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Benthic Invertebrates

At Beach Nourishment Area O-45.1, benthic invertebrate densities (total) were not significantly different between months or transects (ANOVA, P > 0.05) ((Table 27); the lowest mean density occurred in October 1994 (1,647 organisms/m2) and the highest in April 1995 (7,838 organisms/m2) ((Table 28).

The mean numbers of taxa/categories collected in the beach nourishment area ranged from three to five ((Table 29). Major benthic invertebrate taxa collected in the beach nourishment area included oligochaetes, Corbicula fluminea, Corophium salmonis, and Corophium spinicorne ((Table 30). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-45.1 ((Table 27). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 0 organisms/m2 in April 1995 to 687 organisms/m2 in July 1994. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 1,675 organisms/m2 in October 1994 to 14,259 organisms/m2 in April 1995 ((Table 30). Densities of Corophium spp. also varied spatially along each transect (Fig. 7).

Diversity (H) and Equitability (E) were not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-45.1 ((Table 27). Mean H values ranged from 0.83 in April 1995 to 1.46 in January 1995, and mean E values ranged from 0.55 in April 1995 to 0.76 in July 1994 and January 1995 ((Table 29). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-45.1. Mean median grain size in the beach nourishment area ranged from 0.23 mm in July 1994 and April 1995 to 0.24 mm in October 1994 and January 1995 ((Table 31). Percent silt/clay was not significantly different between months or transects (Kruskal-Wallis, P > 0.05). Mean percent silt/clay ranged from 22.8% in April 1995 to 24.8% in July 1994 ((Table 31). Percent volatile solids were not significantly different between months (Kruskal-Wallis, P > 0.05), but they were significantly lower (Kruskal-Wallis, P < 0.05) at stations along the 15-m transect than at stations along the 30-m transect. Mean percent volatile solids ranged from 1.0% in July 1994 to 1.4% in October 1994 ((Table 31).

Benthic Invertebrates

At Beach Nourishment Area O-47.8, benthic invertebrate densities (total) were significantly different between months and transects (ANOVA, P < 0.05) ((Table 32); the lowest mean density occurred in October 1994 (1,306 organisms/m2) and the highest in April 1995 (12,613 organisms/m2) ((Table 33). In all months, higher densities occurred at stations along the 30-m transect than those along the 15-m transect.

The mean numbers of taxa/categories (by month) collected in the beach nourishment area ranged from two to five ((Table 34). Major benthic invertebrate taxa collected in the beach nourishment area included oligochaetes, Corbicula fluminea, Corophium salmonis, and Ceratopogonidae larvae ((Table 35). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-47.8; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect compared to stations along the 15-m transect ((Tables 32 and 35). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 0 organisms/m2 in July and October 1994 to 286 organisms/m2 in January 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 487 organisms/m2 in July 1994 to 19,413 organisms/m2 in April 1995 ((Table 35). Densities of Corophium spp. also varied spatially along each transect (Fig. 8).

Diversity (H) and Equitability (E) were not significantly different (ANOVA, P > 0.05) between months ((Table 32). Mean H values ranged from 0.73 in October 1994 to 1.20 in April 1995, and mean E values ranged from 0.45 in July 1994 to 0.67 in April 1995 ((Table 34). Diversity was significantly higher (ANOVA, P < 0.05) at stations along the 30-m transect compared to stations along the 15-m transect; however, E was not significantly different between transects. 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-47.8. Mean median grain size in the beach nourishment area ranged from 0.32 mm in October 1994 to 0.58 mm in April 1995 ((Table 36). Percent silt/clay was not significantly different between months or transects (Kruskal-Wallis, P > 0.05). Mean percent silt/clay ranged from 0.3% in April 1995 to 2.7% in July 1994 ((Table 36). Percent volatile solids were not significantly different between months (Kruskal-Wallis, P > 0.05), but were significantly higher at stations along the 30-m transect than at stations along the 15-m transect (Kruskal-Wallis, P < 0.05). Mean percent volatile solids ranged from 0.3% in January 1995 to 1.1% in July 1994 ((Table 36). 

