Organic matter in aquatic environments includes dissolved and particulate compounds with varying lability, ranging from labile compounds that turn over rapidly, such as amino acids and carbohydrates, to refractory components that persist for thousands to millions of years. The lability of organic matter influences its fate, either incorporation into microbial biomass, respiration by heterotrophic microbes, or export to various regions. Organic matter lability is influenced by intrinsic molecular properties, as well as biotic factors, such as microbial abundance, enzymes, and community composition. In addition, abiotic factors, such as photochemical reactions, oxygen stress, sorption/desorption, and physical aggregation/disintegration, also influence the transformation and fate of organic matter. While recent advances in chemical analysis and microbial studies have significantly enhanced our understanding of these processes, several big questions remain regarding the fate of organic matter. When and where do biotic versus abiotic factors dominate organic matter transformations? Can we identify common principles that determine the fate of organic matter across all water bodies? In this session, we invite presentations on the lability and fate of organic matter in aquatic environments, including but not limited to chemical characterization, ecosystem-specific studies on organic matter source and fate, microbial production and uptake, and pathways of degradation and transformation. We welcome both field observation and lab experimental studies, aiming to synthesize research across disciplines and better understand the factors shaping organic matter lability and its role in biogeochemical processes in aquatic environments.
Lead Organizer: Shuting Liu, Kean University (liushut@kean.edu)
Co-organizers:
Yuan Shen, Xiamen University (yuanshen@xmu.edu.cn)
John Paul Balmonte, Lehigh University (jpb422@lehigh.edu)
Presentations
06:00 PM
OBSERVING DISSOLVED METABOLITES IN PROCHLOROCOCCUS MARINUS CULTURES ON A DIEL TIMESCALE USING BENZOYL CHLORIDE DERIVATIZATION (9304)
Primary Presenter: Natalie Graham, Woods Hole Oceanographic Institution (Natalie.Dreux.Graham@gmail.com)
Prochlorococcus, a picocyanobacterium adapted to oligotrophic environments and Earth's most abundant photosynthetic organism, fixes CO2, exuding metabolites essential for neighboring microbes. Studies indicate cellular function and growth align with the 24-hour light/dark cycle, suggesting that metabolic profiles may also exhibit diel rhythmicity. However, previous measurements of metabolites released by Prochlorococcus have focused on single time points, obscuring temporal dynamics, and primarily quantified non-polar metabolites. We aimed to determine whether extracellular metabolites from a high-light adapted strain of Prochlorococcus (MIT9301) exhibit diel rhythmicity over time, using benzoyl chloride derivatization coupled with liquid chromatography-mass spectrometry. Axenic cultures were exposed to diel light/dark cycles, and samples were collected every two hours for 48 hours, for extracellular metabolomic profiles. We quantified 30 unique metabolites, with ~50% showing significant diel oscillations. These include metabolites involved in DNA and protein synthesis, such as glutamic acid, proline, and uridine 5’-monophosphate. We also observed the accumulation of metabolites, like glycine and glutathione, in the extracellular space. These findings underscore the need for high temporal resolution in metabolite studies and raise questions regarding the cellular mechanisms controlling the excretion of nitrogen and phosphorus-containing metabolites in nutrient-poor environments.
06:00 PM
METABOLITE EXCRETION RATES OF FOUR MIGRATORY ZOOPLANKTON (9264)
Primary Presenter: Amy Maas, BIOS/ASU (amaas4@asu.edu)
Zooplankton transform and transport nutrients across vertical zones of the ocean food web. Consuming particulate organic matter from a variety of trophic levels, they repackage carbon into biomass and sinking fecal matter. Although less studied than their particulate contributions, zooplankton directly release dissolved organic waste compounds. The identities and quantities of these waste products are poorly characterized, preventing an adequate analysis of their role in microbial ecology. Building on previous work, we measured excreted zooplankton metabolites from four taxonomic orders (calanoid copepod, amphipod, euphausiid, and pteropod), using a novel benzoyl chloride derivitization method for metabolite quantification via liquid chromatography–mass spectrometry. We were able to quantify the production of 42 distinct metabolites, with the sensitivity to take measurements from a single organism. We found that this set of targeted compounds compose up to 18% of the total excreted nitrogen. Our findings demonstrate that not only do excreta from multiple zooplankton taxa consistently contain specific organic nutrients, but that the rates can be measured and applied to extant zooplankton abundance data to estimate source terms for individual ecologically important chemicals. This quantification provides insight into the magnitude of the injection of labile fuel into microbial food webs from these higher tropic levels and highlights substrate availability for specific microbial metabolic pathways that bear further investigation.
