I would keep the cone on but drill several 3/16" holes in it. This will keep anything from being sucked onto it and not being able to get off. The screen alone is still capable of getting a fish stuck on it (believe me, it's happened to me). of course some critters can still get hurt (anemones and brittle stars, etc.) with anything short of a prefilter foam attachment.
Also, what's that red rock on the base of the LR? If it's organ pipe skeleton it will be fine. If it's lava rock, get it out now! Lava rock is very high in phosphates.