Question about compatibility and missing fish

[O.Cunningham]

Hello, this is my first time posting something on one of these

Recently, I bought a dilectis dottyback.
Before I bought him, I did my research and decided to buy him.
The inhabitants of my tank, which is a 50 gallon, are:
2 photon clownfish
Flame hawkish
Pyjama cardinal
Melanarus wrasse
Starry algae blenny
Fire shrimp
Arrow crab
Porcelain anemone crab

And my latest addition is the dottyback

Shortly after I introduced him, he was chill, and is still chill. Had some issues with the blenny swimming at him a few times.

However, I noticed that my wrasse had been swimming in circles, even before the dottyback went into the tank, he is about 5 years old, or would have been in January next year. And now, he is missing, haven't seen him in almost 2 weeks and no sign of a body.
However, I saw him and the dottyback have a little tussle and they both had a small nip on their dorsel fins.
And a little later, I found my arrow crab dead, no sign of a fight or a scratch on him though.

And now whenever my fire shrimp goes in the bottom half of the tank, he is harassed by the dottyback until he leaves, but the moment he goes onto the upper section of the rocks, the dottyback is chill again. Which is fine, I know their territorial nature. However, given that behaviour, what could have happened to my crab and wrasse?
I know the fragile nature of crabs and sometimes they do die for almost no reason. I think it is convenient that he went in and both of them are missing or dead. The wrasse was getting on in age, as I mentioned, so I am unsure if the dottyback is the culprit, given the lack of direct fighting that I have witnessed.

Do you think he has killed them or does it just look like he's the culprit? Especially with the timing of their deaths.
Also I must clarify that the dottyback does not attack or even bother with any of my other tank inhabitants.
When I am thinking about whether he is a killer or not, surely he would bully some of the more passive tank mates I have, rather than two of the stronger or more able to defend themselves, like the arrow crab. No one bothers him, even though hawkfish are sometimes known to attack inverts, even he didn't attack or even look at any of them.
My judgement is, that it is wrong place, wrong time. But, what do you think?

Also, my parameters are fine, given all my anemones are looking great, I have bubble tips and a Magnifica anemone. And the other inverts are fine, I even have snail eggs in my tank

 

[edsbeaker]

I have no answer since its hard to know. Dottybacks can be really mean, so could it be that or coincidence? Sure. I would continue to watch the Dottybacks behavior, and any changes in the other fish behavior, and remove the Dottybacks if you notice anything worrisome. As it gets older and more acclimated to the tank the aggression could get worse.
Hope the wrasse shows up!

 

[O.Cunningham]

I have no answer since its hard to know. Dottybacks can be really mean, so could it be that or coincidence? Sure. I would continue to watch the Dottybacks behavior, and any changes in the other fish behavior, and remove the Dottybacks if you notice anything worrisome. As it gets older and more acclimated to the tank the aggression could get worse.
Hope the wrasse shows up!

I have seen proper aggression between angels before and my clownfish with my hawkfish before and the dottyback hasn't shown anything like that.
I think he's just very defensive over the back quarter of my tank. Which is fine and his natural behaviour.
And I think the wrasse hasn't been himself for quite a while. I think, I will just watch, like you say. Usually I see a body when something dies in my tank, but he could have died in his sleep as he is one of the wrasses that goes into the sand when it goes night time

Also I did move some rocks last night, to make it so the fire shrimp wouldn't go into the dottybacks caves, to avoid him becoming territorial again. And I have looked several times today and things seem to have calmed down, which is very nice

I did know what I was getting into, but I was sure that the arrow crab would be fine, as they are quite bodacious. Maybe it was a parasite? Since they can be vulnerable to them, I am pretty sure
Things like this don't happen very often in my tank and things usually go quite well.
Anyways, thank you for your reply

 

[edsbeaker]

I think things like this are difficult because all you can do is guess. Seems like you are up to the task!

 

[O.Cunningham]

Quick update, haven't seen any more aggression from either side, the shrimp now has his own little ledge he hangs under, which has a tricolour BTA and a green BTA on it.
And the dottyback seems to have calmed down

I am hoping this is a coincidence, as his behaviour right now is fine.
Everything else is looking great!