The Line Islands archipelago is the last major group of islands in the Central Tropical Pacific Ocean before a stretch of more than 5000 km of open ocean west of the Americas known as the Eastern Pacific Barrier. These islands may therefore provide a key stepping stone for dispersal of shallow water marine organisms. Despite their recognized ecological importance and high biodiversity, the foraminiferal fauna in these remote islands has remained largely undocumented. This work addresses that gap by presenting the first species-level, fully illustrated inventory of shallow-water benthic foraminifera from diverse habitats (reef, lagoon, and nearshore beach environments) across six of the northern Line Islands: Kingman, Jarvis, Palmyra, Tabuaeran (Fanning), Kiritimati (Christmas), and Teraina (Washington). The benthic foraminiferal species assemblages of these islands were analyzed, and placed in context of reefal habitats and different levels of anthropogenic environmental impacts across the studied islands. A total of 69 sediment samples were obtained from a variety of settings including shallow nearshore sands, lagoonal patch reefs, shallow fore-reefs, and deeper fore-reefs (up to 40 m depth). Over 25,500 individual foraminifera were picked and identified to species level whenever possible, resulting in a faunal inventory comprising 134 species from 65 genera. Quantitative analyses included species richness counts, Fisher ? and Shannon diversity indices, and community structure assessments using rarefaction, ternary diagrams, nonmetric multidimensional scaling (NDMS), and the FORAM Index (FI) to gauge reef health. Analyses reveal that hyaline-perforate foraminifera dominate the assemblages, followed by porcelaneous forms and agglutinated taxa. Larger symbiont-bearing foraminifera, though representing only 6.7% of the species, accounted for over 57% of the total individuals. Foraminiferal assemblages varied among islands and habitats: Nearshore beach sands showed high proportions of porcelaneous taxa, whereas lagoonal patch reefs were consistently dominated by hyaline-perforate species with minimal agglutinated forms. Shallow fore-reefs displayed the greatest variability in taxonomic composition, while deep fore-reefs showed a narrower range of variation and a slightly higher proportion of agglutinated species. Statistical analysis indicated that species richness and diversity were lowest at shallow nearshore beach sites, increased in fore-reef environments, and peaked at deeper fore-reef sites. NMDS further revealed that shallow fore-reef habitats are more heterogeneous in faunal composition compared to more uniform deep fore-reef and lagoonal environments. A marked difference was observed between inhabited (Kiritimati, Tabuaeran, Teraina) and uninhabited islands (Kingman, Jarvis, Palmyra). Inhabited islands exhibited significantly higher percentages of opportunistic foraminifera, which may be linked to anthropogenic impacts. The FORAM Index values across sites (calculated from both live and dead foraminifera) generally exceeded the critical threshold (FI > 4), suggesting that the water quality is sufficient to support calcifying symbiosis and active carbonate production. This reinforces the role of foraminifera not only as bioindicators but also as key contributors to reef sediment formation. The research provides crucial baseline data for modern Indo-Pacific foraminiferal communities and demonstrates how assemblage structure varies across environmental gradients and human impacts. The relatively low diversity of larger symbiont-bearing species compared to the highly diverse Coral Triangle underscores the steep longitudinal biodiversity gradient in the tropical Pacific. Despite the lower species numbers, the overwhelming abundance of LBF in most habitats indicates their pivotal role in reef carbonate production and structural maintenance. Moreover, the study shows that the Northern Line Islands act less as a stepping stone and more as a last “jumping off point” for dispersal of tropical taxa across the Pacific, positioned at the edge of the Eastern Pacific Barrier (EPB). Indeed, very few species have successfully dispersed even this far east, and even fewer cross the EPB. Overall, the manuscript advances our understanding of foraminiferal biogeography, providing insights into how environmental factors (such as habitat type, depth, and human disturbance) shape community structure. These findings have broader implications for interpreting the fossil record and for reef conservation strategies, particularly in a rapidly changing ocean where anthropogenic impacts are increasingly significant.
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