Congratulations to two successful master thesis presentations

Two master students finished their projects in Dec 2020:

Calum Young: Examination of plankton communities, invaders and harmful algal species within mangrove areas of the Galápagos Islands using eDNA metabarcoding

Phytoplankton are critical components of the marine environment but their understanding within the Galápagos Marine Reserve (GMR) remains largely underexplored with research focused within mangrove systems being further limited. Between November and December, the Galápagos Islands transition from the dry, milder season to the wet, warmer season. By examining the dominant phytoplankton genera within mangrove communities during this time, inference can be made on the communities’ responsiveness to seasonal change. This study utilised environmental DNA (eDNA) metabarcoding of the 18S ribosomal RNA (rRNA) molecular marker to survey the micro-eukaryotic community in surface waters collected from six mangrove sites. Compositions were shown to be influenced by both spatial conditions and seasonality. Diatoms represented a significant proportion of the community and were shown to undergo a strong seasonal shift to dominance by smaller sized taxa, possibly due to their efficient nutrient acquisitional traits. Dominance within dinoflagellates appeared dependent on several eco-physiological strategies; with parasitism and endosymbiosis appearing most advantageous for community dominance. 

Mangrove communities were also examined for invasive and toxic algae species. These groups represent an area of growing concern within the region and exploration of their distribution within the GMR has not previously been conducted using metabarcode sequencing. Here, several new observations of invasive species for the GMR are reported. Additionally, a range of toxin-producing algal species was also detected. However, for both groups, the respective relative abundance of individual species within mangroves communities was minimal. Sites located closer to human activity did not appear to be more impacted by problem species than more isolated areas. The low proportion held by harmful groups is encouraging, but the diversity of species detected warrants improved monitoring to ensure populations and their associated negative impacts remain negligible. 

Vivien Holub: Connectivity through larval dispersal in Kenya and Tanzania: A hydrodynamic connectivity model of marine protected areas   

Marine protected areas (MPAs) are considered as major conservation tools and have been implemented globally to protect marine biodiversity and to support the sustainability of coastal fisheries. Following scientific guidelines, conservation efforts also aim to establish representative MPA networks at various spatial scale, which is expected to enhance the efficiency of individual areas. Yet, degree at which MPA populations are potentially connected by the dispersal of marine organisms remain largely unknown. To address this knowledge gap, the present study investigates connectivity patterns among Kenyan and Tanzanian MPAs (between 0  – 10  and 38 – 47 ) in the Western Indian Ocean, a region where food and livelihood security are highly dependent on coastal fisheries. Interconnectedness is evaluated through a hydrodynamic larval dispersal model parameterized for the seagrass parrotfish Leptoscarus vaigiensis, a heavily targeted fish species by small-scale fisheries in the region. Applying graph theory and various connectivity metrics, this study shows that the Kenyan-Tanzanian MPAs form a weakly connected network where connections are the strongest in the Tanzanian Tanga and Zanzibar region and weakest in the northmost Kenyan MPAs. Poor coherency is likely the result of the predominantly northwardly flow of the regional East African Coastal Current which generates and imbalance of larval migration rate between MPAs on a latitudinal scale. Although connectivity patterns are significantly stronger when the dominant current is temporarily weakened and deflected in North Kenya during NEM season, on average the strength of connectivity remains low. Therefore, the present investigation demonstrates that the regional hydrodynamic patterns poses a challenge for achieving effective MPA network. Continued studies with more conservative model conditions is recommended. However, based on its findings, this study suggest that local governments further increase MPA surface coverage and consider a cross-boundary management of MPAs to improve connectivity.   

New article on evidence of host-parasite interactions in zooplankton

Although parasitism is one of the most prevalent interactions in nature, studies of aquatic food webs rarely include parasites. Syndiniales (Dinophyceae, Alveolata) is a diverse parasitic group of dinoflagellates, common in all marine environments, and are described as dominant components of pelagic ecosystems. However, their temporal dynamics, prevalence, and host-specificity are poorly known. Using DNA metabarcoding to explore trophic interactions of zooplankton, we found a high proportion of Syndiniales sequence reads associated with the targeted consumers. We observed the occurrence of Syndiniales in copepods, cladocerans, appendicularians, and polychaete larvae, ranging between 11 and 36% relative read abundance, encompassing 11 main putative clades. Zooplankton–Syndiniales interactions showed variability in occurrence across the taxa, but also certain host-specificity. The study suggests that the observed copepod–Syndiniales interactions can be both direct parasitic infections and the result of trophic transmission through potentially infected prey by Syndiniales. Our findings emphasize that their interactions should be recognized as key players in the structure and connectivity of plankton food webs.

