Decomposition and Invertebrate Colonization of Carrion in a Deep Coastal Marine Environment

The following studies are ongoing and are performed in collaboration with the Victoria Experimental Network Under Sea or VENUS (www.venus.uvic.ca) (Anderson 2008, 2009). VENUS is an underwater laboratory consisting of an array of oceanographic instruments, cameras and sensors connected to a node via fibre optical cables and to a remote station on shore (www.venus.uvic.ca). This allows researchers to access real-time data from the ocean bed and from their experiments, using an internet connection, from anywhere in the world. VENUS presently has nodes in the Saanich Inlet, a glacially carved 24 km long fjord , close to Vancouver Island in British Columbia (Herlinveaux 1962), as well as the Strait of Georgia and the Fraser Delta, with another node expected to be deployed in the Strait of Juan de Fuca, just south of the Canadian/US border. These present studies were conducted in Saanich Inlet, but plans for the future include all VENUS sites.

The Saanich Site includes the Node which provides and distributes power and communication, the VENUS Instrument Platform (VIP), and a remote still and video camera. The camera, an eight megapixel Olympus C8080, is housed in a copper jacket to prevent fouling and is placed on a camera platform, which supports the camera 2 m above the seabed. The camera is operated remotely and has an array of lights and lasers for scale. All images were taken by this author with the VENUS camera and images are shown here with permission from the VENUS project, University of Victoria. The VIP housed the Seabird Electronics Inc. CTD and the Falmouth Scientific, Inc. CTD, measuring conductivity, temperature and depth via pressure at 1 and 60 s intervals, respectively, as well as a Gas Tension Device, measuring dissolved gas pressure, an oxygen optode, measuring dissolved oxygen and a Sea-Tech Transmissometer measuring clarity of the water (www.venus.uvic. ca). The data from these instruments can be seen and downloaded from the VENUS website. The Saanich Site was at a depth of 94 m for the first two deployments and 99 m for the third. The seabed was made up of fine silt which was approximately 10-20 cm deep, over rock.

Saanich Inlet is a deep water fjord, with a maximum depth of 230 m, which is separated from the Strait of Georgia by a shallow sill which restricts the flow of water in and out of the Inlet (www.venus.uvic.ca). This means that, for much of the year, the inlet is oxygen depleted or hypoxic.

The first carcass was placed at the site on 5 August 2006. It weighed 26 kg and was killed by electricity, then taken to the site by boat. On the boat, it was refrigerated at 4°C until it could be deployed. Due to camera problems, the pig was kept under refrigeration for almost 44 h. The carcass was weighted at the head and rear end by lead weights and rope, and the weights roped together (Fig. 12.1). The weights were required to keep the carcass within view of the camera at all times, rather than to prevent it from floating away, as bloat and therefore refloat do not occur at such depths (Teather 1994).

The carcass was attached to an acoustic transponder then dropped into the ocean. It was then located using the transponder by a remote submarine vehicle, ROPOS (Remote Operated Platform for Oceanic Science). ROPOS retrieved the carcass and carried it to the camera platform, where it was laid on its side, under the tripod holding the camera. The camera platform was approximately 100 m from the VIP where the chemical sensors resided. The transponder was then recovered by ROPOS. Once ROPOS left the site, there was no further direct contact with the carcass. The carcass was observed remotely several times a day, until the carcass was no longer in view of the camera. At 94 m, the ocean is completely dark so lights had to be turned on in order to observe activity at the carcass. An array of lights and light types were available. Each observation session was recorded in its entirety by video tape and still images were taken at will. Salinity, clarity, temperature, and oxygen level were monitored at 1 and 60 s intervals (Anderson 2008, 2009). Days are measured in days since submergence. Once the carcass had been placed it was not disturbed again, except by the turning on of lights during observation times.

The second carcass was deployed at 0800 h, 16 September 2007. It weighed 24.7 kg and was killed by pin-gun on 15 September and kept on ice until deployed by ROPOS. The third carcass was deployed at 0835 h 29 September 2008 at a site close by, which was 4 m deeper, at 99 m. It weighed 23 kg and was killed by pin gun on 28 September and kept in a refrigerated room until deployed by ROPOS.

Further carcass deployments are planned at 65 m in the Saanich Inlet and 170 and 300 m in the Strait of Georgia.

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