Bottom: Biofilm sliders.
After four days transiting across the Pacific, we’ve finally reached the East Pacific Rise. While the 80°F weather and open ocean call for sunbathing all day, the science began before we even reached our study sites. In the main lab the workshop was up and running, with many experiments to build that were to be deployed soon after arriving. The elves were hard at work on these seafloor gifts for the holiday season, creating settlement “sandwiches”, biofilm “sliders”, and larval traps. These will be left on the seafloor to develop bacterial biofilms and assess the larval supply at these hydrothermal vents. Don’t worry, we will be bringing all these back on board before we leave (or picking them up on the next cruise). In total we made nearly 100 sandwiches, and 24 sliders and larval traps.
When working on the seafloor and with submersibles, we must account for buoyancy, ease of deployment, and ease of identification underwater. We have to make sure our experiments don’t float away, tangle together, and are easy to pick up with a robotic claw. To do this, many of these instruments have loops of polypropylene rope that suspend a large circle above them, with bright colored duct tape, and weights on the bottom. Then, we have to make sure that they can all fit on the submersible and actually be deployed. In addition to these deployments, we have a multitude of instruments that we will be using on these dives to sample water, bacteria, temperature, among other things. As these posts continue, I’ll try to highlight the different techniques and tools we are using on this project.
Since we have so many objectives and limited space on the submersible that meant we had a lot of planning to do. In the library, the chief scientist (Shawn Arellano), hosts science meetings where we’ve been having these discussions. In the beginning we introduced our projects to each other, familiarizing ourselves and reminding the teams of the goals for the cruise and for the individual teams. We discussed dive plans, who was diving, the objectives of the early dives, what instruments were to be on the submersible, and the various teams for recovery and deployment of the submersible. We were also joined by the Alvin team for logistics of how to use each of our instruments, where our study sites were, how to organize the submersible basket, and schedule trainings for the sub operations. Importantly we also talked about contingency plans for a potential eruption at the East Pacific Rise. This hydrothermal vent site is volatile, and an eruption could even occur while we are out here, so we need to be prepared incase our study site has completely changed.
It all came down to today. This morning Shawn went with Alvin pilots Bruce Strickrott and Rick Sanger on an exploration dive across our sites. At 0800 the submersible lifted off the deck, swung out with the A-frame, dipped into the water, and started the hour and a half descent to the vents 2,500m below. In the main lab we have limited communications with the sub, so we all waited in suspense of what was being seen below. Alvin operations occur during daylight hours, coming up around dinner time, so we wouldn’t know until 1700 (5pm), unless the dive was aborted early. We held our breath, but went about our days as normal, and getting ready to deploy another of our instruments, a McLane pump for collecting larvae. The dive seemed to go well, with the sub recovery planned as usual. After retrieving Alvin from the surface, we huddled on the aft deck, watching the aquanauts climb out of the vehicle and down the stairs. Shawn approached the group and began recounting her dive.
Good news! There was not an eruption and the animal communities seemed to be thriving! The last cruise for this project was in March of 2021, so after nearly two years, these sites were expected to drastically change. At the bottom, the sub had cautiously approached the seafloor, in case of erupting lava flows or plumes of venting smoke. With the coast clear, they headed towards Tica, one of our target sites. As the vent field came into view, huge groups of Riftia tubeworms (one of the largest benthic invertebrates in the deep sea, up to 9ft tall!) covered chimneys, with groups of Bathymodiolin mussels surrounding them. Crawling all over these animals were Galetheid squat lobsters, Cyanograea crabs, limpets, and Zoarcid (eelpout) fish. The densities of these organisms were much higher than the last time we were here, indicating a healthy and growing community. Surprisingly, there were also gooseneck barnacles and anemones that weren’t there before, suggesting these were late-succession communities.
Photos credit to Dan Fornari’s MISO Cameras.
As the dive went on, heading towards Rifta Mound (not labeled, but near P vent on the map) our team scanned for our deployments from the last cruise, sandwiches that had been left in mesh “purses” to develop bacterial biofilms. Much of the site geology had changed as much as the biology had, with new spires creating a difficult bathymetry to maneuver, and some new chimneys pumping black smoke into the water. Some of the deployments were easy to find, exactly where we left them, while others had animals grown over them, or they had fallen from their previous location. Some we could not find at all. In our science meeting we discussed our game plan for uncovering and finding these pursed sandwiches, we call them “pursewiches”, and deploying new sandwiches next to them, among other deployments and experiments. We’re planning around 20 total dives on this cruise to get all our objectives complete, so every science team member should be getting to experience these sites within the submersible. Tomorrow we’ll begin unpursing these sandwiches, starting at Tica.
