Chronic Sublethal Effects of San Francisco Bay Sediments on Nereis (Neanthes) arenaceodentata; Interpretative Guidance for a Growth End Point

Growth in the polychaete worm Nereis (Neanthes) arenaceodentata has been suggested as a good sublethal end point for marine sediment bioassays. While growth is biologically important, eventual population success is more directly dependent on survival and reproduction. Growth may affect population success indirectly via survival and reproduction. To provide interpretative guidance for bioassays measuring worm growth, the quantitative relationship between growth and reproduction must be established. Juvenile N. arenaceodentata were exposed to five geometrically decreasing food rations. Growth, as individual worm wet weight, was measured after 3, 6, and 9 weeks. A significant gradient in worm growth was observed at each time interval. Eggs were first observed in the coelom of female worms at the 6-week interval. Subsequent reproduction, measured as fecundity and number of juveniles produced, closely mirrored the reduced growth rates. Based on results reported herein, a somatic growth rate greater than or equal 0.65 mg/day measured between 0 to 6 weeks resulted in no significant effect on either survival or reproduction. Growth rates less than or equal 0.45 mg/day resulted in significant reductions in reproduction. Low growth rates (0.05 mg/day) were associated with a nearly complete cessation of reproduction and very poor survival (5 to 11 percent). The importance of distinguishing somatic growth from gametic growth in chronic sublethal sediment bioassays with N. arenaceodentata is discussed.... Bioassay, Reproduction, Growth, Sublethal, Neanthes