An Ethical Question?

A fellow blogger who dives regularly, recently recounted a story in which he helped two hermit crabs find new homes. Another fellow blogger/diver wasn't too happy with the first blogger/diver, and posted the previous blog post about not taking the shells of hermit crabs if a hermit crab was living in it.

That really pissed off the first blogger/diver.

Now.

I fish (not very well) and I eat fish. I eat crab and I've eaten hermit crabs off of the beach.

With that understanding, I pose the following question:

Is it ethical for a SCUBA diver to take the shell from a live crab?

Is taking a shell from a live crab similar to taking the horn from a Rhino (or Saipanda) or the fins from a shark? Or is it more like sheering the wool off of a sheep? Would it have been ethical to take the crabs if the diver had eaten the crabs? Since fishing with SCUBA is illegal, did the diver break the law?

Second, I pose an ethics in blogging question:

Is it ethical to use pictures from another site without permission?

Is it enough to just link back to the original site? Do you have to get permission first?