Climate “winners and losers” are organisms or groups of organisms expected to become more or less (respectively) abundant due to climate change, when climate responses are evaluated at a broad biological scale. -Omics approaches can be used to identify the genetic traits that confer climate resilience or susceptibility and their adaptation rate. Evidence from field studies and in situ observations may be leveraged to make isolated predictions, or to test forecasts made by ecosystem models about future microbial distributions. Likewise, culture manipulations that assess physiological adaptations to different physicochemical conditions can drive predictions of microbial community responses to changing aquatic environments. Whether or not organisms can be accurately and summarily predicted as climate “winners and losers”, either generally or regionally, is an open question with key implications for our language about future impacts of climate change on aquatic microorganisms and the ecosystems they shape. In this session, we invite talks describing evidence for climate resilience or sensitivity of microbial taxa from any aquatic environment. We particularly encourage talks from participants who link empirical and theoretical approaches, or specifically address the capacity of -omics approaches to predict climate impacts on microbial communities. We hope this session will inspire precise language about predicted climate impacts on key groups of aquatic microorganisms and promote dialogue about microbial groups experiencing recent climate impacts.
Lead Organizer: Arianna Krinos, Brown University (akrinos@vt.edu)
Co-organizers:
Christine Palermo, WHOI (christine.palermo@whoi.edu)
Margaret Mars Brisbin, University of South Florida (mmarsbrisbin@usf.edu)
Presentations
02:30 PM
AFTER THE APOCALYPSE: HOW UNPRECEDENTED HEAT WAVES LEAD TO UNPRECEDENTED PHYTOPLANKTON COMMUNITIES (9012)
Primary Presenter: David Hutchins, University of Southern California (dahutch@usc.edu)
One of the most alarming consequences of ocean warming is the increasing frequency and intensity of extreme regional marine heatwaves (MHW). Episodic MHWs now regularly approach or exceed the upper thermal limits of resident phytoplankton species as determined by laboratory reaction norm studies, yet very little is known about the actual consequences for long-term phytoplankton community diversity and function in natural ocean environments. Despite this unfolding climate emergency, uncertainty remains about whether microbial assemblages can fully rebound from these damaging transitory events. Understanding this critical ecosystem recovery process requires learning how resilience to extreme temperatures varies among and within phytoplankton taxa, from major functional groups down to individual species. Recent experimental and observational research suggests that varying abilities to survive and recover from temporary extreme thermal stress can profoundly reshape post-MHW marine microbial communities by selecting for heat-tolerant groups, and even for thermally-resistant subpopulations within a single species. This talk is intended to offer a window into the future ocean where differential resilience to MHWs will reshuffle phytoplankton communities in novel ways, with implications for changing food webs and biogeochemical cycles in marine regimes around the world.
02:45 PM
03:00 PM
UNDERSTANDING THE CLIMATE RESPONSE CONSEQUENCES OF CHANGING ELEMENTAL USE EFFICIENCIES IN PROCHLOROCOCCUS (9506)
Primary Presenter: Bradley Mackett, University of Southern California (mackett@usc.edu)
Anthropogenic climate change is rapidly reshaping the ecology and physiology of biogeochemically significant phytoplankton. While phytoplankton are consistently subjected to multiple interacting abiotic factors, most biogeochemical models are based on data from single-stressor experiments. Ubiquitously abundant between 40°N and 40°S, the photosynthetic cyanobacterium Prochlorococcus plays a vital role in global primary production and supports microbial food webs in oligotrophic regions. This study examines the physiology of high-light Prochlorococcus strains MIT1314 (Station ALOHA, North Pacific) and MED4 (Mediterranean Sea) in a climate-relevant context by growing them across their full thermal range under varying nutrient limitations (nitrogen, phosphorus, and iron). To quantify the synergistic effects of temperature and nutrient availability, we used elemental use efficiencies (EUEs), measuring carbon fixation rates normalized to the cell quota of the most limiting nutrient. Our results reveal strain-specific temperature-nutrient interactions, indicating that regional microdiversity contributes to physiological responses under future climate scenarios. Under warmer, iron-limited conditions, MED4 exhibited higher iron use efficiency (IUE), potentially reflecting greater metabolic efficiency—a response not observed in MIT1314. These findings, alongside other distinct physiological responses, provide mechanistic insights into how temperature-nutrient interactions may shape the functional diversity of this key group of primary producers. Anthropogenic climate change is rapidly reshaping the ecology and physiology of biogeochemically significant phytoplankton. While phytoplankton are consistently subjected to multiple interacting abiotic factors, most biogeochemical models are based on data from single-stressor experiments. Ubiquitously abundant between 40°N and 40°S, the photosynthetic cyanobacterium Prochlorococcus plays a vital role in global primary production and supports microbial food webs in oligotrophic regions. This study examines the physiology of high-light Prochlorococcus strains MIT1314 (Station ALOHA, North Pacific) and MED4 (Mediterranean Sea) in a climate-relevant context by growing them across their full thermal range under varying nutrient limitations (nitrogen, phosphorus, and iron). To quantify the synergistic effects of temperature and nutrient availability, we used elemental use efficiencies (EUEs), measuring carbon fixation rates normalized to the cell quota of the most limiting nutrient. Our results reveal strain-specific temperature-nutrient interactions, indicating that regional microdiversity contributes to physiological responses under future climate scenarios. Under warmer, iron-limited conditions, MED4 exhibited higher iron use efficiency (IUE), potentially reflecting greater metabolic efficiency—a response not observed in MIT1314. These findings, alongside other distinct physiological responses, provide mechanistic insights into how temperature-nutrient interactions may shape the functional diversity of this key group of primary producers.
