trials. The beginning of the cruise was spent mostly in oligotrophic (open ocean) water where 
biological variation was low and organism concentrations were at or below the limits specified 
in Regulation D-2, whereas very high concentrations were observed in the English Channel and 
the North Sea near the end of the cruise. Organism concentrations in the water ranged 
between ~1000 and ~800,000 individuals/m 3 for the > 50 pm size class, and between 0.6 and 
69.7 individuals/ml for the 10-50 pm size class (both as estimated by microscopy). Notably, the 
> 50 pm size class was dominated by dinoflagellates (Ceratium sp. and Protoperidinium sp.) 
comprising, on average, 85% of individuals; remaining taxa typically consisted of copepods, 
rotifers, and tintinnids. The 10-50 pm size class was also dominated by phytoplankton, though 
occasionally small rotifers (e.g. Keratella) were observed in samples. 
3.1 Results for > 50 pm size class 
Seven methods were used to analyze water samples containing organisms > 50 pm: 
microscopy (visual inspection for motile organisms; FDA 'staining' for non-motile organisms), 
two FDA methods (Satake Pulse Counter, MLML bulk FDA), two CFA methods (measure only 
photosynthetic protists; Hach BW680, Walz WATER-PAM), and two ATP methods (MLML ATP, 
SGS ATP aqua-tools). In general, all analytic methods showed a positive correlation between 
recorded measurements and direct microscopy counts, and were sensitive enough to detect 
organisms in the water samples at a range of concentrations (i.e. all measurements for analytic 
methods were non-zero values when the microscope method detected live individuals; Figures 
1; two exceptions/outliers: Walz WATER-PAM). As expected, variation between replicates 
increased with increasing abundance (Figure C.l).