Tubeworms & Mussels & Eelpouts, Oh My!

Shimmering hydrothermal vent fluid in front of Riftia tubeworms and Bathymodiolan mussels at Tica.

On Thursday, January 18th, I was granted the opportunity to dive in the HOV Alvin to one of our study sites, Tica, 2500 meters below the surface (about 1.5 miles deep). I would be diving with one of the Principal Investigators (PI) of the project, Dr. Costa Vetriani from Rutgers University, and Alvin pilot Tony Tarantino. As the second dive of the cruise, I was excited to be one of the first to see how the area had changed since we were last here in December of 2022, and help set-up our cruise-long experiment. The first dive was completed by the chief scientist Dr. Shawn Arellano from WWU and Rutgers PhD student Matteo Selci, where they had seen a huge expansion of the animal communities at Tica. Hearing that, I couldn’t wait to get down there and see how it compares to the last time I dove there. Our goal for this dive, AL5217, was to deploy our sandwiches and tube traps in the Alvinellid and suspension zones of this site, and collect time-series sandwiches from the mussel and suspension zones.

Alvin dive days start early. The scientists need to be ready to get in the sub at 8:00 AM; fed, showered, and wearing natural fibers. I made sure to wear my Oregon State University shirt. Go beavs! Costa and I did some final stretches before getting in for our 8-hour dive, where the three of us are in a 2-meter diameter titanium sphere with little room to stretch. Everyone has their pre-dive habits, and I made sure to wave goodbye to the science party, and wear my lucky deep-sea pearl earring.

We enter the sub, and moved to our respective sides. I go to the starboard (right) side, and Costa goes to the port (left) side, with Tony between us. The hatch is sealed, the pilot coordinates the launch procedure with his team, and we are lifted up by the a-frame. As we are slowly lowered into the water, the submersible rocks slightly and the view out our portholes transitions from the ship to the air to ocean blue. We disconnect from the ship, and the Alvin swimmers prepare us to dive. With the permission of the launch coordinator, the bridge of the ship, and our pilot, we begin our descent. The light blue tropical water turns a deeper blue, then a dark blue, until finally, it’s pitch black. The darkness is alive though. Small flickers of bioluminescent plankton and gelatinous animals pass by, signaling their presence to us. Hunched over the starboard porthole, I hope to get a glimpse of something bigger.

During this hour and a half descent we go over the dive plan: the order of operations, the data to collect, where our samples are being stored on the science basket, and the division of labor between the scientists. We familiarize the pilot with our confusing science terms of “sandwiches”, “pursewiches”, and “paired sandwiches”, and how we plan to recover them. Then, Costa and I get comfortable with the video systems, controlled by iPads, and entering data into Alvin’s logging system. Throughout the descent the pilot communicates with top lab, his team on the ship, relaying our depth; a reminder of how deep we are diving, further traveling away from the known and into the unknown.

The time seems to fly by as we quickly approach the seafloor. We drop a set of weights to slow our descent and watch as the bathyal depths appear into view. Reflective basalt rocks from a previous eruption stretch as far as I can see, with a few shrimp, reddish sea cucumbers with snout-like heads, and some sea squirts populating the rock. We pinpoint our location, find the heading to our target site, turn, and bobble eastward. We enter the axial spreading center, where Tica lies at it’s heart, and open up to an awesome sight.

Our study site, Tica, within the Axial Spreading Center (ASC) of the East Pacific Rise (EPR).

An inundated jungle of Riftia tubeworms lay before us. Growing up to 9 feet long, they had created overlapping mounds, filled the valleys below, and stretched around the sub. With mussels around the base, eelpouts and squat lobsters swimming within, the site was teeming with life. The same general structures from our last visit were still visible but new patches of Riftia obscured the view of markers we had deployed or made sections less accessible. There also seemed to be an increase in other fauna, more anemones and Calyptogena clams. New diffuse flow in the basalt also hinted at the expansion of the site. Tica seemed to be thriving, it was beautiful.

We came here to do some science however, so we shifted into gear to find our past deployments, which could be a challenge. We had a sketched map from an Alvin pilot, Bruce Strickrott, which detailed our markers in relation to major landmarks of the region and our deployments. We also had coordinates and heading of the vehicle from last time, but the adventurer in me was excited to follow the treasure map in our hands. We were searching for marker “DKA 12”, in honor of the late Diana K. Adams, to identify our first station, the Alvinellid zone. These Alvinellid worms inhabit the hottest parts of the vent system, building tubes within the active sulfide rocks that precipitate out of the venting fluid. We had deployed our sandwiches at a small spire inside the valley, but we weren’t finding what we remembered. We triangulated our location from finding the “30” bucket-lid marker, and the “AT50-06” marker from our last cruise, but all that was below us was this huge sulfide spire that couldn’t have been the same one. Until we saw it, two bright yellow polypropylene loops that extended from our purse deployments near the base.

The Alvinellid zone. Two yellow polypropylene loops stick out from just below the temperature probe in the Alvin submersible’s port manipulator arm.

