Skeleton Precedes Polyp: Visualization of Structural Changes During Coral Growth in <i>Montipora capricornis</i>.

Abstract

Scleractinian corals are foundational to coral reefs, vital marine ecosystems under threat from climate change. <i>Montipora</i>, a widely distributed reef-building genus, contributes through continuous corallum mineralization, yet polyp budding and skeleton formation processes remain elusive. This study elucidates temporal and spatial dynamics of skeletal formation and polyp budding in <i>Montipora capricornis</i> using high-resolution micro-computed tomography (micro-CT). We demonstrate that skeleton-canal network formation precedes polyp budding at colony margins, identifying a "transit area" (volumes ~1 mm³, skeleton-to-void ratio 20%-35%) within tubular canals as a pathway for polyp migration to new calices. This feature serves as a morphological budding marker, enabling visualization of polyp trajectories and growth axes. The polyp-canal system undergoes dynamic changes, including concurrent skeleton formation and dissolution. These insights establish a structural framework for biomineralization regulation and colony expansion, contributing to the development of coral growth models, and informing environmental impacts on reef-building in <i>M. capricornis</i>.