Trochus snails or pests?

[FishandFire]

About a month ago I noticed white specs appearing on my ulva and chaeto in my sump. They’ve now grown to be quite large. Initially I thought they were trochus snail offspring, but I am more concerned now that they might be a pest. They are eating holes through the ulva and have almost devoured half of what I had.

For reference I have a 90g with a 40g sump total water volume is 90g with displacement. So far it’s stocked with a pair of clowns, 2 scarlet shrimp, 4 urchins, an emerald crab, and half a dozen trochus snails. (there were 5 nassarius snails in there for about a week before causing problems and being removed)

 

[James M]

Pineapple sponges which are Harmless filter feeders

 

[ISpeakForTheSeas]

Agreed with the above - those are pineapple sponges, and they're filter feeders (so they're not eating your macroalgae; I'd look for other possible causes for the issues you're having with the algae).