Abstract
Fluorescence by naturally occurring dissolved organic matter (FDOM) is a sensitive indicator of ballast water source, with high FDOM in coastal ballast water decreasing typically dramatically when replaced by oceanic seawater during ballast water exchange. In this study, FDOM was measured in 92 ships arriving at Pacific ports on the US west coast and in New Zealand, and used to assess their compliance with ballast water regulations that required 95% replacement of port water to minimize invasive species risks. Fluorescence in many ships that reported ballast water exchange was significantly higher than is usual for oceanic seawater, and in several cases, significantly higher than in other ships with similar provenance and ballast water management. Pre-exchange source port conditions represented the largest source of uncertainty in the analysis, because residual coastal FDOM when highly fluorescent can significantly influence the fluorescence signature of exchanged ballast water. A meta-analysis comparing the intensities of FDOM in un-exchanged ballast tanks with calculated pre-exchange intensities assuming that ships all correctly implemented and reported ballast water exchange revealed notable discrepancies. Thus, the incidence of high-FDOM port waters was seven times lower in reality than would be expected on the basis of these calculations. The results suggest that a significant rate of reporting errors occur due to a combination of factors that may include inadequate ballast water exchange and unintentional or deliberate misreporting of ballast water management.
Highlights
The transfer of ballast water between ports is an effective mechanism for moving a diverse assemblage of marine and estuarine organisms around the globe, posing considerable risk to the marine environment (Carlton and Geller, 1993; Ruiz et al, 1997; Roman and Darling, 2007)
This study presents the first report of dissolved organic matter fluorescence intensities (C3∗ = 370/494 nm) in ballast tanks of randomly-sampled ships arriving to Pacific ports
It was attempted to use these data to verify ballast water exchange (BWE) when reportedly undertaken for those tanks, based upon reconciling fluorescence measurements with ships’ reports without direct information regarding the chemical signatures of the ballast tanks prior to BWE
Summary
The transfer of ballast water between ports is an effective mechanism for moving a diverse assemblage of marine and estuarine organisms around the globe, posing considerable risk to the marine environment (Carlton and Geller, 1993; Ruiz et al, 1997; Roman and Darling, 2007). In New Zealand, economically and socially important fisheries are threatened by large volumes of ballast water discharged each year (Hewitt and Campbell, 2007). In both countries, ballast water is the suspected vector for several marine introductions. Chemical Assessment of Ballast Water species, led in 1993 to the first ballast water exchange (BWE) requirements for ships entering the Great Lakes from outside the US exclusive economic zone. This authority was soon extended to other regions of the country by the National Invasive Species Act of 1996
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