I would guess that the answer would be :'<span>These organisms dig more shallow burrows than they used to.</span>' If the crabs actively dig burrows, as many crab species do, and a layer of oil has persisted in the lower soil strata, it makes sense that the crabs would be reducing the depths of their burrows to avoid contact with the oil. The other possibility is that the crabs might might migrate to deeper waters, but this is less likely because the crabs would be evolved to utilise the intertidal zone.
The Bear population would increase due the the raise in the salmon population.
An earthquake? Is it multiple choice?
The more the people, the more pollutant they generate which will pollute the the water.
