SEATTLE -- Triple-A Tacoma and Double-A Arkansas have been invited to remain the Mariners’ top Minor League affiliates in 2021, but the rest of the club’s farm system will undergo changes under the new MLB player development structure that was announced Wednesday.

The Mariners extended invitations to four communities under the new plan, including the Everett AquaSox as the Class A Advanced affiliate and the Modesto Nuts as the Class A club.

The biggest change would be Everett’s jump from a Class A Short Season club to a full-season affiliate, which means that instead of the previous 76-game schedule starting in mid-June, the AquaSox will play a 140-game slate running from early April to early September.

The move will give Mariners fans in Western Washington an even greater chance to see the club’s top prospects in action. As a Short Season club, Everett’s roster previously was filled primarily with players just drafted out of college or young prospects making the first step up from the Rookie Leagues.

The AquaSox will now feature more developed prospects playing a full season at Funko Field, about 25 miles north of Seattle.

The move also gives the Mariners another nearby club to send Major League players for injury rehab assignments in the first half of the season.

Modesto had been Seattle’s Class A Advanced franchise, but it has been invited to return as the Class A club. The Nuts have been associated with Seattle since 2017, when the Mariners purchased a majority share of the California League franchise.

“We are pleased to invite these four great communities to continue to work with us to develop the next generation of Mariners players,” general manager Jerry Dipoto said in a statement.

Under the new format, the Mariners are no longer affiliated with the West Virginia Power, which was their Class A club the past two years in the South Atlantic League. But they retain their longtime associations with Everett and Tacoma, which have been Mariners affiliates since 1995.

Arkansas and Modesto have been Mariners affiliates since 2017. The Mariners will also continue to have Rookie League teams in Arizona and the Dominican Republic.