Effects of warming on the phytoplankton succession and trophic interactions

The aim of this study was to examine the impact of light and temperature on the spring phytoplankton bloom and disentangle direct and indirect effects of warming on phytoplankton. I conducted two indoor mesocosm experiments with the natural winter plankton and performed a metaanalysis on the effects of warming on primary productivity and diversity-productivity relationship. I found a general direct positive temperature effect on the carbon specific primary productivity. I observed a decline of phytoplankton standing biomass and a decline in phytoplankton size with warming, which effects were related to increased grazing pressure under higher temperature. Higher consumer activity changed community composition and dominance of phytoplankton species and increased phytoplankton diversity. I concluded that the primary productivity in marine pelagic ecosystem depends on the relative strength between direct and indirect temperature effects and on the consumer-producer interactions

Climate change and the spring bloom: a mesocosm study on the influence of light and temperature on phytoplankton and mesozooplankton

We examined the simultaneous effect of climate warming and light availability on the phytoplankton spring bloom using 1400 l (1 m depth) indoor mesocosms. The timing of the spring bloom was advanced both by warming and higher light intensity, but the influence of temperature on the phytoplankton community was stronger than the light effect. Warming affected phytoplankton directly and indirectly via enhanced grazing pressure at higher temperatures. Warming resulted in markedly lower phytoplankton biomass and a shift towards smaller cell sizes. It also led to changes in the community structure of phytoplankton and zooplankton. Among phytoplankton, large-celled diatoms were most negatively affected by warming. Overwintering zooplankton species (Oithona, Pseudocalanus) remained dominant in the cold treatments, while they were replaced by late spring or summer species (Acartia, Centropages, Temora) in the warmed treatments. Our results show that understanding food web interactions might be very important to the study of the effects of climate warming on pelagic ecosystems

Zooplankton Dominance Shift in Response to Climate-Driven Salinity Change : A Mesocosm Study

Climate change predictions indicate global changes in salinity with negative implications for plankton food webs; an important baseline for functioning of marine ecosystems. Current understanding of how salinity change will impact plankton communities is mostly limited to the salinization of freshwater environments, with little known about the effects of changing salinity in marine systems. In this study, we investigate the effect of salinity change on zooplankton communities under different salinity change scenarios of the Baltic Sea. Projections for future salinity change derived from regional physical-biogeochemical models were used to set-up an outdoor mesocosm experiment in the coastal area of the Gulf of Finland. Each mesocosm was inoculated with natural plankton using a mixture of both marine and freshwater communities, mimicking the natural influx of freshwater species from rivers into the Baltic Sea. Zooplankton diversity and composition changed possibly due to different salinity tolerances among the species. Among zooplankton, rotifers dominated in low salinities (74%) and cladocerans and copepods (69%) in high salinities. Our results suggest that the zooplankton community will shift to a rotifer dominated community in areas with declining salinity due to the intolerance of other zooplankton groups to freshening.Peer reviewe

Experimental induction of a coastal spring bloom early in the year by intermittent high-light episodes

Through the use of mesocosm experiments, we show that an unusually early spring phytoplankton bloom can be induced by intermittent high-light periods. We performed mesocosm experiments where plankton assemblages from Kiel Bight (Western Baltic Sea) received a light regime based on the natural seasonal irradiance dimmed to 43% of surface irradiance of cloudless days, starting with irradiance levels of mid-January (6 mesocosms) and mid-February (6 mesocosms). After 6 d, half of the mesocosms received a ca. 2-fold increase in irradiance. In the January mesocosms, a phytoplankton bloom developed only in the treatments with the high-light episode, whereas in the February mesocosms a phytoplankton bloom also developed in the controls. Phytoplankton net growth rates, production:biomass ratios and biomass at the end of the high irradiance episodes were positively correlated to the daily light dose. The relative biomass of diatoms increased with increasing light, whereas the relative biomass of cryptophytes decreased. A bottom-up transmission to mesozooplankton (mainly copepods of the genera Acartia and Oithona) was evident by increased densities of copepod nauplii and egg production under higher light conditions, whereas copepodids and adults showed no responses during the experimental period. The taxonomic composition of the nauplii was shifted to the advantage of Acartia/Centropages (not distinguished at the naupliar stage) under higher light conditions

Intraspecific Trait Variability of a Diatom and a Dinoflagellate Along a Salinity Gradient

Publisher Copyright: Copyright © 2022 Orizar and Lewandowska.The phytoplankton community is a highly diverse group of microscopic, photosynthetic organisms responsible for 50% of the global primary production. The predicted shift in ocean salinity due to climate change threatens phytoplankton, resulting in compositional shifts and changing biodiversity patterns. This study investigates intraspecific multi-trait variability and plasticity of Alexandrium ostenfeldii and Skeletonema marinoi along a salinity gradient. Multiple traits were measured for five strains of each species grown at six salinity levels (0, 5, 15, 20, 30, and 35 psu) and combined in the principal component analysis. Cell size contributed 52% to the total variation in traits composition and significantly differed between species. The trait plasticity of A. ostenfeldii was significantly higher than S. marinoi, and the highest trait plasticity was observed at 15 psu in both species. In addition to morphological traits, A. ostenfeldii was characterized by high plasticity of cellular carbon content and a higher C:P ratio at low salinity levels. Overall, the results suggest a high variation in traits plasticity between phytoplankton strains, emphasizing the importance of intraspecific diversity to maintain ecosystem functions under changing environmental conditions.Peer reviewe

