Molecular characterisation of protistan species and communities in ships’ ballast water across three U.S. coasts

Abstract

AbstractAimWe characterised protistan taxa in ships’ ballast water (BW) arriving to port systems across three U.S. coasts. Our goals were to compare (1) diversity and (2) community composition of protists in BW among and between port systems.LocationChesapeake Bay in Virginia (Port of Hampton Roads), Galveston Bay in Texas (Ports of Texas City, Houston and Bayport) and Prince William Sound in Alaska (Port of Valdez).MethodsWe collected 61 BW samples from 39 vessels from May to August 2013. We conducted amplicon‐based high‐throughput sequencing (HTS) using the hypervariable V4 domain of the small subunit (SSU) gene of the ribosomal RNA (rRNA) complex to identify protistan taxa.ResultsWe detected 8,561 OTUs from protistan taxa, including 35 taxonomic groups. We found high protistan diversity in the BW entering all three port systems, with the dominant taxa belonging to the Alveolata, Rhizaria and Stramenopiles. Thirty‐eight taxa were found in high relative abundance (>10,000 sequences), and some were recovered from multiple samples within and across ports, indicating both a high relative abundance and frequency of introduction events. The composition of the protistan communities entering each of the port systems appeared to vary depending on BW source, with those entering Valdez being consistently more similar to each other than those entering other port systems.Main conclusionsThis study is the most comprehensive assessment of protistan diversity in BW and has important implications for microbial biogeography and invasions. Ships’ BW is importing distinct and diverse protistan communities to U.S. coasts with high propagule pressure for some taxa, creating opportunity for invasion by novel taxa. Further, our results demonstrate the broad‐scale movement of marine protists that has occurred through BW, highlighting a discrepancy between the large magnitude of introductions and limited number of known microbial invasions.