Award: OCE-2048914

Coral reefs sustain biodiversity and provide critical services to humans including food, protection from storms, and tourism valued at over $3.4 billion in the US alone. The growth, function, and survival of corals depends on a consortium of bacteria and other microbes that live symbiotically on and in the surface of corals. These associated microbes are known as the coral microbiome. In this project, we examined how the corals along with their microbiomes respond to a phenomenon of reduced oxygen in seawater known as “deoxygenation”. Deoxygenation can occur naturally in the world’s oceans, but is growing worse due to pollution and fluctuating water temperatures. Relatively little is known about the effects of deoxygenation in the tropics. Studying the effects of deoxygenation on corals and their microbiome is critical because of the value of corals to society, but also because corals can provide general lessons about deoxygenation that are relevant to other ecosystems types worldwide.

 

In our study, we took a multi-pronged approach to understand how corals and their microbiome are responding to deoxygenation. Our approach included monitoring of coral reefs in which we measured oxygen and tracked coral populations and their microbiomes through time, utilizing multiple sites that differ in oxygen concentration for a comparative approach. We also conducted experiments in the field in which we reduced oxygen levels in small portions of reef, and experiments in the lab in which we reduced oxygen levels in aquaria under controlled conditions. We also gathered an interdisciplinary group of experts to better understand the causes and consequences of deoxygenation on coral reefs.

 

We have found that corals species differ in their ability to tolerate deoxygenation, with some species able to survive for weeks in low oxygen conditions that can lead to mortality within days for other species. This limits where some species can live, with less tolerant species restricted to areas where oxygen levels are consistently high. Perhaps surprisingly, deoxygenation does not result in drastic changes to the coral microbiome, whether the corals are tolerant or not. A closer look reveals that there are a few specific microbe species that do show a response to low oxygen conditions. They have physiological functions that seem well suited for low oxygen conditions, which offers a clue to how the microbiome could play a role in the resilience of coral reefs. When we zoom out, we find that oxygen is one of the key factors that ties human wellbeing in coastal communities to the natural environment because it incorporates weather, pollution, and other processes into the health of coral reefs which in turn affects the viability of economic activities including tourism and fisheries. Findings from our study therefore has implications for how we manage coral reef habitats for the benefit of both nature and humans.

 

This project directly supported workforce development opportunities for a postdoc, five graduate students, and 11 undergraduate students who have attained degrees and advanced professionally. Research findings have been featured in scientific publications and dozens of university lectures, national conferences, and international symposia. It has also sparked follow-up projects that will examine the potential for corals and their microbiomes to rebound from deoxygenation events.

 

Last Modified: 07/18/2025
Modified by: Andrew H Altieri