Fine-scale temporal variation of intertidal marine fungal community structure: insights from an impacted Baja California sandy beach in Mexico

Globally, marine sandy beaches face increasing anthropogenic pressures. Long-term maintenance of their functional capacities depends strongly on robust autochthonous biotic community baseline data. However, fine-scale temporal patterns remain poorly understood in human-impacted sites, limiting our knowledge of beach response to stressors. Marine arenicolous fungi represent a neglected group of endopsamon microorganisms (living within sandy sediments) that fulfills key ecological roles mainly as saprobes. Preliminary data suggests that this fungal group is threatened by anthropogenic disturbances in tourist beaches, yet knowledge on their ecological plasticity and fine-scale patterns is lacking. To address this knowledge gap, we investigated marine fungal community composition changes over a fine temporal scale (biweekly, over a four-month period) at an impacted Pacific tourist sandy beach, and explored associations between community composition and key environmental variables. We identified 17 taxa, within four ecological groups: strict marine arenicolous fungi ( Arenariomyces majusculus , Corollospora gracilis , Corollospora maritima , Corollospora sp. 1 and 2), non-arenicolous marine fungi ( Nia sp.), terrestrial borne opportunistic pathogens ( Arthrographis kalrae , Parengyodontium album , Neocosmospora solani , Scopulariopsis sp., and Exophiala sp.), and facultative marine species ( Aspergillus terreus and Penicillium sp.). In agreement with our hypothesis, minor fine temporal scale changes in community structure suggest arenicolous fungi persist on the beach as inoculum. Nevertheless, we detected changes in the intertidal fungal community structure in response to environmental variables, shown by the increase of terrestrial borne pathogenic species in the rainy season. Lastly, our data warn against extensive beach grooming, which may lead to the direct reduction of strict marine arenicolous fungal groups.