Mesophotic habitats could be sheltered from natural and anthropogenic disturbances and act as reproductive refuges, providing propagules to replenish shallower populations. Molecular markers can be used as proxies evaluating the connectivity and inferring population structure and larval dispersal. This study characterizes population structure as well as horizontal and vertical genetic connectivity of the broadcasting coralPocillopora verrucosafrom Ludao, a small oceanic island off the eastern coast of Taiwan. We genotyped 75P.verrucosaspecimens from three sites (Gongguan, Dabaisha, and Guiwan) at three depth ranges (Shallow: 7–15 m, Mid-depth: 23–30 m, and Deep: 38–45 m), spanning shallow to upper mesophotic coral reefs, with eight microsatellite markers. F-statistics showed a moderate differentiation (F_ST= 0.106, p<0.05) between two adjacent locations (Dabaisha 23–30 and Dabaisha 38–45 m), but no differentiation elsewhere, suggesting high levels of connectivity among sites and depths. STRUCTURE analysis showed no genetic clustering among sites or depths, indicating that allPocilloporaindividuals could be drawn from a single panmictic population. Simulations of recent migration assigned 30 individuals (40%) to a different location from where they were collected. Among them, 1/3 were assigned to deeper locations, 1/3 to shallower populations and 1/3 were assigned to the right depth but a different site. These results suggest high levels of vertical and horizontal connectivity, which could enhance the recovery ofP.verrucosafollowing disturbances around Ludao, a feature that agrees with demographic studies portraying this species as an opportunistic scleractinian.

Potential range expansion of scleractinian corals in high-latitude reefs is critically dependent on the coral host-symbiont relationship that determines coral growth and survival. Although increases in coral cover have been observed at higher latitudes, the identities of habitat-building reef corals and their symbionts are underreported. Here, we examine how scleractinian host and symbiont Symbiodiniaceae diversity changes along a tropical–temperate environmental gradient. We use Pocillopora spp. and associated symbiont communities as a model to understand whether they are expanding their range poleward and the role of symbionts in this process. Along the Kuroshio Current, which carries warm equatorial waters northward along the Pacific coast of Japan, we collected coral tissues from 23 (sub)tropical-to-temperate reefs, from southern Iriomote in the Ryukyu Islands (24°N) to northernmost Kushimoto on mainland Japan (33°N). We examined host identities through direct sequencing of the mitochondrial open reading frame (mtORF) and symbiont identities with next-generation sequencing of the internal transcribed spacer 2 (ITS2) region of the ribosomal DNA. Our results show a dramatic reduction of Pocillopora haplotypes and a marked change in dominant symbiont types northward (poleward) from Cape Sata (30°N), Kagoshima. ‘Tropical’ Pocillopora haplotypes were absent from mainland Japan sites. We also demonstrate high host specificity between the subtropical Pocillopora haplotype and Cladocopium symbiont types. Our findings question how common ‘coral tropicalisation’ is, and the location of the coral range expansion front. The specificity of hosts and symbionts in high-latitude corals suggests that high-latitude reefs are unlikely to support the persistence of tropical zooxanthellate corals.

Coral demography reveals how populations persist, recover and grow, offering key insights into individual responses to environmental variability and their role in shaping reef ecosystems. Taxonomy resolution strongly influences how these dynamics are interpreted, yet fine‐scale distinction among scleractinian species remains unclear. Here, we examine the demographic performance of Acropora, Pocillopora and Porites corals at different taxonomic levels to identify the most appropriate resolution for studying coral population dynamics. In Pocillopora, growth did not differ among species or haplotypes, while survivorship varied among species but was also shaped by environmental factors. Comparison between the three genera revealed clear differences in both growth and survival, suggesting that genus‐level and morphological resolution captures sufficient demographic information. Our results highlight the ecological relevance of taxonomic resolution and provide important insights into how population dynamics should be addressed to understand trends and responses to future climate change.