Zamora-Terol, S., Novotny, A. & Winder, M. Molecular evidence of host-parasite interactions between zooplankton and SyndinialesAquat Ecol (2020). https://doi.org/10.1007/s10452-020-09816-3

Schematic representation of potential host-parasite interactions between copepods and Syndiniales based on results from this study and literature information. *Lima-Méndez et al. 2015 and Sassenhagen et al. 2020; **Clarke et al. 2019; ***Cachon 1964 and Sassenhagen et al. 2020

Reconstructing plankton food web interactions with DNA metabarcoding

This study is published in Molecular Ecology and shows for the first time the natural diet of zooplankton under temporal variation of food resources.

Knowledge of zooplankton in situ diet is critical for accurate assessment of marine ecosystem function and structure, but due to methodological constraints, there is still a limited understanding of ecological networks in marine ecosystems. Several target consumers, including copepods and cladocerans, were investigated by sequencing 16S rRNA and 18S rRNA genes to identify prokaryote and eukaryote potential prey present in their guts. During the spring phytoplankton bloom, we found a dominance of diatom and dinoflagellate trophic links to copepods. During the summer period, zooplankton including cladocerans showed a more diverse diet dominated by cyanobacteria and heterotrophic prey. Our study suggests that copepods present trophic plasticity, changing their natural diet over seasons, and adapting their feeding strategies to the available prey spectrum, with some species being more selective. We did not find a large overlap of prey consumed by copepods and cladocerans, based on prey diversity found in their guts, suggesting that they occupy different roles in the trophic web. This study represents the first molecular approach to investigate several zooplankton–prey associations under seasonal variation, and highlights how, unlike other techniques, the diversity coverage is high when using DNA, allowing the possibility to detect a wide range of trophic interactions in plankton communities.

Spring (March, April) and summer (June, July, August) zooplankton trophic interactions for (a) 16S and (b) 18S rRNA gene reads represented as coloured segments in circos plots. Zooplankton consumers are shown at the top and associated prey on the bottom of the plot. The width of the connection ribbons represents the relative abundance of a particular prey of that consumer and the width of each
prey taxon segment is proportional to the relative abundance of each prey considering all samples. Copepod (i.e., Maxillopoda) and parasitic (i.e., order Syndiniales) sequences are excluded in the plots.

New study shows that some populations of the copepod Eurytemora affinis can adapt to a future warmer Baltic Sea

To predict effects of global change on zooplankton populations, it is important to understand how present species adapt to temperature and how they respond to stressors interacting with temperature. Here, we ask if the calanoid copepod Eurytemora affinis from the Baltic Sea can adapt to future climate warming. Populations were sampled at sites with different temperatures. Full sibling families were reared in the laboratory and used in two common garden experiments (a) populations crossed over three temperature treatments 12, 17, and 22.5°C and (b) populations crossed over temperature in interaction with salinity and algae of different food quality. Genetic correlations of the full siblings’ development time were not different from zero between 12°C and the two higher temperatures 17 and 22.5°C, but positively correlated between 17 and 22.5°C. Hence, a population at 12°C is unlikely to adapt to warmer temperature, while a population at ≥17°C can adapt to an even higher temperature, that is, 22.5°C. In agreement with the genetic correlations, the population from the warmest site of origin had comparably shorter development time at high temperature than the populations from colder sites, that is, a cogradient variation. The population with the shortest development time at 22.5°C had in comparison lower survival on low quality food, illustrating a cost of short development time. Our results suggest that populations from warmer environments can at present indirectly adapt to a future warmer Baltic Sea, whereas populations from colder areas show reduced adaptation potential to high temperatures, simply because they experience an environment that is too cold.

