We described algal endosymbiont communities of the coral species M. cavernosa across a depth gradient in Belize. Coral fragments were sampled across 4 depth zones (10, 16, 25, 35 m) from shallow back reef to upper mesophotic zone at 4 sites along the Belize Barrier Reef. The ITS2 region of Symbiodiniaceae rRNA was amplified using Symbiodiniaceae-specific primers and pooled, indexed libraries were sequenced at The University of Texas at Austin’s Genome Sequencing and Analysis Facility (UTGSAF) on Illumina MiSeq v3, 600 cycle.