We applied a multivariate analysis to investigate the roles of host and symbiont on the in situ physiological response of genus Madracis holobionts towards light. Across a large depth gradient (5‐40 m) and for four Madracis species and three symbiont genotypes, we assessed several variables by measuring chlorophyll a fluorescence, photosynthetic pigment composition, or symbiont population descriptors. Most of the variation is...

Symbiotic algae in coral species distributed over a large depth range are confronted with major differences in light conditions. We studied the genetic variation of Symbiodinium in the coral genus Madracis over depth (5–40 m) and at two different colony surface positions. Using polymerase chain reaction–denaturing gradient gel electrophoresis ITS2 nuclear ribosomal DNA analyses, we consistently identified three symbiont genoty...