific watersheds and aquatic species are lacking. Here, we linked climate, hydrology, and habitat models within a coho salmon (Oncorhynchus kisutch) population model to assess how projected climate change could affect survival at each freshwater life stage and, in turn, production of coho salmon smolts in three subwatersheds of the Chuitna (Chuit) River watershed, Alaska. Based on future climate scenarios and projections from a three‐dimensional hydrology model, we simulated coho smolt production over a 20‐year span at the end of the century (2080–2100). The direction (i.e., positive vs. negative) and magnitude of changes in smolt production varied substantially by climate scenario and subwatershed. Projected smolt production decreased in all three subwatersheds under the minimum air temperature and maximum precipitation scenario due to elevated peak flows and a resulting 98% reduction in egg‐to‐fry survival. In contrast, the maximum air temperature and minimum precipitation scenario led to an increase in smolt production in all three subwatersheds through an increase in fry survival. Other climate change scenarios led to mixed responses, with projected smolt production increasing and decreasing in different subwatersheds. Our analysis highlights the complexity inherent in predicting climate‐change‐related impacts to salmon populations and demonstrates that population effects may depend on interactions between the relative magnitude of hydrologic and thermal changes and their interactions with features of the local habitat.     

In situ egg production and hatching success of the marine copepod Pseudocalanus newmani in Funka Bay and adjacent waters off southwestern Hokkaido, Japan: associated to diatom bloom

. Clutch size and egg viability were examined for wild femalesof Pseudocalanus newmani collected from four different stationsinside and outside Funka Bay, southwestern Hokkaido, Japan,during pre-phytoplankton-bloom conditions in 1997, and froma single station outside the bay during the period from pre-to post-blooming seasons in 1998, to examine spatio-temporalvariability of the reproductive parameters and to detect deleteriouseffects of diatom blooms on in situ copepod reproduction. Clutchsize and hatching success in P.newmani were relatively similarat the four stations in 1997. The eggs almost always hatchedcompletely, but deformed nauplii occurred in 20–40% ofthe cases. The proportion of deformed nauplii gradually decreasedwhen the females were fed on non-diatom Pavlova sp. in the laboratory,suggesting that the occurrence of deformed nauplii was relatedto the quality of in situ food particles, including diatoms.Clutch size varied from 12 to 30 eggs female^–1 duringthe study period in 1998; more than 90% of the variation couldbe explained by the body size of the females which dependedon ambient water temperature. Hatching success also varied,from 15 to 80%, but was not related to either clutch size, femalebody size, water temperature or diatom biomass. These resultssuggest that not only egg production but also hatchability shouldbe measured routinely when estimating recruitment of the copepodinto the planktonic population, and show that neither clutchsize nor egg viability are directly affected by diatom biomass.Although we could not obtain clear evidence of in situ deleteriouseffects of diatoms on abnormal embryos and nauplii, this mightbe related to methodological problems and properties or characteristicsof prey–predator interactions. Also, deformities of copepodnauplii have not yet been observed for reasons other than feedingon diatoms.     

Forecasting future recruitment success for Atlantic cod in the warming and acidifying Barents Sea

