Moderate turbidity did not show a consistent heat buffer in repeat-site coral surveys from 1998 to 2019

We tested whether moderate water turbidity reduced the link between heat stress and coral bleaching. We used repeat-year Reef Check surveys from the Global Coral-Bleaching Database, version 2. The model used 5,974 site-month records at 1,305 sites. It controlled for site, ocean-year, ocean-month, and depth. The heat slope in the published moderate turbidity range was 3.65 percentage points lower per four degree-heating weeks than in clearer water. The nominal 95% interval was -7.45 to 0.15 points. Four separate Atlantic and Pacific period samples did not give a common negative contrast after correction for four tests. The Indian Ocean contrast changed sign under month matching and used few heated records. The pooled contrast remained uncertain with month matching, local year controls, another heat measure, and removal of extreme heat doses. These data permit a heat buffer but do not establish a general effect. Nonrandom surveys, fixed broad-scale turbidity, few region clusters, and unmeasured coral composition limit inference. Air pollution and species loss were not measured.

coral bleaching · turbidity · heat stress · observation bias · regional replication · uncertainty