The importance of phytoplankton trait variability in spring bloom formation

About 60 years ago, the critical depth hypothesis was proposed to describe the occurrence of spring phytoplankton blooms and emphasized the role of stratification for the timing of onset. Since then, several alternative hypotheses appeared focusing on the role of grazing and mixing processes such as turbulent convection or wind activity. Surprisingly, the role of community composition—and thus the distribution of phytoplankton traits—for bloom formation has not been addressed. Here, we discuss how trait variability between competing species might influence phytoplankton growth during the onset of the spring bloom. We hypothesize that the bloom will only occur if there are species with a combination of traits fitting to the environmental conditions at the respective location and time. The basic traits for formation of the typical spring bloom are high growth rates and photoadaptation to low light conditions, but other traits such as nutrient kinetics and grazing resistance might also be important. We present concise ideas on how to test our theoretical considerations experimentally. Furthermore, we suggest that future models of phytoplankton blooms should include both water column dynamics and variability of phytoplankton traits to make realistic projections instead of treating the phytoplankton bloom as an aggregate community phenomenon

Scale dependence of temporal biodiversity change in modern and fossil marine plankton

Aim Biodiversity dynamics comprise evolutionary and ecological changes on multiple temporal scales from millions of years to decades, but they are often interpreted within a single time frame. Planktonic foraminifera communities offer a unique opportunity for analysing the dynamics of marine biodiversity over different temporal scales. Our study aims to provide a baseline for assessments of biodiversity patterns over multiple time-scales, which is urgently needed to interpret biodiversity responses to increasing anthropogenic pressure. Location Global (26 sites). Time period Five time-scales: multi-million-year (0-7 Myr), million-year (0-0.5 Myr), multi-millennial (0-15 thousand years), millennial (0-1,100 years) and decadal (0-32 years). Major taxa studied Planktonic foraminifera. Methods We analysed community composition of planktonic foraminifera at five time-scales, combining measures of standing diversity (richness and effective number of species, ENS) with measures of temporal community turnover (presence-absence-based, dominance-based). Observed biodiversity patterns were compared with the outcome of a neutral model to separate the effects of sampling resolution (the highest in the shortest time series) from biological responses. Results Richness and ENS decreased from multi-million-year to millennial time-scales, but higher standing diversity was observed on the decadal scale. As predicted by the neutral model, turnover in species identity and dominance was strongest at the multi-million-year time-scale and decreased towards the millennial scale. However, contrary to the model predictions, modern time series show rapid decadal variation in the dominance structure of foraminifera communities, which is of comparable magnitude as over much longer time periods. Community turnover was significantly correlated with global temperature change, but not on the shortest time-scale. Main conclusions Biodiversity patterns can be to some degree predicted from the scaling effects related to different durations of time series, but changes in the dominance structure observed over the last few decades reach higher magnitude, probably forced by anthropogenic effects, than those observed over much longer durations

Manipulation of Non-random Species Loss in Natural Phytoplankton: Qualitative and Quantitative Evaluation of Different Approaches

Ecological research in recent decades revealed that species loss has a predominantly negative effect on ecosystem functioning and stability. Most of these studies were based on random species loss scenarios, but extinctions in nature are not random. Recent experimental studies using macroscopic communities largely advanced knowledge about the effects of non-random species loss. However, in microscopic communities like the phytoplankton, implementing realistic species loss scenarios is challenging and experimental data are scarce. Creating more realistic experiments to study the role of phytoplankton diversity for ecosystem functioning is particularly important, as they provide up to 50% of global primary productivity, form the basis of all pelagic food webs, and are important for biogeochemical cycling. In this study, we experimentally tested and evaluated three methods for non-random species loss in a natural marine phytoplankton community. Dilution, filtration, and heat stress removed the targeted rare, large, and sensitive species, respectively. All these species groups are extremely vulnerable to extinction in future climate scenarios and play important roles in the communities. Dilution and filtration with a fine mesh additionally decreased initial biomass, which increased the variability of species left in the respective replicates. The methods tested in this study can be used to non-randomly manipulate phytoplankton species diversity in communities used for experiments. However, in studies where species identities are more important than species richness, the dilution and filtration methods should be modified to eliminate the effect of decreasing initial biomass

Climate Change: Warming Impacts on Marine Biodiversity

In this chapter, the effects of temperature change—as a main aspect of climate change—on marine biodiversity are assessed. Starting from a general discussion of species responses to temperature, the chapter presents how species respond to warming. These responses comprise adaptation and phenotypic plasticity as well as range shifts. The observed range shifts show more rapid shifts at the poleward range edge than at the equator-near edge, which probably reflects more rapid immigration than extinction in a warming world. A third avenue of changing biodiversity is change in species interactions, which can be altered by temporal and spatial shifts in interacting species. We then compare the potential changes in biodiversity to actual trends recently addressed in empirical synthesis work on local marine biodiversity, which lead to conceptual issues in quantifying the degree of biodiversity change. Finally we assess how climate change impacts the protection of marine environments