Whats Eating My Star Polyps?

[372xp]

I have 2 colonies of star polyps which I have had for a couple of years now. In the last 2 days they have both been decimated by something. I have a couple of suspects in mind.
1st Red stripe angel, she has only been in the tank for 2 months.
2nd Emerald crab. Caught him eating xenias so he was banished to the sump, felt sorry for him so gave him a reprieve last month.
3rd I have had an outbreak of green slug like things(sea hares?) that hatched in the sump and have now made it to the main tank.
Any ideas?
Water stats all good except calcium is a bit low, oh and my xenias have all shrunk.
Tank sumped aquanano 130, 200ltrs.

 

[SeanTrollope]

it could be the angel as they do kill smaller fish

 

[betta fish]

My money is on the emerald crab or any other crabs you may have? I had the same happen and caught my crabs doing it, I had an emerald too but did also see a red hermit at it too.

 

[372xp]

I was hoping it would be the crab, hes a greedy little git. This makes him easy to catch some krill in a jam jar and 5 minutes hes in there like swimwear. Back to the sump then to lfs.
My hermits are pretty well vegitarian and quite small.
I will evict him and see if they come back.

 

[Donya]

If it is the emerald crab was caught red-handed eating coral and the crab really is Mythraculus sculptus, then it's likely not getting enough meaty food.
 
Have you IDed the slugs? There are many coral-eating sea slug species.

 

[372xp]

these are the critters that appeared in my tank. The slug thing is on the right you can see there eggs all over the return pump. They are even in my skimmer. They get sucked up and into the tank where they seem to graze on the rocks, they are quite happy to drift around in the current. There doesnt seem to be that many of them compared to the amount of egg cases, maybe they are getting eaten as well as eating. I would really like to find out what they are so I know what I need to do.
I couldnt get a better picture as the tank lights are out, the sump light is on now.