Human impacts are causing phase shifts from coral- to algal-dominated reefs on a global scale. As these ecosystems undergo transition, there is an increased incidence of coral-macroalgal interactions. Mounting evidence indicates that microbial dynamics play a major role in determining the outcome of these interactions and ultimately shape the benthic community composition. However, little is known about the way in which microbial-mediated biogeochemistry impacts the local environment and eventually shapes the overall community structure of the reef. We utilized a novel combination of methods including calorimetry, flow cytometry, optical oxygen measurements, metabolomics, and metagenomic analysis of both in vitro and in situ coral-algal interactions to examine the effects of microbial metabolism on coral reef ecosystems. Our results demonstrated that the coral-algal interface had a) larger bacterial cells, b) lower oxygen concentration, c) higher heterotroph to autotroph ratio, and d) higher microbial power output (i.e., energy use per unit time), compared to areas distal from the interaction zone. To investigate how these communities increase power output, we analyzed metabolic pathways in metagenomes and metabolomes from in situ coral-algal interactions. These analyses revealed a shift from efficient glycolytic pathways towards faster, less efficient alternative catabolic pathways at the interface. Furthermore, these small-scale, coral-algal dynamics scale up to yield whole-reef-scale changes in microbial community metabolism. Overall, our results indicate that as coral reefs transition to algal dominated systems, there are higher proportions of heterotrophic microbes that are optimizing maximal power output, as opposed to yield. This yield to power shift (i.e., sacrificing efficiency to proceed at faster rates) offers a possible thermodynamic mechanism underlying the transition from coral- to algal-dominated reef ecosystems currently being observed worldwide. As changes in the power output of an ecosystem may be a significant indicator of the current state of the system, this analysis provides a novel and insightful means to quantify microbial impacts on reef health.
Dr Ty Roach is a postdoctoral research associate at the Biosphere 2 and the Hawai'i Institute of Marine Biology. Ty attended North Carolina State University on a varsity wrestling scholarship where he graduated as valedictorian with a triple major in biology, botany, and chemistry, with a minor in genetics. After graduation, he took a few years off from school to surf professionally and intern for the University of North Carolina Institute for Marine Sciences. More recently Ty received his PhD in Cell and molecular biology from San Diego State and University of California San Diego with his dissertation, Nonequilibrium thermodynamics, microbial bioenergetics, and community ecology.
Ty's research looks at how bacteria and viruses affect biogeochemical cycling, energy flow, and community structuring in coral reef ecosystems. Ty also conducts research in theoretical physics, including the application of finite time thermodynamics to biological processes and the calculation of entropy in open, non-equilibrium systems. All in all, Ty employs a systems science approach, combining theory and mathematical modeling with laboratory experiments and field observations, to better understand coral reef ecosystems at scales ranging from molecules to island chains and from microbes to sharks.