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The size–structure of coral populations can serve as an indicator of demographic structure and response to disturbance. This study examines variation in the size–structure of Acropora and Pocillopora colonies, two regionally dominant coral genera with contrasting life-history traits. The abundance and colony sizes of these genera were studied across reef flats, crests, and slopes, within marine protected areas (MPAs) in New Ireland Province, Papua New Guinea (PNG), an understudied region of the Coral Triangle. While a preponderance of small sized colonies have been previously detected in relatively undisturbed reefs, this study instead found negatively skewed size–structures for Pocillopora and Acropora distributions, reflecting the general persistence of larger and likely older colonies. Pocillopora size-distributions were uniformly more negatively skewed and more peaked than Acropora, whereas, Acropora colonies were significantly larger across all reef positions and nearly all sites, potentially reflecting their high growth rates and ‘competitive’ life-history traits. The size–structure (skewness and kurtosis) of both Pocillopora and Acropora did not significantly vary across reef positions or study sites, whereas mean-colony size decreased significantly with deeper reef positions, suggesting that colonies of all size-classes respond in unison to micro-site reef heterogeneity at the regional scale. Together, this study provides valuable insight into the size–structure of dominant coral taxa with contrasting life-history traits, which will serve as baseline data for future surveys of coral community responses to climate change in PNG.