Zooplankton are fundamental to aquatic ecosystems, influencing not only biogeochemical cycles but also broader ecological dynamics. As primary consumers, they link lower trophic levels, such as phytoplankton, to higher trophic levels, including fish and other predators, thereby shaping food web structures. This session will delve into the ecological roles of zooplankton across aquatic environments, with a focus on their contributions to biogeochemical cycles and their adaptive responses to environmental changes.
In both marine and freshwater systems, zooplankton contribute to carbon cycling through the biological pump. They graze on phytoplankton, respire carbon dioxide, and repackage organic matter into fecal pellets that can sink to deeper waters or sediments, a process crucial for sequestering atmospheric carbon dioxide. Additionally, zooplankton excrete dissolved inorganic nutrients that are rapidly assimilated by phytoplankton, sustaining primary production in nutrient-depleted areas.
We invite contributions on the latest findings in zooplankton ecology, including their distribution, behavior, and interactions with other organisms in both marine and freshwater ecosystems. The session will also encompass studies on zooplankton-mediated carbon and nutrient cycling, examining factors that influence export efficiency, such as species traits, community dynamics, and environmental changes like climate change, ocean acidification, and deoxygenation.
The session will also highlight cutting-edge methodologies advancing our understanding of zooplankton ecology. Innovations in imaging, molecular tools, and biogeochemical modeling are providing new insights into zooplankton distributions, behaviors, and ecological roles. We encourage presentations showcasing these technologies and their applications in contemporary research.
This session aims to synthesize current knowledge, identify research gaps, and prioritize future studies in zooplankton biogeochemistry. We will explore how these small but ecologically vital organisms can be integrated into global biogeochemical models, with implications for climate predictions and resource management.
By bringing together experts in aquatic biology, ecology, limnology, oceanography, and biogeochemistry to foster interdisciplinary collaboration. It is designed to attract researchers, educators, policymakers, and students focused on the ecological and biogeochemical roles of zooplankton and their responses to environmental change. Through this exchange, we aim to deepen our understanding of the ecological importance of zooplankton and their role in maintaining healthy aquatic ecosystems.
The session’s importance lies in its potential to advance our understanding of the critical roles zooplankton as ecological keystones in aquatic environments. As we face unprecedented environmental challenges, it is crucial to integrate zooplankton ecology into broader scientific frameworks to preserve aquatic biodiversity and ensure the sustainability of global biogeochemical cycles.
Lead Organizer: Yuuki Niimi, Arizona State University (yniimi@asu.edu)
Co-organizers:
Leocadio Blanco-Bercial, Arizona State University/Bermuda Institute of Ocean Science (leocadio@asu.edu)
Susanne Neuer, Arizona State University (Susanne.Neuer@asu.edu)
Presentations
09:00 AM
Diversity and abundance of protozoa in the Laurentian Great Lakes, two years of data (8755)
Primary Presenter: Elizabeth Alexson, Natural Resources Research Institute, University of Minnesota Duluth (alexs005@d.umn.edu)
Though there are relatively few studies, literature suggests heterotrophic protists play an important role in Laurentian Great Lakes food webs. In 2022, we incorporated identification and enumeration of these protists into the USEPA’s Great Lakes Biology Monitoring Program, which investigates the base of Great Lakes pelagic food webs. We aim to develop a Great Lakes faunal library for protozoans and examine how these communities change spatially (across all five lakes) and temporally (seasonally and annually). Preliminary data reveal a large diversity of Ciliophora (Oligotrichea, Gymnostomatea, Prostomatea, Oligohymenophorea, and Kinetofragminophora), Choanoflagellates, and Sarcodina. We will present the first two years of data and demonstrate the importance of the continued monitoring of these abundant organisms.
