They are abundant but are also ecologically quite important. Because, not only are they big predators of coral but they are themselves FOOD (and prey!) for other invertebrates in the tropical reef ecosystem!
H. picta is known commonly as the Harlequin or Painted Shrimp owing to their very eye-pleasing designs and colors..
The relative frequency of COTS that are attacked by both shrimp and worm was pretty low (about 0.6%) but very effective. Based on their observations of wounded Crown of Thorns taken to aquaria, individuals attacked by both shrimp and worms died within a week..
So, even if the attacks frequency was not very high-these predators would be very effective and potentially affecting COTS populations (at least in localized regions..)