06:00 PM
HOW DIFFERENCES IN THE COMPOSITION OF MARINE SNOW ACROSS SEASONS WITHIN THE GULF OF MEXICO ALTER ITS FATE (8737)
Primary Presenter: Alyssa Antolak, Texas A&M University at Galveston (akantolak@tamu.edu)
The export of carbon through the water column is linked to the accumulation and formation of fast sinking, organic matter rich aggregates, resulting in the sequestration of carbon into the deep ocean. Phytoplankton blooms and the subsequent creation of marine snow is subject to the heterogeneous nature of the ocean making it difficult to discern which mechanism are impacting aggregate formation. The quantity and composition of marine snow is said to mirror primary production. Phytoplankton community composition and biomass peak in the spring and on a smaller scale in the fall due to light and nutrient flux. Successional studies of marine snow are limited as studies tend to focus on single-point quantity and composition work. This study compared how primary productivity and microbial community composition within the fall, winter, and summer altered composition of marine snow and its contributions to the biological carbon pump. To do so, roller table experiments were used to isolate specific factors that impact marine snow formation while mimicking particle flux through the water column. After rolling for several days in darkness, aggregates (~500 µm) and surrounding seawater were collected and analyzed to determine biomass, photosynthetic efficiency, extracellular polymeric substances, transparent exopolymer particles, 18S and 16S community composition, enzyme activity, total lipids, amino acid concentration, POC/PON, and C13 stable isotope tracking. Overall, differences in marine snow across seasons informs our efforts to better understand the biological carbon pump.
06:00 PM
The Impact of Kaolinite Clay and Saharan Dust on Marine Bacterial Aggregation (9511)
Primary Presenter: Kayla Tran, Arizona State University (ktran6461@gmail.com)
Saharan desert dust plays an important role in supporting marine phytoplankton growth by supplying essential nutrients, such as iron. Consequently, aeolic dust deposition influences the marine food web and impacts oceanic carbon cycling. Previous studies have demonstrated that clay minerals in Saharan dust, such as kaolinite, enhance the production of aggregates and their sinking velocity by acting as a ballasting material. In this study, we investigate the effect of particle size and abundance on the production of marine aggregates. We conducted roller tank experiments with the marine bacterium Marinobacter adhaerens HP15, using three different kaolinite clay concentrations: 0.5, 2 and 5 mg L-1. The abundance of visible aggregates significantly increased with clay concentration, and the aggregates formed at the higher concentrations were less fragile. We will report on the effects of size-fractionated kaolinite and natural Saharan dust and discuss their implications for carbon export and broader impacts on climate change.
06:00 PM
FLUORESCENT DISSOLVED ORGANIC MATTER TRACKS FLUXES OF ORGANIC CARBON IN THE NORTH PACIFIC (9561)
Primary Presenter: Kailee Clarke, Memorial University of Newfoundland (kgclarke@mun.ca)
Recent monitoring has revealed a high spatial and interannual variation in total organic carbon flux in the North Pacific. Evidence suggests that high concentrations of organic carbon at depth are present in the dissolved fraction and represent an active part of the microbial pump, rather than a high particulate flux driven by the biological (sinking) carbon pump. Removal rates inferred by repeated surveys in the region suggest that these sporadic high carbon events are highly labile, with high concentrations not being observed outside of the productive seasons. Samples for total and dissolved organic carbon (T/DOC) were collected along the Line P transect in the Northeast Pacific in 2023 and 2024. Ratios of DOC to TOC are used to assess the relative contribution of the microbial carbon pump to the biological carbon pump during periods of high export flux. Additional fluorescent dissolved organic matter (FDOM) samples were collected, allowing for investigation of different fractions of DOM and their contributions to organic matter fluxes at depth, as well as the role DOM plays in carbon sequestration in the deep Pacific Ocean.
