Dataset: Mitochondrial COI barcode sequencing data for Gigantidas childressi veligers, pediveligers, and juveniles from samples collected on R/V Thompson cruise TN391 in Mississippi Canyon 853 in the Gulf of Mexico during May 2021

Veligers, pediveligers, juveniles, and adult mussels of Gigantidas childressi were collected using the remotely-operated vehicle (ROV) Jason II and automated underwater vehicle (AUV) Sentry (National Deep Submergence Facility, Woods Hole Oceanographic Institution) onboard the R/V Thomas G. Thompson (University of Washington) during cruise TN391. Samples were collected from Mississippi Canyon 853 (28° 7.37’ N, 89° 8.42’ W) in the Gulf of Mexico at a depth of 1070 meters on June 16th, 2021 (Jason dive J2-1337 and Sentry dive S595P). Gigantidas childressi adults were sampled with ROV Jason and recovered to the surface in insulated bioboxes. Pediveligers (swimming larvae with a developed foot that are competent to undergo metamorphosis) and juveniles (metamorphosed) of G. childressi were collected from the interstices of mussel beds with the ROV Jason suction sampler and within samples of adults. Veligers (pre-competent swimming larvae without a developed foot) were collected in the water column at an altitude of 5 meters above bottom with AUV Sentry fitted with the SyPRID plankton sampler with 150-micron mesh nets (Billings et al. 2016).

Plankton samples recovered by the AUV Sentry SyPRID sampler were immediately rinsed from the collectors with cold 0.3-micrometer (um) filtered seawater (FSW) into canisters of chilled FSW. Larvae and juveniles recovered from ROV Jason suction and scoop samples were retained on a 253 um mesh sieve and resuspended in cold FSW. All live plankton and juveniles were maintained below 8 degrees Celsius (°C) (ambient temperature) during subsequent processing. Live G. childressi larvae were immediately sorted from the samples under a dissecting microscope, imaged on a compound light microscope, then preserved individually in 0.5 milliliters (mL) centrifuge tubes with 95% molecular grade ethanol. Adult G. childressi are morphologically identifiable, so gill samples were not sequenced.

All sample processing for DNA sequencing was conducted at Shannon Point Marine Center in Anacortes, Washington. DNA was extracted from individual larvae and juveniles using the Nucleospin Tissue XS kit (Machery-Nagel) following the manufacturer's instructions. The concentration of extracted DNA was quantified using a Qubit fluorometer (2.0). To confirm the identity of the veligers, pediveligers, and juveniles, PCR amplification of the mitochondrial COI (mtCOI) barcode region using bathymodiolin-specific primers (BATH-COI F/R, van der Heijden et al. 2012) was carried out and followed by bidirectional Sanger sequencing (Sequetech, Mountain View, CA). PCR conditions were as follows: 15 minutes at 95°C with 35 cycles of 35 seconds (s) at 94°C, 35s at 48°C, and 70s at 72°C, followed by 7 minutes at 72°C and a final holding temperature of 10°C. PCR products were purified prior to Sanger sequencing using the ExoSAP-IT PCR product clean-up reagent. Mitochondrial COI barcode sequences were processed in Geneious 10.1 (Dotmatic) and compared to those in GenBank using the BLAST search and alignment tool.