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

Cc Becker,Jk Llopiz,L Weber,Jj Suca,Ta Mooney,A Apprill

doi:10.3354/ame01944

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 3 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 9 coastal sites on St. John, US Virgin Islands that spanned 4 km in distance (4 coral reefs, 2 seagrass meadows and 3 mangrove locations within 2 larger bays). Eight samplings occurred over a 48 h period, capturing day and night microbial dynamics over 2 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.

Highlights

Short temporal rhythmicities resulting from daily sunlight cycles and lunar-influenced tidal cycles have governed the dynamics of living organisms throughout evolutionary history
We used a combination of genomic and environmental measurements to determine the extent of tidally influenced microbial dynamics in 3 important and spatially related tropical biomes: mangroves, seagrass meadows, and coral reefs
We found a significant tide-mediated change in environmental and microbial parameters in mangrove environments

Summary

Introduction

Short temporal rhythmicities resulting from daily sunlight cycles and lunar-influenced tidal cycles have governed the dynamics of living organisms throughout evolutionary history. Tidal and diurnal forces play major roles in shaping microbial life in coastal environments. Seawater bacterial and archaeal communities are fundamental to ocean ecosystems. These prokaryotic microbes form the basis of the marine food web because they cycle organic matter, remineralize nutrients, and take part in all major elemental cycles in the ocean (reviewed by Moran 2015). Studies from estuarine and coastal environments showed that tidal mixing and salinity are major drivers of microbial community structure (Lu et al 2015, Chen et al 2019, Neubauer et al 2019). Short-term microbial dynamics likely play a role in structuring seawater microbial communities within coastal tropical marine environments (mangrove, seagrass and coral reef), but these dynamics are largely unstudied

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