Benthic Invertebrates

At Beach Nourishment Area O-57.0, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) ((Table 37); the lowest mean density occurred in October 1994 (14,041 organisms/m2) and the highest in July 1994 (22,065 organisms/m2) ((Table 38). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect ((Tables 37 and 38). In the undisturbed area outside of the beach nourishment area (Stations 1 and 2), mean benthic invertebrate densities were lower than those in the beach nourishment area in all months ((Table 38). No statistical analysis was performed because only two stations were sampled in the undisturbed area.

The mean numbers of taxa/categories (by month) collected in the beach nourishment area were similar, ranging from 6 to 8 ((Table 39). In the undisturbed area, the mean numbers of taxa/categories (by month) collected ranged from 4 to 7. Major benthic invertebrate taxa collected in the beach nourishment area included nemerteans, oligochaetes, Corbicula fluminea, Corophium salmonis, Chironomidae larvae, and Ceratopogonidae larvae ((Table 40). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-57.0; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect ((Tables 37 and 40). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 1,322 organisms/m2 in April 1995 to 3,543 organisms/m2 in July 1994. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 4,274 organisms/m2 in July 1994 to 14,602 organisms/m2 in January 1995 ((Table 40). Densities of Corophium spp. also varied spatially along each transect (Fig. 9). With the exception of July 1994, mean densities of Corophium spp. along the 15-m transect in the undisturbed area (Station 1) outside of the beach nourishment area were higher than mean densities at stations along the 15-m transect in the beach nourishment area ((Table 40). In July 1994 and January 1995, mean densities of Corophium spp. along the 30-m transect in the undisturbed area (Station 2) outside of the beach nourishment area were higher than mean densities at stations along the 30-m transect in the beach nourishment area, whereas in October 1994 and April 1995, the reverse was true.

Diversity (H) was significantly different (ANOVA, P < 0.05) between months, but not between transects in Beach Nourishment Area O-57.0 ((Table 37). Mean H values ranged from 1.18 in July 1994 to 1.78 in January 1995 ((Table 39). Equitability (E) was not significantly different (ANOVA, P > 0.05) between months, with mean values ranging from 0.48 in July 1994 to 0.69 in January 1995. Equitability was significantly higher (ANOVA, P < 0.05) at stations along the 15-m transect than at stations along the 30-m transect ((Table 37). Mean H and E values were higher in the beach nourishment area than in the undisturbed area, except in July 1994 ((Table 39). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-57.0; however, it was significantly higher (P < 0.05) at stations along the 15-m transect (mean = 0.30 mm) than at stations along the 30-m transect (mean = 0.17 mm) ((Table 41). Mean median grain size in the beach nourishment area ranged from 0.22 mm in January 1995 to 0.26 mm in July 1994. Percent silt/clay was not significantly different between months (Kruskal-Wallis, P > 0.05), but it was significantly lower at stations along the 15-m transect (Kruskal-Wallis, P < 0.05) than at stations along the 30-m transect. Mean percent silt/clay ranged from 6.4% in July 1994 to 9.2% in January 1995 ((Table 41). Percent volatile solids were not significantly different between months (Kruskal-Wallis, P > 0.05), but they were significantly lower (P < 0.05) at stations along the 15-m transect than at stations along the 30-m transect ((Table 41). In the beach nourishment area, mean percent volatile solids ranged from 0.8% to 0.9% throughout the study. Mean median grain size was lower in the undisturbed area outside of the beach nourishment area than in the beach nourishment area ((Table 41). With the exception of July 1994, mean percent silt/clay values in the undisturbed area outside of the beach area were higher than mean values in the beach nourishment area. Mean percent volatile solids were 1.8% or less for both the undisturbed area and the beach nourishment area ((Table 41).

Benthic Invertebrates

At Beach Nourishment Area W-70.1, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) ((Table 42); the lowest mean density occurred in January 1995 (3,561 organisms/m2) and the highest in July 1994 (5,541 organisms/m2) ((Table 43). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect ((Tables 42 and 43).

