Coral reef resilience to climate change
Climate change-amplified marine heatwaves are pushing critical coastal ecosystems beyond their limits.
Over a decade of careful monitoring, we have documented the impacts of a globally unprecedented heatwave on Kiritimati’s corals, reef fishes, habitat complexity and more. We are now focused on understanding how coral reefs recover from such mass mortality events, following all of these reef components as well as the recruitment of new corals. We believe that understanding how global climate change is impacting ecosystems means acknowledging the underlying local anthropogenic stressors to which they are also subjected. On coral reefs, this includes everything from coastal development to overfishing. Our research on Kiritimati takes place across the atoll’s spatial gradient of local anthropogenic impacts, from coral reef sites near villages, the port and other infrastructure to very minimally disturbed ones at the remote end of the atoll. Our work on Kiritimati takes place at our long-term monitoring sites, established in 2007, which include reefs near villages and infrastructure subjected to local anthropogenic disturbances and reefs at the remote end of the atoll that were near-pristine prior to the heatwave. Thus far, we’ve found compelling evidence that corals reefs not exposed to local stressors tend to have greater resilience to heat stress. To learn more check out our Kiritimati website.
Marine heatwaves are increasing in frequency and intensity because of climate change. Over the past decade, our team documented the impacts of a globally unprecedented heatwave on coral reefs in the equatorial Pacific Ocean. We are now working to understand the impacts of that same heatwave on kelp forests along British Columbia’s coastline. Our discoveries are changing understanding of how ecosystems respond to and recover from these events.
Heat stress caused by the 2015-2016 El Niño triggered the 3rd ever Global Coral Bleaching event. Our field site Kiritimati (shown centre of map above, due south of Honolulu) was the epicentre of this event, subjected to bleaching Alerts 1 and 2 for almost a year.
Coral Symbioses and Recovery
Reef-building corals obtain most of the energy they need to survive from single-celled photosynthetic algal symbionts, Symbiodiniaceae, that live inside them. This symbiosis is very sensitive to stress and breaks down under conditions such as warm temperatures (a phenomenon known as ‘coral bleaching’). Susceptibility to bleaching varies between corals, and is significantly shaped by their associated microbes (especially the type of Symbiodiniaceae they host, but also their communities of bacteria, fungi and viruses).
In 2014, we initiated a study to track the fate of over 1000 corals on Kiritimati during the forthcoming El Niño. The 2015-2016 El Niño resulted in a heatwave of globally unprecedented duration on the atoll. We conducted 5 expeditions to the atoll during this heatwave, tracking the tagged corals and studying all aspects of the reef ecosystem, at sites around the atoll subjected to varying levels of underlying local anthropogenic stressors. We continue to monitor the reef and record the recovery trajectory. Our discoveries provide new insights into mechanisms of resilience on coral reefs.
Team members: Kristina Tietjen (Project Manager), Alex van Nynatten (PDF), Daisy Buzzoni (PhD Candidate), Mika de Breuyn (Research Assistant)
Recent publications:
Starko, S., J. Fifer, D.C. Claar, S.W. Davies, R. Cunning, A.C. Baker, J.K. Baum. 2023. Marine heatwaves threaten cryptic coral diversity and erodes associations amongst co-evolving partners. Science Advances. 9:eadf0954. DOI: epdf/10.1126/sciadv.adf0954 | PDF
Claar, D.C., S. Starko, K.L. Tietjen, H.E. Epstein, R. Cunning, K.M. Cobb, A.C. Baker, R.D. Gates and J.K. Baum. 2020. Dynamic symbioses reveal pathways to coral survival through prolonged heatwaves. Nature Communications 11,6097. https://doi.org/10.1038/s41467-020-19169-y | PDF
Reef community and structure during recovery
Healthy tropical coral reefs are composed of many different species of corals, each providing something unique to the reef ecosystem such as shelter for small fish and invertebrates or food for reef inhabitants. The spaces in between corals can be filled in with other important reef species such as macro-algae, turf algae, crustose coralline algae, sponges, and non-living materials such as sand. The health of the reef can be characterized by how much of each there is and in general the more coral there is, the healthier it is. However, rising ocean temperatures and associated coral bleaching and mortality events are causing steep declines in the health of coral reefs around the world. Since 2007, the reef community has been characterized around Kiritimati to monitor the state of the reef and in 2015-2016, an El Niño induced marine heatwave caused a 90% mortality event on Kiritimati. Since then we have been monitoring the reef to see if it recovers and the processes it goes through.
