Magical Magmatic Macrofauna

HOV Alvin Launch Timelapse.

With our cruise-long experiments fully deployed, we had two weeks before they would be recovered, but there was still much to be done. We explored inactive vents, sorted larval collections from a high-volume pump, and dissected mussels for worms.

My favorite part was looking through the animal collections and “slurp” canisters for baby mussels and scaleworms with the bonus of all the beautiful macrofauna from our study site.

It all starts with the Alvin launch in the morning. Where a pilot and two scientists descend to the seafloor to conduct research and collect samples. A whole orchestra of engineers, led by the deck coordinator, roll out the submersible on its sled, preparing the machine for its journey. Sensors are checked, cameras attached, window covers removed, and weight stacks attached. The pilot is called first, then the observers. The hatch is sealed and the A-frame swings Alvin over and into the water.

We wait patiently on board, hoping for a successful dive as we usually have a lot of objectives to complete. Around dinner time the submersible returns, with the bucket brigade ready to jump into action. It’s important to keep the samples cold so the animals stay alive and in good condition. Surprisingly most of these animals are seemingly unaffected by the pressure difference, even though their home is 250 atmospheres of pressure deeper.

Once the sub rolls back into the hanger and is secured by the team, we are given the go ahead. Larger animals, slurp containers and rocks are transferred into buckets and transported to the cold room. Meanwhile the bucket brigade siphons out the remaining water, sieves it through a 100-um filter, and rinses the macrofauna into a container chilled on ice, before running that to the cold room too. After a quick bite, the sorting under the microscope begins.

Find the baby mussel!
Settled Bathymodiolus thermophilus larva. Photo by Dr. Tanika Ladd.

Large worms and snails are taken out for Dr. Stephane Hourdez, who is running thermal tolerance experiments under pressure, while the Arellano Larval Lab sorts for baby Bathymodiolus thermophilus mussels. It’s a game of eye-spy. Only around half a millimeter in size, we must sort through all the fluff, in the shells of every limpet, and even the mussel mucus, to find them. These tiny, orange, round, bivalves are easily confused with reddish benthic copepods, ostracods, and baby limpets. Every time one is found, a cheer echoes around the microscope table. With these we hope to do some microbiome work, and FISH (Fluorescent In Situ Hybridization) to see what they’re eating and when they acquired their bacterial symbionts. These bacterial symbionts allow the adult mussels to survive the sulfide-rich hydrothermal vent fluids.

While we search for these there are plethora of other animals we come across which I want to share with you all.

Polychaeta (Worms)

First are the worms, or members of the class Polychaeta. These come in many forms, boasting iridescent colors by their layers of muscles and scales (elytra). Some, like Archinome rosacea and Hesiospina vestimentifera are grazers, scraping biofilms off the substrate, while others like the Lepidonotopodium scaleworms are predators with extendable jaws. Alvinella pompejana and Paralvinella grasslei live on the super-hot sulfide spires where the hydrothermal vent fluid erupts. While Paralvinella are deposit feeders, Alvinella are truly something special. They are some of the most thermally tolerant marine animals, living up to 50°C (or 122°F) and hosting symbiotic bacteria (those white filaments on their back). The final worm, Branchipolynoe symmytilida, are also unique. These are commensal worms that actually live inside of the Bathymodiolus thermophilus mussel. We’ve been finding quite a lot of them as one graduate student onboard, Mel Lemke (WWU), is dissecting mussels to study them. Whether they are parasitic or not is something she is exploring.

Gastropoda (Snails)

Next are the snails in the phylum Gastropoda. This phylum also encompasses the land snails you find eating the tomato plants in your garden. These are generally grazers and deposit feeders, although there are predatory snails as well, such as whelks, and deep-sea chemosymbiotic species like Alviniconcha sp. and Ifremeria nautilei. The Lepetodrilus limpet species are extremely common at our sites, clogging our sieves and covering our deployments, mussels, and tubeworm collections. While cute, they’ve turned into a nuisance when sorting samples. Many of our baby mussels have been found stuck to their feet, or wedged in the side of their shells. Pachydermia laevis is one of my favorite because it looks like a little macaroni pasta. You can see clearly the clear operculum that many snails have, which act as a door they close themselves inside their shells with. I don’t know much about Provanna snails, but they have the coolest shells, with pronounced sculpturing. Eulepetopsis vitrea is another favorite for their mirror-like shells. Made of lathic calcite, small sheets of calcium carbonate refract light to create a transparent shell, hence the name vitrea for vitreous.

Solenogastres and Ophiuroidea

Some other organisms I found were an aplacophoran in the class Solenogastres and a brittle star in the class Ophiuroidea. Aplacophorans are known for not having a shell, but what stands out to me is that they look like a piece of candy. Yes, that is the whole organism. I can’t decide between a Mike and Ike or a Sour Punch straw; either way I would probably eat a whole box in one sitting. These ophiuroids are also pretty common, with legs twisting all over the place, they can also make sorting into a detangling relay. I actually have a tattoo of a larval ophiuroid so I’m partial to them, but I think they are so alien and cool. This close of up its mouth looks like a snowflake.

Of course these pictures are not a full composition of the seafloor macrofauna at the East Pacific Rise, but these are the ones I found frequently, in good condition, and had time to take pictures of. I never thought I’d spend time combing the hairs of deep-sea polychaetes to remove gunk for their photoshoots, but here I am. I hope these pictures have shown you a glimpse of the amazing diversity in the deep-sea, even at just one site. Stay tuned to see what we find on our settlement experiments, hopefully larvae of many of these macrofauna.

HOV Alvin Recovery Timelapse.

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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