Because post-freshet growth at TC was found to have been inconsistent with the growth expected at the higher salinity site, subsequent ANOVA used log-transformed values for MSBB and MIBB of P.
Among initially infected oyster cohorts, mean sample infection intensities (MSBB) ranged from 0.04 cells/g for TC DEBYs to 4.64 cells/g for TC CROSBreeds, and mean infected intensities (MIBB) ranged from 1.25 cells/g for TC DEBYs to 50 cells/g for HP CROSBreeds.
High prevalences did not necessarily predict high means for sample infection intensities (MSBB), however.
There were no differences among strains for MSBB and MIBB (P > 0.55 for both).
Comparisons of MSBB thresholds also revealed a strong location effect (Fig.
marinus infections among local feral oysters (r = 0.63, P = 0.07), log MSBB among experimental oysters (r = 0.60, P = 0.08), log MIBB among experimental oysters (r = 0.60, P = 0.08), and summer salinity (r = 0.59, P = 0.10).
Closer examination of post-freshet dermo disease levels showed that log MSBB and log MIBB levels followed the salinity gradient and were distinctly different at all sites (P < 0.0001).
Therefore, MSBB values below this threshold may reflect samples where the parasite may be present in many, or all, hosts, but where infections would remain undetected by standard methods, and prevalences would be scored as 0 (false negative).
The same pattern was evident in MSBB and MIBB infection intensity measures.
In September 2007 at TC the DEBY MSBB (1.2 x [10.sup.6] cells/g) was 4 times greater than for CROSBreeds (0.3 x [10.sup.6] cells/g), yet mortalities among DEBYs were much lower.