It's not a hole in the coral, IMO. - And it's not a 'hole' in the background. Holes found during testing,
(in the make-up of the background), are usually characterised by changing to the colour of any fish that passes over it. - Most, if not all of those, have now been found.
To me it looks like a light coloured fungi growth, on a broken coral. And if that's what the creator intends, - then who are we to question?
Edit! ..... Sorry, just seen your reply, Jim, - but I spent some time trying to explain that, so I'll leave it, if that's ok.
(Delete it if you wish.
)