09:15 AM
MICROZOOPLANKTON GRAZING DYNAMICS IN RUN-OF-RIVER VERSUS STORAGE RESERVOIRS (9483)
Primary Presenter: McKenzie Frazier, Washington State University (mckenziefrazier97@gmail.com)
Microzooplankton grazers influence phytoplankton growth in freshwater ecosystems. In rivers, microzooplankton grazing dynamics may be influenced by variations in flow rates, temperature, etc. Columbia River Basin (CRB) rivers are heavily impounded by run-of-river (ROR) dams, managed for hydropower/navigation, with low reservoir residence times and high flows, and by storage dams, managed for irrigation and drinking water, with higher reservoir residence times and lower flows. We conducted monthly dilution experiments from May-October, 2023 in a ROR reservoir (Bonneville, Columbia River) and a storage reservoir (Detroit Lake, North Santiam River) to assess how microzooplankton grazing and phytoplankton growth rates varied between these sites over a growing season. There were significant effects of dilution based on changes in chl-a from May to August in the storage reservoir; however, in the ROR reservoir significant effects based on chl-a were only observed in June. Taxonomic analysis indicated that microzooplankton (mostly ciliates and rotifers) exerted positive grazing pressure on diatoms in both reservoirs, but with higher grazing rates in the ROR reservoir. Microzooplankton also exhibited negative taxon-specific grazing rates on all other phytoplankton groups (including cyanobacteria) in both reservoirs. Results show a clear pattern of microzooplankton grazer preference for diatoms, with likely higher grazing impacts in ROR reservoirs with shorter residence times, and have implications for reservoir management, especially where cyanobacteria blooms are a concern.
09:30 AM
Experimental evaluation of microzooplankton grazing methods in the lab and in the field (9620)
Primary Presenter: Jennifer Beatty, University of Southern California (jlbeatty@usc.edu)
Microzooplankton grazing on picoplankton is a fundamental process within aquatic food webs, particularly in low-nutrient oligotrophic regions that are typically dominated by small picophytoplankton. Classical methods employed in the field have been used for decades without rigorous testing in a controlled laboratory setting. Two commonly employed methods for measuring microzooplankton grazing rates in nature were assessed in a controlled laboratory experiment designed to compare the estimated phytoplankton mortality rates by the experimental techniques to the picophytoplankton mortality observed directly in the culture based on changes in cell abundance. The Dilution and fluorescently labeled bacteria disappearance techniques were applied to a culture of the cyanobacterium subjected to a nanozooplanktonic grazer in the presence and absence of a cyanophage. Results indicated that, under laboratory conditions, these methods underestimated picoplankton mortality rates by 50-80%. The techniques were then applied in the field to compare results outside of the laboratory. There was an order of magnitude difference between mortality rates estimated using the techniques, which raises concerns of the validity of the assumptions underlying the techniques. Overall, both techniques provided reasonable, albeit somewhat underestimated microzooplankton-mediated mortality rates under controlled laboratory conditions, but caution should be exercised in interpreting these rates in field studies where the assumptions of the methods may be difficult to meet.
09:45 AM
A NEW METHOD FOR DETERMINING ZOOPLANKTON DIVERSITY AND ABUNDANCE FROM SOUTHERN OCEAN CONTINUOUS PLANKTON RECORDER (CPR) COLLECTIONS USING NANOPORE SEQUENCING (9081)
Primary Presenter: Georgia Pollard, University of Waikato (gp58@students.waikato.ac.nz)
Continuous Plankton Recorders (CPRs) have been deployed from underway vessels to enable wide-ranging and economical zooplankton collection across global oceans for nearly a century. However, samples are often incompletely analyzed due to physical damage to specimens and the time and cost of morphological analysis. Polymerase chain reaction (PCR) amplicon sequencing can improve the speed and accuracy of analysis. PCR primers reliably targeting areas of high DNA sequence variability across taxa are essential to reduce the need for group-specific primer sets. To address patchy sequence coverage for Southern-Ocean species, we generated reference sequences using sanger and nanopore sequencing from specimens identified by a taxonomic expert. DNA extraction and amplification protocols were optimized across 9 phyla covering 120+ taxa, testing multiple primer sets targeting the COI gene and 18S ribosomal RNA operon. Ultimately, a novel primer set was developed specifically suited to taxa playing key roles in Southern Ocean ecosystems, covering a range of phyla. By multiplexing amplicons for individual specimens, this method can achieve high throughput and accuracy while providing abundance data. Nanopore sequencing allows for longer amplicons to be used for species discrimination, facilitates in-house sequencing, and is unaffected by co-amplification of target specimens and their associated organisms. This project considers how to address reference sequence database gaps and how to optimize genetics workflows for whole-community zooplankton research.
