Surviving marginalized reefs: assessing the implications of the microbiome on coral physiology and survivorship

Abstract

Coral reefs are undergoing degradation due to overexploitation, pollution, and climate change. Management and restoration efforts require that we gain a better understanding of the complex interactions between corals, their microbiomes, and their environment. For this purpose, Varadero Reef near Cartagena, Colombia, serves as an informative study system located at the entrance of the Bay of Cartagena adjacent to the Canal del Dique, which carries turbid and polluted water into the bay. Varadero’s survival under poor environmental conditions makes it a great study site for investigating the relationship between the microbiome and coral resistance to environmental stressors. To determine whether the microbiomes of Varadero corals differ from those in less impacted sites, we conducted a reciprocal transplant experiment by relocating coral fragments from Varadero as well as a geographically proximate reef that is less affected by plume dynamics (Rosario) across a gradient of turbidity (low, medium, and high). After 6 months of acclimatization, transplanted corals developed site-specific microbiomes that differed significantly from pre-transplant microbiomes, and corals transplanted to the highly impacted site from both Varadero and Rosario site saw higher mortality and an increase in overall microbial diversity. In combination with physiology and survivorship outcomes pointing to a limit in the corals’ photoacclimative capacity, our results indicate that, rather than surviving, Varadero Reef is experiencing a slow decline, and its corals are likely on the brink of dysbiosis. With continued anthropogenic interference in marine environments, sites such as Varadero will become increasingly common, and it is imperative that we understand how corals and their microbial symbionts are changing in response to these new environmental conditions.

Physiological and ecological consequences of the water optical properties degradation on reef corals

“…This estimation is in close proximity to irradiance variation in other turbidwater reefs due to suspended solids (Anthony et al 2004). Maximum K d 's were higher compared to previous reports at this site (Pizarro et al 2017;Roitman et al 2020) and other turbid-water reefs (Hennige et al 2010;Omachi et al 2019). The extremes within the K d range of variation indicate that irradiance can vary by up to two orders of magnitude only due to changes in water optical properties attributed to meteorological conditions affecting the Dique plume dynamics (Lonin et al 2004;Tosic et al 2019).…”

Physiological and ecological consequences of the water optical properties degradation on reef corals

“…Extremes within this range indicate that underwater irradiance can vary by up to two orders of magnitude only due to changes in water optical properties. Maximum K d ’s were higher compared to previous reports at this site (Pizarro et al 2017; Roitman et al 2020) and other turbid-water reefs (Hennige et al 2010; Omachi et al 2019).…”

The Microbiome of the Reef Macroalga Sargassum ilicifolium in Singapore

“…The presence of macroalgae can reduce the survivorship of marine larvae, which in turn limits settlement and consequently recruitment, thereby inhibiting the potential of degraded reefs to recover [16]. Similarly, coral-macroalgae interactions can alter the coral microbiome [20], which is essential to the coral host health [21][22][23][24]. Notably, coral-macroalgae interactions on degraded reefs are hypothesized to drive dysbiosis of the coral microbiome [25,26], and macroalgae have been implicated as a source of harmful microbes that reduce the fitness of corals [27,28].…”