Dispatches from the D-ARK
Follow Curator of Malacology Jann Vendetti with updates from an expedition into the deep sea caves around Japan's Minami-Daitō Island
Pictured above: JAMSTEC research vessel Kaimei by IikaJzuchiN licensed under CC BY 4.0
Published May 8, 2024
Dr. Jann Vendetti, NHM Curator of Malacology, is joining an international team of scientists aboard Kaimei, the world’s most advanced research vessel, for an expedition exploring biodiversity in the deep sea caves around Minami-Daitō Island in the Philippine Sea. This JAMSTEC (Japan Agency for Marine-Earth Science and Technology) and Ocean Census expedition will use deepsea robots and cutting-edge technology to dive into the lightless caves and uncover the marine life that calls them home in a project called D-ARK: Deep-sea Archaic Refugia in Karst. These semi-isolated limestone caves could provide habitats for relict species—"living fossils"—animals once thought extinct that persist on Earth, like the coelacanth on view at NHM.
Vendetti is bringing us along with Dispatches from the D-ARK, a series of updates from the journey.
Dispatch 2: A Tour of Mollusks
April 30
On the first dive of the expedition, the Kaimei ROV (ROV = remotely operated vehicle) was deployed for exploration and specimen collection. This ROV has filmed and collected specimens for JAMSTEC since 2016 and can descend to 3,000 meters (~9,843 feet).
Near the edge of the Minami-Daitō seamount and at 797 meters deep (2,615 feet) one of the first animals we saw was a cirrate octopus, likely a species of the genus Grimpoteuthis. These mollusks have received some attention recently, being nicknamed the “Dumbo octopus”, and noted for their cuteness. The Dumbo elephant ear-like projections are really a set of paired and ridged fins that attach internally to a shell. That’s right! If you know anything about octopuses, you’re likely confident that they are the one group of living cephalopods (of the squid, cuttlefish, Nautilus, and octopuses) with no internal shell. Nope!
These octopuses have an internal shell that is small but important. It varies from horseshoe-shaped to bow-tie-shaped and connects to the paired fins (ridged from internal cartilage) with specialized muscles, allowing these animals to swim. That is, the cirrate octopuses can power their movement by slowly "flapping" their fins, which is what we observed. These amazing octopuses have semi-gelatinous bodies and live exclusively in the deep sea, having been observed at a maximum of 7,000 meters deep (22,965 feet, ~4.4 miles).* So much is still left to learn about these mollusks; it was thrilling to see one!
*For context, the deepest known place in the world’s oceans is called the Challenger Deep in the Mariana Trench and its depth is about 10,971 meters (35,994 feet, 6.8 miles). That is deeper than Mt. Everest is tall at 8,848.9 meters (29,032 feet, 5.5 miles).
References:
https://www.marineregions.org/
Collins, M.A. and Villanueva, R., 2006. Taxonomy, ecology and behaviour of the cirrate octopods (in Oceanography and marine biology: An annual review 48: 277–322.
May 1
This was the first dive of a small ROV called Crambon during this expedition, and the first time it had been used since 2019.
This ROV collected sediment samples within which was this micro gastropod (= small snail). It is about 0.6 cm long and currently un-identified by me. The shell with the apex (the pointed end) up is usually how snail shells are depicted in books, but in life the head end is that of the aperture (where the shell opening is). This remarkable micro snail covers its shell in a white sheath-like mantle.
Similarly tiny snails were also collected in sediment samples by the Kaimei ROV. The reason they are called micro gastropods is evident here, with a penny for scale.
Over the last week, I’ve been consumed by attempts to identify several snails collected at depth. Here are two, both of which (in a separate HOV dive) were also found “crabbed”, that is, having their empty shells inhabited by hermit crabs:
The first is a gastropod brought up with deep sea Asteroidea, or sea stars, in the genus Brisinga. These sea stars are amazingly long-armed and orange, and the snail with them has a brown and white striped shell, bright yellow body, and a short siphon.
The second is a snail in the family Colloniinae, which are characterized by a round aperture (shell opening) and a calcareous operculum (a hard calcium-rich “trap door”). This one has a pink and white striped shell and brown and white striped foot and looks to be a species of Bothropoma or Collonista.
Finally, this “crabbed” shell is a species in the genus Bursa. You can see this awesome hermit crab securely in the Bursa shell, then nearly completely out. Unlike snails, hermit crabs can leave a snail shell and find a new one when it suits them. For snails, their shell is their forever home, and one of their own making.
Until next time...
Dispatch One: April 27 & 28
I traveled from the Tokyo Haneda airport via a train, the shinkansen, and another train, to Shizuoka, Japan from which the Kaimei Research/Survey Vessel would launch. A half day to acclimate gave me enough time to find and explore a local temple, Seiken-Ji.
Prior to the D-ARK and Ocean Cenus expedition setting off, the returning research cruise disembarked. Although their focus was not deep-sea biodiversity, they collected living Calyptogena sp. clams from a methane cold seep off of Hatsushima Island in Sagami Bay, central Japan, for Enoshima Aquarium in Kanagawa Prefecture. Calyptogena bivalves harbor chemosynthetic bacteria in their gills and have hemoglobin in their soft tissues, making it red.
They live in total darkness at depths between 900–1200 m and were collected using a submersible equipped with a camera, collecting arms, and collection containers. They are going to be included in the Aquariums's Deep Sea exhibit associated with JAMSTEC and be part of research within its Breeding Department Exhibition and Breeding Team: https://www.enosui.com/en/exhibition.html (See Deep Sea Part 1: Joint Studies with JAMSTEC). [Personal note: when I saw these I gasped out loud. We have shells in the NHMLAC collections, but I'd never seen these animals alive. It was amazing.]
We are en route to Minami-Daitō Island in the Philippine Sea, a small island off of which there are deep sea limestone caves, which is the first stop of the research cruise.