Karlsson, K,  Winder, M.  Adaptation potential of the copepod Eurytemora affinis to a future warmer Baltic Sea. Ecol Evol.  2020; 00: 1– 17. https://doi.org/10.1002/ece3.6267

The copepod Eurytemora affinis. Foto credit: Konrad Karlsson

New study shows limited evidence for common interannual trends in Baltic Sea summer phytoplankton biomass

We used dynamic factor analysis to study if there are common patterns of interannual
variation that are shared (“common trends”) among summer phytoplankton total and class-level biomass time series observed across Baltic Sea latitudinal gradients in salinity and temperature. We evaluated alternative hypotheses regarding common trends among summer phytoplankton biomass: Baltic Sea-wide common trends; common trends by geography (latitude and basin); common trends differing among functional groups (phytoplankton classes); or common trends driven by both geography and functional group.

Summer phytoplankton blooms in the Gulf of Finland.

Summer phytoplankton blooms in the Gulf of Finland. Credit: NASA Earth Observatory image by Joshua Stevens and Lauren Dauphin, using Landsat data from the U.S. Geological Survey and MODIS data from LANCE/EOSDIS Rapid Response

Our results indicated little support for a common trend in total summer phytoplankton biomass. At a finer resolution, classes had common trends that were most closely associated with the cryptophyte and cyanobacteria time series with patterns that differed between northern and southern sampling stations. These common trends were also very sensitive to two anomalous years (1990, 2008) of cryptophyte biomass. The Baltic Sea Index, a regional climate index, was correlated with two common class trends that shifted in mean state around the mid-1990s. The limited coherence in phytoplankton biomass variation over time despite known, large-scale, ecosystem shifts suggests that stochastic dynamics at local scales limits the ability to observe common trends at the scale of monitoring data collection.

 

Griffiths JR, Lehtinen S, Suikkanen S, Winder M (2020) Limited evidence for common interannual trends in Baltic Sea summer phytoplankton biomass. PLoS ONE 15(4): e0231690. https://doi.org/10.1371/journal.pone.0231690

Shifting spring phytoplankton blooms in the Baltic Sea

A new publication shows that spring phytoplankton blooms occur 1-2 weeks earlier over the last 20 years in the central Baltic Sea. Warmer temperature advance timing of diatom and dinoflagellates, the two dominant taxonomic groups of the spring bloom, and decrease bloom magnitude. Bloom timing of the entire species composition was, however, buffered by a temperature and ice related shift in composition from early blooming diatoms to later blooming dinoflagellates and the autotrophic ciliate Mesodinium rubrum.

A shift from early blooming and fast sedimenting diatoms to later blooming flagellated groups at higher temperature is expected to increase energy transfers to pelagic secondary production and decrease spring bloom inputs to the benthic system.

Spring phytoplankton blooms contribute a substantial part to annual production, support pelagic and benthic secondary production and influence biogeochemical cycles. Understanding environmental effects on spring bloom dynamics is important for predicting future climate responses for managing aquatic systems.

The full publication is available at:

Hjerne O, Hajdu S, Larsson U, Downing A, Winder M (2019) Climate Driven Changes in Timing, Composition and Magnitude of the Baltic Sea Phytoplankton Spring Bloom. Frontiers in Marine Science. 6. https://doi.org/10.3389/fmars.2019.00482

Seasonal biomass dynamics of major phytoplankton groups in the Baltic Sea

 

New MASMA Project: LARVAL FISH PRODUCTION AND DISPERSAL IN CRITICAL HABITATS OF COASTAL EAST AFRICA

We started a new MASMA project on fish larvae distribution in coastal East Africa in collaboration with the Kenya Marine and Fisheries Research Institute, Mombasa, Kenya, and the Institute of Marine Sciences, Zanzibar, Tanzania.

This project aims to understand to what extent food-provisioning services in the form of fish larval production are threatened by habitat degradation and fragmentation, and how production of this natural resource is related to climate change and development in the coastal Western Indian Ocean region. We will identify sensitive seagrass habitats that need to be protected and threshold values for healthy productive seagrass habitats, and estimate the socio-economic costs of seagrass beds loss to fisheries. Specifically, this will be done by identification of habitat conditions critical for fish recruitment and key drivers for fish larvae production, which will provide scientific information that can lead to improved management and protection strategies in coastal East Africa.