06:00 PM
MICROBIAL METABOLISM AND COMMUNITY SUCCESSION FOLLOWING SEDIMENT RESUSPENSION (9592)
Primary Presenter: Ava Niemczyk, Lehigh University (aen226@lehigh.edu)
Organic matter deposited in marine sediments can be sequestered over geological timescales, but through physical processes may be resuspended and consequently fuel microbial heterotrophy. Microbial responses to resuspended organic matter is not well understood but is potentially controlled by the inherent reactivity of the organic carbon, the carbon degradation capabilities of the present microbial communities, and/or ambient physicochemical characteristics including oxygen and nutrient availability. Here, we performed a series of fjord and continental shelf sediment resuspension experiments to investigate resuspended carbon reactivity, microbial enzymatic responses, and microbial community succession. Surface and subsurface sediments were mixed with bottom waters to simulate sediment resuspension and tracked at multiple time scales (days vs. months). We will present data on measured enzyme activities including various exo- and endo-acting peptidases, glucosidases, and phosphatase to quantify changes in metabolic needs upon microbial exposure to resuspended carbon. In addition, we will present carbon reactivity measurements based on oxygen consumption following resuspension, as well as community composition based 16S rRNA gene amplicon sequencing. These data provide a comprehensive microbial and biogeochemical view of carbon-related processes that ensue following sediment resuspension.
06:00 PM
Potential impacts of Halophila stipulacea invasion on organic matter decomposition and storage in Caribbean seagrass meadows (9312)
Primary Presenter: Jonathan Herald, Kennesaw State University (jherald3@students.kennesaw.edu)
In 2002, Halophila stipulacea (Forsskål and Niebuhr) Ascherson, a seagrass native to the Red Sea, Persian Gulf, and the Indian Ocean was identified in Flamingo Bay, Grenada (Caribbean Sea). The species has since spread to most of the Caribbean Islands, where it often forms large populations and displaces native seagrasses. This restructuring of Caribbean seagrass systems may reduce biodiversity, alter species interactions, and change organic matter storage and nutrient cycling. This study aimed to characterize and compare the contribution of organic matter to the food web and sediment pool by H. stipulacea and native Thalassia testudinum. Standing stock of seagrass and detritus (as coarse particulate organic matter) was quantified via biomass coring, while decomposition rates were estimated using a litter bag experiment. Epiphytic biomass was also compared between the two seagrasses. Initial analysis indicated a slight positive correlation between detritus and T. testudinum biomass, but no correlation between detritus and H. stipulacea biomass was apparent. Finally, elemental analysis was conducted on seagrass detritus, epiphytes, and sediment cores to determine nitrogen and carbon content. H. stipulacea decomposed more rapidly than T. testudinum (7.3±0.2% and 4.3±0.2% material lost per day, respectively; mean±s.d.), suggesting that spread of non-native seagrass may reduce detrital pools and carbon storage in the sediments.
06:00 PM
Temperature-Dependent Hydrolytic Activity of Epipelagic Microbial Communities (9014)
Primary Presenter: Eleanor Hennessey, University of North Carolina at Chapel Hill (ejhennes@unc.edu)
Microbial communities rely on extracellular enzymes to produce substrates sufficiently small to take into their cells. The activities and structural specificities of these enzymes help determine the lability of organic matter in the ocean. As part of a larger investigation, we measured temperature effects on enzymatic hydrolysis, incubating samples at 4°C to mimic deep sea conditions of sinking particles, and compared those hydrolysis rates to rates at 20°C, a temperature more representative of surface seawater. We focused on polysaccharide hydrolysis, since polysaccharides are common components of marine organic matter. Fluorescently-labeled polysaccharides were incubated in surface water from two stations in the North Atlantic. We found a strong correlation between incubation temperature and hydrolytic activity, with lower hydrolysis rates at lower temperatures. Although the trend was the same for all polysaccharides, the reduction in activity varied considerably by polysaccharide. At the most productive station, laminarin hydrolysis decreased by 32% at a temperature of 4°C, whereas the decrease was only 19% for pullulan and 15% for xylan. These results suggest these three enzyme activities (and the underlying enzymes) differ in their abundance in surface seawater and/or have different susceptibilities to colder temperatures. Surface-derived enzymes that are exported with sinking organic matter therefore likely also have varying levels of activity in the deep sea.
