Abstract
Ships’ ballast tanks have long been known as vectors for the introduction of organisms. We applied next-generation sequencing to detect dinoflagellates (mainly as cysts) in 32 ballast tank sediments collected during 2001–2003 from ships entering the Great Lakes or Chesapeake Bay and subsequently archived. Seventy-three dinoflagellates were fully identified to species level by this metagenomic approach and single-cell polymerase chain reaction (PCR)-based sequencing, including 19 toxic species, 36 harmful algal bloom (HAB) forming species, 22 previously unreported as producing cysts, and 55 reported from ballast tank sediments for the first time (including 13 freshwater species), plus 545 operational taxonomic units (OTUs) not fully identified due to a lack of reference sequences, indicating tank sediments are repositories of many previously undocumented taxa. Analyses indicated great heterogeneity of species composition among samples from different sources. Light and scanning electron microscopy and single-cell PCR sequencing supported and confirmed results of the metagenomic approach. This study increases the number of fully identified dinoflagellate species from ballast tank sediments to 142 (>50% increase). From the perspective of ballast water management, the high diversity and spatiotemporal heterogeneity of dinoflagellates in ballast tanks argues for continuing research and stringent adherence to procedures intended to prevent unintended introduction of non-indigenous toxic and HAB-forming species.
Highlights
Ships’ ballast water and sediment in ballast tanks have been demonstrated as important vectors for the transportation of exotic phytoplankton among different regions of the world [1,2,3,4,5,6,7]
Venn diagrams showed that cysts of some species commonly found in marine sediments, e.g., Biecheleria brevisulcata, B. cincta, and Scrippsiella acuminata, were present in many samples and at most ports, overall there was a limited number of operational taxonomic units (OTUs) shared among ports, ships, and sometimes even between samples collected on the same day from different tanks of the same ship
This study’s detection of its East Asian Ribo-type suggests its expanded distribution to North American waters. These results indicate the role of ships in transporting, releasing, and potentially introducing non-indigenous dinoflagellates, and very likely phytoplankton species in general, has been significantly underestimated using traditional methods of identification
Summary
Ships’ ballast water and sediment in ballast tanks have been demonstrated as important vectors for the transportation of exotic phytoplankton among different regions of the world [1,2,3,4,5,6,7]. A variety of viable cysts produced by toxic dinoflagellates and diatom resting stages were identified in ballast tanks of vessels entering Australian ports [3,10]. These studies strongly implicated ships’ ballast water and ballast tank sediments as responsible for the dispersal of toxic microalgae. Definitive proof of a particular organism’s introduction via ballasting operations is lacking, many studies have provided strong evidence for the role of ballast tanks in the global dispersal of dinoflagellates, including potentially harmful/toxic forms. Hamer et al [15] identified 48 dinoflagellate species from sediments in ships arriving to English and Welsh ports, including toxic, bloom-forming, and non-indigenous species. Margalefidinium polykrikoides (= Cochlodinium polykrikoides Margalef, 1961 [18]), can cause massive fish mortality [19], but was not problematic at the ports sampled
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