Due to prolonged exposure to the elements, surfers ear is best described as bony growths (exotosis) of the ear canal, due to the ear trying to naturally protect the ear from continual exposure to water and wind.
In most cases it causes a slight narrowing of the ear canal that does not need medical intervention but can cause some minor issues such as increased likelihood of ear infections (swimmers ear), minor reduction in hearing and the likelihood of a build-up of earwax (cerumen) due to the increasingly small space.
In severe cases the growths can be significant enough that they may be removed surgically.