The most immediate impact of the trade is that it clears a 40-man roster spot, one the Dodgers might need for when they make their reported signing of Yaisel Sierra official.
The club was running out of spots for Wieland, who the Dodgers acquired in December 2014 as part of the Yasmani Grandal / Matt Kemp trade with the Padres. Wieland, in his first full season in four years in 2015 — after Tommy John surgery in July 2012 and arthroscopic elbow surgery early in 2014 — was 10-5 with a 4.59 ERA in 22 games with Triple-A Oklahoma City, including 21 starts, striking out 92 and walking 25 in 113⅔ innings.
Wieland, who turns 26 on Jan. 21, made two starts with the Dodgers in 2015, allowing eight runs on 10 hits in 8⅔ innings, with five walks and four strikeouts. The club avoided salary arbitration with Wieland in December, signing him to a one-year, $590,000 contract for 2016.
The Dodgers already have a full major league rotation with Clayton Kershaw, Scott Kazmir, Kenta Maeda, Brett Anderson and Alex Wood, plus have Hyun-jin Ryu angling for an April return after missing 2014 with shoulder surgery. There is also Mike Bolsinger, Carlos Frias and Brandon Beachy, all of whom could be sent to Triple-A if needed.
Then there are the prospects, all of whom have at least a shot at some sort of claim on a potential rotation spot in Oklahoma City, including Zach Lee, Jharel Cotton, Frankie Montas and Ross Stripling, and that's just on the 40-man roster. The club's two top pitching prospects, Julio Urias and Jose De Leon, will likely be in Triple-A much sooner than later.
Whatever number Wieland was in that logjam, he likely moved up relatively on his new organizational depth chart.
In Mejia, the Dodgers get a speedy infielder who has seen time at both shortstop and second base in the Seattle system. The Dominican infielder, who turned 21 in November, hit .282/.346/.339 in 51 games in 2015, the bulk of which (36 games) came at low Class-A Everett in the Northwest League.
Mejia stole 20 bases in 21 attempts in 2015, and in the last two seasons has stolen 33 bases in 36 attempts in 80 minor league games.
The 5'11, 155-pound switch-hitter has just one home run in 528 professional plate appearances, hitting .273/.353/.362 in 134 games. He has fared a little better from the right side against left-handed pitching, to the tune of .276/.341/.417 in 177 plate appearances.
Mejia was rated by Baseball America as the No. 28 prospect in the Mariners system heading into 2015. Their 2016 Seattle rankings haven't been published yet, due out on January 22.
Baseball Prospectus did not list Mejia among their top 10 Mariners prospects in December.