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

Abstract

23Through the continuous growth of their carbonate skeletons, corals record invaluable information 24 about past environmental conditions and their effect on colony fitness. Here, we characterize 25 century-scale growth records of inner and outer reef corals across ~200 km of the Florida Keys 26Reef Tract (FKRT) using skeletal cores extracted from two ubiquitous reef-building species, 27Siderastrea siderea and Pseudodiploria strigosa. We find that corals across the FKRT have 28 sustained extension and calcification rates over the past century but have experienced a long-term 29 reduction in skeletal density, regardless of reef zone. Notably, P. strigosa colonies exhibit 30 temporary reef zone-dependent reductions in extension rate corresponding to two known extreme 31 temperature events in 1969-70 and 1997-98. We propose that the subtropical climate of the FKRT 32 may buffer corals from chronic growth declines associated with climate warming, though the 33 significant reduction in skeletal density may indicate underlying vulnerability to present and future 34 trends in ocean acidification. 35

Nearshore coral growth declining on the Mesoamerican Barrier Reef System

“…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 (). Data for the individual cores analyzed in this experiment, including length of each growth record, are provided in Table S1.…”

“…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).…”

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

“…t Tests and 95% CIs were used to identify slopes that were significantly different from zero (Figures and ; Table S3 and S4). This method has previously been utilized to analyze coral core data (Barkley & Cohen, ; Castillo et al, ; Rippe et al, ) 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, ).…”

Environmental records from coral skeletons: A decade of novel insights and innovation

“…Although such studies have been conducted by gamma densitometry (Lough & Barnes, 1990) for decades (as reviewed by Barnes & Lough, 1996; Lough, 2008, 2010; Lough & Cantin, 2014; Lough & Cooper, 2011), these new approaches permit comparably rapid assessment of multiple tracks along a slab and within 3D coral cores (Figure 2b). Application of these techniques have: (1) determined the effect of warming and ocean acidification (OA) on coral growth (e.g., Cantin et al, 2010; Cooper et al, 2012; Helmle et al, 2011; Mollica et al, 2018; Rippe et al, 2018) and bioerosion (from boring bivalve, worms, and sponges, DeCarlo, Cohen, et al, 2015); (2) identified historical bleaching‐related growth anomalies (Barkley et al, 2018; Barkley & Cohen, 2016; Cantin & Lough, 2014; Carilli et al, 2010, 2012; DeCarlo et al, 2019); (3) estimated bleaching susceptibility (e.g., percentage of the coral community bleached, Barkley & Cohen, 2016; Mollica et al, 2018); and (4) assessed reef recovery following disturbance (Cantin & Lough, 2014).…”