Table of Contents

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

To estimate larval supply to the seafloor, two replicate larval tube traps were simultaneously deployed for approximately two weeks at the base of a vent chimney at each site (except Mariner or Mata Tolu) in an animal-free patches. These self-opening tube traps (described in Young et al. 2015) consisted of four tubes made of three 50-mL Falcon tubes conjoined with cyanoacrylate adhesive to form a single tube that was 23 cm high with a 3-cm in diameter opening (7.6 aspect ratio) with two internal funnels in the middle preventing resuspension during recovery. The four tubes were fit in a PVC frame with a central weight. Two tubes on each trap were prefilled with RNA preservative for DNA preservation and the other two were filled with hypersaline 10% formalin buffered for morphological preservation. Tubes were deployed covered with plastic wrap held by rubber bands attached with A2 galvanic time releases that dissolve in 4 °C seawater within 24 hours. After recovery, the samples in RNA preservative were rinsed and stored in fresh RNA preservative, and formalin-fixed samples were rinsed then stored in 70% ethanol at -20 °C until processing. The sorting of larval trap samples was later conducted at Shannon Point Marine Center where samples were imaged and sorted into morphological groups using a dissecting microscope. All RNAlater-preserved gastropod samples in the traps were set aside for mtCO1 genotyping. 

A Large Volume Water Transfer System WTS-LV50 (McLane Research Laboratories, Inc.) was used to collect and quantify larval abundances in the water column among vent chimneys. A mooring suspended the pump ~ 2 meters above the bottom (mab) for 7-18 hour deployments at each site. The pump gently drew water onto a 63-µm Nitex mesh filter, running for 7.3 -18.7 hours and filtering 11.9-30.5 m³ into an insulated compartment upstream from the filter. Upon recovery, live specimens on the pump filter were immediately rinsed with 0.3-µm filtered seawater onto a 63-µm sieve, examined under dissecting microscopes, sorted into morphological groups, and imaged with an Olympus EP50 Camera mounted on an Olympus CX43 compound microscope at 40-100X magnification. Larval samples were then stored in 95% EtOH at -20 °C for CO1 genotyping.

AUV Sentry (National Deep Submergence Facility, Woods Hole Oceanographic Institution) equipped with SyPRID (Sentry Precision Robotic Impeller Driven Sampler) was used to collect larvae in the water column around the periphery of the vent fields and above the vent fields. This device uses an impeller pump to gently suction plankton from the water onto a 150-µm Nitex mesh filter in the cod end (Billings et al. 2016). At each vent field, AUV Sentry collected two SyPRID samples (~11-hour duration each): one sample around the periphery and one above the vent structures, filtering up to 3,619 m³ of seawater per sample. The periphery sample was collected from 8-15 mab in a repeating back-and-forth pattern around the periphery of the target vent field. At Tahi Moana, periphery samples were collected at 30 mab rather than 8-15 mab due to tall vent features and strong currents. At ABE, due to the proximity of a ~20 m tall wall feature to the west, half of the periphery sample was acquired from the base of the wall and the other half was acquired from the top of the wall.  Above vent field samples were taken in a series of parallel tracks back and forth over a standard area over each vent field at approximately 26-45 m above the tallest known hydrothermal chimney structures. The sampling pattern was planned such that spaces between tracks reduced over successive passes and were offset to avoid repeating tracks, encouraging wide sample coverage over the select area. Upon recovery, all SyPRID samples were immediately rinsed with 0.3-µm filtered seawater onto a 63-µm sieve, sorted into morphotypes using dissecting microscopes, imaged with an Olympus EP50 Camera mounted on an Olympus CX43 compound microscope at 40-100X magnification, and stored in 95% EtOH at -20°C for mtCO1 genotyping.

All larvae were sorted under a dissecting microscope, imaged, and identified to larval type by morphology. Gastropod, bivalve, and zooea larvae were identified to the lowest taxonomic level possible using a combination of morphology and sequencing. Sorting and sequencing was conducted between July 2022 and September 2025. 

For sequencing, DNA from individual gastropod larvae was extracted using the Nucleospin Tissue XS DNA (Machery-Nagel, Inc.) and eluted into 30-µl volumes. PCR amplification and sequencing of the mtCO1 gene was conducted for each larva as described above. Morphological identifications were made using the hydrothermal vent larvae identification guide (Mills et al., 2009) and our own identification guides when possible. 

Sequences and images have been submitted to the Barcode of Life Data System v4 (BOLD4) and NCBI. 

