Initial macroalgal cover gave no clear heat-slope change in four Atlantic and Pacific coral samples in 1998-2019

We tested whether initial macroalgal cover strengthened the link between heat and annual hard-coral cover loss. HeatCRD version 1 gave 1,111 pairs at 427 sites. We matched site, source, month and depth in consecutive years. Four Atlantic and Pacific period models controlled initial heat, initial coral cover, year, month and source. Heat-by-macroalgae slopes were -0.14, +0.25, +0.37 and +1.49 cover points per four TSA degree-heating weeks per ten macroalgal cover points. All four corrected intervals included zero. Only 0, 3, 6 and 6 pairs had both heat of at least four and initial macroalgal cover of at least ten percent. Exact follow-up was sparse and Reef Check supplied most pairs. These selected records do not establish a repeated increase in heat-related loss at higher macroalgal cover. They do not show that macroalgae have no effect. Survey-date heat can miss earlier damage, and missing visits and unmeasured local stress limit inference. The package gives matched data, source hashes, code, figures and independent numerical checks.

coral cover · macroalgae · marine heat stress · HeatCRD · observation bias · interaction · regional replication · null result