Power analysis for biomarkers in mussels for use in coastal pollution monitoring

Data from literature on neutral red retention time (NRRT) in lysosomes, micronucleus (MN) frequency and condition index (CI) in mussel Mytilus, especially Mytilus edulis and Mytilus galloprovincialis, were re-analyzed to ascertain their statistical power in detecting a minimum 20% spatial/temporal change in field studies. Results showed that CI largely displayed higher statistical power (>90%) than lysosomal NRRT and MN frequency (<50%), suggesting that data from the latter two biomarkers may lead to erroneous conclusions if sample size is inadequate. Samples of green-lipped mussel Perna viridis were also analyzed in Hong Kong. To achieve statistically valid power, the optimal sample sizes for monitoring lysosomal NRRT, MN frequency, CI and gonosomatic index (GSI) were determined as ≥34, ≥90, ≥16 and ≥29, respectively. Natural variability of lysosomal NRRT and MN frequency was significantly greater than CI and/or GSI in mussels, rejecting the general belief in the greater variability of higher-tiered hierarchical biomarkers.