Corals sustain growth but not skeletal density across the Florida Keys Reef Tract despite ongoing warming

Abstract

Through the continuous growth of their carbonate skeletons, corals record information about past environmental conditions and their effect on colony fitness. Here, we characterize century-scale growth records of inner and outer reef corals across ~200 km of the Florida Keys Reef Tract (FKRT) using skeletal cores extracted from two ubiquitous reef-building species, Siderastrea siderea and Pseudodiploria strigosa. We find that corals across the FKRT have sustained extension and calcification rates over the past century but have experienced a long-term reduction in skeletal density, regardless of reef zone. Notably, P. strigosa colonies exhibit temporary reef zone-dependent reductions in extension rate corresponding to two known extreme temperature events in 1969-1970 and 1997-1998. We propose that the subtropical climate of the FKRT may buffer corals from chronic growth declines associated with climate warming, though the significant reduction in skeletal density may indicate underlying vulnerability to present and future trends in ocean acidification.

Evidence for a biological source of widespread, reproducible nighttime oxygen spikes in tropical reef ecosystems has implications for coral health

“…As discussed in the introduction, coral have also previously been DO spikes presented in this study at this time. Increased calcification could also be a response to hypoxia, as suggested by Wooldridge respiration similar to those in our study and speculated that a link between increased calcification 2014; Rippe et al, 2018). Calcifying red and green algae (e.g., CCA) are also known to use the hypoxic stress and then give way to more drastic reductions in metabolic activity, similar to the 7 2 6 general response curves described by Nelson and Altieri (2019).…”

Nearshore coral growth declining on the Mesoamerican Barrier Reef System

“…To validate the use of linear extension as a proxy of coral calcification in this study, skeletal density and calcification rate were also calculated for all cores collected and CT scanned in 2015 ( n = 68 cores). Coral density standards of known mass and volume were obtained from coral cores with the same diameter as those used in the study and scanned alongside the corals to construct a standard curve for each scanning session that correlated Hounsfield unit values (CT scan output) to density (g/cm 3 ; DeCarlo et al, ; Rippe et al, ). In this study, extension rate was well correlated with calcification rate ( p < .001, R 2 = 0.919 for S. siderea and p < .001, R 2 = 0.598 for P. strigosa ), while density is not ( p < .001, R 2 = 0.052 for S. siderea and p < .001, R 2 = 0.002 for P. strigosa ; Figure S2).…”

“…The entire length of the core was analyzed in this manner, or until it was no longer possible to resolve annual growth bands due to the effects of bioerosion and/or loss of seasonal density banding. Additional details on this methodology, including example images of coral CT scans, can be found in Figure S1 and in Rippe et al (2018). Data for the individual cores analyzed in this experiment, including length of each growth record, are provided in Table S1.…”

“…This mixed effects modeling approach was employed to address the inherent hierarchical nature of coral skeletal extension data. See Castillo et al (2011) and Rippe et al (2018) for further details on the advantage of this approach with respect to interpreting coral extension data.…”

“…Statistical analyses were carried out using the nlme package (Pinheiro et al, 2017) CIs were used to identify slopes that were significantly different from zero (Figures 2 and 3; Tables S3 and S4). This method has previously been utilized to analyze coral core data (Barkley & Cohen, 2016;Castillo et al, 2011;Rippe et al, 2018) and has been shown to be sensitive enough to assess significant differences between small slopes (on the order of 10 -3 cm/year) and zero (Castillo et al, 2011).…”