Pink line disease (PLD) is characterized by linear, annular, circular or irregular band of pink pigmented tissue separating recently killed skeleton and normal tissue. Generally, the line of recently denuded tissue is very narrow, up to about 2-3 mm in width. It progresses relatively slowly (a few mm per month) but can persist for years. The discoloured tissue may also be blue, light brown or purple. In some cases it may be associated with a cyanobacteria or fungus.
An example of a very narrow band, consisting of a ring that is progressively expanding in size is shown in the upper right. The colony in the lower left has a wider area of affected tissue, recently denuded skeleton colonized by filamentous algae and the presence of a cyanobacterial mat forming a narrow band separating previously denuded skeleton and the affected tissue.
PLD is only reported to affect massive and branching colonies of Porites.
It is important to note that pink-coloured pigmentation observed in Porites can be caused by many factors, including injuries and abrasions, fish bites, and infestation by trematodes (see Trematodiasis).