So I was offered a position to UC Merced and have to reply by April 13th but I am also waiting to hear back from ucsd, uc sb, and ucla ( they come out after may 1st). If I accept UC Merced, does that automatically cancel my waitlist position to the other UCs? Should I take the offer from Merced?
No, you will not lose your waitlist positions. You will need to accept one school before the May 1 deadline and you will probably not hear until after that date about your waitlist decisions. Take the offer at UCM and if you get off the waitlist at any of the other schools, you will only lose your UCM deposit.