Before introduction to mesocosms, initial samples of amphipods were taken for baseline (day 0) reburrowing trials. With the exception of the L1 baseline trials, only juvenile amphipods were used. Juveniles are defined as individuals retained on a 500um sieve after passing through 1.1mm and 710um sieves.
Clean sediment was collected from Thorton's Creek, a tributary of the Severn River in Virginia three days prior to the reburrowing assay. The sediment was not sieved because preliminary trials indicated amphipods avoided the sieved sediment. Test chambers were prepared by filling plastic condiment cups 1/3 full with sediment. Glass culture dishes were used on 6/12/00 but all other days utilized the plastic cups described above. After filling, the test chambers were carefully submersed into plastic tubs of flowing filtered seawater for 48 hours. Twenty-four hours prior to the test, the tubs were drained and refilled with seawater adjusted to the salinity of the mesocosms and gently aerated. On the morning of the assay, the tubs were drained half way and transported to the test lab.
Juvenile amphipods for the assay were collected from each mesocosm. An amphipod was haphazardly selected for an individual trial and released into the center of a test chamber just below the surface of the water using a plastic 1ml pipette. The time required for the amphipod to burrow was then recorded using a stopwatch. Time began when the amphipod initially contacted the sediment surface and stopped when no part of the amphipod was longer visible at the sediment-water interface. A new test chamber was used for each trial.
Amphipods from Queen's Creek a tributary of the York River, VA were cultured in clean York River and contaminated Baltimore Harbor sediment for 18 days. The cultures were static renewal with a 60% water change and feeding (2mg/amphipod) occurring every other day. After 18 days, the culture were sampled as in the L1 and L3 mesocosm studies. Juveniles were collected and individually used in reburrowing trials. Test chambers were prepared as above except that both Thorton's Creek and Baltimore Harbor sediment was used. Amphipods from both the clean and contaminated cultures were allowed to burrow into test chambers containing either clean or contaminated sediment following the same reburrowing protocol described earlier.
Methods and illustration from Schaffner and Vogt's Chesapeake Ecotox Research Project (CERP): Quantifying Ecological Risks of Contaminated Sediments on Living Resources in Supporting Decisions on Habitat Restoration Strategies in the Chesapeake Bay, in prep. Please do not cite. Funded by National Oceanographic and Atmospheric Administration.