Productivity of marine fish stocks is known to be affected by environmental and ecological drivers, and global climate change is anticipated to alter recruitment success of many stocks. While the direct effects of environmental drivers on fish early life stage survival can be quantified experimentally, indirect effects in marine ecosystems and the role of adaptation are still highly uncertain. We developed an integrative model for the effects of ocean warming and acidification on the early life stages of Atlantic cod in the Barents Sea, termed SCREI (Simulator of Cod Recruitment under Environmental Influences). Experimental results on temperature and CO₂ effects on egg fertilization, egg and larval survival and development times are incorporated. Calibration using empirical time series of egg production, temperature, food and predator abundance reproduces age‐0 recruitment over three decades. We project trajectories of recruitment success under different scenarios and quantify confidence limits based on variation in experiments. A publicly accessible web version of the SCREI model can be run under www.oceanchange.uni-bremen.de/ ;SCREI. Severe reductions in average age‐0 recruitment success of Barents Sea cod are projected under uncompensated warming and acidification toward the middle to end of this century. Although high population stochasticity was found, considerable rates of evolutionary adaptation to acidification and shifts in organismal thermal windows would be needed to buffer impacts on recruitment. While increases in food availability may mitigate short‐term impacts, an increase in egg production achieved by stock management could provide more long‐term safety for cod recruitment success. The SCREI model provides a novel integration of multiple driver effects in different life stages and enables an estimation of uncertainty associated with interindividual and ecological variation. The model thus helps to advance toward an improved empirical foundation for quantifying climate change impacts on marine fish recruitment, relevant for ecosystem‐based assessments of marine systems under climate change.     

Have we been underestimating the effects of ocean acidification in zooplankton?

Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. The perception that copepods are insensitive to OA is largely based on experiments with adult females. Their apparent resilience to increased carbon dioxide (pCO₂) concentrations has supported the view that copepods are ‘winners’ under OA. Here, we show that this conclusion is not robust, that sensitivity across different life stages is significantly misrepresented by studies solely using adult females. Stage‐specific responses to pCO₂ (385–6000 μatm) were studied across different life stages of a calanoid copepod, monitoring for lethal and sublethal responses. Mortality rates varied significantly across the different life stages, with nauplii showing the highest lethal effects; nauplii mortality rates increased threefold when pCO₂ concentrations reached 1000 μatm (year 2100 scenario) with LC₅₀ at 1084 μatm pCO₂. In comparison, eggs, early copepodite stages, and adult males and females were not affected lethally until pCO₂ concentrations ≥3000 μatm. Adverse effects on reproduction were found, with >35% decline in nauplii recruitment at 1000 μatm pCO₂. This suppression of reproductive scope, coupled with the decreased survival of early stage progeny at this pCO₂ concentration, has clear potential to damage population growth dynamics in this species. The disparity in responses seen across the different developmental stages emphasizes the need for a holistic life‐cycle approach to make species‐level projections to climate change. Significant misrepresentation and error propagation can develop from studies which attempt to project outcomes to future OA conditions solely based on single life history stage exposures.     

The effects of short-term pH decrease on the reproductive output of the copepod Acartia bifilosa – a laboratory study

This laboratory study reports some reproductive responses of the copepod Acartia bifilosa to rapid variations in pH. The imposed changes mimic those that copepods could experience due to coastal upwelling, changed mixing conditions or vertical migration. We measured effects of low pH on egg production, hatching and early nauplii development (H₀: no effects on response variables between low and ambient pH). On treatment with low pH, we found positive effects on egg production rate and nauplii development time. The positive response to low pH could be an initial stress response or show that A. bifilosa is tolerant to the experimental pH values. The result suggests that A. bifilosa is adapted to pH changes as it performs daily migrations between the depths with differing pH. It could also be advantageous for population development if eggs hatch at high speed and so reduce the possibility that they will sink into anoxic and low pH waters.     

Contrasting consequences of climate change for migratory geese: Predation,density dependence and carryover effects offset benefits of high‐arctic warming

