AME 82:87-104 (2018)  -  DOI: https://doi.org/10.3354/ame01884

ABSTRACT: The anchialine ecosystem, defined as tidally influenced, nearshore bodies of water with subterranean freshwater and seawater connections, has been relatively unstudied regarding its microbial communities. Notably, anchialine habitats of the Hawaiian Archipelago, specifically the Cape Kinau (Maui) and Kona (Hawaii) regions, can possess distinctive, laminated orange cyanobacterial-bacterial crusts found nowhere else worldwide. However, nearly nothing is known about the degree to which seasonal fluctuations in water chemistry might influence shifts in their community composition. To test the hypothesis that taxonomic diversity and relative sequence abundance exhibit dynamics correlating to particular seasonal environmental factors, benthic and water column microbial communities from 6 habitats in these 2 geographical regions were examined during 2 wet and 2 dry seasons via high-throughput sequencing of hypervariable V6 (Bacteria-specific) and V9 (micro-Eukarya-biased) regions from rRNA genes. Although significant seasonal variation occurred in water chemistry characteristics such as salinity, ammonium, dissolved organic carbon, total dissolved nitrogen, and nitrite + nitrate during the same period, overall benthic and water column microbial community structure instead correlated with spatial factors such as latitude and annual rainfall. Despite this, approximately half of the identified third-level clades (i.e. approximately class-level nomenclatures) within these communities exhibited variation in relative sequence abundances between wet and dry seasons. Furthermore, relative abundance changes for approximately three-quarters of these clades correlated with at least one seasonally varying factor. Thus, while microbial communities in the Hawaiian anchialine ecosystem did not show stable composition year-round, overall community structure correlated more strongly with the spatial, rather than temporal, context of any given habitat.

KEY WORDS: Illumina amplicon sequencing · Microbial diversity · Seasonal variation · Sediment · V6 hypervariable region 16S rRNA gene · V9 hypervariable region 18S rRNA gene · Water