MEPS 425:47-61 (2011)  -  DOI: https://doi.org/10.3354/meps08999

ABSTRACT: This research uses the concept of propagule pressure (number of individuals introduced and number of introduction attempts) to investigate human-mediated bioinvasion patterns. We quantified diatoms in the sediments of ballast tanks of commercial ships arriving on both Canadian coasts during 2007 to 2009. Diatom cell concentrations varied from non-detected to 10⁵ cells g^–1 wet weight (10¹¹ cells per tank). Although the lowest values were often found in tanks that underwent ballast water exchange, the highest concentrations (10⁹ to 10¹¹ cells per tank) were detected in all voyage categories: transoceanic with ballast exchange (TOE), and intra-coastal with exchange (ICE) and without exchange (ICU). For the west coast, 36% of tanks carried detectable quantities of diatoms and there was no statistical difference between ship categories. For the east coast, 60% of tanks contained diatoms; ICU represented a bioinvasion pattern based on more frequent events with consistently lower cell concentrations, whereas ICE and TOE corresponded to less frequent events, though more variable in cell concentrations. Diversity reached 40 taxa per tank, including resting stages and cells that were supposedly growing vegetatively. New records may lead to introduction hypotheses that ought not to be accepted uncritically. Cell viability was tested using the vital stain fluorescein diacetate; parallel counts of protoplasm integrity and chlorophyll autofluorescence revealed that all 3 indicators gave results within the same order of magnitude. Inoculation of 0.2 to 0.5 ml of the slurry into culture media led to the growth of diatoms, even of taxa not initially detected. Within 7 d, cultured assemblages reached cell concentrations equivalent to 1.8 to 4.4 doublings of the original inoculation.

KEY WORDS: Diatoms · Biological invasion · Ballast sediment · Propagule pressure · Phytoplankton viability