Climate change is most rapid in the Arctic, posing both benefits and challenges for migratory herbivores. However, population‐dynamic responses to climate change are generally difficult to predict, due to concurrent changes in other trophic levels. Migratory species are also exposed to contrasting climate trends and density regimes over the annual cycle. Thus, determining how climate change impacts their population dynamics requires an understanding of how weather directly or indirectly (through trophic interactions and carryover effects) affects reproduction and survival across migratory stages, while accounting for density dependence. Here, we analyse the overall implications of climate change for a local non‐hunted population of high‐arctic Svalbard barnacle geese, Branta leucopsis, using 28 years of individual‐based data. By identifying the main drivers of reproductive stages (egg production, hatching and fledging) and age‐specific survival rates, we quantify their impact on population growth. Recent climate change in Svalbard enhanced egg production and hatching success through positive effects of advanced spring onset (snow melt) and warmer summers (i.e. earlier vegetation green‐up) respectively. Contrastingly, there was a strong temporal decline in fledging probability due to increased local abundance of the Arctic fox, the main predator. While weather during the non‐breeding season influenced geese through a positive effect of temperature (UK wintering grounds) on adult survival and a positive carryover effect of rainfall (spring stopover site in Norway) on egg production, these covariates showed no temporal trends. However, density‐dependent effects occurred throughout the annual cycle, and the steadily increasing total flyway population size caused negative trends in overwinter survival and carryover effects on egg production. The combination of density‐dependent processes and direct and indirect climate change effects across life history stages appeared to stabilize local population size. Our study emphasizes the need for holistic approaches when studying population‐dynamic responses to global change in migratory species.     

Local adaptation of reproductive performance during thermal stress

Considerable evidence exists for local adaptation of critical thermal limits in ectotherms following adult temperature stress, but fewer studies have tested for local adaptation of sublethal heat stress effects across life‐history stages. In organisms with complex life cycles, such as holometabolous insects, heat stress during juvenile stages may severely impact gametogenesis, having downstream consequences on reproductive performance that may be mediated by local adaptation, although this is rarely studied. Here, we tested how exposure to either benign or heat stress temperature during juvenile and adult stages, either independently or combined, influences egg‐to‐adult viability, adult sperm motility and fertility in high‐ and low‐latitude populations of Drosophila subobscura. We found both population‐ and temperature‐specific effects on survival and sperm motility; juvenile heat stress decreased survival and subsequent sperm motility and each trait was lower in the northern population. We found an interaction between population and temperature on fertility following application of juvenile heat stress; although fertility was negatively impacted in both populations, the southern population was less affected. When the adult stage was also subject to heat stress, the southern population exhibited positive carry‐over effects whereas the northern population's fertility remained low. Thus, the northern population is more susceptible to sublethal reproductive consequences following exposure to juvenile heat stress. This may be common in other organisms with complex life cycles and current models predicting population responses to climate change, which do not take into account the impact of juvenile heat stress on reproductive performance, may be too conservative.     

Growth,toxicity and oxidative stress of a cultured cyanobacterium (Dolichospermum sp.) under different CO2/pH and temperature conditions

Cyanobacteria blooms are a worldwide nuisance in fresh, brackish and marine waters. Changing environmental conditions due to upwelling, changed mixing conditions or climate change are likely to influence cyanobacteria growth and toxicity. In this study, the response of the toxic cyanobacterium Dolichospermum sp. to lowered pH (?0.4 units by adding CO₂) and elevated temperature (+4°C) in an experimental set‐up was examined. Growth rate, microcystin concentration and oxidative stress were measured. The growth rate and intracellular toxin concentration increased significantly as a response to temperature. When Dolichospermum was exposed to the combination of elevated temperature and high CO₂/low pH, lipid peroxidation increased and antioxidant levels decreased. Microcystin concentrations were significantly correlated with growth rates. Our results show, although oxidative stress increases when exposed to a combination of high CO₂/low pH and high temperature, that growth and toxicity increase at high temperature, suggesting that the cyanobacterium in general seems to be fairly tolerant to changes in pH and temperature. Further progress in identifying biological responses and predicting climate change consequences in estuaries experiencing cyanobacteria blooms requires a better understanding of the interplay between stressors such as pH and temperature.     

