Different algal symbionts explain the vertical distribution of dominant reef corals in the eastern Pacific

TLDR

Reef corals occupy the full photic zone but most species show distinct vertical zonation within the light gradient. The study tests whether host vertical distribution is driven by symbionts adapted to specific light regimes. The authors performed genetic and physiological analyses of algal populations in two dominant Pacific corals across their vertical ranges in the Gulf of California. Each coral species hosts a distinct light‑adapted algal taxon, and this differential light use by symbionts explains their vertical distribution.

Abstract

Symbiotic reef corals occupy the entire photic zone; however, most species have distinct zonation patterns within the light intensity gradient. It is hypothesized that the presence of specific symbionts adapted to different light regimes may determine the vertical distribution of particular hosts. We have tested this hypothesis by genetic and in situ physiological analyses of the algal populations occupying two dominant eastern Pacific corals, over their vertical distribution in the Gulf of California. Our findings indicate that each coral species hosts a distinct algal taxon adapted to a particular light regime. The differential use of light by specific symbiotic dinoflagellates constitutes an important axis for niche diversification and is sufficient to explain the vertical distribution patterns of these two coral species.