Month-matched heat slope contrasts included zero in four Atlantic and Pacific coral samples in 2003-2019

We compared coral bleaching slopes for heat changes within reefs and heat differences between reefs. We used 5,336 repeated-site monthly records from Reef Check in two oceans and two periods. Full decompositions included heat, depth, survey year and calendar month. The within-minus-between slopes were -11.24 bleaching points per four TSA degree-heating weeks in the later Atlantic sample and +2.85 in the later Pacific sample. Four-test intervals excluded zero under country, year and ecological-region error groups. Both early-period intervals included zero. After the same-calendar-month rule, all four intervals included zero. Restricting the records alone also removed the two clear contrasts. The data therefore do not isolate survey timing as their cause. Selected visits, missing reports, sparse high heat and unmeasured reef changes limit inference. These results do not establish a climate-change, pollution or adaptation effect.

coral bleaching · heat stress · observation bias · within-between model · survey timing