Sara E. Cannon, PhD

I’m thrilled to share the first publication from my Ph.D. dissertation research, out last month in the open-access journal PLoS One (and available for download here). This paper will be the first chapter of my dissertation, and it’s great to (finally) see it out in the universe!

For this paper, my co-authors (including my advisor at the University of British Columbia, Simon Donner, and our collaborators from Kiribati’s Ministry of Fisheries and Marine Resources Development, Erietara Aram, Toaea Beiateuea, Aranteiti Kiareti, and Max Peter) and I documented how coral reef communities in the Gilbert Islands had changed after experiencing more than a decade of multiple stressors (specifically, two coral bleaching events caused by heat stress — one in 2004-2005 and one in 2009-2010 — and an outbreak of the Crown-of-Thorns starfish, which preys on corals, in 2014). We compared these changes across two neighbouring atolls in the Gilbert Islands of Kiribati, Tarawa and Abaiang. Tarawa, the capital of Kiribati, is home to about 65,000 people (more than half of the population of Kiribati), while its neighboring atoll, Abaiang, has a much smaller population of about 5,500 people.

The paper goes into details about the changes in important reef-building coral taxa over time. However, here I will highlight just two of our key findings that I think are broadly relevant to people interested in coral reefs and climate change, as well as the ways that local activities may interact with climate-driven threats. First, coral reefs in the Gilbert Islands of Kiribati are unique because of their location on the equator in the central Pacific Ocean. During Central Pacific (or Modokai) El Niño events, warm water pools in this region of the Pacific. This means that reefs in the Gilberts are exposed to warmer ocean temperatures more frequently than reefs in other parts of the world, although this may change in the future as the oceans continue to warm. Our study may therefore provide a snapshot of how reefs that do not yet experience heat stress as often as those in the Gilberts might respond to heat stress in the future. This glimpse at the future of coral reefs could give communities that depend on reefs more opportunity to prepare and adapt.

Also, we found that the reefs in Tarawa, which were exposed to higher intensities of local human influences (for example, sedimentation from construction, and pollution and overfishing related to the number of people living there) were less affected by the bleaching events than the less-trafficked reefs in Abaiang. Tarawa’s reefs were less affected by heat stress because the local human stressors had driven a phase shift to a coral community dominated by a single species of ‘weedy’ coral, Porites rus, which thrives in degraded environments. In Abaiang, where the corals experienced fewer and less intense local stressors prior to the bleaching events, the coral reefs were more diverse and home to more sensitive species. As a result, almost all of the coral taxa in Abaiang were wiped out by bleaching events, except for the mounding coral, massive Porites. Unfortunately, many of the massive Porites that survived bleaching in Abaiang were later eaten by the Crown-of-Thorns starfish during the outbreak in 2014, leaving reefs that were mostly covered in short, grass-like algae called turf.

This phenomenon — that coral reefs experiencing more local disturbance may also be more resistant to the impacts of climate change — was first discussed by two scientists I greatly admire, Isabelle Côté and Emily Darling, in 2010 (paper here, open-access). Our paper joins several others since that provide evidence for their arguments, and also adds to their calls to question the ways that we attempt to protect coral reefs in the future. For example, one of the most common ways that people attempt to conserve coral reefs is to reduce the number of local disturbances, through management actions like marine protected areas (MPAs). There is some evidence that MPAs can help coral reefs recover more quickly after bleaching events. However, because MPAs may also make coral reefs more vulnerable to climate impacts in the first place (by encouraging the growth of taxa that are sensitive to heat stress), implementing them could mean sacrificing resistance to bleaching for the sake of recovery (as discussed by Darling and Côté in 2018 here). One thing I am interested in studying in the future is identifying the trade-offs for people who depend on reefs in each of these places; for example, can the reefs in Tarawa, which are now covered almost entirely in the weedy coral P. rus, protect shorelines from erosion as effectively as those in Abaiang? Do they harbour diverse populations of reef fish? Will the answers to these questions change 10 years from now, if reefs in Abaiang are able to recover?

One other thing to note: I strongly believe that the ways that coral reef scientists discuss local human impacts on coral reefs omit integral context. Without this context, it is easy to assume that local people are to blame for degraded ecosystems through their “failure” to protect their resources or address threats like pollution. However, where I’ve worked in the Pacific Islands (and I assume in many other parts of the Pacific and the world more broadly), local degradation was driven by policies put in place during colonization (as detailed briefly in the paper). I hope more non-local scientists will take time to learn and name the historic contexts of the places where we work, to raise awareness of the ongoing impacts of colonialism (as well as our roles in these impacts). After all, if scientists fail to identify the underlying drivers of the environmental problems we aim to address, our attempts to find solutions* will be misguided from the start.

You can read more in our paper here, and the press release from the University of British Columbia here. You can also listen to my radio interview discussing this work with with Simi Sara on CKNW (from August 12, 2021) here, or read an article about our findings here.

_{*although ideally, we will support local efforts to identify and implement solutions rather than attempting to impose them.}