Turbidity gave no clear reduction in the heat response of coral bleaching in three oceans in 2002-2019

We tested whether site mean turbidity reduced the link between heat stress and coral bleaching. We used repeated Reef Check surveys from the Global Coral-Bleaching Database, version 2. The pooled model used 5,424 site-month records at 1,191 sites in 2002-2019. It controlled for site, ocean-year, ocean-month, and depth. The heat slope changed by -1.99 percentage points per four degree-heating weeks for each +0.05 per metre of turbidity. Its nominal 95% interval was -5.56 to +1.58. All six ocean-period intervals included zero after correction for six tests. Indian Ocean estimates were positive but changed with model and timing controls. No sensitivity test showed a common protective interaction across all samples. Small region counts, selected surveys, mean optical exposure, and unmeasured site response differences limit inference. This is not evidence that turbidity has no effect. It does not measure air pollution or establish a causal climate effect. The package contains the derived panel, code, source hashes, all estimates, figures, and reproduction checks.

coral bleaching · turbidity · heat stress · observation bias · regional replication · null result