Huge losses. Donald "Duck" Dunn anchored, along with Al Jackson, one of the nation's best R&B rhythm sections. With Booker T. Jones and Steve Cropper those guys backed up such musical luminaries as Sam & Dave, Al Green, Otis Redding and any/everybody else that was even obliquely associated with STAX records. That's him playing bass for John Belushi and Dan Ackroyd in The Blues Brothers.
Not much that can be said about Levon Helm that already hasn't been. A great old-school drummer possessing one of rock's most recognizable voices. With his passing there remains nobody from Bob Dylan's first electric back-up BAND aside from Garth Hudson and Robbie Robertson.
Don't know that it's surprising Doc Watson might have died given his age. Nor could you say he'd been particularly active of late. Still, Gun Grape's posted video of Deep River Blues indicates the tremendous talent Watson possessed as a musician.
Welch played guitar, sang and wrote songs for at least four of Fleetwood Mac's best albums- Bare Trees, Future Games, Mystery To Me and Heroes Are Hard To Find. That band had more than its share of brilliant but fcuked-up guitarists-Peter Green, Jeremy Spencer, Danny Kirwin and, evidently, Bob Welch. I wouldn't have guessed Welch as the first choice to off himself among those four.