Bodies at sea—oxygen levels may impact scavenger response
An ocean's oxygen levels may play a role in the impact of marine predators on bodies when they are immersed in the sea, according to Simon Fraser University researchers in a new study published in the journal PLoS One.
SFU criminologist Gail Anderson led the study, based on the deployment of a trio of pig carcasses into Saanich Inlet at a depth of 100 metres and studied over the past three years.
Anderson assessed scavenger activity while co-author and SFU criminologist Lynne Bell continues her investigation into what happens to submerged bones.
They’re conducting the research with the Victoria Experimental Network Under the Sea (VENUS), a cabled underwater laboratory that researchers use to monitor their experiments and equipment via the Internet.
The VENUS sensors recorded oxygen levels, temperature, pressure, salinity, density and other factors every minute. Anderson could control the VENUS camera from anywhere, including while at a conference in Mexico.
The researchers found that scavenger response in the first two deployments were similar, with the carcasses reduced to skeletons within a month. The third, however, remained intact for several months. Anderson says the big difference was in the dissolved oxygen levels.
“Saanich Inlet is hypoxic (deficient of oxygen) most of the year and anoxic (without oxygen) at some times,” she explains.
“While the animals there are adapted to low oxygen, the last carcass was deployed when it was extremely low, which kept out all the big scavengers such as the shrimp and Dungeness crab, leaving the Squat lobsters, which were unable to break through the skin. This now gives us a better understanding of what happens to bodies in such waters.”
Anderson used a remotely operated submarine with an underwater camera to place each carcass. Work is ongoing to remove the skeletal remains from these sea-floor deployments.
The VENUS sensors continuously measured several other parameters to give the researchers additional data, including water chemistry and physics details.
Using this information, Anderson earlier demonstrated to the media and the public that feet naturally disarticulate.
“So the so-called mystery of the ‘floating feet’ washing up on shores along the West Coast was not a mystery, but a natural occurrence in the marine environment,” she says.
Anderson and Bell have just deployed the tenth set of pig carcasses in a marine setting, which the public can view at venus.uvic.ca (click on “live video”; note that the lights turn on every 15 minutes).
The Saanich Inlet study was the first of a series of experiments, with carcasses deployed in spring and fall in three different habitats and at three different depths in the Salish Sea.
Anderson and Bell now plan to take the study much deeper into Barkley Canyon east of Vancouver Island.
The work is part of Anderson’s forensic investigative research spanning more than two decades at SFU, and for the past three years, it has been part of Bell’s ongoing marine taphonomy investigations.
The Canadian Police Research Centre funded the research, with support from VENUS, led by Verena Tunnicliffe. Anderson was the first external researcher to work with VENUS, which is part of Ocean Networks Canada.