Fungal diversity and dispersal along the land-sea continuum in New Caledonia

This study examines fungal and fungal-like stramenopile communities along the land-to-sea continuum to test microbial connectivity between terrestrial and marine ecosystems. Beyond providing new ecological insight into coastal assemblages, we assessed the presence of terrestrial fungi and their potential as bioindicators of riverine influence on marine waters. We collected 131 environmental samples (soil, sediment, and water) across New Caledonia (southwest Pacific), spanning spatial gradients and seasonal conditions, including dry periods and immediately after a cyclone-induced runoff event. Full-length ITS rRNA gene amplicons were sequenced with high-throughput long-read technology to achieve high taxonomic resolution. Communities showed clear niche partitioning among soil, sediment, and water, with significant differences in richness and diversity. The runoff pulse temporarily increased terrestrial fungal taxa in coastal waters but only for a short (<2-day) window, and few taxa were recovered thereafter. Overall, this work provides the first comprehensive characterisation of fungal communities along New Caledonia's coastal gradient, highlights dispersal as a key element of land-sea connectivity, and underscores their promise for environmental monitoring.