Just out – new paper on plankton phenology

Here we analyzed 15 yr of monitoring data to identify trends and drivers of timing and magnitude of bloom-forming phytoplankton and diverse zooplankton taxa throughout the season in the central Baltic Sea.

We show that the timings of phytoplankton blooms advance, whereas crustacean zooplankton seasonal timings remain constant. This increasing offset with the spring bloom is linked to the decline of Pseudocalanus, a key copepod sustaining pelagic fish production. The majority of copepod and cladoceran taxa, however, are co-occurring with summer blooms. We also find new developing fall blooms, fueling secondary production later in the season. Our study highlights that response to climate change differs within and between functional groups, stressing the importance of investigating plankton phenologies over the entire annual cycle in pelagic systems.

See also SU’s press release:

English: Earlier spring bloom disrupt the balance of the Baltic Sea

Swedish: Allt tidigare algblomningar rubbar den känsliga balansen i Östersjön

The full article is available here: Plankton blooms over the annual cycle shape trophic interactions under climate change. Limnology and Oceanography Letters

Plankton succession in the central Baltic Sea from 2008 to 2022. Seasonal timing, peak magnitude and bloom duration of (a) total spring and summer phytoplankton and total copepod and cladoceran biomass, and (b) dominating phytoplankton and zooplankton taxa. Point positions (x-axis) correspond to the average peak timing (week), point sizes to the average peak magnitude (zooplankton: μg L⁻¹; phytoplankton: μg C L⁻¹) and the horizontal bars to the average initiation and termination (week) of their respective growing seasons.

Open Postdoc position (2 years) in Marine Molecular Ecology – deadline 12 April 2024

We offer a 2-year position with a focus on fish adaptation (forms of spring and autumn spawning herring Clupea harengus membras) to the seasonal dynamics of the Baltic Sea financed by a postdoctoral Fellowship from Carl Trygger Foundation. 

The successful applicant will be part of a team aiming to understand how different herring spawning stocks are adapted to the seasonal dynamics of plankton and temperature to predict which stocks are most sensitive to environmental change. We will use molecular approaches to determine in situ dietary composition and spawning subpopulation structure, which will be combined with fish condition and continuous plankton monitoring. Outcomes of this project will make an important and novel contribution to make recommendations on which coastal ecosystems and herring population diversity should be protected to promote population and fisheries recovery.

Your work tasks

• Field sampling and laboratory DNA analysis of fish larvae and plankton communities (DNA metabarcoding, genomics)
• Bioinformatics and statistical analysis
• Interaction with multiple research groups
• Publication and scientific communication of the results

Your profile

• PhD degree in biology, ecology, bioinformatics, or related sciences
• Profound knowledge in fish and/or plankton ecology 
• Experience with DNA metabarcoding or genomics
• Good data analysis skills and bioinformatics
• Willingness to collaborate
• Excellent written and spoken English communication skills

Our offer

We offer an exciting job in a stimulating and international working environment. The 2-year postdoc is financed by a Fellowship from the Carl Trygger Foundation. The selected candidate will work in the group of Prof Monika Winder at the Department of Ecology, Environment and Plant Sciences and with Prof Henrik Svedäng at the Baltic Sea Centre. 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.

Application

The application should include:

• A personal letter (max 3 pages) where the applicant describes her/himself in relation to the above-described requirements, a motivation to why the applicant is interested in the position and a short description of the candidate’s research interests.
• CV with academic qualifications and publication list.
• Contact information for 2-3 reference persons.
• Other relevant documents.

Your complete application, written in English or Swedish, marked with the subject head Postdoc Application, should be sent in a pdf document to monika.winder@su.se. Deadline is 12 April 2024. 

The fellowship begins as soon as possible or according to agreement. 

Contact

Further information about the position can be obtained from Prof Monika Winder, monika.winder@su.se.

