LB 12-153 - Spatial patterns of pink lesions on the massive coral Porites spp. during 2 outbreaks in Moorea, French Polynesia suggest a potential link to anthropogenic stress

Background/Question/Methods:

Infection outbreaks can alter ecosystem services and function, and evidence suggests outbreaks may be increasing in marine systems. Thus, understanding spatial patterns of infection and associated factors that may promote outbreaks is increasingly important in the Anthropocene. Coral in the genus Porites responds to infection by forming raised pink polyps. In July 2016 and 2021, we observed an outbreak of pink lesions (PL) on coral on the north shore of Moorea, French Polynesia. We quantified spatial patterns in prevalence and dispersion patterns of PL on individual coral colonies. We surveyed the north shore fringing and back reefs and the two bays with developed watersheds. We specifically quantified dispersion by choosing a high prevalence site and determined the infection patterns using Morisita’s index. We hypothesized there is a gradient of infections, with prevalence and dispersion is greater in the bay and decreasing with distance from human impacts along the north shore.

Results/Conclusions:

In both years, prevalence was highest in the bays and decreased with distance from the bays. At low and medium prevalence sites in 2016, 15-20% of colonies had PL compared to 11% in 2021, while high prevalence sites exceeded 90% infected in both years. Overall, aggregation decreased with prevalence, with the low prevalence site highly clustered and the high prevalence site randomly dispersed. Thus, it is unlikely for a colony to be heavily infected unless surrounded by infected colonies. At one impacted site, prevalence was higher in 2021 than in 2016, which could infer that human development has worsened conditions in that area or outbreak cycles along the northern shore can be site dependent. Overall, our results imply PLs in Porites of Moorea are linked to anthropogenic stressors from developed watersheds, which contrasts with patterns found in other reef systems where infection tends to be higher in pristine sites. One possible explanation for this contrast is that the infections are from trematodes and snail densities (intermediate host) may be higher in human impacted sites in Moorea. Understanding the cause of these contrasting results may further our understanding of the drivers of this coral infection’s dispersion, density, and its' host susceptibility.