Mesophotic corals on the subtropical shelves of Lord Howe Island and Balls Pyramid, south-western Pacific Ocean

Abstract

Subtropical reefs are predicted to be dynamic areas of change under increased warming of global sea-surface temperature. A critical knowledge gap exists for deeper, mesophotic corals in these higher-latitude settings, where little is known about their spatial and depth distributions. At the latitudinal limits of coral-reef growth in the Pacific Ocean, abundant mesophotic corals were revealed on the shelf surrounding the subtropical, mid-ocean island of Balls Pyramid, which is a World Heritage-listed and marine park-protected area. Our study extended these findings to the nearby Lord Howe Island shelf to assess mesophotic coral cover and explore spatial patterns in mesophotic benthic communities. Underwater towed-video data collected around Lord Howe Island (24 sites) were combined with existing benthic data from the Balls Pyramid shelf. Results showed that similar habitats occur across both shelves, with communities varying among inner-, mid- and outer-shelf zones. Corals were most prevalent on the Balls Pyramid mid-shelf, with selected locations around the Lord Howe Island mid-shelf reporting similar cover (maximum site-average cover of 24%). The benthic data presented in this study provide important baseline information for monitoring coral cover and detecting potential shifts in community composition under ongoing climate change.