Chen Carla C M, Bourne David G, Drovandi Christopher C, Mengersen Kerrie, Willis Bette L, Caley M Julian, Sato Yui
Australian Institute of Marine Science, Townsville, QLD, Australia.
ARC Centre of Excellence for Mathematical & Statistical Frontiers, Queensland University of Technology, Brisbane, QLD, Australia.
PeerJ. 2017 Jun 12;5:e3438. doi: 10.7717/peerj.3438. eCollection 2017.
Seawater temperature anomalies associated with warming climate have been linked to increases in coral disease outbreaks that have contributed to coral reef declines globally. However, little is known about how seasonal scale variations in environmental factors influence disease dynamics at the level of individual coral colonies. In this study, we applied a multi-state Markov model (MSM) to investigate the dynamics of black band disease (BBD) developing from apparently healthy corals and/or a precursor-stage, termed 'cyanobacterial patches' (CP), in relation to seasonal variation in light and seawater temperature at two reef sites around Pelorus Island in the central sector of the Great Barrier Reef. The model predicted that the proportion of colonies transitioning from BBD to Healthy states within three months was approximately 57%, but 5.6% of BBD cases resulted in whole colony mortality. According to our modelling, healthy coral colonies were more susceptible to BBD during summer months when light levels were at their maxima and seawater temperatures were either rising or at their maxima. In contrast, CP mostly occurred during spring, when both light and seawater temperatures were rising. This suggests that environmental drivers for healthy coral colonies transitioning into a CP state are different from those driving transitions into BBD. Our model predicts that (1) the transition from healthy to CP state is best explained by increasing light, (2) the transition between Healthy to BBD occurs more frequently from early to late summer, (3) 20% of CP infected corals developed BBD, although light and temperature appeared to have limited impact on this state transition, and (4) the number of transitions from Healthy to BBD differed significantly between the two study sites, potentially reflecting differences in localised wave action regimes.
与气候变暖相关的海水温度异常与珊瑚疾病暴发的增加有关，这已导致全球珊瑚礁衰退。然而，对于环境因素的季节性变化如何在个体珊瑚群落层面影响疾病动态，我们知之甚少。在本研究中，我们应用多状态马尔可夫模型（MSM）来研究在大堡礁中部佩洛鲁斯岛周围的两个珊瑚礁地点，从看似健康的珊瑚和/或一个称为“蓝藻斑块”（CP）的前期阶段发展而来的黑带病（BBD）的动态，这与光照和海水温度的季节性变化有关。该模型预测，在三个月内从BBD转变为健康状态的群落比例约为57%，但5.6%的BBD病例导致整个群落死亡。根据我们的模型，健康的珊瑚群落在夏季更容易感染BBD，此时光照水平最高，海水温度正在上升或处于最高值。相比之下，CP大多发生在春季，此时光照和海水温度都在上升。这表明，健康珊瑚群落转变为CP状态的环境驱动因素与转变为BBD的驱动因素不同。我们的模型预测：（1）从健康状态转变为CP状态最好用光照增加来解释；（2）从健康状态到BBD状态的转变在夏初到晚夏更频繁发生；（3）20%受CP感染的珊瑚发展为BBD，尽管光照和温度似乎对这种状态转变影响有限；（4）两个研究地点从健康状态到BBD状态的转变次数存在显著差异，这可能反映了局部波浪作用模式的差异。
