Id and Treating sudden necrosis (pic)

[schiller2300]

My softy and LPS tank has been running for several years very successfully. Suddenly, several days ago my neon green finger developed several rather large areas of dark black necrosis. I have not seen anything like this, nor come across this is forumns. I have waited to frag the coral to see if and how the necrosis progesses. The only change that I can think of in the past 4 months is the addition of a parrot wrasse. Any suggestions would be very much appreciated.