Seasonal abundance, reproduction and development of four key copepod species on the Faroe shelf

The copepod community on the Faroe shelf is dominated by Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp. The species composition, abundance and development of the copepod community varied considerably during the season 2004. These variations reflected to a large extent the different life strategies of the copepods. Both nauplii and copepodites of C. finmarchicus were most abundant during spring and early summer. The two neritic copepods T. longicornis and A. longiremis were present in low numbers during spring but dominated the copepod community later during the productive period. Pseudocalanus spp., on the other hand, occurred throughout the year, but showed no clear numerical response in abundance to the spring bloom. The egg production measurements of C. finmarchicus and T. longicornis showed some pre-bloom egg production, but as the spring bloom started the egg production rate increased significantly, especially for C. finmarchicus. There seemed to be a substantial loss of nauplii and copepods from the shelf ecosystem during the productive season. It was, however, not possible to determine whether this was mainly due to mortality or advective loss.     

Impacts of elevated terrestrial nutrient loads and temperature on pelagic food‐web efficiency and fish production

Both temperature and terrestrial organic matter have strong impacts on aquatic food‐web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food‐web dynamics and food‐web efficiency in a plausible future scenario with respect to these abiotic variables in a large‐scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food‐web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food‐web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.     

Regulation of gene expression is associated with tolerance of the Arctic copepod Calanus glacialis to CO2‐acidified sea water

Ocean acidification is the increase in seawater pCO₂ due to the uptake of atmospheric anthropogenic CO₂, with the largest changes predicted to occur in the Arctic seas. For some marine organisms, this change in pCO₂, and associated decrease in pH, represents a climate change‐related stressor. In this study, we investigated the gene expression patterns of nauplii of the Arctic copepod Calanus glacialis cultured at low pH levels. We have previously shown that organismal‐level performance (development, growth, respiration) of C. glacialis nauplii is unaffected by low pH. Here, we investigated the molecular‐level response to lowered pH in order to elucidate the physiological processes involved in this tolerance. Nauplii from wild‐caught C. glacialis were cultured at four pH levels (8.05, 7.9, 7.7, 7.5). At stage N6, mRNA was extracted and sequenced using RNA‐seq. The physiological functionality of the proteins identified was categorized using Gene Ontology and KEGG pathways. We found that the expression of 151 contigs varied significantly with pH on a continuous scale (93% downregulated with decreasing pH). Gene set enrichment analysis revealed that, of the processes downregulated, many were components of the universal cellular stress response, including DNA repair, redox regulation, protein folding, and proteolysis. Sodium:proton antiporters were among the processes significantly upregulated, indicating that these ion pumps were involved in maintaining cellular pH homeostasis. C. glacialis significantly alters its gene expression at low pH, although they maintain normal larval development. Understanding what confers tolerance to some species will support our ability to predict the effects of future ocean acidification on marine organisms.     

Do marine phytoplankton follow Bergmann's rule sensu lato?

Global warming has revitalized interest in the relationship between body size and temperature, proposed by Bergmann's rule 150 years ago, one of the oldest manifestations of a ‘biogeography of traits’. We review biogeographic evidence, results from clonal cultures and recent micro‐ and mesocosm experiments with naturally mixed phytoplankton communities regarding the response of phytoplankton body size to temperature, either as a single factor or in combination with other factors such as grazing, nutrient limitation, and ocean acidification. Where possible, we also focus on the comparison between intraspecific size shifts and size shifts resulting from changes in species composition. Taken together, biogeographic evidence, community‐level experiments and single‐species experiments indicate that phytoplankton average cell sizes tend to become smaller in warmer waters, although temperature is not necessarily the proximate environmental factor driving size shifts. Indirect effects via nutrient supply and grazing are important and often dominate. In a substantial proportion of field studies, resource availability is seen as the only factor of relevance. Interspecific size effects are greater than intraspecific effects. Direct temperature effects tend to be exacerbated by indirect ones, if warming leads to intensified nutrient limitation or copepod grazing while ocean acidification tends to counteract the temperature effect on cell size in non‐calcifying phytoplankton. We discuss the implications of the temperature‐related size trends in a global‐warming context, based on known functional traits associated with phytoplankton size. These are a higher affinity for nutrients of smaller cells, highest maximal growth rates of moderately small phytoplankton (ca. 10² µm³), size‐related sensitivities for different types of grazers, and impacts on sinking rates. For a phytoplankton community increasingly dominated by smaller algae we predict that: (i) a higher proportion of primary production will be respired within the microbial food web; (ii) a smaller share of primary production will be channeled to the classic phytoplankton – crustacean zooplankton – fish food chain, thus leading to decreased ecological efficiency from a fish‐production point of view; (iii) a smaller share of primary production will be exported through sedimentation, thus leading to decreased efficiency of the biological carbon pump.     

