Welcome back! While we’ve been mostly focusing on the active, high-density sites, I’d like to offer some context of vents and delve into another part of this cruise, exploring inactive (dead) hydrothermal vents.
We are studying at the East Pacific Rise (EPR), a raised region of the seafloor formed by a spreading center, where tectonic plates are moving away from each other. As these plates are pulled apart, the Earth’s crust is fractured, and magma rises that cool into new seafloor. When this magma touches seawater, it creates hydrothermal fluid and is why hydrothermal vents are common around these spreading centers. This fluid is rich in minerals that precipitate out and are used by bacteria for chemosynthesis. The “black smoker” chimneys are from iron sulfides in the venting water. In the chimneys we’ve collected we’ve found these precipitates, one of them golden pyrite crystals, an iron sulfide mineral. Inactive vents are regions where hydrothermal fluid no longer flows, and what remains are spires and extinct chimneys made of sulfide rocks that were shaped by animals that used to live there. Because of these minerals, hydrothermal vents have been a target for deep-sea mining, a strategy to harvest these mineral-rich crusts. Seafloor mining is a destructive process and disrupts these communities, so many mining companies have shifted towards inactive vents, where animals are not thought to be found. However, I want to show you the work we’re doing at inactive sites at the EPR and how alive they truly are.
The inactive sites we’re focusing on in this cruise are called Lucky’s Mound and Sentry Spire that were discovered by the AUV Sentry in 2019 and 2021 respectively, and explored by ROV Jason on the 2021 cruise RR2102. Members of WHOI Dr. Lauren Mullineaux’s Lab are particularly interested in these sites and have been working with videos and multibeam scans of these sites leading up to this cruise. On the previous cruise, a rock collected from Sentry Spire was covered in a limpet species called Neolepetopsis which grazes on bacterial biofilms at active vents. It’s theorized that there are unique fauna at inactive vents that graze on bacteria from chemosynthetic rock processes rather than from the hydrothermal fluid. Members of the Mullineaux Lab are interested in exploring the food webs and animal communities at these understudied inactive vents.
Exploring Lucky’s Mound
On December 18th and 19th, divers Michael Meneses (WHOI), Dr. Lauren Dykman (WHOI) on AL5134, and Vanessa Jimenez (WWU) and Dr. Stephane Hourdez (CNRS) on AL5135 explored Lucky’s Mound. And Lucky indeed in this mound. When Michael and Lauren landed on the bottom, they landed right next to the elevator and lander platforms that were deployed the night before (which also descended perfectly)! Even when moving the elevator, they hit the jackpot with a heading of 77.7!
These two platforms we deployed are providing different methods of data collection on this dive. The large elevator has two instruments on it that Tanika Ladd (WWU) is using to compare food webs and the influence of primary production from active and inactive sites. The multicolored tubes are niskin bottles that collect water samples from the seafloor when triggered. Tanika Ladd will filter this water back on the ship to assess the “food pool”, essentially what organisms are living in the water that animals could be feeding on. On the other end of this elevator is a McLane plankton pump. This pump filters water at 30 L / min for up to 24 hours and collects swimming organisms onto a 60-micrometer mesh. When returned to the ship, we sorted through the contents, where Tanika is particularly looking for copepods, but we also found some of their larvae called nauplii, and polychaete worms. Copepods are holoplankton, organisms that spend their entire lives as plankton, and can act as a vector transferring this primary production outside of the vent community. With these copepods, Tanika will extract the DNA inside their guts to see what they are eating. Most marine scientists do not like copepods because they are extremely abundant, clogging samples, and for our lab, sometimes eating our precious larvae! Even still, they are very important members of the community.
The smaller lander is being used by Dr. Dykman to assess the grazing rates and behaviors of animals that live on inactive vents. Using a MISO camera mounted on a small tripod that faces downward, she will record 4K video of the grazers, mostly snails and amphipods, lit from a light on the lander. She hopes to explore how these animals move and interact with each other. If they remain in one place, or are very mobile, as well as if they react differently around transitions between substrate types. We only get snapshots of these animals and their behaviors when we dive and collect samples, so having a long video or time lapses will help us discover how these communities function over longer time scales.