The mean numbers of taxa/categories collected in the beach nourishment area were similar for each month, ranging from four to five ((Table 44). Major benthic invertebrate taxa collected in the beach nourishment area included oligochaetes, Corbicula fluminea, and Corophium salmonis ((Table 45). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-70.1; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect ((Tables 42 and 45). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 12 organisms/m2 in January 1995 to 221 organisms/m2 in July 1994. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 3,067 organisms/m2 in October 1994 to 4,307 organisms/m2 in April 1995 ((Table 45). Densities of Corophium spp. also varied spatially along each transect (Fig. 10).

Diversity (H) and Equitability (E) were not significantly different (ANOVA, P > 0.05) between months ((Table 42). Mean H values ranged from 1.04 in July 1994 to 1.41 in April 1995, and mean E values ranged from 0.49 in July and October 1994 to 0.72 in January 1995 ((Table 44). Diversity was significantly higher (ANOVA, P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect; however, E was not significantly different between transects ((Table 42). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area W-70.1. Mean median grain size in the beach nourishment area ranged from 0.45 mm in October 1994 and January 1995 to 0.52 mm in April 1995 ((Table 46). Percent silt/clay was not significantly different between months or transects (Kruskal-Wallis, P > 0.05). Mean percent silt/clay ranged from 0.6% in July 1994 to 1.7% in October 1994 ((Table 46). Percent volatile solids were significantly different between months (Kruskal-Wallis, P < 0.05), but they were not significantly different between transects (Kruskal-Wallis, P > 0.05). Mean percent volatile solids ranged from 0.4% in July 1994 and January and April 1995 to 0.7% in October 1994 ((Table 46). 

Benthic Invertebrates

At Beach Nourishment Area O-75.8, benthic invertebrate densities (total) were significantly different between months (ANOVA, P < 0.05) ((Table 47); the lowest mean density occurred in January 1995 (1,611 organisms/m2) and the highest in July 1994 (8,622 organisms/m2) ((Table 48). Benthic invertebrate densities were significantly different between the 15- and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect ((Tables 47 and 48).

The mean numbers of taxa/categories (by month) collected in the beach nourishment area ranged from three to six ((Table 49). Major benthic invertebrate taxa collected in the beach nourishment area included oligochaetes, Corbicula fluminea, Corophium salmonis, and Ceratopogonidae larvae ((Table 50). 

Densities of Corophium spp. were significantly different (ANOVA, P < 0.05) between months in Beach Nourishment Area O-75.8; the highest mean density occurred in October 1994 and the lowest in January 1995 ((Table 50). In addition, mean densities of Corophium spp. were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect ((Tables 47 and 50). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 0 organisms/m2 in January 1995 to 3,672 organisms/m2 in October 1994. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 66 organisms/m2 in January 1995 to 4,488 organisms/m2 in July 1994 ((Table 50). Densities of Corophium spp. also varied spatially along each transect (Fig. 11).

Diversity (H) was significantly different (ANOVA, P < 0.05) between months, with mean H values ranging from 1.19 in January 1995 to 1.88 in April 1995 ((Table 49). Diversity was significantly higher (ANOVA, P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect. Equitability (E) was not significantly different (ANOVA, P > 0.05) between months or transects ((Table 47). Mean E values ranged from 0.67 in July 1994 to 0.84 in April 1995 ((Table 49). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-75.8. Mean median grain size in the beach nourishment area ranged from 0.40 mm in October 1994 to 0.51 mm in July 1994 ((Table 51). Percent silt/clay and percent volatile solids were not significantly different between months or transects (Kruskal-Wallis, P > 0.05). Mean percent silt/clay ranged from 0.4% in July 1994 and January 1995 to 2.9% in October 1994, and mean percent volatile solids ranged from 0.5% in January and April 1995 to 0.8% in October 1994 ((Table 51).

The regression relationship for median grain size and Corophium spp. density was significant (P < 0.05). The regression equation was log10(Corophium spp. density + 1) = 3.13 - 2.51 x median grain size (mm); F = 22.66, P = 0.000, and r2 = 0.05. Median grain size was a poor predictor of Corophium spp. density, explaining only 5% of the variation in Corophium spp. density (transformed).

