The Microbiome of Coastal Sediments

Coastal zones are among the most productive marine environments and many are highly impacted by anthropogenic activity. Coastal zones are key regions for the transformation of land-based inputs of nutrients and pollutants and provide many essential ecosystem services for human society. Periods of tidal exposure and submergence, coupled with seasonal variation in land-based inputs, result in intertidal habitats characterized by highly variable environmental conditions that pose crucial adaptive challenges for organisms. This review focuses on the microbiome of coastal sediments consisting of protists (especially diatoms), bacteria, archaea, and fungi. The diversity, distribution, production, adaptations, and interactions between these groups are reviewed. Coastal microbiomes are characterized by high rates of biogeochemical activity. Photoautotrophic diatoms exhibit complex patterns of behavior to cope with a highly variable light climate. Multiple species–species interactions between autotrophs and heterotrophs contribute to the cycling of carbon and nitrogen. In sediments, autotrophic and heterotrophic processes are closely coupled both spatially and temporally. Bacteria and archaea control the nitrogen- and carbon cycles while taxonomic diversity is influenced by gradients of organic matter, nitrogen compounds, sulfide, and oxygen. Fungi are important components of coastal salt marsh sediment microbiomes but their role in unvegetated sediments is less well understood. This review considers the high human impact on coastal sediments and the importance of nutrient gradients and pollution pressures (hydrocarbons) in affecting diversity and species distribution.