Skeletal Density Shifts in Corals Exposed to Hurricane Irma on the Florida Keys Reef Tract

Background/Question/Methods

Coral reef health is at risk due to various global and local stressors. Recent climate models predict that climate change will increase the frequency and intensity of hurricanes. This increase will compromise coral reef structures and habitats for reef-dwelling organisms, including across the Florida Keys Reef Tract (FKRT), the most extensive tropical reef system along the US coast. While several studies reveal the chronic impacts of hurricanes on corals, little is known about the direct effects of hurricanes on coral growth and how these effects vary over spatiotemporal scales. Here, we characterize the skeletal growth of two common mounding coral species, Siderastrea siderea and Pseudodiploria strigosa, before and after Hurricane Irma, to investigate the storm’s impact on coral skeletal growth on inner and outer reefs of the FKRT. Coral cores were extracted from both species at four inner and four outer reef sites in May 2015, before Hurricane Irma struck the Florida Keys in September 2017. Subsequently, 33 micro-cores were collected in May 2019, two years after the storm traversed our previously-cored coral colonies. A three-way ANOVA model was used to assess the impact of the storm on each of three growth parameters: skeletal density, linear extension and calcification rates.

Results/Conclusions

Results reveal no difference in the coral annual skeletal growth parameters pre- and post-Hurricane Irma, although previously quantified differences in these growth parameters across species and location were observed. We found that some growth parameters were impacted by species, location, and the species and location interaction on the FKRT. Further analysis of the ‘yearly’ change in annual skeletal growth parameters showed significant differences in skeletal density across groups before and after Hurricane Irma, but not for linear extension and calcification rates. Our findings improve understanding of the direct impacts of hurricanes on coral growth and offer new insights into how we can employ corals’ innate growth capacities to help conserve coral reefs under climate change.