VICTORIA, BC – Some marine species will venture into “dead zones” demonstrating a surprising tolerance to low levels of oxygen, suggests new research conducted by researchers using the VENUS network on the British Columbia coast.
The study, led by University of Victoria marine biologist Dr. Verena Tunnicliffe, used pig carcasses placed on the ocean floor to see what marine scavengers showed up for a meal and how well they fared in the oxygen-depleted water of Saanich Inlet near Victoria.
“Saanich Inlet was ideal for the study because it is a deep basin with naturally occurring layers of low to no oxygen—similar to ocean dead zones,” says Tunnicliffe.
The number of low-oxygen dead zones in the ocean is doubling every decade, partly due to climate change. “This trend could result in massive die-offs of fish and other marine species, such as those that happened in 2006 off the Oregon and Washington coasts,” says Tunnicliffe.
The VENUS network provides live feed from instruments, cameras and hydrophones on the seafloor. Cameras are strictly controlled to limit the effects of light on marine life. By controlling a seafloor camera at 100m depth from their laboratories, the study team watched as scavengers gathered within a day, drawn from the shallows, to feed on the carcasses.
Three crab species, shrimp, octopus, sharks and even seals arrived within two days despite oxygen levels considered extreme from prior laboratory manipulations. They remained at the carcass which was consumed in four weeks. Conversely, in near zero oxygen, no breakdown occurred illustrating how dead zones will inhibit degradation and nutrient cycling.
The research demonstrates the tolerance—and the limits—of certain species to rapidly growing dead zones. Within hours of low oxygen pulses, nearly all species had fled. “We have found that several species can tolerate low oxygen levels as long as they remain relatively stable. But when these levels fluctuate, for example, when pulses of low oxygen are delivered by tides, only rare well-adapted species will remain.” says Tunnicliffe.
The study provides scientists with valid field limits of oxygen levels for some important commercial species in conditions in which the animals had a major incentive to stay, says Tunnicliffe: The implications of this work are twofold: first, that marine species often live on the end of their limits and are easily overwhelmed with large oxygen drops; on the other hand, after major dead zone “kills” the clean-up crew can arrive fairly quickly if they have survived to recycle the dead and help restore the habitat.
An additional surprise for forensic researchers was the rapid rate of disappearance of a pig carcass through the scavenging process. The study will help researchers determine exact rates and processes of decomposition in deep ocean water, providing valuable insight into criminal investigations.
“VENUS provides a phenomenal opportunity to study what happens to bodies in the ocean—in real time.” says Dr. Gail Anderson, a forensic criminologist at Simon Fraser University who participated in the study.
The VENUS (Victoria Experimental Network Under the Sea) network, led by Ocean Networks Canada, has two instrumented cable networks in operation on the BC coast—one in Saanich Inlet and the other in the Strait of Georgia near Vancouver. For more information on VENUS visit www.venus.uvic.ca.
The study was funded by the Natural Sciences and Engineering Research Council of Canada.
Media contacts:
Verena Tunnicliffe, University of Victoria, verenat@uvic.ca, 250 721-7135
Richard Dewey, VENUS, rdewey@uvic.ca, 250 472-4009
Nikolai Korniyuk, VENUS, nnk@uvic.ca, 250 472-5366
