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.

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