Question

An oil spill happened at the Wild Harbor salt marsh on Cape Cod, Massachusetts in 1969. The oil has persisted in the ground since then. How is the green crab used as evidence for the idea that oil still exists in the lower layers of the soil?

These organisms show increased reproductive rates compared with previous rates.
These organisms show increased predation on other species than prior to the spill.
These organisms dig more shallow burrows than they used to.
These organisms migrate to deeper waters than they did before.

Answer 1

I would guess that the answer would be :'These organisms dig more shallow burrows than they used to.' 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.