Hurricane Irma Linked to Coral Skeletal Density Shifts on the Florida Keys Reef Tract

Abstract

Coral reefs are at risk due to various global and local anthropogenic stressors that impact the health of reef ecosystems worldwide. The most recent climate models predict that climate change will increase the frequency and intensity of tropical storms. This increased storm occurrence and strength will likely 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 recent studies reveal the chronic impacts of tropical storms on corals, relatively little is known about the effects of major storm events on coral growth and how these effects vary over spatiotemporal scales. Here, I characterize the skeletal growth of two common Caribbean reef-building 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 with storm, species, and reef location as the three factors was used to assess the impact of the storm on each of three growth parameters: skeletal density, linear extension, and calcification rates. 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. However, 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 an understanding of the impacts of tropical storms on coral skeletal growth and offer new insights into how we can employ corals' innate growth capacities to help conserve coral reefs under climate change.

Fig. 1

Inner-outer reef micro-core extraction sites along the Florida Keys Reef Tract. Map of core extraction sites where S. siderea and P. strigosa were obtained. The circles indicate the inner reef sites, while the squares indicate the outer reef sites. Each abbreviation represents the following sites: West Washerwoman (WW) Eastern Sambo (ES), Cheeca Rocks (CR), Alligator Reef (AR), Basin Hills (BH), Carysfort Reef (CF), Bache Shoals (BS), and Fowey Rocks (FR).

Fig. 2

(A–C) Coral annual skeletal growth parameters across reef locations. Annual growth data, skeletal density (A), linear extension (B), and calcification rate (C), are shown for Siderastrea siderea and Pseudodiploria strigosa pre-Hurricane Irma (2009–2016) and post-Hurricane Irma (2017–2018). Each color is coded by species and location combination. Siderastrea siderea/inner (filled triangle) S. siderea/outer (open triangle) P. strigosa/inner (filled diamond); P. strigosa/outer (open diamond). Dashed lines show average trends. The solid black line indicates the year Hurricane Irma transversed in 2017.

Fig. 3

(A–C) “Yearly” Changes in Coral Annual Skeletal Growth Parameters. Some yearly skeletal growth parameters are potentially impacted by hurricane exposure. Yearly skeletal growth parameter changes, skeletal density (A), linear extension (B), and calcification rate (C) are shown for Siderastrea siderea and Pseudodiploria strigosa pre-Hurricane Irma (2009–2016) and post-Hurricane Irma (2017–2018). Each color is coded by species and location combination. S. siderea/inner (filled triangle); S. siderea/outer (open triangle); P. strigosa/inner (filled diamond); P. strigosa/outer (open diamond). Dashed lines show average trends. The solid black line indicates the year Hurricane Irma transversed in 2017.

Fig. 4

(A–D) Visualization of the “Yearly” changes in coral average annual skeletal density across reef locations. Yearly skeletal density is potentially impacted by hurricane exposure. Visualizations of the average yearly skeletal density growth change are given for time (A), species (B), location (C), and species and location (D). Species (S. siderea and P. strigosa )and locations (inner and outer) are listed. .