Lihini Aluwihare - US grants

0216643
Charles
This Major Research Instrumentation award to University of California at San Diego provides funds for acquisition of an isotope ratio mass spectrometer for shared use in studies of climate and global climate change, ocean sciences and anthropology at the Scripps Institution of Oceanography and other UCSD departments. The award is supported by the Division of Ocean Sciences at NSF. UCSD will provide cost-share support from non-federal funds for 33% of total project costs.
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ABSTRACT

OCE-0242160
OCE-0241363

Even though the meso- and bathypelagic regions beneath the euphotic zone contain nearly all of the oceans volume, little is known about the biogeochemical processes that function in this region. For this reason, a PI from Scripps Institute of Oceanography will collaborate with a PI from Harvard University to determine which carbon sources fuel prokaryotic production in the meso- and bathypelagic ocean. Specifically, the PIs wish to address the following two questions: (1) Is freshly-produced organic matter the primary dissolved organic carbon (DOC) pool that is accessible to deep ocean heterotrophic prokaryotes or is "old" DOC also bioavailable?; and (2) Is chemoautotrophic fixation of inorganic carbon by planktonic archaea an important component of the deep ocean carbon cycle? To address these questions, the PIs plan to measure the radiocarbon (14C) concentration of the carbon source pools and the resulting prolaryotic (bacterial and archaeal) biomass at the surface, meso (500-600 m) and bathypelagic (>900 m) depths. In addition, fluorescent in-situ hybridization (FISH) and genetic diversity analysis by denaturing gradient gel electrophorsis (DGGE) will provide a complementary picture of the biological community. Lastly, to obtain the large quantities of biomass-derived carbon needed for this study, the PIs plan to develop an in-situ, battery powered, submersible pump capable of pumping 20,000L of seawater per deployment during the first year of the study.

The marine dissolved organic matter (DOM) reservoir is often conceptualized as a "capacitor" for carbon because of its potential for storage and exchange with the other active reservoirs. Yet, despite its size and potential importance, the dynamics of DOM have not been fully assessed, and therefore the ultimate role of this reservoir for the global and marine carbon and nitrogen cycle remains to be established. To resolve the dynamics of the complex DOM reservoir, a young investigator from the University of California San Diego will develop a spatially resolved time-series of fraction-specific d15N and D14C measurements of DOM. This time series will be placed within the California Current System which experiences physical/climate variability on a variety of timescales (e.g. seasonal, interannual, decadal). The climate-associated disturbances (deepening/shoaling thermocline or nutricline, changes in wind field) are expected to lead to measurable excursions in the isotopic composition of surface inorganic dissolved CO2 and NO3-pools. These excursions are ultimately recorded by organic matter fractions that are recently produced in surface waters; and when placed within the context of a time series, fraction-specific isotopic variability will, for the first time, directly identify DOM cycling on annual to multidecadal timescales. In addition, the time series will also help identify relative proportions of refractory and young DOM components in surface waters and delineate some of the physical and biological processes that control the size and age of the DOM reservoir.

As part of this CAREER award, a new, inquiry based, undergraduate course will be created to place the theoretical coupling between large scale phenomena such as climate-ocean-atmosphere and smaller scale phenomena such as ocean physics-chemistry-biology within a tangible, region-specific, real-world framework. A fundamental goal of this course will be for students to learn experientially how science "works"; students will design class projects that use archived time-series data to explore the above connections and collect oceanographic data on a 4-7 day educational cruise to the California Current System.

Among the broader impacts, this study will be one of the most comprehensive, long-term investigations of the interrelation between climate and biogeochemistry. The infrastructure of the larger, ongoing scientific programs in the region will provide context, and enhance the dissemination of scientific data collected as part of this proposal to a broad audience through both web-based tools and written and verbal communication. Through the four specific goals of the Education and Outreach plan, the PI will teach and mentor ~100 undergraduates, mentor ~8 high school students, empower both student groups to be more critical, better environmental decision-makers, provide ~8 educators with valuable scientific experience to take back to their own classrooms and so reach even a larger number of students, and also provide ~100,000 citizens with a valuable window into the marine ecosystem in their own backyards. In addition, the high school students that will be targeted represent some of the most under-served youths in San Diego County.

