Two butterflyfish species had opposite count changes at six Moorea sites between 2006–2007 and 2016–2018

We tested whether coral-feeding butterflyfish counts returned as coral cover recovered at six Moorea fore-reef sites. We compared 2006–2007 with 2016–2018 in open MCR LTER data. The primary sample used two fixed transects per site and the same divers in both periods. Mean Chaetodon reticulatus counts fell from 9.29 to 1.92 fish per 250 square metres. Mean C. pelewensis counts rose from 9.25 to 13.50. Both directions occurred at all six sites. Across all focal species, increases offset 59% of the observed decreases. The primary total-count ratio was 0.86. Its 95% site resampling interval was 0.71–1.04; its t interval was 0.65–1.13. The total ratio was 0.64 with 2006 alone as the initial year, but 1.37 with 2007 alone. The two common species kept opposite changes under all nine fixed count rules. Mean stony coral cover rose from 35.05% to 40.76%, but one site had not recovered. This later check agrees with earlier evidence from Moorea that a return of total abundance can conceal a different species mix. It does not establish a lasting total-count deficit or identify a cause. Limits include six fixed sites, short initial and later periods, and uncertain visual detection. The package preserves source data, provenance, complete count grids, all results, code, figures, and independent source-value checks.

Moorea · butterflyfish · coral recovery · species composition · long-term monitoring · baseline sensitivity · open data