Contributed Session.
Lead Organizer: Paola Ayala-Bord, University of Lethbridge (p.ayalaborda@gmail.com)
Co-organizers:
Frieda Taub, University of Washington (taub@uw.edu)
Presentations
09:00 AM
READS WITH RELEVANCE: QUANTIFYING DNA METABARCODING FOR IMPROVED UNDERSTANDING OF PROTISTAN COMMUNITIES (9749)
Primary Presenter: Fran Webber, University of Rhode Island (fwebber@uri.edu)
DNA metabarcoding is a powerful and popular technique for investigating the composition of protistan communities, revealing the presence of cryptic and hard-to-visualize taxa. Despite its many advantages, metabarcoding results can be difficult to interpret because the commonly-used 18S rRNA gene can vary by orders of magnitude among individuals. Furthermore, DNA metabarcoding yields compositional data, giving relative rather than absolute abundances. Together, these characteristics impede translation of metabarcoding data into ecologically useful metrics. Here, we conducted metabarcoding of mock and in situ communities using multiple primer sets and both DNA and cDNA as PCR templates. Mock communities were constructed from uni-algal cultures of taxonomically diverse phytoplankton and in situ samples were collected weekly over one month from the Narragansett Bay Long-Term Plankton Time Series. These communities were used to identify correlation coefficients of metabarcoding results and ecologically useful metrics such as cell number and biomass. As expected, our results highlight that relative read number is poorly correlated with relative cell number at the V4 region of the 18S rRNA gene. On-going analyses will yield quantitative correlations of metabarcoding data with other gene regions and nucleic acids yielding important insights into how metabarcoding can and cannot be used to interpret the composition and quantity of natural communities.
09:15 AM
Seasonal Dynamics of Planktonic Protist Diversity and Community Assembly in the Northern East China Sea (9615)
Primary Presenter: Kwang Young Kim, Department of Oceanography (kykim@chonnam.ac.kr)
This study investigated planktonic protists in the northern East China Sea (NECS) to evaluate their diversity, community assembly processes, and primary production across seasons. Sampling took place during three cruises in May, July, and October 2023. Using small organelle-enriched metagenomics, we identified 537 operational taxonomic units (OTUs) throughout the NECS. While regional differences were negligible, significant seasonal changes emerged, with higher phylogenetic clustering in summer—indicating strong environmental influences on community assembly. Metagenomic analysis revealed diverse protist taxa across surface (SUR), deep chlorophyll maximum (DCM), and bottom (BOT) layers. Microbial eukaryotes—including Bacillariophyta, Cryptophyta, Dinoflagellates, and Ochrophyta—displayed significant variability in community composition across depths. Bacillariophyta and Ochrophyta dominated the DCM and BOT layers, suggesting that nutrients and light influence microbial communities. Analysis of trophic modes unveiled vertical stratification with six modes identified. Obligate Photoautotrophs (OPA) and Constitutive Mixotrophs (CM) dominated all depths, highlighting the importance of mixotrophy. The SUR layer exhibited greater diversity, including opportunistic and competitive modes, while the DCM and BOT layers were characterized by neutral and heterotrophic modes. Heterotrophs (HET) increased in the DCM and SUR layers. General and Engulfing Specialist Non-Constitutive Mixotrophs (GNCM, eSNCM) were less common; Parasitic Specialist Non-Constitutive Mixotrophs (psSNCM) were rare. Non-metric multidimensional scaling (NMDS) analysis revealed significant seasonal but no depth-related differences, emphasizing that temperature and nutrients primarily drive protist dynamics in the NECS. Community assembly analysis indicated that 85.2% of the communities were undominated by specific ecological processes, with environmental selection and dispersal mechanisms playing minor roles. These findings highlight mixotrophy as a key adaptive strategy in the variable marine environment of the NECS.
09:30 AM
USING MULTIPLE METRICS TO ANALYZE BLOOM DYNAMICS DURING THE SUMMER OF 2023 IN THE GULF OF MAINE (8989)
Primary Presenter: Madison Hurley, University of New Hampshire (madison.hurley@unh.edu)
Phytoplankton diversity is a critical indicator of ecosystem health and function, playing a crucial role in the health of higher trophic levels and biogeochemical cycling. The Gulf of Maine typically experiences a prominent spring bloom dominated by diatoms. However, in 2023, an extensive and intense bloom of the dinoflagellate Tripos muelleri was observed, with concentrations exceeding 50,000 cells L-1, an order of magnitude higher than previously recorded. The bloom’s intensity contributed to biogeochemical shifts in water quality parameters, including low pCO2 and high pH. Here, we use multiple methods including 18S rRNA amplicon sequencing, image analysis, and pigment analysis to reconstruct the bloom’s community structure. In addition, community composition was integrated with concurrent oceanographic data, to identify the potential triggers of the bloom’s persistence and demise. Our findings aim to enhance the understanding of phytoplankton dynamics in the context of changing marine environments.
