Individual study: Implications of viability of invertebrate eggs exposed to saltwater for Great Lakes' ship ballast management; a laboratory experiment, Ontario, Canada
Gray D.K., Bailey S.A., Duggan I.C. & MacIsaac H.J. (2005) Viability of invertebrate diapausing eggs exposed to saltwater: implications for Great Lakes' ship ballast management. Biological Invasions, 7, 531-539
International shipping has been a major vector of non-native species introductions to the Great Lakes of North America. Apparent recent invasions stem from organisms within ship ballasts; as no-ballast-on-board (NOBOB) vessels currently dominate inbound traffic to the Great Lakes, it has been proposed that live or dormant organisms contained in residual ballast may be partly responsible for these invasions. In this study, an experiment was undertaken to assess if exposure to seawater reduced the viability of invertebrate eggs in ballast sediments. If exposure markedly reduced egg viability or the resulting species richness of hatched organisms, then ballasting a small amount of saltwater into NOBOB ships could reduce the future introduction risks.
Sediment samples: Sediment samples from ballast tanks were taken from three transoceanic ships entering the Great Lakes between November 2001 and June 2002. Due to the unknown origin of these sediments, and possible previous exposure to saltwater, samples were also collected between June and December 2002 from natural freshwater habitats.
Treatments: In the laboratory, two treatments were applied to subsamples of these sediments: exposure to seawater (salinity 32â€°) collected from a loaded ballast tank, or exposure to freshwater. The treated sub-samples were stored in the dark at 4ºC for 10 days (the maximum length of a typical trans-Atlantic voyage).
Egg viability: Egg viability, assessed as the abundance of taxa hatched between sediments, was determined.
Exposing zooplankton diapausing eggs to seawater did not reduce total abundances or consistently affect the species richness of hatched invertebrates: egg viability was not affected by exposure; species richness of hatched eggs was reduced by saltwater exposure in only one of seven trials. Ballasting a small amount of saltwater into NOBOB ships therefore, does not appear to be an effective technique to reduce introductions of non-native organisms via ship ballast to the Great Lakes.
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