Data and code for: Dietzel et al. Long-term shifts in the colony size structure of coral populations along the Great Barrier Reef

The age or size structure of a population has a marked influence on its demography and reproductive capacity. While declines in coral cover are well documented, concomitant shifts in the size frequency distribution of coral colonies are rarely measured at large spatial scales. Here we document major shifts in the colony size structure of coral populations along the 2,300km length of the Great Barrier Reef over the past two decades. Coral colony abundances on reef crests and slopes have declined sharply across all colony size classes and in all coral taxa compared to historical baselines. Declines were particularly pronounced in the Northern and Central regions of the Great Barrier Reef, following mass coral bleaching in 2016 and 2017. The relative abundances of large colonies remained relatively stable, but this apparent stability masks steep declines in absolute abundance. The potential for recovery of older fecund corals is uncertain given the increasing frequency and intensity of disturbance events. The systematic decline in smaller colonies across regions, habitats and taxa, suggests that a decline in recruitment has further eroded the recovery potential and resilience of coral populations.

Methods
All coral abundance data were collected using line-intercept transects with a hierarchical sampling design. 12 major coral taxa were distinguished

Using intercept lengths as proxy of colony size, long-term changes in size-class abundances and shifts in colony size structure were assessed on reef crests and reef slopes along the Great Barrier Reef.

Further information about sampling design and statistical analyses can be obtained from the corresponding publication.