Impact of environmental gradients on juvenile coral demography across the Great Barrier Reef and Torres Strait

Demographic rates of juvenile corals are critical to reef recovery, yet their variation across environmental gradients remains understudied. Over three years, we assessed juvenile coral vital rates across the Great Barrier Reef (GBR) and Torres Strait (TS), spanning 14° latitude and diverse inshore to offshore environments. Environmental conditions varied, with annual temperatures ranging 24–28°C, high turbidity in the southern inshore GBR, and elevated chlorophyll a in the southern offshore GBR. Despite these differences, juvenile assemblages of five common coral groups ( Montipora , Acropora , Pocilloporidae, Merulinidae, and Porites ) were broadly similar. Recruitment patterns varied with Acropora highest in southern offshore and central reefs, and Porites in southern offshore and northern reefs. Annual mortality rates were consistent across locations but taxa-specific negative responses to turf height and sedimentation were observed. Net juvenile density increased by 3 m⁻² yr⁻¹, with higher gains for Acropora in southern offshore reefs (3.8 m⁻² yr⁻¹) and Porites in northern offshore reefs (3.5 m⁻² yr⁻¹). Individual survival improved with size, and temperature effects were taxon-dependent – negative for Acropora , neutral for Montipora and Pocilloporidae, and positive for Merulinidae and Porites . Temperature did not correlate with linear growth in any group, but water flow positively influenced growth in most taxa. Fast-growing Acropora and Pocilloporidae showed positive size-growth relationships, unlike slower-growing Merulinidae and Porites . These findings provide baseline demographic data across the GBR and TS, revealing both congruence and divergence with ecological theory. They offer essential input for predictive models, site-specific restoration planning, and evaluating interventions relative to natural background dynamics.