UCLA

Coral reefs are vital marine ecosystems increasingly threatened by disease and other lesions of unknown causes. Key knowledge gaps include the distribution, prevalence, intensity of lesions on coral, the identity of the causal agents, and whether human-induced factors influence lesion dynamics. Stony corals in the genus Porites respond to damage by developing small multifocal swollen pink spots (SMSPS). To explore these gaps, I quantified two recent SMSPS outbreaks along the north shore of Mo’orea, French Polynesia using three approaches. Overall, my dissertation furthers our understanding of the factors contributing to SMSPS in the South Pacific with results suggesting SMSPS are linked to human-induced stressors from developed watersheds. I first analyzed spatial patterns of SMSPS on Porites during outbreaks in 2016 and 2021. The highest prevalence and intensity of both outbreaks occurred in human-impacted bays, while SMSPS were less prevalent and intense along the less impacted north shore, suggesting a positive relationship between SMSPS and human influences. The dispersion of SMSPS during the outbreaks was Poisson distributed, likely due to factors such as the life cycles of the causative agents, and selective predation. Second, I documented temporal dynamics of prevalence, intensity, and weekly percentage change in SMSPS during the 2021 outbreak. A four-week photographic time series of affected colonies in the impacted bays revealed SMSPS were consistently in high prevalence and intensity, in all but one site. Further, SMSPS outbreaks consistently increased in intensity in one bay but fluctuated in the other. This has led to several testable hypotheses about the role of ecological factors in outbreaks of SMSPS. Third, I used three methods to identify agents causing SMSPS on Porites. I collected coral samples with lesions over three sampling periods using photography, histology, and tissue squashing. I found that both endosymbiont barnacles and trematodes were in polyps with SMSPS but never in unaffected polyps and that both agents can exist simultaneously within a colony. I made a novel discovery that these agents can coexist within an individual polyp. I also found several unidentified structures in SMSPS that deserve further investigation.