Bacterivory in obligate phototrophic algal flagellates may be an important strategy for acquiring nutrients during periods of inorganic nutrient limitation.Several marine algal flagellates were shown to increase bactivory when phosphate was limited. Grazing on bacteria by algal flagellates was found during blooms of Prymnesium parvum in Sandsljorden, western Norway, in 1989 and Chrysochromulina polylepis on the south and west coast of Norway in 1988. Dissolved phosphate was not detectable in these situations. Algal flagellates may graze bacteria to obtain phosphate, which may permit these algal flagellates to develop blooms when phosphate becomes limited.
Since 2005, five different ballast water management systems (BWMS) based on chlorination treatment have been tested by Norwegian Institute for Water Research (NIVA) according to guidelines from the International Maritime Organization (IMO). 25 % and >50 % of all the tested discharge samples exhibited acute and chronic toxic effects on algae, respectively. In most cases this toxicity was plausibly caused by a high free residual oxidant (FRO) level (>0.08 mg Cl/l). Of the 22 disinfection by-products (DBPs) that were identified in treated water at discharge, four compounds were at times found at concentrations that may pose a risk to the local aquatic environment. However, there seemed to be no clear indication that the measured DBP concentrations contributed to the observed algal toxicity. The addition of methylcellulose instead of lignin in the test water to comply with IMO requirements seemed to limit the formation of DBP.
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