Planktonic organisms are important for the functioning of aquatic ecosystems and biogeochemical cycles. Understanding the changes in plankton communities in the past, present, and future is fundamental to unveiling the response of the Earth system as a whole. It is challenging to document and predict shifts in plankton communities as long-term efforts are required in both observational time-series and experimental studies. Moreover, diverse sampling, identification and quantification methods reveal different aspects of plankton dynamics. In this session, we aim to bring together scientists who study planktonic organisms – phytoplankton, zooplankton and mixoplankton - over different time scales and use different conceptual approaches as well as different methodologies, such as microscopy, cytometry, pigment analysis, amplicon sequencing, meta-omics in experimental, observational or modeling studies. Changes of interest include, but are not limited to anthropogenic increase of temperature and acidification, shifts in nutrient availability and trophic dynamics. The session aims to document changes in plankton communities occurring on a range of timescales and the overall goal is to promote understanding of the mechanisms underlying these changes and their consequences for food webs and biogeochemical cycles.
Lead Organizer: Kristė Makarevičiūtė, GEOMAR Helmholz Centre for Ocean Research Kiel (kmakareviciute@geomar.de)
Co-organizers:
Andrew Barton, Scripps Institution of Oceanography, University of California San Diego (adbarton@ucsd.edu)
B.B. Cael, National Oceanography Centre, UK (cael@noc.ac.uk)
Alexandra Z. Worden, GEOMAR Helmholtz Centre for Ocean Research Kiel, Max Planck Institute for Evolutionary Biology (azworden@geomar.de)
Presentations
03:00 PM
Response of biomineralizing marine phytoplankton to environmental changes in the Mediterranean Sea over the last decade: insights from high-throughput automated workflows (4780)
Primary Presenter: Camille Godbillot, Aix-Marseille Université (godbillot@cerege.fr)
Studies have documented a decrease in pelagic fish sizes in the Gulf of Lions (NW Mediterranean) over the last decade, leading to a crisis in fish catches. Most explanations for this change invoke a decline and/or change in phytoplankton production and diversity caused by decreasing nutrient inputs, increasing sea surface temperatures, or ocean acidification. As of yet, the changes affecting the phytoplankton community in the region remain relatively unconstrained. Here, we explore the use of deep-learning algorithms to study the changes in phytoplankton production and bloom dynamics in the Mediterranean Sea. We apply automated microscopy imaging to the record of nanno- and microplankton shells retrieved from a sediment trap series in the Gulf of Lions between 2010 and 2018. We use a machine learning-based workflow for calcareous nannoplankton classification to study the changes in species abundance, size, and calcification; we explore a novel workflow to study the siliceous microplankton record (diatoms, silicoflagellates). Our results show a decrease in overall coccolith production and mass over the interval of study, and a growing proportion of deep-dwelling species in the total coccolith assemblage. These results suggest increasing oligotrophic conditions in the Gulf of Lions which can, at this stage, be attributed to increasing column stratification in the region. We will compare these results to trends in siliceous plankton production, with the particular aim to describe the sequence of blooms in the region, and its alteration in the context of environmental change.
03:15 PM
Intraspecific differences in thermal acclimation impact the ecological niche of coccolithophores (6566)
Primary Presenter: Arianna Krinos, MIT-WHOI (akrinos@mit.edu)
Coccolithophores are a diverse, ecologically-important phytoplankton group ubiquitous in the global ocean and more abundant in colder, oligotrophic waters. Recent studies have suggested that coccolithophores are the least resilient phytoplankton functional type to high (>30<sup>o</sup>C) water temperatures, while others show that warm coastal areas are important coccolithophore habitats. To examine how intraspecific diversity and acclimation shape plankton populations, we grew 13 strains of <em>Emiliania huxleyi</em>, isolated from regions of different temperature, for ~45 generations (2 months), each at 6-8 temperatures. We characterized the thermal response curve and flow cytometry-derived cell sizes of each strain. There was a mean difference of 0.63±0.3 day<sup>-1</sup> between maximum and minimum growth rates observed within-strain, while different strains had up to a 0.89 day<sup>-1</sup> difference in maximum growth rate. Even with virtually identical temperature optima and overlapping cell size, strain growth rates varied between 0.45--1 day<sup>-1</sup>. While some thermal curves were effectively symmetrical, others had slowly declining growth rates above the “thermal optimum”. We place our experimental results in global context using an ecosystem model simulation of coccolithophores in which several “thermal types” are scaled by cell size, and show how coccolithophore realized niches vary. Taken together, these observed intraspecifically-diverse thermal traits may reveal coccolithophores’ capacity to persist under unusually warm temperatures and exploit seasonal nutrient limitation in a changing ocean.
