SEATTLE -- The revolving door on the Mariners' bullpen took a few more spins on Friday as right-handers Matt Festa and Ryan Garton were called up from Triple-A Tacoma, with starter Erik Swanson optioned back to Tacoma and lefty reliever Zac Rosscup designated for assignment.

Festa opened the season with the Mariners, posting a 6.43 ERA in six appearances before being sent down. Garton will be making his season debut in Seattle, though he pitched 13 games with a 1.54 ERA for the Mariners in 2017.

The Mariners have already used 19 relievers this year; Garton will become No. 20 if he gets into a game, as general manager Jerry Dipoto searches for solutions for a group that has been completely made over since last year.

“We have a lot of season left to play,” said manager Scott Servais. “We’re going to see a lot of players continue to join our roster as this thing moves forward. We knew that when the season started. Here we sit in the middle of May and you’re starting to see a little turnover. It happens.”

Seattle now has 10 relievers on its 25-man roster, but only three starting pitchers as Felix Hernandez is on the 10-day injured list and Swanson now is headed back to Tacoma after going 1-5 with an 8.04 ERA in seven outings (six starts).

Lefty Wade LeBlanc (strained right oblique) will be activated off the injured list to start Saturday’s 7:10 p.m. PT game against the Twins, but the club will either need to call up another starter or use a bullpen day on Tuesday in Texas when Swanson’s next turn comes up.

The biggest surprise Friday was the decision to designate Rosscup for assignment, given he’d posted a 3.21 ERA over 14 innings in 19 outings and was one of the more dependable veterans in the ‘pen as a 30-year-old who’d signed as a free agent with Seattle in December for $610,000. The club needed his spot to add Garton, who wasn’t on the 40-man roster.

“With our bullpen set up the way it is, we don’t really have a spot for him,” Servais said. “Zac really is a left-on-left guy; that’s what he’s good at. He’s got the left-handed breaking ball. We’re not really built that way. We need guys that can go out and pitch for one-plus or two innings. It’s not doing him any favors [to pitch extended outings]. He’s just not built that way. That’s not what he does.”

When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster. Within seven days of the transaction (had been 10 days under the 2012-16 Collective Bargaining Agreement), the player can either be traded or placed on irrevocable outright waivers.

Garton, 29, has been one of Tacoma’s top relievers with a 3.46 ERA and 28 strikeouts with nine walks over 26 innings in 12 games. He worked multiple innings in seven of his 11 outings with the Rainiers this year, which was one of his draws as the Mariners look to add versatility to their young group.

Festa, 26, is also capable of pitching multiple innings and has a 6.30 ERA with 13 strikeouts and four walks over 10 innings in eight appearances, including a 1.42 ERA in his last five outings.

Swanson, the Mariners’ No. 9 prospect per MLB Pipeline, will join Tacoma’s rotation and continue working to develop his slider and changeup to offset his fastball.

“I liked a lot of the things he brings to the table,” Servais said. “It’s just the consistency and location of his pitches, giving him an opportunity to regroup. He got hit around a little bit. We certainly saw it last night. He kind of got cornered into some fastball counts, everybody knows that’s his pitch and they got on it. He’ll make a concerted effort to work on the off-speed pitches down there.”

Worth noting

• Seattle claimed right-hander Andrew Moore off waivers from the Giants and assigned him to Double-A Arkansas, with reliever Nick Rumbelow designated for assignment to open a spot on the 40-man roster.

Moore was a second-round Draft pick of the Mariners in 2015 and pitched 11 games (nine starts) for Seattle in ’17. The 24-year-old was DFA’d by San Francisco on Saturday after struggling at the Triple-A level for both the Giants and Rays at Triple-A this year, going 0-3 with a 14.21 ERA in six games (five starts).

Rumbelow, 27, pitched three games in relief for Seattle this year, allowing four earned runs in 1 1/3 innings, then posting a 9.19 ERA in 13 relief outings for Tacoma.

• Kyle Seager went 2-for-4 with a pair of singles while playing five innings at third base in his second rehab game for Tacoma on Thursday as he prepares for a May 25 return from the 60-day injured list following hand surgery in the spring.

• Reliever Sam Tuivailala (Achilles' tendon surgery) will be promoted from Advanced-A Modesto to Tacoma this weekend, according to Servais. Fellow right-hander Gerson Bautista (strained right pec) is also close to being promoted from Modesto to either Double-A Arkansas or Tacoma.