Rolls-Royce Holdings is set to cut 600 jobs in its marine business by the end of 2015, in a bid to reduce costs amid challenging market conditions.In a statement released on Monday, the FTSE 100 group said the reductions will be worldwide, with approximately 50% of the cuts to take place in Norway."It is never an easy decision to propose reductions in our workforce, but it is a sign of the challenging market in which we operate," said Mikael Makinen, president of Rolls-Royce's marine division.Rolls-Royce shares were down 0.59% to 1,007.00p at 12:29 on Monday.