Comparative effects of the water accommodated fraction of three oils on mussels. 1. Survival, growth and gonad development.

1. Mussels, Mytilus galloprovincialis, were exposed to the water accommodated fraction (WAF) of two crude oils (types Ural and Maya) and of a commercial lubricant oil for 91 days. Synchronous spectrofluorometry showed that the aromatic hydrocarbon composition of the WAFs obtained from the three oils were significantly different (Maya-WAF heaviest, Ural-WAF lightest). 2. No significant mortality occurred in mussels exposed to the WAFs of the two crude oils, while all the animals exposed to lubricant-WAF died after 49 and 77 days in intermediate and high doses respectively. 3. Flesh and shell growth of mussels exposed to the WAFs was reduced significantly with respect to controls as demonstrated by several size, condition and allometric parameters. The response to petroleum hydrocarbon exposure is not dose-dependent, maximal responses being measured in low (Ural) and intermediate (Maya) doses. This seems to depend on a behavioural reaction (shell valve closure) against high doses of pollutants which may avoid the sublethal damage to some extent. 4. Shell abnormalities or changes in shell thickness were not detected. 5. The histological study of gonad tissue revealed that gamete release is retarded and hemocytic infiltration of mature gonad tissue is increased after exposure to low and intermediate doses of the WAFs. On the other hand, spawning is readily induced under exposure to high doses of the WAFs.