The results of an investigation of a new coral disease affecting Indo-Pacific reefs are
presented. Porites ulcerative white spot disease (PUWS) is characterized by discrete, bleached, round
foci, 3 to 5 mm in diameter, that may either regress or progress to full tissue-thickness ulcerations that
coalesce, occasionally resulting in colony mortality. Monitoring of 25 diseased and 5 healthy refer-
ence colonies for 17 mo revealed that advanced stages of the disease were characterized by lesion
coalescence, partial colony death (i.e. portions of the colony still alive; n = 17) and total colony death
(n = 2). Field transmission experiments revealed that 95% of healthy colonies developed lesions
within 5 wk after continual exposure to diseased branches, while 60% of the reference colonies
remained healthy. The host range of PUWS includes branching and massive Porites spp., and preva-
lence per species was positively correlated with species density. On 10 reefs surveyed in the Central
Philippines, 22 ± 7 % (mean ± SE) of poritid colonies were infected, and the disease was present on
80 % of the surveyed reefs. Poritids are dominant Indo-Pacific reef builders; a disease targeting this
genus could cause major shifts in community structure over time. This report contributes to the lim-
ited knowledge of PUWS impacts in this region.