If the first one have a black line across its eyes, it could be a bandit crab, which is considered a good acro crab.
Bandit coral crab (Tetralia nigrolineata) on the Shores of Singapore
Fact sheet with photos on flora and fauna of Singapore's intertidal shoreswww.wildsingapore.com
IMO, the second one I would toss as they will wear out patches in your sps. Similar to how clown gobies will cause dead spots where they sit.
Parasitism is a type of symbiosis so a crab can harm the coral and still have a symbiotic relationshipIf it has blue eyes it’s probably cymo andreossyi - a type of acro crab. I have a couple of these living in a Mille right now. They are considered symbiotic I think but they do eat polyps and I think are considered a pest. But they aren’t going to do nearly the damage (or get nearly as big) as a gorilla.
Parasitism is a type of symbiosis so a crab can harm the coral and still have a symbiotic relationship
I love the little bandit acro crabs. I got one once from an import, but it was stressed and couldn’t cling to the coral hard enough, and it disappeared the next week
Although my corals were much smaller back then, not much to hide in. Maybe I should try again soon