Data are raw counts.

Identifications

Individual identities were assigned according to mtCOI sequences matches within the NCBI database with at least 97% pairwise identity. However, due to the novelty of many deep- sea organisms, many successfully sequenced individuals did not match to known organisms with sequences in NCBI. For these individuals, a mixture of phylogenetic analysis and morphological characteristics were used to identify the lowest possible taxonomic level. For phylogenetic analysis, sequences were aligned using the MUSCLE PPP algorithm alignment in Geneious and assembled into phylogenetic trees using PHYML with a GTR substitution model and aLRT statistics.  Identities based on morphology or the combined method are listed as 'Taxonomic Group' in the data sheet. 

- Loaded data from "FINAL_Meroplankton_Counts_12.10.25.xlsx" (sheet 1, Excel format), treating "", "nd", and "NA" as missing values, using filename as resource name
- Renamed 15 fields, replacing dot notation with underscores and removing embedded units from field names: Sample.Volume.m3 to Sample_Volume, Time.Deployed.hrs. to Time_Deployed, Ash.depth.cm. to Ash_depth, Meters.Above.Bottom to Meters_Above_Bottom, Ash.Average to Ash_Average, Sample.ID to Sample_ID, Larval.Type to Larval_Type, Identification.Type to Identification_Type, Taxonomic.Level to Taxonomic_Level, Taxonomic.Group to Taxonomic_Group, Top.BLAST.Hit to Top_BLAST_Hit, Pairwise.Identity to Pairwise_Identity, Less.than.97 to Less_than_97, BOLD.Collection.Code to BOLD_Collection_Code, and Individuals.per.SampleID to Individuals_per_SampleID
- Output written to "997940_v1_eslc_vfr_meroplankton_counts.csv"

NSF Abstract:

Symbiosis with microbes is ubiquitous and critical to fundamental biological functions such as development and nutrition. Thus, the success of a host animal may depend on its ability to find and associate with its microbial partner(s). While some hosts directly transmit their symbionts from parent to offspring in order to guarantee this, acquisition of microbial symbionts from the environment is vital for the survival of many obligately-symbiotic animals. An understanding of the free-living symbiont population and how the host acquires those symbionts is fundamental to our comprehension of ecological processes in all ecosystems, yet almost nothing is known about either. Hydrothermal vent ecosystems provide important opportunities to investigate the role of microbial symbionts in host-, community-, and ecosystem-level ecology, since these ecosystems are dominated by animals whose survival is clearly linked to the acquisition of one or a few specific symbionts. This project begins to fill a gap in our understanding of the factors driving community structure at hydrothermal vents by addressing the potential for free-living symbiont populations to affect host animal establishment, while also expanding our general knowledge regarding the impact of host-associated microbes on fundamental ecological processes that apply across ecosystems. The results of this project will be shared via educational videos and live-broadcasts to the Smithsonian Institution's National Museum of Natural History and University-run museums. The investigators will also design and implement an educational program about symbiosis and hydrothermal vent biology suitable for middle and high school classes. Finally, the investigators will train a diverse group of undergraduate and graduate students in both research and the development of science educational programs.

This project will focus on two sister genera of snails, Alviniconcha and Ifremeria, which predominate at vents in the southwestern Pacific. At vents in the Lau Basin (Tonga), three species of Alviniconcha and one species of Ifremeria coexist. These four species all host distinct lineages of chemoautotrophic proteobacteria in their gill tissue as adults that provide the bulk of their nutrition. Previous work in this region showed a structured snail species distribution that corresponds to the concentrations of key chemical substrates for symbiont chemoautotrophic metabolism, suggesting that snail species are sorting into geochemical habitats based on symbiont physiology. It is not clear if this sorting is occurring among established snail-bacteria symbioses, or whether environmental effects on the availability of specific symbionts are influencing the recruitment of host species, since arriving and developing snail larvae must obtain their symbionts from the environment. This study aims to 1) assess the larval supply and population structure of symbiotic vent snails via collections of larval, juvenile, and adult snails, 2) investigate the developmental timing of symbiont acquisition through microscopy and marker gene sequencing of gametes, larvae, and juveniles, and 3) use metagenomic sequencing to quantify the availability of free-living symbionts in the environment to arriving larvae. Altogether, this series of interlinked efforts will allow for an improved understanding of free-living bacterial symbiont populations, the timing of symbiont acquisition, and host snail life history, as well as how these things interact to shape vent communities.

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.