See also at: https://www.su.se/department-of-ecology-environment-and-plant-sciences/about-the-department/work-with-us/postdoc-position-2-years-in-marine-molecular-ecology-deadline-12-april-2024-1.721413

Dynamics of Gut Bacteria Across Different Zooplankton Genera

Zooplankton-associated bacteria potentially have a great impact on the structure of ecosystems and trophic networks by providing various metabolic pathways and altering the ecological niche of host species. To understand the composition and drivers of zooplankton gut microbiota, we investigated the associated microbial communities of four zooplankton genera from different seasons in the Baltic Sea using the 16S rRNA gene.

Among the 143 ASVs (amplified sequence variants) observed belonging to heterotrophic bacteria, 28 ASVs were shared across all zooplankton hosts over the season, and these shared core ASVs represented more than 25% and up to 60% of relative abundance in zooplankton hosts but were present at low relative abundance in the filtered water. Zooplankton host identity had stronger effects on bacterial composition than seasonal variation, with the composition of gut bacterial communities showing host-specific clustering patterns. Our results suggest that the patterns of gut bacteria dynamics are host-specific and the variability of gut bacteria is not only related to host taxonomy but also related to host behavior and life history traits.

The study is available here: Xu, T., Novotny, A., Zamora-Terol, S., Hambäck, P., Winder, M. Dynamics of Gut Bacteria Across Different Zooplankton Genera in the Baltic Sea. Microb Ecol 87, 48 (2024). https://doi.org/10.1007/s00248-024-02362-7

Figure: Relative abundance of shared and core ASVs compared to water (inner ring). a Relative abundance of shared ASVs present in all zooplankton hosts across months at class level (outer rings) compared to water. b Relative abundance of core ASVs across months (outer ring) for each zooplankton host and their relative abundance in water samples (inner ring)

New study shows that climate change affects the activation of plankton resting stages with consequences for community composition and trophic mismatch

A large majority of plankton species overwinter as resting stage in the sediment. The resting life stage is, however, often overlooked in climate change research, although emergence of planktonic organisms originating from resting stages from the sediment is a key driver for pelagic population dynamic and community composition.

Here we ask to what extent the recruitment of plankton resting stages is affected by proposed climate change. For this, we investigated  phyto- and zooplankton recruitment from oxic sediments in the Baltic Sea in a controlled experiment under proposed temperature and light increase during the spring and summer. 

We find that emergence of resting stage differs between seasons and the abiotic environment. Phytoplankton recruitment from resting stages were high in spring with significantly higher emergence rates at increased temperature and light levels for dinoflagellate and cyanobacteria than for diatoms, which had highest emergence under cold and dark conditions. In comparison, hatching of copepod nauplii was not affected by increased temperature and light levels. These results show that activation of plankton resting stages are affected to different degrees by increasing temperature and light levels, indicating that climate change affects plankton dynamics through processes related to resting stage termination with potential consequences for bloom timing, community composition and trophic mismatch.

You can find the full article here:

Hedberg P, Olsson M, Höglander H, Bruchert V, Winder M (2024) Climate change effects on plankton recruitment from coastal sediments. Journal of Plankton Research. https://doi.org/10.1093/plankt/fbad060

Investigating recruitment of resting stages from Baltic Sea sediments. Foto: Per Hedberg.

Welcome to the new master students and a new semester!

Our first lab meeting of the new semester started online as many were abroad.

Baptiste successfully defended his PhD – Congratulations Dr. Serandour!

Thank you for a great presentation and an interesting discussion with the opponent Prof. Eric Goberville. Well done Baptiste!

The introduced Arapaima gigas in the Bolivian Amazon: Trophic position and isotopic niche overlap with native species

In this study we assess the potential impact of the introduced Arapaima gigas on native fish assemblages in two oxbow lakes of the Bolivian Amazon. Stable isotope data were used to determine trophic position (TP) and isotopic niche overlap, to evaluate potential predation and competition interactions, respectively. Results suggest that A. gigas is more an omnivore than a top predator, as often claimed. Arapaima gigas occupied an intermediate TP between detritivore/herbivore and piscivore fish species and showed broader isotopic niche compared to most native species analysed. Increasing our understanding on the processes generating impact of these introductions on resident communities through food web ecology will pave the way for better resource management and conservation efforts.

