Zunino appeared in 243 big league games over the past two seasons with Seattle, though the move Friday wasn't viewed as a surprise.
"It's intriguing. There's big-time power there," manager Scott Servais said. "But being able to get to the power and being able to make consistent contact, his contact rates have to improve. His strikeout rate [37.7 percent of his at-bats] was not in a good spot last year.
"There's quite a bit of separation from where his at-bats are and where I perceive they should be."
The 24-year-old Zunino, who was the third overall pick in the 2012 Draft, went 3-for-19 (.158) this spring. He hit 22 home runs in '14 for Seattle, but he had a slash line of just .199/.254/.404. He fell to just .174/.230/.300 with 11 homers last season.
"I think every player hits a point in his career … where you have to decide which way you're going to go," Servais said. "Your job, your career comes to a crossroads. There does come a point where you get either over the hump or you don't."
Powell, 23, has only played 56 games at the Triple-A level. He did so a year ago with the Rays' top Minor League affiliate in Durham, when he batted .257/.360/.364. Powell was part of the six-player trade the Mariners made in November with the Rays.
"I thought he had a very good camp … kind of as advertised as what we were getting there," Servais said. "[He's] a high-energy player. There are some things he needs to get better [at] in his game.
"I think he could be a guy who can help us at some point this year."
Martin posted a 4.50 ERA in eight innings this spring, allowing 10 hits with three walks and seven strikeouts.
"He knows where he's at. The thing about Cody is he can swing -- he can start, he can relieve," Servais said. "He's projected to go into the rotation in Tacoma, and we'll see how that goes for him."
• Stefen Romero, who is hoping to win a job on the Mariners' bench as a backup outfielder and first baseman, was scratched from Thursday's game with what Servais termed on Friday as a "cramping-type issue" in his lower back. Servais indicated Romero was doing better Friday morning and that he could return to games soon. Romero is hitting .480 this spring in 25 at-bats.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.