Award: OCE-1737145

An interdisciplinary team of students and scientists from three universities used the Remotely Operated Vehicle Jason and the Sentry Autonomous Underwater Vehicle to investigate the interface between symbiosis and reproduction in a multi-species assemblage of large snails that dominates the deep-sea hydrothermal vent communities in the Lau Back-Arc Basin off Tonga. From previous work, we knew that the species of bacterial symbionts in these snails shifts with latitude, and also that one of the snail species has a unique larval form protected from the harsh vent environment in a special pouch in the foot of the mother. Using genetics, embryological rearing of living embryos and larvae, and electron microscopy of the development stages, we explored whether the different larval forms correspond with the latitudinal patterns, and whether any of the species transmit symbionts to the next generation through the swimming larvae. We found no evidence to support this hypothesis, but were able to rear the larval forms of all species and to collect several species from the water column for observations of larval behavior and swimming. The ship arrived at the study sites near Tonga soon after the enormous Hunga Tonga volcano erupted, creating a major tsunami and spewing a huge cloud of volcanic ash into the atmosphere. The formerly lush and diverse communities of hydrothermal vent animals in the region of the volcano were blanketed with thick deposits of ash, often more than a meter thick, killing most of the species that lived there. The phenomenon was similar to the burial of Pompeii by Vesuvius, but had never been observed previously at a hydrothermal vent. We shifted the focus of the cruise for several days to carefully document the event and its impact. These baseline data provided the background for follow-up studies of the recovery, which will certainly depend on the immigration of larval forms, including those of the snail species that we studied carefully in this cruise. Last Modified: 01/13/2025 Submitted by: CraigMYoung