As far as we can tell, collection of ornamental fish does not impact the crown-of-thorns populations at all. Hawaii has fewer and smaller outbreaks than many places where there is less aquarium collecting, and there are outbreaks of COTs happening in places where there has never been aquarium collecting.

The data indicate that it is most likely nutrient enrichment (primarily from fertilization of the nearshore waters from terrestrial runoff around homes, golf courses and sewage outputs) that drive outbreaks because the nutrients feed algal blooms that in turn feed the larval sea stars.

An individual sea star can produce a million offspring and they may all survive if they have enough food.

There are no more small tropical fish to eat those crown-of-thorn
larvae. Those tiny tropys are usually in and out of those tiny
rock holes.