João Ribas, the museum’s artistic director, handed in his resignation on Friday saying he was “no longer able to lead the institution,” the Público newspaper reported.
According to Público, Mr Ribas stepped down after the administration decided to restrict access to the exhibition to anyone under the age of 18, with some of Mapplethorpe’s works having been removed for being sexually explicit.
The exhibition, which was inaugurated on Thursday, includes 159 works from the artist’s career, from early polaroids to images of flowers, nudes, sexuality and portraits of notable artists including Patti Smith and Iggy Pop.
A notice at the exhibition’s entrance advises visitors of the sexual nature of the images.
The board of directors of the Serralves Foundation said they did not take down any works of the 159 selected by Mr Ribas.