Astreas are crab fodder. Gave up on them a long time ago. Crabs won't fool with Nassarius, large turbos or banded trocus snails. I have a variety of crabs, some large, and a mix of snails. Every now and then I'll pick up a few more to replenish the stock.
Crabs will attack anything if there's no food for them. My first cleanup crew ate each other as I was told not to feed them. I feed everything and they are happy boys and girls. My tank stays nice and clean.