Mean turf cover gains exceeded macroalgal cover gains 3–5 years after large coral losses at 52 Great Barrier Reef reefs

We tested which algal groups increased after large hard coral losses in AIMS Long-Term Monitoring Program data. We selected each reef's first observed loss of at least 50%, from starting coral cover of at least 10%, across a survey gap of at most 2.5 years. Fifty-two reefs had 70 surveys three to five years later. Loss surveys were in 1997–2019 and follow-up surveys were in 2001–2023. Each reef had equal weight. Mean turf cover rose by 15.43 percentage points. Its 95% interval from resampling eight geographic sectors was 10.29 to 21.78 points. Conservative source-category bounds placed the mean macroalgal rise between 1.27 and 1.41 points. Turf change exceeded the upper bound for macroalgal change by 14.02 points, with a sector interval of 9.00 to 19.82. Mean coral cover was 34.05% before loss, 9.46% at loss, and 14.41% later. The larger turf gain remained under all nine fixed rule changes. These observed sequences do not identify a cause, establish a stable state, or rule out short macroalgal blooms between visits. The package preserves code, source URLs and hashes, aggregate results, figures, independent checks and exact-repeat instructions. Exact source data and reef-level tables are retained separately under their original terms.

coral reefs · turf algae · macroalgae · benthic cover · Great Barrier Reef · reproducible research · ecological change