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Foto: Dr. Jacob Ochiewo, Prof. Monika Winder, Dr. James Mwaluma at a meeting in Nairobi.

Open PhD position in Marine Biology focusing on ecological network modelling

We have an open PhD position in ‘Ecological network modelling of plankton food webs’ in our group.

This is a 4-yr position with the goal to use existing environmental, species and sequencing data gathered in extensive monitoring and metabarcoding studies to describe patterns of biotic interaction strength and explore their implications for food web dynamics. We will quantify the strength of diverse biotic interactions – trophic, symbiotic and parasitic – and how these interactions affect community dynamics, food web functioning and stability. We expect that outcomes of this project will provide essential understanding of how communities are organized and respond to changes.

We are looking for a highly motivated and self-directed student with an excellent diploma or master degree in biology, ecology, and/or aquatic science. We expect a strong interest in general ecological questions and great enthusiasm for scientific work. Ideally, the student will have experience in ecological and statistical modelling, knowledge of plankton ecology or molecular ecology analysis. Good analytical  skills, excellent interpersonal and communication skills, a strong sense of determination to succeed, and the ability to express his or her ideas in English is further expected.

The student will conduct the research at Stockholm University within the Department of Ecology, Environment and Plant Sciences. This is a collaborative project with other PhD students and researchers from Stockholm University.

The position will be based within a dynamic and active group working on current topics in aquatic ecology. We use a multi-disciplinary research approach, combining descriptive field studies, experimental and long-term ecological research to understand the consequences of environmental dynamics for food web processes and ecosystem functions. We offer state-of-the-art experimental and analytical facilities that allow properly addressing current ecological questions.

For mor information and link to the application site, please visit the Stockholm University website.

For more information, please contact project leader Prof. Monika Winder, telephone: +46 8 16 1741, monika.winder@su.se.

New paper on: Life-history responses to changing temperature and salinity of the Baltic Sea copepod Eurytemora affinis by Konrad Karlsson et al.

To understand the effects of predicted warming and changing salinity of marine ecosystems, it is important to have a good knowledge of their capacity to adapt to environmental changes. In this study we investigated how different populations of the copepod Eurytemora affinis from the Baltic Sea respond to varying temperatures and salinity conditions. We collected copepods in the Stockholm archipelago, Bothnian Bay, and Gulf of Riga and conducted common garden experiments.

Our main finding was that low salinity has a detrimental effect on development time, the additive effects of high temperature and low salinity have a negative effect on survival, and their interaction has a negative effect on hatching success. We observed no variation in survival and development within populations, and all genotypes had similar reaction norms with higher survival and faster development in higher salinities.

This suggests that there is no single genotype that performs better in low salinity or high salinity; instead, the best genotype in any given salinity is best in all salinities. Our results suggest that E. affinis can tolerate close to freshwater conditions also in high temperatures, but with a significant reduction in fitness.

Eurytemora-female

Female of Eurytemora affinis with an egg sack from the Baltic Sea. Foto credit: Simona Puiac.

Eurytemora-nauplia

Nauplia life stage of Eurytemora affinis. Foto credit: Simona Puiac.

New project on the Galapagos Archipelago

We started an exciting collaboration with José Marin at the Charles Darwin Foundation and Rafael Bermudez at Universidad San Francisco de Quito (USFQ) on research in the Galapagos Archipelago and visited the islands in January.

The Galapagos are famous for their large number of endemic species with beautiful and interesting ecosystems. Planktonic organisms are however largely understudied. Stefan Eiler, a master student from Stockholm University started to work on a joint project to investigate spatial and temporal dynamics of crustacean plankton and population genetics for key crustacean species. He stays Charles Darwin station for some months. More on this later as the project evolves.

Thanks to José and Rafael for hosting us.

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View to the Charles Darwin station on Santa Cruz island, Galapagos.

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Stefan Eiler, Santa Cruz, Galapagos Island