Day 2: Clam dig at a deep seep
May 19, 2013
We started our day with a remotely operated vehicle (ROV) dive at a methane seep mound visited by Peter Brewer and his team on May 14. We found extensive bacterial mats of different colors—orange, red, yellow, and white—some thick and flat, others long and filamentous resembling a furry shag carpet from the 1970s. We sampled tubeworms, clams, and snails from this area to compare with animals that we have collected at other seep locations. These collections will fill a geographic gap in our collections of chemosynthetic animals between the Northeastern Pacific, Monterey Bay, and the Gulf of California. More information can be found here.
Different colors of bacterial mats covering a carbonate outcrop.
Tube-dwelling folliculinid ciliates sometimes form dense bright blue mats (growing on Lamellibrachia tubes in this image) resembling shag carpet, which grows at both hydrothermal vents and cold seeps [note: ciliates are a type of protozoan or single-celled eukaryote]. They have been observed in many locations worldwide and scientists onboard are interested in the ability of these ciliates to use methane emitted from the seep for energy. –Shana Goffredi
ROV pilots use the manipulator arm holding this clam scoop to dig for clams at seeps.
Lisa Levin and Ben Grupe from Scripps Institution of Oceanography have visited this site once before with the Scripps ROV. It was first discovered as a seep site during an expedition led by graduate students in July 2012, when they sampled the seafloor with a multicore and found chemosynthetic worms, a vesicomyid clam, filamentous bacteria, and carbonate rocks in their samples—signals that the area had active seeping. Returning in December 2012 with the Scripps ROV, these researchers observed the area for the first time with a video camera. Lisa and Ben join us on this cruise to quantify the diverse assemblage of organisms that inhabit this seep community. They've sampled everything from bacteria to large invertebrate predators, and will compare these samples to other seep communities they have previously investigated. Push cores were used to collect and analyze small animals (less than 0.3 millimeters) in the top 10 centimeters (five inches) of the sediment, and carbonate rocks were sampled to investigate the organisms that inhabit the surfaces. Previous research has found completely different types of communities occur on seep carbonates compared to sediments, so their research is designed to measure how the community structure and biodiversity of this seep vary among microhabitats. In addition, samples were taken 20-30 meters (65-100 feet) outside the seep to compare the organisms living on the surrounding muddy seafloor and determine if this community is also fed by chemosynthetic production. Information from this expedition will help the scientists develop detailed descriptions of who is living in and around seeps, and provide better understanding of the seep food web.
— Kris Walz
Push cores used to sample microhabitats in seep area—some within the bright orange bacterial mat and some just outside of it. The two red dots are lasers from the ROV, they are 29 cm apart.
Following our ROV dive days, Julio Harvey and Haibin Zhang are collecting daily zooplankton samples to investigate population genetics of calanoid copepods and other small invertebrates. Their 200-micrometer mesh nets typically capture a broad diversity of organisms. Julio and Haibin employ both a standard plankton net (circular opening, one meter (three feet) diameter by three meter (nine feet) length) for vertical tows, sampling to 30 meters (100 feet) depth, and a Neuston net (rectangular opening, 0.5 meter (1.5 feet) by one meter (three feet) by three meter (nine feet) length) for sampling surface waters. Comparing samples collected during the day with those collected at night allows them to investigate genetic diversity of organisms known to exhibit diel vertical migration behavior, an evolutionary adaptation to avoid predation by larger, zooplanktivorous organisms. High-throughput gene-sequencing methods will be used to assess community variation when these samples are returned to shore. The tow-net samples will be compared to similar samples from the Monterey Bay, California. This approach will not only reveal population genetic differences between southern and central California, but will also allow us to describe taxonomic differences in zooplankton communities among sampling sites.
— Julio Harvey and Haibin Zhang
Haibin (left) and Julio (right) prepare to deploy the circular plankton net at 30 meters (100 feet) deep.
The Tanker Tango
We discovered that there is more traffic while working at sea in Southern California than what we are used to in Monterey Bay. This morning our dive was stationed in a busy shipping area, and Captain Andrew McKee was in regular communications with the captains of two very large ships (one was 1,000 feet long) since we were sitting in their trajectory. They were transferring oil from one ship to the other while underway at a slow speed, and they were headed our way. With the ROV deployed at 1,000 meters (3,000 feet), it’s not easy to quickly move to a new location. Eventually the ships gradually changed their heading and passed within two miles of the R/V Western Flyer.
— Kris Walz