Scotland's college merger programme will have to find more savings in the face of continued funding cuts, the public spending watchdog has warned.
Audit Scotland said the sector's income fell 9% between 2011-12, with further drops in the next two years.
Ministers said savings generated through mergers would protect full-time further education places.
The move has been been strongly criticised by the government's opponents, who said it was flawed.
In a new report, Audit Scotland said that, between 2011-12, cuts included a £56m reduction from the Scottish Funding Council - the college sector's main funding source.
Over the same period, full-time equivalent staff numbers were cut from 12,800 to 11,600, with most reductions falling on teaching staff.
The spending watchdog also said colleges were hitting their targets, but added that a government emphasis on full-time courses had led to a drop in the total number of students, and warned that prioritising learning opportunities for young people could limit opportunities for people older than 24.
Audit Scotland also said the sector's overall finances were "generally sound", with a small surplus of £2.2m.
But Scotland's Auditor General, Caroline Gardner, added: "Income has fallen significantly and this will continue for the foreseeable future.
"Colleges will have to manage these funding reductions and changes in structure and status while meeting local communities' demands for further education."
The Scottish government welcomed the report, adding: "The report confirms colleges are continuing to deliver our commitment to maintain student numbers with full-time equivalent student numbers remaining steady.
"This strong record of achievement is a result of the Scottish government's commitment to our colleges.
"They are at the heart of our aims for economic growth and this is reflected in the addition of £61m to the sector earlier this year, providing for an unprecedented funding 'floor' of £522m this and next year."
In 2011, there were 37 incorporated colleges in Scotland, serving 258,000 students.
The merger programme will reduce the number to 21, under 13 new regions, by the end of the year.
Labour, the Conservatives and the Liberal Democrats have previously accused the government of forcing colleges into "shotgun marriages" and seeking to diminish the independence of the sector.