Karapani, a shining light in the grand final win last year, was slapped with a $1001 fine by Queensland Police and issued with a public nuisance offence in Fortitude Valley at approximately 3.30am on Saturday.
He will miss Saturday night's away clash with Gold Coast as a result.
"It's important everyone knows the standards and culture of this club that we are setting is above any player or person in this organisation," Reynolds said.
"Everyone needs to jump on board or you risk facing some time away from the team.
"Josiah is fully aware of the mistake he has made and is fully apologetic towards the group. I am sure he won't make that mistake again. He is a big part of our team but unfortunately he won't be there this week."
Reynolds said the leadership group got all the facts on Monday morning before making the tough call.
Veteran Ben Hunt, also a part of the leadership group, said when you are a Bronco there is no hiding from bad behaviour.
"It is a huge club here," Hunt said.
"It is still in a way a one-club town. I know the Dolphins are here now but there is so much spotlight on this club.Â
"You go out and you make a mistake and you are going to get found out. There are some boys still learning some lessons and Kara is one of them."
Hunt was also confident Karapani would bounce back.
"I'll back him. He is a good kid and was very apologetic," he said.
"He came in this week and trained as hard as he could. He will keep working hard and will be back in there at some stage."
With winger Grant Anderson out for 10 to 12 weeks with a knee injury, Jesse Arthars has been recalled on the wing and Gehamat Shibasaki moves from the bench to starting centre.
Reynolds said he was "extremely proud" of the way both Arthars and Shibasaki had handled disappointment on the selection front.
"Obviously for Jesse to miss out the back end of last year and the first chunk of this season, he hasn't whinged or carried on," he said.
"He has been super professional in the way he has trained and when he has gone back to Q Cup he has been a leader.
"So too Gehamat. He didn't kick stones. He got on with life and made sure he trained hard and did everything he could possible to get himself back in the frame."
The Broncos have named prop Payne Haas, who missed last week's win over the Dolphins with a shoulder injury. Brisbane train late Wednesday and Hunt said it was a key session for Haas to get through.
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