Dynamics and drivers of coral disease on Indo-Pacific reefs

Haapkylä, Jessica (2011) Dynamics and drivers of coral disease on Indo-Pacific reefs. PhD thesis, James Cook University.

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Coral reefs are currently declining worldwide and coral diseases have been recognised as a major contributor to this pattern. This thesis investigated the dynamics and potential environmental drivers of coral diseases on reefs spanning 20 degrees of latitude in the western Pacific: equatorial reefs in the Wakatobi Marine National Park (WMNP), South-East Sulawesi, Indonesia; Magnetic Island reefs in the central Great Barrier Reef (GBR) Marine Park, Australia; and Heron Island reefs in the southern GBR Marine Park.

Surveys conducted in the WMNP revealed that both disease prevalence and the numbers of diseases affecting corals increased between 2005 and 2010. Disease progression rates were comparable to those found in the Caribbean and on the GBR, indicating that diseases may have serious impacts on coral populations in the WMNP. Similar numbers of coral taxa were recorded as diseased in the WMNP and at Heron Island, with species of staghorn Acropora being the most susceptible group at both locations. In the WMNP, high sedimentation rates may have increased disease prevalence at the site with the greatest disease prevalence in 2007. At this site, a dramatic decline in coral cover from 75% in 2007 to 18% in 2010 was documented, with six diseases: Porites ulcerative white spots syndrome (PUWS), ulcerative white spots (UWS), growth anomalies (GA), skeletal eroding band (SEB), white syndrome (WS) and black band disease (BBD) present in 2010. Highly significant decreases in coral cover between 2005 and 2007 at all sites in the WMNP demonstrate that even reefs in this remote area of the Coral Triangle are experiencing deteriorating coral health mainly due to the over-exploitation of marine resources which is likely to have significant impacts on this global biodiversity hot spot. Although both the prevalence and number of coral diseases have increased, the overall disease prevalence still remains low in the WMNP.

Disease prevalence was generally higher on Heron Island reefs than in the WMNP. A total of six coral diseases were found at Heron Island with brown band (BrB), UWS and GA being the most abundant. The prevalence of UWS was higher in the Austral summer, whereas, for the first time, a higher prevalence of BrB was detected in the Austral winter. No clear seasonal trend in GA prevalence was detected, but prevalence increased over the 3 years of the study. Disease prevalence on Heron Island reefs was dependent on the coral community composition, with sites having high abundance of staghorn Acropora and platelike Montipora experiencing the highest levels of disease prevalence. Diseases were most common at sites with intermediate host coral cover in comparison with sites with high coral cover. A shift in the coral community structure was observed from a community dominated by tabular Acropora in 2007 to a community dominated by Goniastrea, bushy Acropora, Coscinarea and Stylophora in 2009. Since the surveys were conducted half-yearly, it is not possible to conclusively attribute this shift to disease, highlighting the importance of regular long-term monitoring to detect change in reef ecosystems.

A two-year study of environmental drivers of the coral disease atramentous necrosis (AtN) was conducted at two sites around Magnetic Island, an inshore fringing reef. At the study sites, AtN primarily affects the plating coral Montipora aequituberculata. The abundance of AtN was strongly negatively correlated with low salinity and strongly positively correlated with particulate organic carbon. A weaker positive relationship was observed between AtN abundance and seawater temperature, as recorded 7 days prior to and including the sampling date. An aquarium-based study investigating the impacts of salinity and temperature on AtN rates of progression provided corroborative evidence of the importance of these two environmental parameters in driving disease dynamics in the field. The highest mortality rates caused by AtN were recorded in the high temperature (32°C) and low salinity (20) treatments. Results from both the field and experimental studies highlight the importance of the combined impacts of high temperature and low salinity, conditions that prevail typically in the austral summer, as important environmental drivers of AtN.

The results of this thesis demonstrate the important role that coral diseases have in altering reef ecosystems and the potential they have to lead to phase shifts. Identifying drivers of disease help in implementing more effective management strategies that will aim to protect coral reefs as this ecosystem will be subject to increasing stress levels in the future due to climate change.

Item ID: 29250
Item Type: Thesis (PhD)
Keywords: Wakatobi Marine National Park (WMNP); South-East Sulawesi, Indonesia; Magnetic Island reefs; Heron Island reefs; coral disease; disease prevalence; phase shift; environmental drivers; salinity; temperature; Great Barrier Reef; GBR; Coral Triangle
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Haapkyla, Jessica, Unsworth, Richard K.F., Seymour, Adrian S., Melbourne-Thomas, Jessica, Flavell, Mike, Willis, Bette L., and Smith, David J. (2009) Spatio-temporal coral disease dynamics in the Wakatobi Marine National Park, South-East Sulawesi, Indonesia. Diseases of Aquatic Organisms, 87 (1-2). pp. 105-115.

Chapter 3: Haapkylä, J., Melbourne-Thomas, J., Flavell, M., and Willis, B.L. (2010) Spatiotemporal patterns of coral disease prevalence on Heron Island, Great Barrier Reef, Australia. Coral Reefs, 29 (4). pp. 1035-1045.

Chapter 4: Haapkylä, Jessica, Unsworth, Richard K.F., Flavell, Mike, Bourne, David G., Schaffelke, Britta, and Willis, Bette L. (2011) Seasonal rainfall and runoff promote coral disease on an inshore reef. PLoS ONE, 6 (2). pp. 1-10.

Date Deposited: 11 Oct 2013 04:11
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 100%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments @ 100%
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