Spatial and Temporal Patterns of Australian Subtropical White Syndrome at East Australian Reefs: Host Range, Prevalence, and Progression of Tissue Necrosis

Australian subtropical white syndrome (ASWS) has been observed affecting dominant coral species on subtropical reefs throughout northern New South Wales since 2000. Using replicate two metre belt transects, spatial and temporal patterns of ASWS prevalence were determined at three locations between 29.5 - 31.5°S; Solitary Islands Marine Park (SIMP), Lord Howe Island (LHI) and South West Rocks (SWR). Additionally, within the SIMP, photographic methods were employed to monitor 90 stressed coral colonies, from five common species, through time. Australian subtropical white syndrome was observed at all locations investigated, including LHI, which lies approximately 600 km east of mainland Australia. Disease prevalence ranged between 0.38 - 9.88% and was highest at the most southerly mainland location, SWR. Thirty-three corals species from six families (26% of all species present at the study locations) were observed with ASWS-like signs over the duration of the study. Dominant coral species were more susceptible to ASWS, with 'Turbinaria' spp. more affected at reefs adjacent to mainland Australia, and 'Acropora' spp. more susceptible at LHI. Prevalence of ASWS within the SIMP was significantly higher during summer compared to cooler seasons, and there was a significant concordance between coral density and prevalence of disease at this location. Patterns in disease prevalence showed a clumped distribution, which is suggestive of an infectious disease. Rate-of-spread of disease through affected colonies also followed seasonal patterns with significantly more coral tissue loss occurring during summer months. Recurrence of ASWS was observed and, through time, led to the complete mortality of 40% of the monitored colonies. Transmission of ASWS was observed in situ between colonies of the same species, between species within a genus and between genera. Finally, results from this study indicate that ASWS is a chronic stress that, through time, may lead to the loss of dominant subtropical corals along the east coast of Australia.