The proposal requests funds for a gas-chromatograph time-of-flight mass spectrometer with a preparatory fraction collector and a liquid chromatograph-linear ion trap mass spectrometer with multiple sample ionization modes and an analytical fraction collector. The instrumentation will be used by the PI and her students to characterize and purify biomolecules from complex environmental samples for chemical, biological and geological research efforts. The facility will be used to support existing and proposed research efforts at SIO, including identification of membrane lipid and protein modifications associated with temperature and pressure tolerance of deep-ocean bacteria, and genomics enabled studies of membrane lipid biosynthesis. The facility will also be used to develop new analytical methods, and train graduate students in instrumentation operation and use. Use of the facility by outside users is by invitation.

Broader impacts
The PI has a strong record of enhancing the participation of women in science by hosting female high school students. The proposed instrumentation will complement and expand the capabilities of SIO researchers, as well as invited outside researchers. Seminars will be held for either the Marine Chemistry and Geochemistry or Marine Biology seminar series demonstrating the facility capabilities and results to the larger SIO populace

Recently the distribution of polybrominated diphenyl ethers (PBDE analogs) - the methoxylated and hydroxylated derivatives (MeO-BDE and OH-BDE) and polybrominated dibenzo-p-dioxins (PBDDs)- as well as congeners of the halogenated methyl bipyrroles (MBP) and dimethyl bipyrroles (DMBP) have been examined in a variety of wildlife and humans, where they can often be present at higher concentrations than anthropogenic pollutants. Like anthropogenic pollutants they also bioaccumulate, seem to biomagnify, and toxicity has been demonstrated for at least a subset! However, systematic studies aimed at linking the distribution of HOCs present in apex marine predators to potential source environments through examination of prey and primary producers (a focus of PI and P2) are rare. In this proposal, Aluwihare and Hoh build on an existing collaboration to combine a non-targeted analytical method with a food web-based research approach to assess sources and fates of the entire suite of HOCs in the Southern California Bight Region. In the initial phase of this project the relatively high concentration and unlimited sample size represented by stranded marine mammals will be leveraged to identify and definitively characterize the suite of HOCs (> 200) bioaccumulating in wildlife. This non-targeted approach is facilitated by a novel application of comprehensive wo-dimensional gas chromatography with time- of-flight mass spectrometry (GCxGC/TOF-MS), and relies on collaboration with NOAA and the Southern California Coastal Water Resources Project (SCCWRP). Discovery of new compounds identified by the non-targeted method, will be aided by a variety of authentic standards provided for us by PI and P2. To definitively identify HOC contributions from marine biogenic sources a compound specific radiocarbon and stable isotope approach will also be applied. A recently designed 2D preparative GC will make this research possible. To further establish source, collaborations with PI and P2 will screen a variety of habitat specific primary producers, lower trophic level organisms and pure bacterial cultures for their ability to make HOCs of interest. These major areas of research are tightly integrated with the Analytical Core. To assess human exposure, relevant HOCs will be examined in breast milk samples, and epidemiological investigations will assist in the interpretation of these results with respect to participants' seafood consumption habits. This work will be carried out in collaboration with Christina Chambers, Michelle Leff and Jae Kim (all at UCSD), These data will further inform a study design to examine HOC distributions in relevant seafood products available to consumers. The exposure studies are planned to ultimately assess HOC dietary intake by age and sex from food consumption, and will be done in collaboration with Melbourne Hovell and Jenny Quintana (SDSU). A final component, headed by Kristin Pangallo (Colgate) will begin to interrogate the toxicity of a subset of natural HOCs synthesized and/or isolated by PI and P2. Delineating sources and fates of marine natural HOCs with respect to human health will better inform fisheries management and aquaculture practices, assist with quantifying risks associated with diet, and help to design relevant multiple exposure studies with respect to HOC toxicity.

