Research Brief:
Influence of Food Ration on Sediment Toxicity in Neanthes arenaceodentata (Annelida: Polychaeta)

Research/Objectives     

Design: A 3 x 2 factorial experiment was conducted to evaluate the influence of food ration on observed toxicity in Neanthes arenaceodentata. Worms were fed one of three food rations: 0.25x, 1.0x, and 6.0x. The 1.0x ration was composed of 4 mg Tetra/Marin/worm/w and 2 mg alfalfa/worm/w. Worms in each food ration were exposed to one of two sediments: a clean control sediment collected from Sequim Bay, Washington, USA (SC) or a contaminated sediment collected from Black Rock Harbor near Bridgeport, Connecticut, USA (BRH) that was diluted with SC such that the final concentration of contaminated sediment was 12 percent. Survival and growth were monitored every 2 weeks for 8 weeks. Sediment treatment and food ration had strong effects on survival and growth patterns in N. arenaceodentata.

Survival: Most of the mortality within any given treatment combination occurred during the first 2 weeks of the experiment. This decline in survival was greatest for worms exposed to BRH. Survival was significantly lower for worms in BRH compared to SC at the 0.25x and 1.0x ration levels. Survival was not reduced for worms in BRH compared to SC at the 6.0x ration level.

Growth Pattern: Worm size during the course of the experiment was positively related to ratio level. Significantly reduced size in BRH worms was observed at each monitoring period within the 0.25x and 1.0x rations, but only at weeks 6 and 8 for the 6.0x ration level. The percent difference is size between worms exposed to BRH and SC, when those worms were fed the 0.25x or 1.0x rations, ranged between 55 and 66 percent. The percent difference in size observed between BRH and SC worms fed the 6.0x ration was much smaller (9-17%).

U.S. Army Engineer Research and Development Center

July 1998
www.erdc.usace.army.mil
www.wes.army.mil/el/dots

Results/Products    

The results of this study demonstrate that food ration has a strong influence on observed toxicity in N. arenaceodentata. The importance of food ration effects on toxicity must be considered while designing chronic sublethal bioassays. To ensure the relevance of bioassay results, the food ration used during a chronic bioassay should produce a pattern of growth in control animals that is similar to patterns of growth observed in nature.

Research Team    

Todd S. Bridges, Ph.D., ERDC; J. Daniel Farrar and B. Maurice Duke, contract support U.S. Army Engineer Research and Development Center
Waterways Experiment Station
3909 Halls Ferry Road, Vicksburg, MS 39180