The second chapter of my PhD research is now published in Marine Ecology Progress Series (not open-access, but if you don’t have access through an institution and would like a copy please send me an email and I’d be happy to share a copy!).
Coral reefs are one of the most diverse ecosystems on our planet, but they are facing serious threats from climate change and local human disturbances. This study investigates how these stressors affect coral reefs in the central equatorial Pacific.
The study took advantage of a latitudinal gradient across 4 atolls in the Gilbert Islands, Kiribati, and the Republic of the Marshall Islands, where the frequency of heat stress decreases away from the equator due to the El Niño / Southern Oscillation. We compared the benthic communities at 40 sites across these atolls, representing gradients in local chronic human disturbance and past frequency of bleaching-level heat stress.
We found that the effects of intense, ongoing local disturbance may mask the influence of heat stress on coral reef communities. However, the frequency of heat stress did explain 8.0% of the differences in community compositions across all sites, while local anthropogenic stressors explained 16.2%, and the combined effects explained 7.0%.
We also found that interactions between stressors were multiplicative and acted synergistically to increase the percent cover of macroalgae and a stress-resistant coral called Porites rus. The prevalence of P. rus at locally disturbed sites drives the positive relationship between local stress metrics and live coral cover. However, half of the multiplicative interactions were antagonistic, suggesting that actions that reduce local stressors may help some coral taxa respond to climate stress, but possibly at the expense of other taxa.
Overall, this study highlights the complex interactions between global climate change and local human disturbances on coral reef ecosystems. The findings suggest that reducing local stressors may help some coral taxa respond to climate stress, but a more comprehensive and holistic approach is needed to protect these important ecosystems for the future.
To read more, please download the paper here (or if you would like a copy but don’t have access, please send me an email).
Sara E. Cannon, PhD 