Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Particles were collected off the coast of Monterey Bay, California using in situ filtration (WTS-LV, McLane Research Laboratories) on four consecutive days (July 31-August 3, 2017) at three discrete depths per day aboard Monterey Bay Aquarium Research Institute's R/V Paragon. Pumping duration was between 90 and 165 minutes, longer at deeper sampling depths and pumps filtered approximately 400-600 L of seawater. The vessel drifted freely during collection; start and end locations are recorded in the dataset. One pump failed to initiate pumping, and filters recovered from this pump were used as full process blanks. The three size classes were collected using three filters mounted on mini-MULVFS 3-tiered filter holders (Bishop, Lam, and Wood, 2012: 100 µm nylon (Nitex) mesh with 150 µm nylon (Nitex) mesh backing, 20 µm nylon (Nitex) mesh with 150 µm nylon (Nitex) mesh backing, and two, stacked 0.7 µm pre-combusted glass microfiber filters (GF/F). Nitex was pre-cleaned using 10% hydrochloric acid and methanol. After collection, filter holders were stored in a cooler with ice packs frozen at -80°C for two hours until processing in the lab, where filters were photographed, folded, and stored in combusted foil at -80°C until analysis.

Before analysis, particles collected on the 100 µm nylon (Nitex) and 20 µm nylon (Nitex) filters were resuspended in 0.2 μm filtered seawater in an acid-cleaned plastic bottle with gentle shaking and sonication, then re-filtered onto combusted 47-mm GF/Fs; this process was repeated three times. All filters were lyophilized and inspected under a dissecting microscope (10-40x magnification) to remove Nitex, plastic fibers, or swimmers. Filters were quantitatively split; approximately 1/8 to 1/4 of the filter was used for compound-specific isotope analysis.

Filter splits for Compound-Specific Stable Isotope Analysis of Amino Acids (CSIA-AA) were hydrolyzed to extract amino acids (20 hours at 110° C, 6N hydrochloric acid), purified on cation exchange resin columns (50W-X8, 100-200 mesh) and derivatized to trifluoroacetyl/isopropyl esters for gas chromatography following the methods of Hannides et al. (2013) and identical to Doherty et al. (2021). The derivatized amino acids were analyzed for nitrogen isotopic composition on a Thermo Trace 1310 gas chromatograph with a BPX5 column (50 m x 0.32 mm, 1.0 μm film thickness) through a combined combustion/reduction interface (Thermo Isolink II, 1000° C) and liquid nitrogen cold trap, interfaced to a Thermo Conflo IV and MAT 253 isotope ratio mass spectrometer. Three injections were made for each sample where possible, with norleucine and aminoadipic acid with known δ¹⁵N values as co-injection standards. Analytical uncertainty for each amino acid δ¹⁵N value was derived from the standard deviation of replicate injections. For some samples, only one injection was obtained due to low particle concentration. For these samples a conservative uncertainty estimate of 1‰ was assumed. A standard solution of 14 amino acids with known δ¹⁵N values was also analyzed with each set of three injections to track instrument performance, and to correct for instrument drift, including that due to oxidation state of the reactor (Hannides et al., 2013). Data from standards injected over the lifetime of the instrument were used to correct for relationships between measured δ¹⁵N values and peak area on the instrument.

A standard solution of 14 amino acids with known δ¹⁵N values was analyzed with each set of three injections to track instrument performance, and to correct for instrument drift, including that due to oxidation state of the reactor (Hannides et al., 2013). Data from standards injected over the lifetime of the instrument were used to correct for relationships between measured δ¹⁵N values and peak area on the instrument. Analytical uncertainty for each amino acid δ¹⁵N value was derived from the standard deviation of replicate injections. Analytical uncertainty <0.2 ‰ was adjusted to 0.2 ‰ to account for instrument performance in most amino acids, for glycine uncertainty <0.5‰ was adjusted to 0.5‰ . For some samples, only one injection was obtained due to low particle concentration, and for these samples a conservative uncertainty estimate of 1‰ was assumed. 

- Imported "Monterey_particle_BCO-DMO_v2.csv" into the BCO-DMO data system
- Converted date and times to create new fields for ISO formatted UTC start datetimes and end datetimes
- Renamed original time fields to indicate local PST timezones
- Exported file as "958460_v1_particle_csia-aa.csv"

Food webs describe who eats whom, tracing the flow of energy from plants up to large animals. While many connections in food webs on land are quite familiar (lions eat antelope and antelope eat grass, for example), there are large gaps in our understanding of ocean food webs. Closing these gaps is critical to understanding how nutrients and energy move through ocean ecosystems, how organisms interact in the ocean, and how best to manage ocean resources. This project will study ocean food web structure with a focus on siphonophores, an abundant group of predators in the open ocean that range in length from less than an inch to more than one hundred feet. Siphonophores are closely related to corals and many jellyfish. They are known to be important predators within ocean food webs, but they are difficult to study because they live across great ocean depths and are gelatinous and fragile. The details of what they eat, as well as many other features of their biology, remain poorly known. This project will combine direct observations of feeding, genetic analysis of siphonophore gut contents, and stable isotope analyses to identify what different species of siphonophores eat. The team will also examine why they eat what they do. This will provide a new understanding of how the structure of food webs arise, aiding in our ability to predict future changes to food webs as the global climate shifts. Siphonophores feed in a very unique manner--they have highly specialized tentacles that are used solely for capturing prey--thus, the prey captured is determined largely by the anatomy and function of these tentacles. The project will describe these tentacles, reconstruct their evolutionary history, and investigate how evolutionary shifts in tentacle structure have led to changes in diet. This project will train one PhD student, one Master's student, a postdoc, and undergraduate students, including individuals of underrepresented groups. This project will support the production of scientifically rigorous yet engaging videos, foster the expansion of a citizen-science program, and create K-12 teaching modules. 

This project will advance three scientific aims: First, it will identify the diet of a diverse range of siphonophores using DNA metabarcoding of gut contents and prey field, remotely operated vehicle (ROV) video of prey encounters, and stable isotope analysis. These approaches are highly complementary and allow for extensive cross validation. Second, the project will characterize the selectivity of siphonophore diets by comparing them to the relative prey abundances in the habitats of each of these species. Third, the project will characterize the structure of the siphonophore prey capture apparatus across species through detailed morphological analysis of their tentacles and nematocysts. These data will be integrated in an ecological and evolutionary framework to identify predator features associated with prey specialization. In a larger context, addressing these questions will advance our understanding of oceanic predation by revealing how evolutionary changes in predator selectivity correspond to evolutionary changes in habitat and feeding apparatus and how these changes shape current food web structure in the open ocean. We will test and refine an integrated approach to describing the structure and origin of food web topology, and evaluate the potential for phylogenetic relationships to explain prey selectivity. 

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.