I 



Figure 3. — Radioisotopes can be accumulated by marine animals from their food. In this study, zinc 65 and chromium 51 

 are being followed through four trophic levels of a marine food chain. Newly hatched brine shrimp (second trophic 

 level) are being removed here from hatching trays and placed in flasks where they feed on radioactive phytoplankton 

 (first trophic level). After 24 hours, the brine shrimp are fed to postlarval fish (third trophic level), which in turn 

 are fed to mummlchog (fourth trophic level). 



