I wouldnt think the shrimp is the culprit. I usually use a cup over my sun to feed but after i take it off, my cleaner and fire shrimp work over the sun for at least 20 minutes. Ive never seen any ill effects from my shrimp messing with my sun.
Are you sure that this just happened? Could it have happened over a few days? If so, it may just be receding and not getting fed enough. You may want to try some meatier food like a mix of shrimp, clam, squidd, etc. soaked in selcon or zoecon.