Bilge water as a vector for the spread of marine pests: a morphological, metabarcoding and experimental assessment
Vessel movements are considered the primary anthropogenic pathway for the secondary spread of marine non-indigenous species. In comparison to the well-studied mechanisms of hull fouling and ballast water, the importance of bilge water for domestic and cross-regional spread of non-indigenous species is largely unknown and has the potential to compromise the overall effectiveness of biosecurity management actions. In this study, the diversity and abundance of biological material contained in bilge water from 30 small vessels (<20 m) was assessed using traditional and molecular identification tools (metabarcoding of the 18S rRNA gene). Laboratory-based studies were also used to investigate the relationship between voyage duration and propagule success. A large taxonomic diversity in organisms was detected, with 118 and 45 distinct taxa identified through molecular and morphological analyses, respectively. Molecular techniques identified five species recognised as non-indigenous to the study region in 23 of the 30 bilge water samples analysed. Larvae and fragments passed through an experimental bilge pump system relatively unharmed. Time spent in the bilge sump was found to affect discharge success, particularly of short-lived and sensitive larvae, but survival for 3 days was observed. Our findings show that bilge water discharges are likely to pose a non-negligible biosecurity threat and that further research to identify high-risk vessel operating profiles and potential mitigation measures are warranted.
KeywordsAnthropogenic spread Dispersal High-throughput sequencing Non-indigenous species Pathway management Translocation
We are grateful to Rebecca Stafford-Smith (University of Birmingham), Marc Jary and Patrick Cahill (Cawthron Institute), Megan Carter (NIWA) and Bruce Lines (Diving Services New Zealand Ltd.) for their assistance with various aspects of the laboratory and field studies, as well as Oliver Floerl (Cawthron Institute) for helpful review comments on an earlier version of the manuscript. Sincere thanks are also expressed to Paul Jonkers (Nelmac Ltd.) for assistance with boat arrivals, and the numerous boat operators who allowed access to their vessels. This work was funded by the National Institute of Water and Atmospheric Research Ltd (NIWA) under Coasts and Oceans Research Programme 6, Marine Biosecurity (SCI 2014/15).
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Conflict of interest
The authors declare that they have no conflict of interest.
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