Benthic Biology 2013 Expedition

October 24-28, 2013

The benthic biology research group studies the biology and ecology of marine seafloor communities, with a goal of understanding interactions among environmental factors and biological adaptations that influence the survival, growth, and reproduction of organisms, ultimately determining their distribution and abundance. Their recent work emphasizes the influence of climate change on ocean animals and ecosystems. On this cruise, researchers return to several sites to collect and sample materials and animals left on the seafloor during prior cruises. They will also be measuring the sensitivity of deep-sea crabs to ocean acidification and low oxygen levels, and will retrieve sea urchins to determine the influence of urchins on the smaller animal assemblage.

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Are deep-sea animals more sensitive to climate change and ocean acidification than shallow water animals? Could crop debris left in fields after a harvest be packaged and sunk to the deep waters of the ocean to help reduce the effects of carbon dioxide emissions to the atmosphere? Do terrestrial logs that float over the ocean and sink to the deep-sea attract a specialized suite of animals? If so, does the size or species of wood matter? Do deep-sea urchins plowing through the muddy bottom in the deep waters along the continental margin affect the macrofauna in the mud—the small worms, molluscs, and crustaceans that comprise the prey for many megafaunal animals? These are some of the research questions the benthic biology group is addressing on the October cruise on the Western Flyer as they continue studies initiated over the past several years.

Researchers’ top priority for the cruise is to measure the sensitivity of deep-sea crabs to ocean acidification and low oxygen levels, two consequences of fossil fuel emissions to the atmosphere—it is amazing to think emissions are affecting animals at the bottom of the sea. The benthic respiration system will be deployed over the side of the ship, and followed to the seafloor with the remotely operated vehicle (ROV) Doc Ricketts. Next, the suction sampler will be used to slurp up small galatheid crabs, which will be placed gently into one of eight respiration chambers. Over the next six weeks, the system will automatically measure the respiration rates of the crabs under normal deep-sea conditions, as well as under more acidic, or lower oxygen conditions, or both. Ultimately results from these deep-sea studies at 3,100 meters depth will be compared to similar studies with shallower living crabs.

In 2006, researchers sank a large bale of corn stover—what remains from a corn plant when the cobs are harvested—into 3,100 meters water depth about 50 nautical miles from Moss Landing. They are returning to the bale to determine how rapidly it is decaying. If the rates are extremely slow, they might be able to consider sinking crop residue like this to the deep-sea to help offset rising carbon dioxide levels in the atmosphere. This idea sounds pretty wild, but we need to consider, and evaluate carefully, our plans to cope with climate change.

Nearby, the researchers will be sampling a number of logs placed on the seabed at 3,100 meters several years ago. These logs will be returned to the lab to see what animals have colonized them, using classical taxonomic methods identifying animals through the microscope, and also molecular methods to evaluate more carefully the specific taxonomic relationships among many of the smaller species on the logs.

Finally, the ROV Doc Ricketts will dive on a site at 1,000 meters depth where deep-sea urchins were placed in mesh cages two years ago. Three of six cages (two meters width by two meters length and 30 centimeters high) included 15 urchins, and three cages had no urchins. The urchins will be gathered with a suction sampler and numerous sediment cores will be collected. Once the samples are on board, the science team will sieve the sediment to separate the little animals—the macrofaunal worms, and the meiofauna, the microscopic animals. In the lab, these samples will be analyzed and comparisons will be made of the fauna sampled in cages with or without urchins to determine the influence of urchins on the smaller animal assemblage.

Logbook

urchin frame

Squeezing in two dives on our last day

As expected, the wind rose last night and by 6:00 a.m., the start of our day, it was blowing between 25 and 30 knots – too windy and rough to launch ROV. The forecast was for the winds to drop through the day, so we decided to wait it out and hope for the best.
examining galatheid crabs

Collecting corn-bale animals and the last logs

Our day started a little later this morning, since we didn’t need to deploy any elevators over the side of the ship. The remotely operated vehicle (ROV) launch proceeded as scheduled at 6:30 a.m., and we were viewing the bottom at 3,200 meters just before 8:30 a.m.
corn bale critters

Corn stover and respiration experiments

We had two primary goals for today’s ROV dive. First, to deploy the benthic respiration system (BRS), then set it up to measure the oxygen consumption of some deep-sea crabs. Second, we planned to inspect a bale of “corn-stover” (like a large hay bale, except made of corn stalks) that we sank to the seafloor five years ago, to evaluate its rate of decay and effects on seafloor animals.
benthic elevator

Elevator to the seafloor

We started today before the crack of dawn, deploying a “benthic elevator” over the side of the Western Flyer, and allowing it to sink down 3,200 meters to the seafloor. A benthic elevator is basically a big platform used to carry gear from the surface down to the seafloor, or back from the seafloor up to the surface - sort of like an underwater pickup truck.
cages

Urchin cages

As expected, the wind rose last night and by 6:00 a.m., the start of our day, it was blowing between 25 and 30 knots – too windy and rough to launch ROV. The forecast was for the winds to drop through the day, so we decided to wait it out and hope for the best. It turned out that it didn’t take long.