What I want to know is, at +60m would there be more or less islands?
My grandfather pointed out that some islands are made from coral/organic stuff and naturally exist close to the surface. So if you up the surface 60m, all other things equal, there will probably be slightly less islands. I figure you'd break even on the elevation related stuff, so I buy his answer.
A coral reef grows at 0.3 to 2 centimeters per year and should be able to keep up with sea level rise. It's hard to guess how many places there are like Mont-Saint-Michel that are connected to land now and might become islands with a higher sea level. I don't know if there are a lot of islands that don't have coral formations, and so would be swallowed up.
I believe the idea is that if an ice shelf decides to crash into the ocean the sea will rise rather more suddenly. Presumably this will kill all the coral on the planet, which is highly sensitive to the diffusion level of its light source. But I'm guessing.