After setting up these two landers to collect science, the rest of the dives were focused on exploration and targeted collections. On the last cruise, Lucky’s Mound was only explored on the northern side, so we took the opportunity to further explore the southern side. Thanks to Ayinde Best (WHOI), here we can see the tracks that Alvin took during these dives. Ayinde has been using the ReNav navigation data from Alvin to plot the course our scientists take on every dive. This helps us orient ourselves with our study sites, see where deployments and samples were conducted or collected and improve our records of dives and cruises. During these dives we found many large animals calling these inactive sites home including Boloceroides anemones, crinoids, Galetheid squat lobsters, cusk eels, and sponges. Ayinde is also involved with these inactive sites, spending his summer studying species and feeding strategies of megafauna that live around Sentry Spire. He hopes to collect video transects of Sentry Spire and collect some animals to build on his past work.
While exploring Lucky’s Mound, sulfide and basalt rock samples were taken, and opportunistic use of Alvin’s slurp hose to collect animals around this site. We try to take as little as possible, since these inactive vents have no more active precipitation and are permanently impacted. With these animals, Michael Meneses (WHOI) plans to dissect and remove their guts to look at what they’re eating. The rocks will also be used to assess the bacterial community through transcriptomics, cell counts, and imaging the biofilms. Back on the ship he sorted through the rocks with assistance from many other scientists on board including Susan Mills (WHOI) and Dr. Stephane Hourdez (CNRS), whose taxonomic expertise at these sites are unparalleled, and already found some interesting discoveries. Hidden amongst the rocks were polychaetes, aplacophorans, slit-limpets, and snails, some potentially new to science. These might be members of a unique community only found at inactive vents. We’re very excited to delve into these samples further.
Photos taken by Michael Meneses (WHOI).
The last way we were studying these sites was through the use of a spot-sensing probe developed by Dr. Nadine LeBris (Sorbonne University). This handheld instrument allows for measurements of pH (acidity), eH (redox potential), sulfide measurements, and temperature at specific spots. For this cruise she has also developed an auto-sensor, that can be deployed within our animal regions and takes measurements every minute.
This allows us to read the chemical conditions these animals experience in situ, how they might be manipulating the chemistry of the water and relate animal behaviors to chemical changes over time. Sometimes she attaches a camera that allows us to view exactly where the sensor is measuring and has even placed one inside of a tubeworm before! Using the spot-sensor at these inactive sites has shown us that there are no temperature anomalies near the chimneys and rocks compared to the surrounding seawater, sitting around 2C, when at active vents these temperatures have been measured up to 325C during this cruise. Interestingly, we did see a change in the pH of the water when collecting a rock sample, that the sulfides in the released sediment impacted the seawater and made it more acidic.
Overall, there’s a lot more work that needs to be done at these inactive vents. While the active vents host charismatic and highly adapted animals, we’ve only begun to discover and understand the animal communities at these inactive sites. Hydrothermal vents are inherently ephemeral systems, meaning they exist on relatively short time scales. A change in lava flow or geological movements can cause a vent to stop and the community will shift. Active vents will become inactive sites so we’re curious about how this transition occurs and what the stable communities look like. They may be inactive in terms of the geology and chemistry, but they are certainly still active in terms of the animals that live there.
Next time we’ll dive into the microbes that convert these chemicals into biomass and make these communities possible.
Subsurface photos taken with MISO camera, WHOI Dan Fornari. Shawn Arellano, chief scientist, Western Washington University; Alvin Operations Group; National Science Foundation; ©Woods Hole Oceanographic Institution.
EPR Biofilms4Larvae project is a multi-institutional NSF grant: OCE-1948580 (Arellano), OCE-1947735 (Mullineaux), OCE-1948623 (Vetriani).