Mussel histopathology: and effects of season, disease and species

We assessed seasonal histological changes as markers of health status in mussels Mytilus spp. sampled from Southampton Water, Hampshire, UK and the River Exe, Devon, UK between November 2004 and October 2005. A total of 29 health parameters related to pathogens, inflammatory and non-specific pathologies, and reproductive and physiological condition were recorded monthly from individual mussels collected from these 2 sites. We then assessed the diffential prevalence of these health parameters according to species. M. edulis, M. galloprovincialis and their hybrids were identified using the Glu-5' gene and the ME15 and ME16 primer sets that distinguish alleles specific to M edulis (180 bp), M gafloprovincialis (126 bp) and hybrids (180 bp/126 bp). Although no overall annual differences were observed between species with respect to median levels of adipogranular (ADG) tissue and reproductive status, specific differences in reproductive status were observed within individual months. During these months (August to October), M edulis exhibited a relatively lower reproductive status compared to M galloprovincialis and hybrids. With respect to all remaining health parameters (pathogens, inflammatory and non-specific pathology), principal components analysis revealed no overall differences between species throughout the year. However, greater differences were observed between species during the autumn and winter than during the spring and summer, thus indicating that species differences may be exacerbated by season. This study highlights how species can affect the accurate interpretation of histopathology data collected during biological effects monitoring programmes. Whether species can also affect the biomarker response of Mytilus mussels to contaminated environments remains to be shown. The results are discussed in the context of biological effects monitoring utilising mussels.