06:00 PM
Vertical biochemical composition of particulate organic matter in the Seychelles-Chagos Thermocline Ridge (SCTR), southwestern Indian Ocean (9744)
Primary Presenter: Sanghoon Park, Pusan national university (mossinp@pusan.ac.kr)
The Seychelles-Chagos Thermocline Ridge (SCTR) in the southwestern Indian Ocean exhibits unique physical characteristics and heightened biological activity relative to non-SCTR areas. This study analyzed the vertical distribution and biochemical composition of particulate organic matter (POM) in these contrasting regions. The SCTR displayed a shallower thermocline and cooler surface temperatures, consistent with upwelling, correlating with significantly higher chlorophyll-a levels (t-test, p < 0.05). Micro-sized phytoplankton dominated in the SCTR, accounting for 13.6 ± 3.0% of the total phytoplankton biomass, compared to 5.6 ± 1.6% in non-SCTR regions. CHEMTAX analysis showed distinct phytoplankton communities, with diatoms four times more abundant in the SCTR (16.5 ± 4.5%) than in non-SCTR areas (4.2 ± 1.2%). Prochlorococcus dominated both regions but contributed less in the SCTR (25.2 ± 3.9%) than in non-SCTR (46.8 ± 7.1%). The macromolecular composition of POM highlighted regional contrasts, with lipid concentrations in the SCTR’s photic layer significantly higher (61.3 μg L⁻¹) than in non-SCTR (23.4 μg L⁻¹). The total food material concentration in the SCTR’s photic zone was over double that of non-SCTR (96.3 μg L⁻¹ vs. 40.9 μg L⁻¹), indicating enhanced productivity. Elevated macromolecule levels extended into the SCTR’s aphotic layer, with a less marked decline in the protein-to-carbohydrate ratio from photic to aphotic layers, suggesting fresher POM sinking to the deep ocean. These findings underscore the SCTR's role in enhanced biological productivity and efficient carbon sequestration, with notable implications for the biological carbon pump in the Indian Ocean.
06:00 PM
High frequency organic carbon and oxygen measurement reveal variability in respiratory quotients (9753)
Primary Presenter: Rachel Sandquist, University of California at Santa Barbara (rasandquist@ucsb.edu)
The respiratory quotient (RQ), defined as the ratio of oxygen consumed to organic carbon removed during organic matter remineralization, is a critical metric for understanding organic carbon flux and storage in the ocean. Traditional oceanographic studies often rely on a fixed RQ value (~1.4), based on Redfield stoichiometry. However, recent research reveals considerable variability in RQs associated with dissolved organic matter, with values ranging from 0.3 to over 3.1. Constraining this variability is essential for accurately modeling organic carbon and oxygen dynamics in marine systems. Using high-frequency measurements of dissolved organic carbon (DOC) and oxygen in mixed culture bioassays, we detected shifts in RQs that may reflect changes in bacterial community composition, organic matter composition, and dominant metabolic pathways. Our results demonstrate dynamic temporal changes in RQs, often obscured by lower-frequency sampling methods. Here, we present our high-frequency sampling methodology and highlight how heterotrophic bacterioplankton dynamics influence RQ variability. These findings highlight the role of environmental and biological factors in shaping RQs and offer new insights into organic carbon and oxygen cycles in marine ecosystems.
06:00 PM
Dissolved Organic Matter as a Potential Nutrient Source from the Kuroshio Current to the Subtropical Gyre (9601)
Primary Presenter: YuChen Yen, National Taiwan University (r12241405@gmail.com)
Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are important components of dissolved organic matter (DOM) in the marine environment. While DOC serves as the major energy source to sustain microbial metabolism, DON can serve as a supplemental source of nitrogen when inorganic forms are scarce. Recent global models suggest that accumulated DON at the ocean margins must be an alternative source of nutrients that is laterally transported to the subtropical gyres. Prior studies that have identified periodic net accumulation of DOM in marine environments suggest that microbial communities become limited by nutrient availability but also that the accumulated DOM can become bioavailable when introduced to a new community. This study seeks to investigate the bioavailability of DOM transported from the Kuroshio Current into the subtropical gyre when exposed to various microbial communities. Using water collected in August 2024, we conducted a series of dark incubation experiments comparing the effects of mixing of surface and subsurface water within and between water masses. Samples were collected to measure changes in DOC and DON, accompanied by inorganic nutrient concentrations, bacterial abundance, DOM and 16S community compositions, as well as dissolved oxygen consumption rates over time. Conclusions from these experiments are forthcoming but are expected to highlight (1) the metabolic potential of the microbial community composition in determining the bioavailability of DOM and (2) the rates of remineralization and nutrient regeneration during lateral transport from the Kuroshio Current to the subtropical gyre.