Facility Core Summary The Facility Core for Small Molecule Mass Spectrometry (SMMS) is integral to the Center's research mission by enabling high-resolution detection and isolation of halogenated organic compounds (HQCs). This Core does not replicate any analytical services or facilities currently available at the Scripps Institution of Oceanography (SIO). The SMMS Facility Core will be directed by P3 Leader Aluwihare, and technical oversight for the facility will be provided Co-Director Dr. Yongxuan Su. Daily operation and routine maintenance will be the responsibility of Mr. Matthew Woolery. The facility will include several uniquely configured gas chromatography-mass spectrometry (GC-MS) instruments that are intimately integrated with the Center's research mission to identify the suite of HOCs accumulating in the marine environment, discover new HOCs of concern in wildlife and humans, and evaluate environmental sources of HOCs. The overall goal of PI is to identify organisms and habitats of interest with respect to HOC production in the Southern California Bight. A GC Electron Capture Detector (|JECD)/MS capable of screening these samples for relevant HOC production will be available through the Core. Project 2 aims to identify and characterize the prevalence of polybrominated HOC biosynthetic pathways in the marine environment. As such, P2 will rely on the same instrumentation to screen cultures and insure that organisms under investigation are producing compounds of interest. The overall goalof P3 is to identify the suite of small, natural HOCs available to enter human populations through seafood consumption. This research will be supported by the analytical capabilities of two GCXGC instruments integrated into the proposed Facility. The >200 HOCs that bioaccumulate in apex predators and humans cannot be adequately separated from co-eluting compounds for definitive identification and quantification without comprehensive GCXGC separation. To establish the biogenic origin of HOCs of interest, P3 will also conduct stable isotope studies on pure compounds that are isolated from apex predators, purified and concentrated for isotope measurement. A uniquely configured, preparative GCXGC instrument that is included in the Facility will support this research. Two liquid chromatography-mass spectrometry (LC-MS) instruments will also be housed in the Core to analyze fermentation extracts and synthetic organic preparations. The Internal Advisory Committee will discuss Facility business during monthly meetings, and the External Advisory Committee will evaluate the Facility Core for its performance annually.

Identifying the chemical structure of compounds that constitute the refractory dissolved organic matter (RDOM) reservoir will yield new insights into the processes that control the accumulation and removal of organic matter from aquatic environments. A scientist from Scripps Institute of Oceanography will be working to optimize an existing chemical reduction technique to render oxidized aliphatic and aromatic dissolved organic matter (DOM), two compounds which together comprise as much as 60% of the carbon in RDOM, more amenable to gas chromatography (GC) separation. This will allow for the characterization of this important RDOM component.

Much of the time and effort associated with the proposed research will be invested in identifying backbone structures of reduction products. To assist with this structural characterization, the proposal also seeks to adapt and modify existing GC×GC time of flight mass spectrometry techniques to better separate the complex mixture of reduction products. In addition to enabling more accurate compound characterization, this technique will also allow a more rapid determination of structural homogeneity within aquatic DOM. As part of this proposal, a preparatory GC×GC will also be modified such that methods developed using the previous instrument can be easily applied to isolate relevant compounds for further characterization (including isotope measurements). This work will also generate an MS library the aliphatic and aromatic reduction products that will be made available to other investigators interested in pursuing a similar avenue of research.

Besides continuing to further develop the analytical method, the researcher also plans to apply the method to test three hypothesis, namely (1) that reduction will yield several aromatic compounds, some of which resemble degraded lignin; (2) that reduction will yield a range of alicyclic compounds including terpane derivatives; and (3) that GC×GC separation will confirm the presence of structurally related families of aromatic and aliphatic compounds. Samples for this study include Suwannee River fulvic acids and natural organic matter, ultrafiltered DOM isolated from the eastern tropical Pacific Ocean and western tropical Atlantic Ocean, DOM isolated from Circumpolar Deep Water in the Southern Ocean isolated using Agilent Bondesil PPL, and one surface and one deep water sample collected in the North Pacific subtropical gyre obtained using reverse osmosis/electrodialysis that will serve as an ad-hoc marine, reference DOM. Analyses of these four different DOM sample types will help to determine reaction and GC/MS-based analysis parameters to be optimized for each sample type and compound class under study.

The analytical method to be developed and the mass spectrometry library for reduction products would be of interest to the science community. One graduate student would be supported and trained as part of this project. Two high school summer interns chosen with the help of the Ocean Discovery Center would also participate in the study. Students from this program tend to be underrepresented minorities.

