Head, C. E. I. | Search bioRxiv

bioRxiv2026

Genomic and oceanographic evidence of reef connectivity across the western and central Indian Ocean

Connectivity among coral populations, via larval dispersal, is one of the key mechanisms supporting reef recovery after climate-driven bleaching events. This study examines reef connectivity of remote atolls of the understudied central and western Indian Ocean seascape, focusing on a key reef-building species, Acropora aff. tenuis. Using genomic data from ultra-conserved elements alongside particle-tracking simulations, we investigate patterns of population structure and gene flow, and the influence of ocean currents. Results show asymmetrical connectivity: strong gene flow occurs within the Chagos Archipelago and between Chagos and the Inner Seychelles, highlighting their importance as regional larval sources. In contrast, the Outer Seychelles mainly functions as a larval sink, and IIes Glorieuses appears to be the least connected. Whilst population structure suggests a partially permeable dispersal barrier between the Inner and Outer Seychelles. Differences between genetic patterns and simulated ocean-driven dispersal suggest that ocean currents are not the only important driver of connectivity patterns. Additional factors, such as stepping-stone dispersal among atolls, fine-scale oceanographic processes, and species biology likely play important roles. Overall, we find widespread genomic connectivity across this seascape, which has positive implications for reef resilience, though future resilience will depend on frequency and severity of future bleaching events.

ecology↗

bioRxiv2019

Record highest mesophotic fish diversity found in Raja Ampat

Mesophotic coral ecosystems (MCEs; reefs 30-150 m depth) are poorly studied, with existing research heavily geographically biased away from the most species-rich reef regions. Yet, MCEs are of high interest because of their unique species and potential to act as refuges from the impacts of fishing. Using baited remote underwater video systems, we surveyed reef fish communities from 2 to 85 m depths throughout the Raja Ampat archipelago in West Papua, Indonesia - an area considered the heart of the Coral Triangle where coral reef biodiversity is greatest. We sought to provide the first assessment of fish communities across this depth gradient in the region and identify whether human population density and market access differently affected fish abundance based on depth. Here we show that--similar to shallow reefs--Raja Ampat MCEs are exceptionally diverse, with 152 fish species recorded at depths greater than 40 m. We found that fish community structures were highly depth driven, with declines in fish abundance at increased depth. In contrast to previous studies elsewhere in the world, we found that the proportion of planktivores declined across the shallow reef to MCE depth gradient. While greater human population density correlated with lower Epinephelidae and Lutjanidae abundance (two key fisheries families), we did not find evidence that MCEs provide a depth refuge from fishing. Surprisingly, we also found that fish abundance declined at greater distances from the major regional market - likely caused by historical fisheries pressure in more remote areas. These results both expand upon and contrast some previously established MCE-depth patterns and human impact patterns on fish communities, suggesting that regional context and historical pressures matters. Our findings highlight the need for future MCE studies within the Coral Triangle region.

ecology↗