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Ulcerative White Spot Disease (UWS)


Ulcerative White Spot Porites spp.
Notes: Multifocal lesions without tissue that are coalescing (arrow).
Photo: Andrew Bruckner;


Ulcerative White Spot Porites spp.
Notes: Several lesions have coalesced and areas without tissue are being colonized by filamentous green algae (arrows).
Photo: Andrew Bruckner


Ulcerative White Spot (small white spots) Porites spp.
Notes: The colony is also affected by White Syndrome (large, central focal lesion).
Photo: Andrew Bruckner


Ulcerative White Spot Porites spp.
Notes: Multifocal lesions scattered across the colony.
Photo: Andrew Bruckner

Ulcerative White Spot Disease identification

UWS includes lesions first described on Porites as Porites ulcerative white spot (PUWS) and more recently similar white spots (UWS) on other taxa. The disease is characterized by one or more small circular to irregular areas of bleached tissue that is still living or bare white skeleton. The lesions are generally less than 5 cm diameter, progressing to multifocal patterns of tissue loss.

Lesions typically start as discrete, bleached, round foci, 3 to 5mm in diameter, affecting 3-5 polyps. Affected regions may still be alive, but over time bleached tissue may progress to full tissue ulcerations devoid of living tissue. Occasionally, the lesions coalesce and can cause whole colony mortality. In other cases full colony recovery may occur.

Lesions with signs that are similar to UWS can be caused by fish bites. Parrotfish lesions can be distinguished by the presence of skeletal damage, while the tubelip wrasse, Labrichthys unilineatus will remove tissue without damaging the skeleton.

  • Note: Early stages of UWS, characterized by the presence of bleached, but living tissue would be characterized as colour change, loss of pigmentation in the level 1 diagnosis.

Ulcerative White Spot Disease and monitoring effort over time

Global occurrence of UWS