This award will provide NSF support for the establishment of the Scripps Center for Oceans and Human Health at the Scripps Institute of Oceanography of the University of California - San Diego. The Scripps COHH research team will apply a multidisciplinary approach to elucidate the marine cycling of small, natural, brominated, aromatic compounds that share chemical characteristics with some anthropogenic contaminants. The study will be focused in the Southern California Bight where we have applied a new non-targeted analytical approach to demonstrate the presence of >300 halogenated organic compounds in dolphins - an apex marine predator - feeding either offshore or inshore. As many as 30% of these compounds contain bromine and have no known anthropogenic source. In some cases, similar compounds have been previously hypothesized to be of natural origin in other marine environments. Given that these compounds bioaccumulate in apex marine predators they must be available to enter human populations through seafood consumption.

These brominated, likely natural organic compounds will be the focus od Center activity for two main reasons. First, although several studies have documented the presence of these purported natural compounds in top predators, most have been unable to delineate trophic transfer, and no study has definitively identified source organisms. the team has recently identified a biosynthetic cluster in a marine bacterium that is capable of producing most of the carbon skeletons and bromination patterns of interest. To establish spatial patterns and ubiquity of source organisms they will continue to characterize this biosynthetic pathway through culture studies and examine environmental distributions through metagenomics. Furthermore, by using our non-targeted analytical approach to comprehensively survey all trophic levels in benthic and pelagic habitats they will directly demonstrate how these compounds enter apex predators. This will further enable us to delineate potential pathways by which these compounds enter human populations.

Secondly, the presence of these compounds in apex predators indicates that they must enter the human population via seafood consumption, but this has not been documented. To test this the team will apply a non-targeted method to analyze breast milk from local mothers who have been surveyed to document their seafood consumption habits. Since these compounds resemble anthropogenic contaminants such as PBDEs, PCBs and PCDDs, they are expected to have similar toxic effects in both humans and wildlife. Brominated, natural compounds that are most abundant in dolphins have pyrrole backbones and their toxic impacts are poorly documented, and so, they will examine the potential toxicity of these compounds in the zebra fish model. Together, these efforts seek to identify source organisms and biosynthetic mechanisms of production, and also delineate modes of transfer to human populations.

Broader Impacts. A more complete picture of the marine cycling of these compounds will enable us to assess how global change may impact sources -- something that up to now has been impossible. Furthermore, we will be in a position to assess the role that the burgeoning aquaculture industry and general seafood consumption plays in transferring these compounds to human populations. The Center organizational structure and ongoing collaborations with NOAA and local water resources management agencies will insure that the research approach and findings benefit from the input of individuals who dictate public health policy decisions, carry out environmental monitoring, and manage resources. The Center web portal (www.scohh.ucsd.edu) and personal outreach efforts will also keep the public informed and engaged in our research activities through interaction with K-12 classrooms and local communities. A special effort will be made to engage URM undergraduates in the Center's research through participation in the UCSD STARS program, the SIO NSF-sponsored SURF program and the UCSD-Howard University Pathways program.

JOINT FUNDING BY NSF AND NIEHS: The original proposal on which this project is based (P01 ES021921-01) was submitted to the National Institutes of Environmental Health Sciences (NIH/NIEHS) in response to Funding Opportunity Announcement RFA-ES-11-012 , "Centers for Oceans Human Health (P01)?" an opportunity jointly sponsored by NSF. This project is cooperatively funded through separate awards from NSF and NIEHS.

This project will purchase an off-the-shelf instrument that has an unprecedented capability to separate individual molecules found in complex matrices and more precisely access their composition (through accurate measurement of mass). The environmental matrices that will be studied in this research and the innovative sample processing methods that will be employed to reduce the natural complexity of relevant samples represents a novel application of this instrument. Examples of new knowledge that will be created include a better understanding of how contaminants are transformed in the environment, how microscopic organisms regulate bloom dynamics through communication, and how known biochemicals are transformed into molecules that can be preserved on long timescales, thus contributing to the production of oxygen and the sequestration of carbon dioxide. Such a molecular-level understanding of these processes is essential for determining the environmental factors that regulate them and how these processes may respond in the future. The data produced with this instrument will be publically available as a mass spectral library that will be of use to other fields including drug discovery, petroleum research, and metabolomics. In addition, several graduate students and post doctoral researchers will receive hands-on access to this instrument, providing valuable training that will prepare them well for careers in both academia and industry.

