Seasonality of tropical airborne algae: a 16-month study based on high-throughput sequencing in the Hawaiian Islands

Abstract

The airborne environment is a critical juncture linking terrestrial and aquatic habitats, yet the algae of this environment are not well-characterised and understood. The goal of this study was to examine seasonality patterns of airborne algae in a tropical environment. Airborne algae were collected monthly in spore traps on a building rooftop on the island of Oʻahu, Hawaiʻi, U.S.A. from December 2015 to March 2017. Metabarcoding of Universal Plastid Amplicon (UPA) and 16S ribosomal RNA (rRNA) markers was used to characterise the algal diversity in the samples relative to meteorological data. Modelled back-trajectories of air masses arriving at the site demonstrated that months with the highest rainfall corresponded to those with the strongest tradewind signal. Thirty airborne algal Exact Sequence Variant (ESV)s were identified using the UPA marker including Cyanobacteria (20), Chlorophyta (4), Streptophyta (3), Chrysophyceae (1), Synurophyceae (1), and unknown Stramenopila (1). Forty-four ESVs were identified using the 16S marker and consisted of Cyanobacteria (43) and plastids of Streptophyta (1). The number and diversity of sequence reads obtained varied strongly both among samples for a given time period and from month to month. Highest rainfall and air temperatures corresponded to months with the largest cyanobacterial relative abundance according to the UPA marker. Although cyanobacteria were the most common group identified using the 16S marker, the dominant cyanobacterial taxon varied by month. Diversity or abundance patterns were not explained by meteorological conditions, which may be due to the relatively small annual amplitude in conditions in the Hawaiian Islands.