Diversity and Dispersal of Fungi Along a Subtropical Land-to-Sea Continuum.

This study examines the fungal and fungal-like stramenopile communities along the land-to-sea continuum to explore microbial connectivity across terrestrial and marine ecosystems. In addition to providing new ecological knowledge on coastal communities, the objectives were to assess the presence of terrestrial fungi and evaluate their potential as bioindicators of riverine influence on marine environments. Conducted in New Caledonia (southwest Pacific), the research involved 113 marine samples (water and sediment) and 148 additional soil samples from tropical/subtropical Pacific regions. Sampling spanned spatial and temporal gradients, including dry periods and a post-cyclone runoff event. We used high-throughput long-read amplicon sequencing of the full-length ITS rRNA gene, complemented by inference of fungal ecological traits from genus-level annotations. In total, 1653 fungal OTUs were identified in marine samples, with distinct communities in sediment and water. Terrestrial fungal taxa were also detected in marine environments, with 306 genera exhibiting varying occurrence across sample types and periods. The cyclone runoff temporarily increased the richness of terrestrial fungal taxa by up to threefold, underscoring the impact of extreme events on marine coastal assemblages. Overall, this work provides the first study of fungal communities along New Caledonia's coastlines, highlighting fungal dispersal as a key component of land-to-sea connectivity.