This project will acquire a comprehensive gas chromatograph (GC×GC) coupled to a Pegasus HRT (High Resolution TOF) Mass Spectrometer (MS), which will be initially utilized to examine the diversity of organic molecules accumulating in aquatic environments and also to identify degradation products of chemical contaminants accumulating in various environment matrices. Organic geochemistry and environmental chemistry necessarily deals with complex matrices where thousands to millions of compounds derived from various sources, acted upon by abiotic and biotic processes, accumulate on short to millennial (and beyond) timescales. Chemical structures of these compounds carry critical information regarding source, mechanisms of transformation and residence time. Access to advanced analytical instrumentation continues to increase access to such information. Comprehensive gas chromatography, together with advanced mass deconvolution afforded by the high scan rates of the identified instrument (200 full mass range mass spectra per second) enables unprecedented ?separation? of complex mixtures of organic molecules. Additionally, the sub-ppm mass accuracy greatly enhances the likelihood of unknown compound identification. Together these two features make this instrument unique. Knowledge about the processes that shape the chemical composition of various environmental reservoirs will scale with the extent to which these complex samples can be chemically described. As such, there is a significant reward associated with comprehensively characterizing the chemical composition of such samples.

This research project will identify biological sources and chemical structures that are responsible for the long-term storage of carbon in the ocean. Each year, microscopic marine plants remove about as much carbon dioxide from the atmosphere as do land plants. Respiration returns much of this carbon to the ocean as carbon dioxide, but some is locked in the remnants of living organisms. These remaining compounds are modified by pathways that involve bacteria, sunlight, chemical reactions, and other processes that lead to storage of carbon for thousands to millions of years. Some compounds eventually contribute to the petroleum reservoir. Building on previous results, this project will study the reactions and oceanic lifetime of a particular set of biochemicals, called carotenoids, as a possible organic carbon storage pathway. Carotenoids are abundant in very many marine organisms, increasing the likelihood that they are part of this long-term carbon storage and petroleum formation. These compounds also have unique chemical properties that make them subject to specific chemical reactions. For this reason, they have been marketed as powerful antioxidants. Therefore, scientific outcomes from this research on carotenoid chemistry will not only inform ocean carbon cycles but could also benefit studies of their properties as antioxidants. The project will determine the lifetime of carotenoids and their degradation products in seawater to provide new insights into pathways that transfer carbon from the atmosphere through biota and into long-term storage reservoirs. Graduate students and underrepresented undergraduate students will be engaged in the research.

Previous work has identified specific chemical backbones of compounds that are broadly distributed within the marine dissolved organic matter (DOM) reservoir. A high-resolution analytical approach that combines nuclear magnetic resonance (NMR) spectroscopy with comprehensive gas chromatography-mass spectrometry (GC-MS) has detected DOM compounds with unique structures closely related to carotenoids. Photochemical reactions of a representative carotenoid in laboratory experiments has further linked compounds detected in seawater to carotenoid degradation products (CDP). These preliminary studies show promise that the work funded here will be able to identify specific CDP structures and establish the quantitative significance, lifetimes, and timescales of CDP accumulation in seawater. The project will combine laboratory experiments, high resolution analyses, and chemical synthesis methods to determine the chemical composition of CDP and their abundance in seawater. The novel analytical methods developed through this research will be relevant for other carotenoid-focused studies in petroleum formation, soil chemistry, as well as food chemistry. Ramped pyrolysis oxidation (PyrOx) coupled to radiocarbon measurements will be used to determine the radiocarbon content of CDP-enriched DOM and seek to estimate the accumulation timescale of these dissolved molecules in the environment, and it is hypothesized that deeper, older ocean water will contain a relatively higher proportion of radiocarbon-depleted CDP. Collecting samples from different depths in the North Pacific Ocean where CDP-enriched DOM will be isolated following established sample processing methods will provide insights and new information on the mechanisms that control the amount and timescale of carbon redistribution among Earth?s various reservoirs.

