Cays on the Great Barrier Reef (GBR) are dynamic low-lying carbonate sedimentary landforms that adopt various morphologies in response to the complex interplay between physical processes and sediments. This study presents a preliminary analysis of the drivers which most strongly influence cay morphodynamic activity. Focusing on two contrasting examples from the GBR, a small unvegetated cay (Taylor Cay) and a large, vegetated cay (Masthead Island), we assessed cay morphodynamic activity against geomorphic variables and variables associated with exposure to energy. We found significant (p < 0.05) negative correlation between cay activity and significant wave height and maximum annual days of cyclone exposure, and positive correlation with geomorphic predictors (average cay area, length, width and volume). The outcomes indicate that cays are most geomorphologically active when exposed to greater hydrodynamic energy over the tidal cycle. Geomorphic characteristics including larger size can buffer against shoreline perturbations driven by hydrodynamic energy exposure. Thus, more vulnerable cays can be identified and prioritized for management using the quantitative spectrum of drivers of cay morphodynamic activity.