Third Deployment 2008

The third carcass was deployed in late September, 6 weeks later in the year than carcass one and 2 weeks later in the year than carcass two. The animal was again euthanized by pin-gun and was weighted as carcass two. The carcass was deployed at a slightly different site, about 65 m from the first site. The substrate was again a thick layer of silt with some cobble over rock but this site was close to a large rock and was 4 m deeper than the earlier site, at a depth of 99 m.

The carcass sank immediately, as in the previous deployments. However, in contrast to past deployments, this carcass was only very slightly attractive to fauna, with only a few Munida quadrispina attracted. No Pandalus platyceros or Cancer magister were attracted during the first few months. This is probably a result of the much lower oxygen levels at the time of deployment (Fig. 12.35). Oxygen levels at time of deployment were ~0.3 mL/L and remained around 0.1-0.5 mL/L until a sudden and rapid increase in late December with oxygen reaching levels of 1-2.5 mL/L. Temperatures remained similar to the previous studies at around 9.2°C until late December when they dropped by 1°C and remained at ~8.2°C until the end of the experiment. The effect of this change in environment on the carcass colonization and taphonomy, particularly the change in oxygen levels, was very clearly seen. The carcass remained completely intact for months. At first, a few squat lobsters were observed picking at the skin, creating small grazed areas, but they were unable

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Fig. 12.35 Dissolved oxygen levels during the 2008 VENUS pig study (VENUS Project, University of Victoria)

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Fig. 12.35 Dissolved oxygen levels during the 2008 VENUS pig study (VENUS Project, University of Victoria)

Fig. 12.36 Day 27, 2008. Small grazed areas seen on thighs and around abdominal line caused by Munida quadrispina (VENUS Project, University of Victoria)

to break the skin (Fig. 12.36). After a few weeks, even squat lobsters were no longer observed at the carcass. The carcass became covered in silt and a bacterial mat developed over the entire body (Fig. 12.37). This mat is thought to be a result of the activity of filamentous sulphur bacteria, which occur in low oxygen

Fig. 12.37 Day 79, 2008. Bacterial mat covering entire carcass. Carcass still almost entirely intact (VENUS Project, University of Victoria)

environments where decomposition produces hydrogen sulphide (Juniper 2009; Herlinveaux 1962). This mat was removed in places on several occasions, probably caused by the movement of Lyopsetta exilis (slender sole) across the body, removing the silt layer and the biofilm. Lyopsetta exilis were seen frequently in the area and were seen to swim over the carcass. Their action may have simply dislodged the accumulated biofilm and silt without actually breaking the skin. During this acute hypoxic period these were virtually the only fish observed.

In late December, almost 3 months post submergence, the oxygen levels rapidly rose to above 2 mL/L and immediately, very large numbers of fish were seen close to the carcass (Fig. 12.38) as well as the first C. magister. Numbers of arthropods increased over subsequent days with several C. magister and very large numbers of P. platyceros feeding on the carcass (Fig. 12.39). Interestingly, much fewer M. quadrispina were seen at this time. The water in the area around the carcass became extremely hazy with the sudden and rapid rise of animal activity which is thought to be correlated with the rapid rise in oxygen levels and related to the animal activity, particularly that of the fish (Yahel et al. 2008).

Tissue loss was slow but steady from this point until the carcass was mostly skeletonized by mid February, 135 days after submersion.

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