Funnily enough I was looking at this this morning (for study, not to plan any theft! ) so just for fun here's an answer:
So yip, you can steal corals. You can, under s 209, only kidnap a person.
Oh and just to add to the fun it doesn't matter who physically reaches into the tank, the one distracting will have equal liability as a party to the crime under s 66(1)(b) as, given their intention, their distraction of the shopkeeper would certainly amount to "an act for the purpose of aiding any person to commit [a] offence."
Back to the coral though, davidb, that purple bonsai acro is AWESOME!