Tubeworms seen at Mariner

Towards the end of our dive at Mariner, we spotted some tubeworms.  The most obvious invertebrates in the Lau Basin are snails (Ifremeria and Alvinichoncha) and mussels, shrimp and crabs. So seeing tubeworms is quite unusual. We did see some in our research cruise to this area in 2006, but never at Mariner.  A very healthy community was spotted this time on a huge hydrothermal pillar near our "toilet bowl" sampling area. Crabs were happily munching away on a tube or 2 about 2 cm (200mm, ~ 1 inch) long.   There were thick communities of this tiny little tubeworm. They appear to be Arcovestia ivanovi, found in the Lau and Manus hydrothermal basin areas.

Tubeworms have an interesting lifestyle.  The have no mouth or digestive system like other worms. They are essentially a sack (trophosome) of bacteria or endosymbionts, and a plume (the red structure) that captures hydrogen sulfide, carbon dioxide and oxygen.  These gases are transported from the plume to the trophosome, where they are food (energy and carbon sources) for the bacteria. The chemolithoautotrophic bacteria oxidize the sulfide, and use the energy in that redox reaction to fix carbon dioxide into organic carbon. The tubeworm is then sustained by the endosymbionts organic carbon.  Sulfide levels are quite low at Mariner relative to other deep-sea vent sites where tubeworms thrive, so it is indeed curious that we found them here.

Notice the crabs eating the tubes