Apparent timing of density banding in the Caribbean coral Siderastrea siderea suggests complex role of key physiological variables

Abstract

Skeletal growth bands in massive reef-building corals are increasingly used as proxies for environmental records despite an incomplete understanding of their formation. While the bands are known to arise from seasonal changes in light and temperature, conflicting reports about the timing of constituent high- and low-density growth bands have complicated the dating and interpretation of environmental signals recorded in corals’ growth histories. Here, we analyze 35 Siderastrea siderea cores extracted from inshore and offshore reef zones along the Florida Keys Reef Tract to investigate potential drivers of banding variability in this species. A previously proposed model of banding variation is applied to assess its potential to explain band timing in S. siderea. Colony growth characteristics and the timing of band deposition were obtained from the cores via computed tomography and were coupled with tissue thickness measurements and gender identification. Apparent time difference, or the perceived lag in coral growth response to changes in environmental conditions, was quantified for each coral core. Results suggest that linear extension, tissue thickness, and gender together do not fully explain the timing of band formation in S. siderea and therefore do not fully resolve the density patterns observed within this species. This finding suggests that other factors yet to be identified are partially determining the formation and appearance of density bands in S. siderea. The continued characterization of banding variability on scales ranging from the individual colony to entire reef systems will enrich our understanding of both coral growth and the environmental conditions to which corals are exposed.