Read the full article here 

https://onlinelibrary.wiley.com/doi/full/10.1111/eff.12734

Arapaima is the largest freshwater fish with scales, home to the tropical waters of the Amazon basin.

New study shows that trophic transfer of essential nutrients is complex

Variation in fatty acid content among benthic invertebrates in a seasonally driven system

Read the full study in Limnology and Oceanography Letter.

In this study we test whether the succession from nutritious spring blooms to summer cyanobacteria is reducing food quality for benthic primary consumers and their fatty acid (FA) profiles. Contrary to expectations, we find low seasonal variability in FA content of five benthic macroinvertebrates spanning two trophic levels in the Baltic Sea, a system with high seasonal variation in phytoplankton species composition. However, levels of the major FA groups vary greatly between benthic species. This suggests that seafloor animals have evolved mechanisms to adapt to low-quality food inputs and that species composition of seafloor animals is important for determining food quality for fish. Moreover, this indicates that the transfer of essential biomolecules from primary producer to upper trophic levels is more complex and not directly related to the taxonomic composition and content of phytoplankton. 

Figure (A) Seasonal averaged content of PUFAs (including EFAs and their precursors ALA and LIN). The number reports the ω3:ω6 PUFA ratio. (B) NMDS clustering of benthic macroinvertebrate species, sediment and seston based on the proportion of individual FAs over the whole sampling period. 

DNA metabarcoding highlights cyanobacteria as the main source of primary production in a pelagic food web model

In this study we used data from dietary metabarcoding studies of zooplankton to calculate prey selectivity indices and assess energy fluxes in a pelagic resource-consumer network. We show that food web dynamics are influenced by prey selectivity and temporal match-mismatch in growth cycles and that cyanobacteria are the main source of primary production in the investigated coastal pelagic food web. The latter challenges the common assumption that cyanobacteria are not supporting food web productivity, a result that is increasingly relevant as global warming promotes cyanobacteria dominance. While this study provides a method for how DNA metabarcoding can be used to quantify energy fluxes in a marine food web, the approach presented here can easily be extended to other ecosystems.

Read the full article here 

https://www.science.org/doi/10.1126/sciadv.adg1096

and a related news report here (in Swedish)

https://www.su.se/nyheter/algblomning-spelar-en-nyckelroll-för-östersjöns-fiskbestånd-1.654858

Fig. 2. Consumer-resource network of the pelagic Baltic Sea. Link width is proportional to fluxes of energy (kJ/m2) between resources (phytoplankton, bottom) and consumers (zooplankton, top). The width of the nodes (taxa) corresponds to each population’s contribution to annual secondary production. The diameter of each plot is proportional to the square root of the total production.

New study using metabarcoding shows niche partitioning between planktivorous fish

Here, we investigate diet overlap between these three planktivorous fishes in the Baltic Sea, utilizing DNA metabarcoding on the 18S rRNA gene and the COI gene, targeted qPCR, and microscopy. Our results show niche differentiation between clupeids and stickleback, and highlight that rotifers play an important role in this pattern, as a resource that is not being used by the clupeids nor by other zooplankton in spring. We further show that all the diet assessment methods used in this study are consistent, but also that DNA metabarcoding describes the plankton-fish link at the highest taxonomic resolution. This study suggests that rotifers and other understudied soft-bodied prey may have an important function in the pelagic food web and that the growing population of pelagic stickleback may be supported by the open feeding niche offered by the rotifers.

The study is available here: Novotny A, Jan KMG, et al. Scientific Reports 2022

Figure 4: (a) Microscopic count of gut content of the planktivorous fish. Rotifers were identified as rotifer eggs. (b) Eggs were observed in the gut content of stickleback, originating from the rotifer genus Synchaeta. (c) Female of the rotifer genus Synchaeta carrying three eggs as identified from water samples. Scales are the same for (b) and (c). Source: https://www.nature.com/articles/s41598-022-15116-7/figures/4