As mentioned above, these rich and varied coral forms provide structurally complex habitat for the many fish and invertebrate species that inhabit tropical reefs. This habitat complexity underpins the ecological functioning of coral reefs and is threatened from climate change. Despite the increased frequency of coral bleaching events, few studies have examined changes in three-dimensional (3D) reef structural complexity following coral mortality. Working in collaboration with John Burns of the Mega Lab, we have used structure-from-motion photogrammetry to construct 3D models of permanent plots at our sites around Kiritimati since before the El Niño and are now characterizing the changes in structure through reef recovery. Check out some of our 3D models on SketchFab.
Team members: Kristina Tietjen (Project Manager), Dominica Harrison (PhD Candidate)
Recent publications:
Maucieri, D.G., S. Starko, and J.K. Baum. 2023. Tipping points and interactive effects of chronic human disturbance and acute heat stress on coral diversity. Proceedings of the Royal Society B. 290:20230209. DOI: 10.1098/rspb.2023.0209 | PDF
Baum, J.K., D.C. Claar, K.L. Tietjen, J.M.T. Magel, D.G. Maucieri, K.M. Cobb, J.M. McDevitt-Irwin. 2023. Transformation of coral communities subjected to an unprecedented heatwave is modulated by local disturbance. Science Advances. 9(14):eabq5615. DOI: 10.1126/sciadv.abq5615 | PDF
Check out our past projects
Kiritimati, Kiribati
We are fortunate to have been able to work with the I-Kiribati on Kiritimati (pronounced ‘Christmas’), in the central equatorial Pacific Ocean for over a decade. Kiritimati is the home of our major field program, and we are deeply committed to the atoll and its people. Between 2009 and 2024 we conducted 17 research expeditions to Kiritimati (3 year hiatus due to COVID-19 travel restrictions).
The world's largest atoll, Kiritimati, has a strong gradient of local disturbances, from its heavily impacted northwest coast where the population is concentrated, to the remote uninhabited end of the atoll, which has some of the world’s healthiest reefs. Our research includes a coupled ecological-socioeconomic monitoring program, that was started by collaborator Sheila Reddy in 2007, and includes 40 monitoring sites around the atoll’s forereefs. During the 2015-2016 El Niño, Kiritimati experienced globally unprecedented heat stress, and suffered mass coral mortality. The atoll is thus an ideal location to study how global climate change and local human disturbances interact to change coral reefs, and to understand what factors will enable reefs to resist and recover from these stressors.
To answer these questions, we study many components of the coral reef ecosystem, from the corals and their associated microbial communities, to the overall benthic community structure and complexity, and the reef fishes and urchins. We work in collaboration with Kiribati’s Ministry of Fisheries and Ministry of Environment, Lands, and Agriculture Development, and with the Cobb Lab, who have also worked long-term on the atoll. We also work with other researchers, including Ross Cunning, Andrew Baker, Becky Vega-Thurber, and John Burns, on the broad array of data we collect on Kiritimati. We encourage you to get in touch if you are interested in collaborating with us.
Key Publications: Baum et al 2023 Science AdvancesMaucieri & Baum 2021 Biological ConservationClaar et al. 2020 Nature Communications; Magel et al. 2020; Claar et al. 2020 Molecular Ecology; Robinson & Baum 2016
Photo: Kiritimati Atoll from space, Google Earth
Photo Credits: Banner photo (Kristina Tietjen), Bottom photo (Baum Lab)