03:30 PM
Characterizing the impact of glacier-derived nutrients on marine phytoplankton in the Canadian Arctic Archipelago (7194)
Primary Presenter: Patrick White, University of Alberta (pwhite1@ualberta.ca)
Coastal ocean ecosystems are at risk from global warming-induced retreat of marine-terminating (tidewater) glaciers. Increased phytoplankton growth near tidewater glaciers has been observed in a range of locations, but it remains unclear exactly how these systems serve to elevate production. Recent work has suggested that both glacial meltwater and upwelled deeper marine waters brought to the surface by buoyant submarine discharge plumes may provide polar phytoplankton with essential nutrients throughout the summer. To test this hypothesis, we conducted a novel incubation experiment in Ausuittuq (Grise Fiord), Nunavut during summer 2021 to uncover how Canadian Arctic Archipelago (CAA) phytoplankton respond to different glacier-derived nutrient sources. Here, phytoplankton were supplied with glacial meltwater and/or deep seawater representing meltwater and upwelled nutrients respectively, and were monitored for chlorophyll a, nutrient consumption, and protein expression patterns. Phytoplankton exposed to deep water exhibited chlorophyll a concentrations that were four times higher than treatments exposed to meltwater only. These results suggest that the success of CAA phytoplankton near tidewater glaciers is largely due to upwelled macronutrients. Protein expression including meta-proteomics and Rubisco measurements of specific phytoplankton groups reveal molecular responses to these glacier-driven changes and shed light on how future tidewater glacier retreat is likely to impact primary producers in future climate warming scenarios.
03:45 PM
Synechococcus strains show differential proteome responses to nitrogen substrate switching and starvation (7017)
Primary Presenter: Angela Boysen, Pacific Lutheran University (aboysen@plu.edu)
In the marine environment, nitrogen often limits phytoplankton growth and influences microbial metabolism, community structure, and function. Microorganisms that rely on fixed nitrogen are likely switching between nitrogen sources frequently as local resources of preferred nitrogen compounds are depleted or replenished. Strains of the globally important picocyanobacteria Synechococcus have differing capability to use a variety of nitrogen sources, potentially contributing to their ubiquity. Our understanding of Synechococcus nitrogen use predominantly comes from laboratory studies that provide a single nitrogen substrate, thus there remain open questions associated with the metabolic effects of a switch between two nitrogen sources. To address these questions, we grew several strains of Synechococcus on a mixture of ammonium and nitrate and measured quantitative changes in protein abundance during the N-source switch from the former to the latter. Using 15N stable-isotope tracing proteomics, we determine which proteins are being built with which nitrogen source as well as the rates of production of different peptides. The switch to nitrate was accompanied by changes in protein synthesis and protein abundance in all three strains, and these metabolic changes were mostly unique to each strain. These results allow insights into how Synechococcus in the marine environment may be modifying their metabolisms to adjust to dynamic resource availability. The differences between strains highlight tradeoffs in resource allocation used to adapt to dynamic environments.
04:00 PM
AMMONIA-DRIVEN POLYAMINES OVEREXPRESSION ENHANCES DIATOM SILICIFICATION (5047)
Primary Presenter: Hao Zhou, East China Normal University (759094714@qq.com)
Diatoms are critical for regulating carbon and silicon cycles in the ocean. Several studies show that nitrogen enrichment can lead to diatom miniaturisation and increase silicification which are negative to carbon export in the ocean. Physiological and biochemical pathways linking nitrogen and silicification in diatoms remain unclear, however. Here, we propose a link between nitrogen, polyamines, and biogenic silica in the diatom Paralia sulcata. P. sulcata was evaluated as the experimental species in this study; it is a small and heavily silicified diatom that produces blooms in the North Sea and Yellow Sea after nitrogen enrichment. We examined the relationship of nitrogen concentration and source with polyamines overexpression. The response of polyamines, critical amino acids (aspartate, arginine, andornithine), and enzymes (arginine decarboxylase and ornithine decarboxylase) to four nitrogen conditions demonstrated that ammonia caninduce polyamines overexpression in the urea cycle. This increases long-chain polyamine synthesis, connecting to silane polypeptides to form Si-precipitating proteins, and promotes biogenic silica production. These findings are of great significance for understanding the coupling of nitrogen and silicon, and in particular the impact of diatom silicification on silicon cycling in the ocean.
04:15 PM
Diatoms co-existing in the HNLC subarctic Pacific have taxon-specific genetic modulation to low Fe within the same metabolic pathways (7237)
Primary Presenter: Bethany Jenkins, University of Rhode Island (bjenkins@uri.edu)
Diatoms are significant contributors to carbon expor,t even in HNLC regions. To understand how changes in diatom metabolism in reaction to environmental variables might alter their role in food web dynamics and carbon export, we conducted metatranscriptome analysis of a time-series of surface water samples paired with incubation experiments with manipulated nutrients. Sampling was conducted as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign conducted late summer in the HNLC subarctic Pacific. Diatom communities were taxonomically and metabolically similar across three weeks of sampling, consistent with similarities in surface water N, P, Si and growth-limiting Fe concentrations. In situ diatom communities demonstrated upregulation of metabolism consistent with Fe stress. Experimental alleviation of Fe stress revealed genera-specific responses in expression of photosynthetic components and in glycan, carbohydrate, amino acid and lipid metabolism. Taxonomic comparison of responses within in situ communities reveals that Fe-sensitive metabolism in Pseudo-nitzschia spp. is uniquely and favorably adapted to low Fe environments with other taxa (e.g. Chaetoceros and Thalassiosira spp.) showing much higher regulatory impacts of low Fe on Fe-sensitive pathways. Taken together, our data show that this HNLC environment differently impacts potential nutritional quality and carbon fixation amongst prevalent diatoms with implications for food webs and carbon export.
SS029E Causes and Implications of Changes in Plankton Communities Across Timescales
Description
Time: 3:00 PM
Date: 9/6/2023
Room: Auditorium Mallorca