Collaborative Research: Characterizing microbial transformation of marine dissolved organic matter at the molecular level using untargeted metabolomics

Dissolved organic matter is an important component of the global carbon cycle. Dissolved organic matter provides food and energy for microbes living in the ocean and influences microbial diversity. Microbes convert some dissolved organic matter to CO2 (respiration) whereas other forms of dissolved organic matter are altered by microbial processes and persist in the ocean. Thus, it is important to understand how microbes change dissolved organic matter composition and reactivity. This project will examine the chemical structure of dissolved organic matter to identify: 1) molecules that fulfill carbon demand (biomass produced minus losses from respiration) and 2) transformation processes that result from microbial activity. The project will combine lab experiments and field studies at the Moorea Coral Reef Long Term Ecological Research site. The project will support training for three graduate students in marine biogeochemistry. Undergraduate training is aimed at sustained mentoring of underrepresented minority (URM) students. Undergraduates will be recruited from existing programs at Minority Serving Institutions at San Diego State University and the University of Hawai?i at M?noa. Undergraduates will participate in the Scripps Institution of Oceanography SURF Research Experiences for Undergraduates program, where they will conduct research in marine chemistry. The goal is to provide a mentoring approach that can successfully overcome roadblocks to URM engagement in STEM and increase retention of these students in marine science.

This work will combine field and lab studies using advanced molecular-level chemical characterization tools to explore how bacteria alter the composition and bioreactivity of organic compounds dissolved in seawater. Additionally, this project will develop informatics-based tools to identify a larger proportion of chemical structures in marine dissolved organic matter (DOM) than is currently possible using traditional approaches. The project will use tandem mass spectrometry and networking techniques to comprehensively classify organic compounds into molecular families and determine common chemical transformations. Then, using a well-developed field-based experimental ecosystem to produce diverse labile DOM pools the research team will track microbial transformation using expression of hydrolytic enzymes and measure selection for particular microbial taxa and metabolisms. This approach defines the reactivity of individual molecules and broader compound classes participating in carbon fluxes that underpin DOM-microbe interactions. Field surveys conducted within the Moorea Coral Reef Long Term Ecological Research program will explore methods to track transformation of specific molecules in the environment and validate experimental observations of compound classes that appear to accumulate as semi-labile DOM. By integrating laboratory and field experiments and oceanographic surveys with the refinement of analytical tools for untargeted metabolomics, this project will characterize the fate of reactive DOM in the ocean.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Coastal upwelling regions are found along the eastern boundaries of all ocean basins and are some of the most productive ecosystems in the ocean. This award is supporting the California Current Ecosystem Long Term Ecological Research (CCE LTER) site in a major upwelling biome. It leverages the 73-year California Cooperative Oceanic Fisheries Investigations (CalCOFI) program which provides essential information characterizing climate variability and change in this system. The CCE LTER addresses two over-arching questions: What are the mechanisms leading to ecological transitions in a coastal pelagic ecosystem? And what is the interplay between changing ocean climate, community structure, and ecosystem dynamics? The investigators are working towards diagnosing mechanisms of ecosystem change and developing a quantitative framework for forecasting future conditions and how these might affect the management of key living marine resources, including numerous fishes, invertebrates, marine mammals, and seabirds. They are training graduate and undergraduate students, as well as providing educational opportunities for teachers. Public programs and outreach efforts in collaboration with the Birch Aquarium at Scripps Institution of Oceanography are increasing public awareness and understanding of climate effects on coastal pelagic communities and connecting the public to cutting-edge ocean research.<br/><br/>This project is adding to understanding of the mechanisms underlying abrupt ecological transitions with three interrelated foci: (1) investigation of marine heatwaves and resultant multiple stressors on organisms and communities, (2) elucidation of ecological stoichiometry and the response of multiple trophic levels to altered elemental ratios of source nutrients, and (3) analysis of top-down pressures mediated by a diverse suite of organisms. It is sustaining multi-scale measurements of five core LTER variables and responses to ocean warming, increased stratification, acidification, deoxygenation, and altered nutrient stoichiometry in the Northeast Pacific. The investigators are using long-term, spatially-resolved time series at multiple spatial scales to evaluate community shifts at multiple temporal scales, with new measurements allowing interrogation at finer taxonomic levels. They are conducting in situ multi-factorial experiments (temperature, macronutrients, micronutrients, light, grazing) in combination with genomic and transcriptomic analyses. These will complement time series measurements, inform next-generation biogeochemical models, and test hypotheses related to ecological stoichiometry and marine heatwaves. The team is also using a suite of imaging techniques, molecular and morphological methods, and active and passive acoustic approaches to quantify vertical structure and cooccurrence of organisms across trophic levels and test hypotheses about top-down control of the ecosystem.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.