Seasonal Variability Of Pristane In Mussels (Mytilus Trossulus) In Prince William Sound, Alaska

Abstract

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 nearshore zooplanktivores, especially juvenile pink salmon (Oncorhynchus gorbuscha), and I evaluate whether the increase may be used as an index of foraging success, and hence early marine survival, of pink salmon. Pristane is biosynthesized by Neocalanus copepods. Examination of the trophic and temporal distribution of pristane found in 3,007 samples implicates Neocalanus copepods as the source of pristane in PWS. Neocalanus copepods often dominate the zooplankton biomass during spring in PWS. 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 ~100,000,000 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. Hence, the forage value of Neocalanus copepods may be considerably lower than is usually assumed.

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 nearshore zooplanktivores, especially juvenile pink salmon (Oncorhynchus gorbuscha), and I evaluate whether the increase may be used as an index of foraging success, and hence early marine survival, of pink salmon. Pristane is biosynthesized by Neocalanus copepods. Examination of the trophic and temporal distribution of pristane found in 3,007 samples implicates Neocalanus copepods as the source of pristane in PWS. Neocalanus copepods often dominate the zooplankton biomass during spring in PWS. 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 ~100,000,000 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. Hence, the forage value of Neocalanus copepods may be considerably lower than is usually assumed.