09:45 AM
Diversity-informed carbon conversion factors for open-ocean phytoplankton (9376)
Primary Presenter: Charlotte Eckmann, Marine Biological Laboratory (caeckmann@gmail.com)
Phytoplankton are integral to the ocean's carbon cycling, and the fate of their fixed carbon has implications for atmospheric carbon dioxide levels. Here, we examined phytoplankton communities in the Bay of Bengal to identify key ecotypes of Prochlorococcus, Synechococcus, and photosynthetic eukaryotes using analysis of V1-V2 16S rRNA gene amplicons. We compared these communities at the ASV level to those collected from the Bermuda Atlantic Time-series Study (BATS) site in order to delineate ecotypes spanning tropical and subtropical regions. For a subset of samples, we used V1-V2 16S rRNA gene amplicon-based taxonomy to refine estimations of carbon per-cell and overall carbon contributions derived from flow cytometry bulk cell abundances. Estimates of phytoplakton carbon content are important to understanding carbon flow through the marine food web. While it is common practice to assign one carbon value to all cells in a broad category (e.g, picophytoplankton), this approach can mask relevant nuances in carbon content. Our analyses collectively provided deeper insights into both the diversity and carbon contributions of Prochlorococcus, Synechococcus, and photosynthetic eukaryotes including prasinophytes, pelagophytes, prymnesiophytes, and diatoms. The results should improve estimates of biomass from photosynthetic communities under current conditions and aid future modelling work.
10:00 AM
THE SUCCESSION OF UNSUNG HEROES BENEATH OUR FEET; THE STUDY OF PRIMARY SUCCESSION IN A SHALLOW FRACTURED AQUIFER (COVEY HILL, QUEBEC, CANADA) (9189)
Primary Presenter: Samuel beauregard-tousignant, UQAM - GRIL (samuel.beauregard.t@gmail.com)
Aquifers in the continental subsurface have long been exploited for their resources. However, given the technical difficulties in accessing recurring subsurface samples, the communities of microorganisms living there and their temporal dynamics remain largely misunderstood. Here, we investigated the effects of time and organic and inorganic carbon on primary succession of microorganisms belonging to the Bacteria and Eukaryote domains colonizing rock surfaces from a shallow fractured aquifer. We recreated its physicochemical environment in triplicate bioreactors and let the communities grow for 24 days. The planktonic and sessile communities were sampled daily in independent experiments and characterized based on their 16S (Bacteria) or 18S (Eukaryote) rRNA genes. Time was the parameter with the strongest correlation both with alpha and beta diversity and the first few days of the incubations fluctuated more in composition than the latter days. Eukaryotes were mainly photosynthetic despite growing in the dark and Bacteria were mostly heterotrophs. The alpha diversity of planktonic and sessile communities varied following similar patterns, but the planktonic ones varied with a wider amplitude. Also, the early day planktonic communities, especially the eukaryotes, were more like the ones of the latter days than the mid-incubation ones. Finally, organic and inorganic carbon played a much smaller role than expected as we believe other parameters such as pH and light limited microorganism growth.
10:15 AM
Unique redox couplings enable microbial survival and methane mitigation in methanogenic sediments (9221)
Primary Presenter: Orit Sivan, Ben Gurion University of the Negev (oritsivan@gmail.com)
A complex and active microbial population was observed to exhibit both aerobic and anaerobic microbial activity in methanogenic lake sediments. This study shows how communities manage to survive under such energy limited, highly reduced conditions, through redox cycles of Mn-Fe-N-CH4 that control the emissions of the greenhouse gas methane to the atmosphere. The cycles were quantified using geochemical and microbial profiles and stable isotope probing (SIP) experiments close to natural conditions. Profiles surprisingly revealed an increase of nitrite concentrations together with elevated dissolved iron and manganese levels, decreased methane concentrations and a notable increase of NC10 bacteria activity. Controlled anaerobic incubation experiments with methanogenic sediment labeled with 15N-ammonium indicated anaerobic production by ammonium oxidation, most likely coupled to manganese oxide reduction. A sink for nitrite was observed by a series of on-top-core experiments, and it was shown to be coupled to ferrous oxidation, which is partly originated from anaerobic oxidation of methane (AOM). Nevertheless, NC10 activity in this setting is responsible for dark production of oxygen through N-methane coupling, which enables aerobic methane oxidation. The complex microbial couplings demonstrated here are significant in mitigating methane emissions and provide insight for survival mechanisms of microbes under limited energy conditions.
CS05 - Community Ecology
Description
Time: 9:00 AM
Date: 28/3/2025
Room: W206A