06:00 PM
Processing of dissolved organic matter by the green finger sponge, Iotrochota birotulata (9274)
Primary Presenter: Emma Rasco, Appalachian State University (rascoe@appstate.edu)
Sponges are filter-feeding animals that process vast amounts of water, removing particulate and dissolved nutrients and releasing waste products. On coral reefs, sponge processing of seawater is likely to be an important factor structuring the composition and availability of dissolved organic matter (DOM) yet our understanding of this process and the impact to the reef is acutely limited. Here, we leveraged the low microbial symbiont diversity of the sponge, Iotrochota birotulata, with metagenomic analysis of the sponge to predict how the sponge and the single dominant bacterial symbiont (an uncharacterized gammaproteobacterium) may alter the DOM profile. Field-collected samples of incurrent and excurrent seawater for I. birotulata were used to create a profile of DOM for each sample type. DOM was extracted by solid phase extraction and analyzed by liquid chromatography and high-resolution mass spectrometry. Total organic carbon was lower on average in the excurrent water than the incurrent, although not significantly different. However, preliminary analysis of mass spectrometry data indicates a distinct profile of DOM between incurrent and excurrent samples. The predicted metabolite profile from the bacterial symbiont and the sponge will be compared to the observed DOM profiles to determine potential overlap in compounds. This work will deepen our understanding of factors that influence DOM composition on coral reefs and provide insight into the mechanism of how sponges, which are prominent filter feeders on many reefs, alter DOM composition.
06:00 PM
CHARACTERIZING ORGANIC MATTER AVAILABILITY AND ITS POTENTIAL LINK TO THE METHANE CYCLE IN THERMOKARST LAKES (9028)
Primary Presenter: Oren Magori Cohen, Ben-Gurion University of the negev (orenmag@post.bgu.ac.il)
In northern latitudes, thawing permafrost leads to the formation of thermokarst lakes, surrounded by a thawed zone (talik), in which anoxic conditions prevail. Under these conditions, methane is produced by microorganisms (methanogenesis). Organic matter serves as a substrate in one of the two methanogenesis pathways. It can also act as an electron acceptor or shuttle, enabling more efficient metabolic pathways alongside methane oxidation, mitigating methane emissions. This research aims to characterize the availability of organic matter for microbial degradation in thermokarst settings and its potential link to the methane cycle. Three 5-m cores were extracted from the talik near a thermokarst lake, from: (1) lake sediments, (2) lake margin, and (3) lake terrace. Porewater was analyzed for chemical composition and dissolved organic carbon (DOC). Sediment was collected for total soil organic carbon (SOC) characterization, and incubation experiments were conducted to measure methane accumulation rates. Methanogenesis was dominant in depths greater than 2 meters in the margin and terrace, while in the lake's sediments, it prevailed across the profile, with higher methane accumulation rates in shallow depths. Low DOC freshness index values suggest that DOC is mainly derived from leaching of SOC. At shallow depths in the lake's margin, root exudates may contribute to a "fresher" DOC pool and provide oxygen, which suppresses methanogenesis. Also, a correlation between SOC fractions and methanogenesis rates offers insight into methane emissions during lake evolution.
06:00 PM
The potential role of marine fungi in organic matter degradation and transformations (8855)
Primary Presenter: Shuting Liu, Kean University (liushut@kean.edu)
Marine fungi (mycoplankton) are ubiquitous in all marine habitats but often understudied compared to their terrestrial counterparts. As organoheterotrophs, mycoplankton consume organic matter for energy and carbon and are capable of degrading both labile organic matter and recalcitrant organic matter such as lignocellulose. Although enzymatic and genomic analyses reveal mycoplankton’s ability to catabolize organic matter in the marine water column, evidence regarding their preference for dissolved organic matter (DOM) vs. particulate organic matter (POM) at an environmental-relevant concentration is scarce. Using Ascomycota strains isolated from the Sargasso Sea, we inoculated mycoplankton cultures in filtered seawater medium amended with different organic matter substrates, including glucose, lignin, cellulose, and chitin (the latter three not totally dissolved in water), at 10 mM C and incubated under dark for 1-4 weeks. Responding mycoplankton biovolumes were higher in the lignin, cellulose, and chitin treatments than in the glucose treatment, suggesting their preference for POM, possibly due to hyphal penetration into solids. After ~4 weeks, dimorphism from hyphae to yeast occurred in the lignin treatment, suggesting a potential switch of mechanism in growth and organic matter utilization. With further analysis of POM and DOM in the incubations, it is possible to link mycoplankton ecology to organic matter degradation and transformation.
SS11P - Biotic and abiotic influences on the lability and fate of organic matter
Description
Time: 6:00 PM
Date: 29/3/2025
Room: Exhibit Hall A