Not only had the Riftia in this area exploded in ground cover, but the sulfide spires had grown taller and wider, crafting larger chimneys expelling hydrothermal fluid. It was covered in Alvinella worms, their smaller red crowns dotting the white rock. We couldn’t believe how fast it had grown. We had deployed our purses at the top of the spire last year, it must have been at least a few meters taller. Our pilot Tony expertly lowered us down, careful of the life and rock faces we were sandwiched between. Out my starboard viewport, I saw the siphons of feeding Bathymodiolius thermophilus mussels, and the cute faces of Thermarces cerberus eelpouts, whom I’ve all named Rufus as they all look like little old men (or perhaps a subconscious reference to Kim Possible). Out Costa’s port viewport, the basalt rockface nearly pressed against the submersible. “Small movements” our pilot directed. We were perfectly positioned.

We worked quick. First, taking temperature measurements of our deployments, to capture the conditions our biofilms had formed under. We recovered and redeployed the sandwiches within the purses, and then deployed new paired sandwiches and tube traps close by. We took notes on their positions, and video recordings of the deployments and new spire, then inched our way out, to move to the next station.

We moved into the suspension zone, away from the high biomass and warm temperatures of these vent communities, to clear basalt mostly inhabited by scavenging crustaceans, white Serpulid worm tubes and other suspension feeders. This area had more ambient deep-sea temperatures, closer to 2°C.

This area was much easier to work in, with space to sit the sub down, and stretch the manipulator arms out. It looked the same as we had left it, and we located it immediately. We collected the time-series sandwiches into our “lunchbox” on the science basket, then opened our purses, and again deployed sandwiches and tube traps to set up our new experiment. We’ll be back to pick those up in about two weeks.

My dive notes from AL5217

All this sandwich talk reminded us that we too needed to eat lunch. We opened our packed lunches – peanut butter & jelly, ham & cheese sandwiches, and a KitKat. Out the window I notice a small octopus,Vulcanoctopus hydrothermalis, slinking past the sub, observing us but keeping a safe distance. It was a reminder that we were the aliens visiting their habitat, typically cloaked in darkness, and were quite the presence.

After our short break, we had one more task, to recover our last time-series sandwiches in the mussel zone. We had seen the “AT50-06” marker earlier where these experiments were deployed last year, so we could quickly get back. As we reached the marker, the Riftia had made it a little trickier to get back, and the Alvinellid spire jutted from below. Nothing Tony couldn’t handle. He talked us through his thought process as he decided the best way to approach without disturbing the ecosystem. He pivoted the sub, with micro adjustments to the heading and depth, so he could reach around the mound with a long-hooked tool and scoop up the sandwiches by their looped handles. In this moment I imagined Alvin pilots must be incredibly good at the arcade crane games I can never seem to win. We loaded the sandwiches, which were covered in anemones and animals, again into the lunchbox and had completed our objectives for the dive. We backed out, as a swarm of amphipods swirled above, with tubeworms passing out port holes, and began to explore with the little time we had left.

Exploring Tica with “False wall” and “Bishop spire” visible and “Tica Prime” looming in the background.

We soared over the ever-growing sulfide spires, along walls of more Riftia, and appreciated the complexity of the trough we were just within. Before we knew it, it was time to return to the surface, back to where humans are supposed to be. We moved away from the main site, communicated with top lab to commence our journey, and dropped our weights to begin our ascent.

After reminiscing on past expeditions and old friends between Costa and Tony, we began to see the bright blue waters of the shallows. I don’t feel anxious being so deep in the ocean, but the light is comforting and familiar. We were welcomed by some decent waves, though. As the sub heats up in the tropical water, coupled with being in a lower-oxygen sphere and rocking in every direction, I was starting to feel a little seasick. Tony hands me a plastic bag “just in case”, which I tuck under my clipboard as I try and focus my body and mind. After about 20 minutes, the hands of the a-frame pull us in and set us gingerly on the deck. We’ve returned. The hatch above is opened, along with a pressure difference that pop our ears, and we are able to climb out. Welcoming us is our science team aboard the R/V Atlantis, cheering and eagerly awaiting our report of how the dive went.

AL5217 divers – Dr. Costa Vetriani (left), Tony Tarantino (center), Dexter Davis (right).

Underwater photographs belong to Shawn Arellano, Chief scientist, Western Washington University; Alvin Operations Group; National Science Foundation; © Woods Hole Oceanographic Institute.

EPR Biofilms4Larvae project is a multi-institutional NSF grant: OCE-1948580 (Arellano), OCE-1947735 (Mullineaux), OCE-1948623 (Vetriani).

Also find us on Instagram @larvallab, #Biofilms4Larvae

The Inactive Sulfides project is a multi-institutional NSF grant: OCE-2152453 (Mullineaux & Beaulieu), OCE-2152422 (Sylvan & Achberger).

Also find us on Instagram @jasonsylvan, #LifeAfterVents

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