Comparison of the functional and numerical responses of resistant versus non-resistant populations of the copepod Acartia hudsonica fed the toxic dinoflagellate Alexandrium tamarense

The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from 25 to 500 μgC L⁻¹, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise.     

Response of Copepods to Elevated pCO2 and Environmental Copper as Co-Stressors – A Multigenerational Study

We examined the impacts of ocean acidification and copper as co-stressors on the reproduction and population level responses of the benthic copepod Tisbe battagliai across two generations. Naupliar production, growth, and cuticle elemental composition were determined for four pH values: 8.06 (control); 7.95; 7.82; 7.67, with copper addition to concentrations equivalent to those in benthic pore waters. An additive synergistic effect was observed; the decline in naupliar production was greater with added copper at decreasing pH than for decreasing pH alone. Naupliar production modelled for the two generations revealed a negative synergistic impact between ocean acidification and environmentally relevant copper concentrations. Conversely, copper addition enhanced copepod growth, with larger copepods produced at each pH compared to the impact of pH alone. Copepod digests revealed significantly reduced cuticle concentrations of sulphur, phosphorus and calcium under decreasing pH; further, copper uptake increased to toxic levels that lead to reduced naupliar production. These data suggest that ocean acidification will enhance copper bioavailability, resulting in larger, but less fecund individuals that may have an overall detrimental outcome for copepod populations.     

Increases in the evolutionary potential of upper thermal limits under warmer temperatures in two rainforest Drosophila species

Tropical and subtropical species represent the majority of biodiversity. These species are predicted to lack the capacity to evolve higher thermal limits in response to selection imposed by climatic change. However, these assessments have relied on indirect estimates of adaptive capacity, using conditions that do not reflect environmental changes projected under climate change. Using a paternal half‐sib full‐sib breeding design, we estimated the additive genetic variance and narrow‐sense heritability for adult upper thermal limits in two rainforest‐restricted species of Drosophila reared under two thermal regimes, reflecting increases in seasonal temperature projected for the Wet Tropics of Australia and under standard laboratory conditions (constant 25°C). Estimates of additive genetic variation and narrow‐sense heritability for adult heat tolerance were significantly different from zero in both species under projected summer, but not winter or constant, thermal regimes. In contrast, significant broad‐sense genetic variation was apparent in all thermal regimes for egg‐to‐adult viability. Environment‐dependent changes in the expression of genetic variation for adult upper thermal limits suggest that predicting adaptive responses to climate change will be difficult. Estimating adaptive capacity under conditions that do not reflect future environmental conditions may provide limited insight into evolutionary responses to climate change.     

Examining the reproductive success of bull kelp (Nereocystis luetkeana,Phaeophyceae, Laminariales) in climate change conditions

