PORTLAND — The state has approved new rules that cut the amount of first-floor space that must be reserved for marine businesses in waterfront buildings.

The city had required that all first-floor space be set aside for marine uses, but the Portland City Council voted in December to reduce that to 55 percent. The rest can be rented to non-marine uses after the wharf owner has made a good-faith effort to find marine-related tenants.

Upper floors may continue to be rented to non-marine uses.

Pier owners had complained that they were unable to rent all their first-floor space to non-marine uses and the lack of tenants cut into revenues needed to help maintain the wharves and buildings.

The state Department of Environmental Protection notified the city that it had approved the modification. The DEP’s review and approval was required because the city’s waterfront zoning falls under state Shoreland Zoning rules.

The approval marks “the beginning of new opportunity for the city’s waterfront,” said Mayor Nicholas Mavadones, who noted that the new rules were developed with input from pier owners, marine businesses and non-marine interests.

Portland’s Central Waterfront Zone stretches from the Maine State Pier to the International Marine Terminal.