should be rapid and easy to operate, typically measuring biological, physical, or chemical 
parameters that can be related to the number of viable organisms in a sample to provide an 
indication of potential non-compliance [gross exceedance] with Regulation D-2 (Bailey, 2015; 
Frazier et al., 2013; IMO, 2013). Indicative methods rely on various indicators to assess the 
viable biomass and/or viability of organisms in samples collected, including adenosine 
triphosphate (ATP) methods that detect cellular energy (Wright, 2012), fluorescence 
measurements that rely on the natural photosynthetic activity of chlorophyll-containing cells 
(phytoplankton) (Veldhuis et al., 2006; Wright, 2012), and fluorescein diacetate (FDA) methods 
that detect enzymatic activity (non-specific intracellular esterases or enzymes; Welschmeyer & 
Maurer, 2011)(Gollasch & David, 2010). Some indicative methods use calibration curves to 
convert the measured parameter to an estimated organism concentration. Several promising 
approaches have been developed but require further study in the field to understand their 
methodological differences and to assess their comparability, accuracy, and precision (Gollasch 
and David, 2010; Gollasch et al., 2012; Gollasch et al., 2015). 
In this paper, we report the results of a series of trials that were undertaken to compare 
methods for ballast water sample analysis by conducting replicated, comparative testing on 
marine water samples collected onboard the research vessel 'Meteor' in transit from Mindelo, 
Cape Verde to Hamburg, Germany. Water samples were collected from the ship's ballast water 
system and analyzed in parallel by multiple analytic methods for the > 50 pm and 10-50 pm size 
classes (7 and 9 techniques, respectively) to assess comparability between methods, with 
particular reference to microscopic analysis as the standard method. In so doing, we evaluated 
the sensitivity and precision of the different methods and provide an overview of the benefits