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AME prepress abstract   -  DOI: https://doi.org/10.3354/ame01944

Microbial and nutrient dynamics in mangrove, reef, and seagrass waters over tidal and diurnal time scales

Cynthia C. Becker, Laura Weber, Justin J. Suca, Joel K. Llopiz, T. Aran Mooney, Amy Apprill*

*Corresponding author:

ABSTRACT: In coral reefs and adjacent seagrass meadow and mangrove environments, short temporal scales (i.e. tidal, diurnal) may have important influences on ecosystem processes and community structure, but these scales are rarely investigated. This study examines how tidal and diurnal forcings influence pelagic microorganisms and nutrient dynamics in three important and adjacent coastal biomes: mangroves, coral reefs, and seagrass meadows. We sampled for microbial (bacteria and archaea) community composition, cell abundances and environmental parameters at nine coastal sites on St. John, U.S. Virgin Islands that spanned 4 km in distance (4 coral reefs, 2 seagrass meadows and 3 mangrove locations within two larger systems). Eight samplings occurred over a 48-hour period, capturing day and night microbial dynamics over two tidal cycles. The seagrass and reef biomes exhibited relatively consistent environmental conditions and microbial community structure, but were dominated by shifts in picocyanobacterial abundances that were most likely attributed to diel dynamics. In contrast, mangrove ecosystems exhibited substantial daily shifts in environmental parameters, heterotrophic cell abundances and microbial community structure that were consistent with the tidal cycle. Differential abundance analysis of mangrove-associated microorganisms revealed enrichment of pelagic, oligotrophic taxa during high tide and enrichment of putative sediment-associated microbes during low tide. Our study underpins the importance of tidal and diurnal time scales in structuring coastal microbial and nutrient dynamics, with diel and tidal cycles contributing to a highly dynamic microbial environment in mangroves, and time of day likely contributing to microbial dynamics in seagrass and reef biomes.