03:15 PM
PHYTOPLANKTON RESPONSE TO SEASONAL PROGRESSIONS IN MILWAUKEE HARBOR: UNDERSTANDING PATTERNS AND INFLUENCES ON DIATOM BLOOMS (9586)
Primary Presenter: Mary Larson, University of Wisconsin-Milwaukee (larso329@uwm.edu)
Phytoplankton abundance and community composition respond to changing environmental factors, including light, temperature, nutrients, and physical disturbances. In 2023, diatom biomass notably increased in Milwaukee Harbor, continuing into 2024. Water samples for nutrient analysis, phytoplankton biomass and counts, temperature, and light data were collected from north and south basins of Milwaukee Harbor. Important, but less immediate results, such as counting cells, are in progress. Chemical analysis revealed silicate concentrations oscillated throughout the observed period (February-August 2024), showing drawdowns of dissolved silicate (DSil) as particulate silicate (PSil) increased and vice versa. Between sampling expeditions taken in June and August, DSil decreased in the south from 65.4 µM to 33.4 µM; PSil increased from 4.6 µM to 28.2 µM. During this time, a new dominant phytoplankton species took over. No biomass nutrient was limiting in this harbor; therefore, other factors were controlling phytoplankton community composition. For example, we found that intrusions of Lake Michigan water during wind events were able to temporarily separate locations with respect to chemical composition and abundance of phytoplankton. Weather-driven variability in nutrient fluxes and changes in phytoplankton abundance and community composition have implications for climate-induced alteration of biogeochemical cycles. Observing these progressions helps us to understand phytoplankton dynamics in a freshwater harbor system, giving insight into factors driving diatom blooms.
03:30 PM
Future Ocean Warming Threatens Key Photosynthetic Microbes (9258)
Primary Presenter: François Ribalet, University of Washington (ribalet@uw.edu)
Prochlorococcus, the most abundant photosynthetic organism on Earth and a crucial component of oceanic food webs, faces increasing threats from rising global temperatures. Yet, its sensitivity to temperature remains poorly understood, hindering our ability to predict its response under future climate change scenarios. This presentation will examine the thermal niche of Prochlorococcus using a decade-long record of in-situ measurements across vast regions of the surface ocean. We will present novel findings on the temperature dependence of Prochlorococcus division rates, revealing a critical thermal threshold with significant implications for its productivity and distribution. Furthermore, we will discuss the potential for shifts in phytoplankton community structure and trophic interactions as a consequence of future Prochlorococcus decline, based on projections from an ecosystem model incorporating our empirical findings. Our results underscore the vulnerability of Prochlorococcus-dependent marine food webs to future warming and highlight the urgent need to understand the ecological consequences of ongoing climate change.
03:45 PM
Battling Trophic Modes: How Do Mixotrophs Respond to Iron Limitation in Upwelling Zones? (8988)
Primary Presenter: Emily Speciale, University of North Carolina at Chapel Hill (speciale@unc.edu)
Mixotrophs, defined as phytoplankton capable of both phototrophy and heterotrophy, are an emerging topic of interest due to their role in ocean food webs and carbon cycling. As climate change is expected to reduce iron bioavailability within upwelling zones, mixotrophs may have an advantage due to an array of possible iron acquisition strategies. We paired physiological measurements with metatranscriptomics to investigate the molecular mechanisms of mixotrophs within an upwelling zone as a function of iron status. Our study occurred during a biologically productive upwelling season within the California Current System, typically dominated by large phototrophic diatoms. Subsurface waters from an active upwelling site were incubated for 14 days under control (Ctrl), iron-replete (Fe), and induced iron-deplete (DFB) treatments. Results at day 7 revealed differing phytoplankton communities; Ctrl/Fe communities had high biomass and RNA reads dominated by diatoms, whereas the DFB community had low biomass and a higher proportion of mixotroph reads. DFB mixotrophs downregulated photosynthetic processes while upregulating those linked to iron stress, signal transduction, and the phagolysosome compared to Fe mixotrophs. This response contrasted with phototrophic diatoms, which showed less change in photosynthetic machinery or signal transduction under iron limitation. Our results suggest mixotrophy as a viable strategy used by phytoplankton to cope with iron limitation, and although diatoms dominate under high-iron scenarios, low-iron scenarios may pose a different outcome.
SS19A - Climate “winners and losers”: predicting and assessing microbial responses to climate change
Description
Time: 2:30 PM
Date: 29/3/2025
Room: W205CD