Climate change is affecting marine ecosystems in many ways, including raising temperatures and leading to ocean acidification. From 2014 to 2016, an extensive marine heat wave extended along the west coast of North America and had devastating effects on numerous species, including bull kelp (Nereocystis luetkeana). Bull kelp is an important foundation species in coastal ecosystems and can be affected by marine heat waves and ocean acidification; however, the impacts have not been investigated on sensitive early life stages. To determine the effects of changing temperatures and carbonate levels on Northern California's bull kelp populations, we collected sporophylls from mature bull kelp individuals in Point Arena, CA. At the Bodega Marine Laboratory, we released spores from field-collected bull kelp, and cultured microscopic gametophytes in a common garden experiment with a fully factorial design crossing modern conditions (11.63 ± 0.54°C and pH 7.93 ± 0.26) with observed extreme climate conditions (15.56 ± 0.83°C and 7.64 ± 0.32 pH). Our results indicated that both increased temperature and decreased pH influenced growth and egg production of bull kelp microscopic stages. Increased temperature resulted in decreased gametophyte survival and offspring production. In contrast, decreased pH had less of an effect but resulted in increased gametophyte survival and offspring production. Additionally, increased temperature significantly impacted reproductive timing by causing female gametophytes to produce offspring earlier than under ambient temperature conditions. Our findings can inform better predictions of the impacts of climate change on coastal ecosystems and provide key insights into environmental dynamics regulating the bull kelp lifecycle.     

Multiple stressors,nonlinear effects and the implications of climate change impacts on marine coastal ecosystems

Global climate change will undoubtedly be a pressure on coastal marine ecosystems, affecting not only species distributions and physiology but also ecosystem functioning. In the coastal zone, the environmental variables that may drive ecological responses to climate change include temperature, wave energy, upwelling events and freshwater inputs, and all act and interact at a variety of spatial and temporal scales. To date, we have a poor understanding of how climate‐related environmental changes may affect coastal marine ecosystems or which environmental variables are likely to produce priority effects. Here we use time series data (17 years) of coastal benthic macrofauna to investigate responses to a range of climate‐influenced variables including sea‐surface temperature, southern oscillation indices (SOI, Z4), wind‐wave exposure, freshwater inputs and rainfall. We investigate responses from the abundances of individual species to abundances of functional traits and test whether species that are near the edge of their tolerance to another stressor (in this case sedimentation) may exhibit stronger responses. The responses we observed were all nonlinear and some exhibited thresholds. While temperature was most frequently an important predictor, wave exposure and ENSO‐related variables were also frequently important and most ecological variables responded to interactions between environmental variables. There were also indications that species sensitive to another stressor responded more strongly to weaker climate‐related environmental change at the stressed site than the unstressed site. The observed interactions between climate variables, effects on key species or functional traits, and synergistic effects of additional anthropogenic stressors have important implications for understanding and predicting the ecological consequences of climate change to coastal ecosystems.     

Global changes may be promoting a rise in select cyanobacteria in nutrient‐poor northern lakes

The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.     

Maternal Effects May Act as an Adaptation Mechanism for Copepods Facing pH and Temperature Changes

Acidification of the seas, caused by increased dissolution of CO₂ into surface water, and global warming challenge the adaptation mechanisms of marine organisms. In boreal coastal environments, temperature and pH vary greatly seasonally, but sometimes also rapidly within hours due to upwelling events. We studied if copepod zooplankton living in a fluctuating environment are tolerant to climate change effects predicted for 2100, i.e., a temperature increase of 3°C and a pH decrease of 0.4. Egg production of the copepod Acartia sp. was followed over five consecutive days at four temperature and pH conditions (17°C/ambient pH; 17°C/low pH; 20°C/ambient pH; 20°C/low pH). Egg production was higher in treatments with warmer temperature but the increase was smaller when copepods were simultaneously exposed to warmer temperature and lowered pH. To reveal if maternal effects are important in terms of adaptation to a changing environment, we conducted an egg transplantation experiment, where the produced eggs were moved to a different environment and egg hatching was monitored for three days. When pH changed between the egg production and hatching conditions, it resulted in lower hatching success, but the effect was diminished over the course of the experiment possibly due to improved maternal provisioning. Warmer egg production temperature induced a positive maternal effect and increased the egg hatching rate. Warmer hatching temperature resulted also in earlier hatching. However, the temperature effects appear to be dependent on the ambient sea temperature. Our preliminary results indicate that maternal effects are an important mechanism in the face of environmental change.