May 7, 2010

Rocks and Animals

Rocks and Animals on the Seabed in the NE Lau Basin
Ken Rubin

One of the activities on this expedition is systematic high-resolution photographic surveys of the sea floor. Why do we want to do that? To learn what is there. After all, the deep sea floor is Earth’s final frontier and we are driven to explore it. But why go to the NE Lau basin, instead of some place closer to home? We already know that many areas on the sea floor are vast monotonous plains of sediments, and that other parts are as rich with features as the land above sea level. The NE Lau basin is one of those feature-rich places. Sonar maps tell us that it has a larger than usual number of hills, ridges, basins and cracks that are characteristic of volcanic landscapes. Chemical surveys of the overlying sea water tell us that some number of these hills is hydrothermally active. So, we’ve come to this area to learn which areas have young volcanic rocks, hydrothermal mineral deposits and/or animals that thrive at active volcanoes.

Large brown gastropods colonize hydrothermal chimney structures on one of the volcanoes of the North Mata group. As Tim Shank (a colleague at Woods Hole Oceanographic Institution) explains, these seamounts may have faunal differences between them that are related to geography, the age of the venting system, recent disturbances, or some combination thereof.

By photographing the sea floor, we can see first hand what types of rocks are there, what condition they are in, and what organisms might be living on them. We have chosen our survey spots mostly from sonar maps and sea water chemical data. But we also use a bit of horse sense and rely on a bit of luck to hopefully put the camera down in the best spots. So far, we have completed 7 camera surveys, and our luck has been with us. We have discovered relatively young (less than a century or so old) volcanic rocks at each site, and active hydrothermal systems at two of them.

Young, fresh pillow lava in a newly discovered lava flow erupted near Tafu volcano on the NE Lau Spreading Center. The white deposits on the surfaces of the cracks usually only lasts for a few years after eruption.

Young sheet lava overlies fresh pillow lava, showing a sequence of lava effusion conditions (slower at first, and then faster) at this spot during the eruption near Tafu.

These photos also provide invaluable first hand information about the types and numbers of animals that live these at submarine volcanic sites. The animals tell us where nutrient and energy rich hydrothermal fluids are venting from the rocks (which is sometimes difficult to see with the naked eye). But more importantly, they inform us about the ecological conditions that allow some of Earth’s most unusual critters to grow, reproduce, migrate and colonize the isolated spots in the deep sea they are adapted to live in. So far, we have discovered two sites that are rich in such fauna on this expedition and by harnessing the R/V Kilo Moana’s reliable and speedy Internet link to send photos to shore, we have been able to learn a great deal about these communities. Dr. Tim Shank, a colleague at Woods Hole Oceanographic Institution, who was unable to come with us on the expedition, tells us that these sites are rich in fauna, some found elsewhere in the region, and some that might be new discoveries. Some notable examples are included in the last two pictures on this page.

Crabs, Phymorhychus gastropods (large white snails) and small actinarian anemones populate a volcanic substrate with active diffuse hydrothermal venting. None of the species, or those in the first picture on this page, were found at actively erupting West Mata volcano during our remotely operated vehicle dives in 2009.