10:00 AM
Life cycle and survival strategies of Noctiluca scintillans: Gamete physiology and reproduction (8851)
Primary Presenter: Jeffery Lee, National Taiwan Ocean University (jl042430064@gmail.com)
Noctiluca scintillans is a dinoflagellate species known for causing red tides in tropical and subtropical regions worldwide. Its reproductive cycle includes both asexual reproduction via binary fission and sexual reproduction through gametogenesis. Traditionally, it was believed that during sexual reproduction, Noctiluca scintillans transformed into gametocyte mother cells, which released gametes into the surrounding water. These gametes would then combine to form zygotes, maturing into trophont cells. Gametes were thought to possess only swimming ability, with no capability for reproduction or grazing. However, in this study, we observed that isolated gametes from mature Noctiluca scintillans cells exhibited signs of asexual reproduction, with increasing gamete concentration over time in closed environments. This discovery led us to investigate the reproductive and grazing behaviors of the gametes, as well as their diet and optimal cultivation condition. Due to the low natural rate of sexual reproduction (~1%), we employed previously established methods to induce gametocyte production and generate sufficient gametes for experimentation. Multiple culture experiments were conducted to assess the environmental factors influencing asexual reproduction in these gametes. Our results indicate that Noctiluca scintillans gametes are capable of reproduction and do not perform photosynthesis, suggesting that gametes represent an alternate generational form in the species’ life cycle. Further grazing experiments demonstrated that gamete concentration closely follows bacterial concentration trend, indicating that gametes feed primarily on bacteria or prey smaller than 2μm. Specifically, high rates of asexual reproduction were observed when the gametes were fed exclusively with Vibrio parahaemolyticus, showing stable population growth over 72 hours. These findings suggest that this alternate form of generation may act as a survival strategy toward the end of a bloom. When the adult form struggles to find sufficient prey, gametogenesis produces gametes that can feed on smaller-sized prey, such as bacteria, which remain abundant. This shift in feeding behavior allows the population to persist in low-prey conditions, ensuring the species' survival during periods of environmental stress.
10:15 AM
Impacts of microzooplankton grazing on size-fractionated transparent exopolymer particle (TEP) production in the California Current (8877)
Primary Presenter: Mikayla Cote, University of New Hampshire (mikayla.cote@gmail.com)
Transparent exopolymer particles (TEP) are gel-like polysaccharides ubiquitous in oceanic habitats. These carbon-rich sticky particles, produced by phytoplankton are crucial for marine aggregate formation, providing an important mechanism by which carbon and other material are transported to depth. In addition, as major consumers of phytoplankton, microzooplankton have the potential to alter TEP production. Consumption of TEP and/or affecting TEP production by microzooplankton could alter the size distribution of aggregates, subsequently affecting sinking rates, therefore impacting carbon flux. Over a 28-day expedition in the California Current during May-June 2024, 24 h size-fractionated TEP production and dilution experiments were performed concurrently every other day to estimate rates of size-fractionated TEP production (<20 µm, <200 µm, and unfiltered seawater), phytoplankton growth, and microzooplankton grazing. In this chain-forming diatom dominated system, we found that the majority of TEP was produced in the unfiltered seawater and <200 µm treatments and there were minimal contributions of the <20 µm treatment to bulk TEP measurements. Phytoplankton growth generally exceeded microzooplankton grazing, however, the production of TEP in the <20 and <200 µm treatments was likely reduced due to microzooplankton grazing. Our results improve estimates of TEP production and highlight the importance of considering microbial interactions such as microzooplankton grazing as drivers of TEP and marine snow dynamics.
SS44D - Ocean and Freshwater Zooplankton Ecology
Description
Time: 9:00 AM
Date: 30/3/2025
Room: W207AB