Exxon Valdez Oil Spill

Pristane (2,6,10,14-tetramethylpentadecane) concentrations in mussels (Mytilus trossulus) increase abruptly during spring in Prince William Sound (PWS), Alaska. This increase is mainly due to ingestion by mussels of pristane-laden feces produced by near-shore zooplanktivores, especially juvenile pink salmon (Oncorhynchus gorbuscha). Examination of the trophic and temporal distribution of pristane found in 3,007 samples implicates Neocalanus copepods, which often dominate the zooplankton biomass in PWS during spring, as the source of pristane. Juvenile pink salmon, preying on Neocalanus, produce pristane-laden feces that are accumulated by mussels 52 times more efficiently than is dissolved pristane. Releases en masse of ~ 10 juvenile pink salmon from a hatchery at the peak of the Neocalanus bloom were immediately followed by increases in pristane concentrations of nearby mussels monitored during 1996 and 1998. Accumulation of dissolved pristane, or of fecal pellets produced by Neocalanus copepods, were substantially less important pathways of pristane transfer to mussels. The transfer pathway to mussels via feces produced by zooplanktivores preying on Neocalanus is the basis for a potential linkage between pristane accumulation by mussels and survival of juvenile pink salmon, because it reflects indirectly the magnitude of Neocalanus prey consumed. Annual survival values of hatchery pink salmon were weakly correlated (P = 0.10) with pristane concentrations monitored in mussels at 25 stations distributed throughout PWS from 1995 through 2001. Although Neocalanus copepods are considered important forage for juvenile pink salmon, feeding experiments reported herein confirm previous studies implicating growth inhibition by pristane, implying a lower forage value of Neocalanus than is usually assumed.