The effects of diesel oil on mussel morphology

Oil spills in and around shipping and recreational boating harbours is ubiquitous. Spills of light oil in the form of diesel is particularly common, however the impact from such spills on benthic organisms in the marine environment has not been fully recognized as significant relative to larger crude oil spills. In order to assess the effects of diesel oil, the blue mussel (Mytilus edulis) was investigated. Mussels were exposed to a seawater-accommodated fraction (WAF) of diesel to replicate the fraction of diesel mixed in the water column after a spill. Physical biomarkers of valve gape, byssal threads, closing reaction time and survivability, were compared against cellular biomarkers of digestive gland atrophy after a chronic 96 hour exposure. A relative Health Score incorporating the physical and behavioural biomarkers measured, indicated greater sensitivity to WAF exposure compared cellular biomarkers of atrophy. After 96 hours, evidence of stress quantified by Health Score could be seen at concentrations as low as 12.5% diesel WAF, and at 25% diesel WAF using digestive tubule atrophy. Both biomarker sets provided evidence of a quantifiable detrimental effect of diesel oil on overall mussel health. While using a formula to incorporate physical biomarker and behavioural biomarkers has potential to provide a more sensitive measure of health of mussels exposed to a wide range of contaminants.