Figure 3. Mean survival of E. estuarius in Lauritzen Channel/Richmond Harbor sediment and R. abronius n Palos Verdes Shelf sediment

ERDC TN-DOER-C23

September 2001

ΣDDT concentration and mortality of the amphipod E. estuarius in 10-day laboratory sediment

toxicity tests (Figure 3). An analysis of amphipod abundance along the same contamination gradient

failed to show a statistically significant correlation (R2 = 0.19, p = 0.23 for the Lauritzen

Channel/Richmond Harbor sediments) (Figure 4). One amphipod species, Grandidiarella japon-

ica, showed increasing abundance with increasing ΣDDT concentration. It was not clear why the

abundance of G. japonica was positively correlated with sediment toxicity and ΣDDT concentra-

tions since this species shows similar sensitivity in aqueous exposures to reference toxicants

compared with other amphipod species. It is possible, although not suggested by the authors, that

the benthic communities present at the sites may have adapted to contaminant levels in these

sediments. If so, the potential for adaptation may present a challenge to the correlative/observational

approach.

Figure 3. Mean survival of E. estuarius in

Lauritzen Channel/Richmond

Harbor sediment and R. abronius

in Palos Verdes Shelf sediment in

relation to the carbon-normalized

ΣDDT concentration in sediment

(OC = organic carbon) (adapted

from Swartz et al. 1994)

Figure 4. Mean abundance of amphipods

(excluding G. japonica) in relation

to ΣDDT normalized to organic

carbon for Lauritzen/Richmond

Harbor and Palos Verdes Shelf

sediments (adapted from

Swartz et al. 1994)

Finally, pooling data with their earlier studies of a contamination gradient on the Palos Verdes Shelf,

Swartz et al. (1994) showed similar relationships for sediment toxicity (Pooled R2 = 0.60, p <<

0.001) and amphipod abundance (Pooled R2 = 0.08, p = 0.11) compared with organic carbon

normalized ΣDDT sediment concentrations (Figures 3 and 4) (Swartz et al. 1994).

McGee and Fisher (1999) and McGee et al. (1999) also used the correlative approach to evaluate

the relationship between sediment-associated contaminants, abundance of the amphipod L. plumu-

losus, and toxicity to L. plumulosus in 10-day laboratory-based bioassays. The study evaluated