Trans-Pacific shipboard trials on planktonic communities as indicators of open ocean ballast water exchange

摘要

A trans-Pacific voyage from Japan to New Zealand via Singapore was used to assess planktonic (and sediment-dwelling) communities as indicators of open ocean ballast water exchange (BWE). The research was part of a larger project to develop methods for verifying whether international shipping has complied with mandatory controls and voluntary BWE guidelines. The dilution efficiency of exchanges was compared with changes in the composition and abundance of ballast tank phyto- and zooplankton taxa. Changes in the planktonic communities were measured by sampling the source port, the ballast water at the source and recipient ports and immediately before and after BWE, and the open ocean water during exchanges. Although exchanges appeared relatively effective at reducing the abundance (90 to 100%) of phyto- and zooplankton indicator taxa (i.e. taxa in the ballast water uploaded from the source port that were not present in open ocean samples or were present at < 0.001 the original concentration), such reductions must be considered in the light of variation in survivorship in the control tank. Relatively high rates of mortality were associated with a rapid warming (i.e. 14.0 to 27.8 ℃) of the exchanged and control ballast tanks as the vessel entered the tropics. The rapid decline in the abundance of indicator taxa after BWE contrasted with a less effective reduction (i.e. 30.3 and 25.0% for the first and second exchanges, respectively) in the total number of phyto- and zooplankton taxa. Management controls and guidelines should place greater emphasis on whether the water uploaded during BWE is sufficiently oceanic to minimise the risk of uploading harmful coastal organisms.