The smooth, rich notes that filled the air Wednesday in Monument Square hinted that this was no ordinary street musician playing the tenor sax as locals perused the day’s offerings at the Portland farmers market.

Blowing into his horn was 72-year-old Jamaican Glen DaCosta, a former member of legendary reggae act Bob Marley & The Wailers. You can hear him on six Marley albums, and he was with the group on the 1979 “Survival” Tour.

As the clouds gave way to lunchtime sunshine, DaCosta picked up his horn and played his original song “You’re My Everything (The Prayer),” a mid-tempo piece that exploded at the end with high notes.

“He’s excellent. He’s had a lot of people come up to him and ask about his music,” said Austin Chadd of Cape Elizabeth. Chadd’s Green Spark Farm was selling vegetables next to where DaCosta played, and he was surprised to learn that DaCosta was reggae royalty.

“Really? That’s amazing. I’m always listening to reggae. That’s awesome,” Chadd said.

But what on earth was the musician doing busking in Portland?

“It keeps me in tune musically, and it’s good exposure,” said DaCosta, who considers himself a people person, making the busy square an ideal venue. “If people hear me play they’ll support me and come see me again.”

The story begins with Maine pianist and singer-songwriter Kate Schrock, who met DaCosta in 2003 when both were performing in Kentucky.

“He was on tour with The Wailers, and Glen walked in on my sound check and ended up staying for the show,” Schrock said. “We were instant buds.”

DaCosta invited her to Jamaica to help him finish a project, for which she provided backing vocals and percussion.

In 2006, Schrock was preparing to record her “Invocation” album and invited DaCosta to play on it. They recorded some of the cuts in Jamaica. DaCosta’s flute and saxophone can be heard on all but one song on the album.

“He’s one of my best friends, and we help each other through rough waters and to stay on track creatively,” Schrock said.

After Marley’s death, DaCosta stayed on as a Wailer through the band’s 1984 “Legend” tour. He rejoined the band in 1999 and has been playing with the group off and on ever since. Wailer Aston “Familyman” Barrett recently contacted DaCosta to enlist his help for an upcoming Wailers record. (For a glimpse of what it was like in DeCosta’s early days as a Wailer, check out YouTube footage of “Bob Marley Live at the Santa Barbara Bowl 1979.”)

DaCosta just wrapped up four performances with Schrock around Maine. They will perform together again Jan. 3 at the St. Lawrence Arts Center in Portland.

Schrock thinks that DaCosta’s Portland busking feeds him musically.

“Playing sax for him is like eating and breathing,” she said. “He gets filled up and it puts some cash in his pocket.”

On Wednesday, there wasn’t an obvious place to put tips, but DaCosta didn’t seem concerned about that as he sang his song “I Really Wonder.”

“We need a world to give us hope, to motivate our children,” he sang. “A world of love and harmony to make things right.”

For a few hours on a Wednesday in Portland, DaCosta and his horn did indeed seem to make things right in Monument Square.

Mindy Pieper, 41, of Portland, who was sampling coffee and cider at a shop near where DaCosta played, said his presence was the kind of thing that makes Portland, and market day in particular, something special.

“I absolutely love it – a random guy out in the square who played with Bob Marley,” she said.