Assessing the standing crops of benthic invertebrates, particularly Corophium spp., in the lower Columbia River is one of the most important means of determining the habitat values of various areas for fishes, including migrating juvenile salmonids. Corophium salmonis is an important food for juvenile salmonids (McCabe et al. 1983, 1986; Kirn et al. 1986). Corophium salmonis and C. spinicorne were the dominant prey for juvenile salmonids collected during spring 1984 at Bonneville Dam (Muir and Emmett 1988). Benthic invertebrate communities are relatively stable on a short-term basis, in contrast to fish communities, which can change rapidly. For example, large numbers of juvenile salmon may be present in a particular area of the river after hatchery releases, which are then followed by a dramatic decline as the juveniles migrate out of the area.

At times, C. salmonis is also an important prey for nonsalmonid fishes in the river, including American shad (Alosa sapidissima), peamouth (Mylocheilus caurinus), threespine stickleback (Gasterosteus aculeatus), and starry flounder (Platichthys stellatus) (McCabe et al. 1983). Also, juvenile white sturgeon (Acipenser transmontanus) in the lower Columbia River prey heavily on C. salmonis (Muir et al. 1988, McCabe et al. 1993a).

Juvenile salmonids use both nearshore and main channel areas of the lower Columbia River as they migrate to the Pacific Ocean (McCabe et al. 1983, Dawley et al. 1986, Hinton and Emmett 1994). We would expect that juvenile salmonids would migrate along the 10 beach nourishment areas that we studied. In addition, we would expect juvenile salmonids to feed on the abundant populations of Corophium spp. in at least some of the these areas.

With the exception of Beach Nourishment Area O-75.8, Corophium spp. densities in the beach nourishment areas were not significantly different (P > 0.05) between months. In a benthic invertebrate study between RKm 40 and 42 in the Columbia River estuary, Corophium spp. densities were significantly higher (P < 0.05) in May and September than in July 1993; however, densities for May and September were not significantly different (P > 0.05) (Hinton et al. 1995). Densities of C. salmonis were significantly higher (P < 0.05) in September than in July at three wetlands in the Columbia River estuary in 1992 (McCabe and Hinton 1993). At Cottonwood Island (RKm 110-114) in the lower Columbia River, C. salmonis densities were not significantly different (P > 0.05) between July and November 1987, yet densities were significantly higher (P < 0.05) in July 1988 than in December 1988 (McCabe et al. 1990).

Benthic invertebrate densities (total and Corophium spp.) were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect except at Beach Nourishment Area O-45.1, where there was no significant difference (P > 0.05) between transects. Apparently the habitat along the 30-m transects provides a better environment for benthic invertebrate colonization than does the habitat along the 15-m transects, which are closer to the high tide mark on the beach. Generally, the stations along the 30-m transects were in deeper water than stations along the 15-m transects (Appendix Table).

All 10 beach nourishment areas supported substantial standing crops of Corophium spp. (most of which were C. salmonis) at times, particularly at stations along the 30-m transects. To show the true value of these habitats it would have been ideal to have collected benthic invertebrate samples in channel areas away from the shoreline, and then to have compared these collections to those made in the beach nourishment areas. Unfortunately, there is little information available documenting standing crops of C. salmonis in channel areas away from the shoreline in the beach nourishment study area. Densities of C. salmonis in the 10 beach nourishment areas were generally much higher than densities in 8 channel areas (River Mile (RM) 28-131) during comparable seasons in 1988 and 1989 (McCabe et al. 1993b) ((Table 52). With the exception of RM 28, standing crops of C. salmonis in the 8 channel areas were usually less than 400 organisms/m2; whereas in the 10 beach nourishment areas, densities generally exceeded 1,100 organisms/m2.

In conclusion, densities of benthic invertebrates, including Corophium spp., generally varied spatially at the 10 beach nourishment sites, with the highest densities typically occurring at stations farthest from the high tide mark on the shore. Although some beach nourishment areas had higher standing crops of Corophium spp. than others, all areas supported substantial numbers of Corophium spp. at times. Since Corophium spp. are important prey for juvenile salmonids, and juvenile salmonids migrate along the beach nourishment areas, it is important to insure that Corophium spp. populations in these areas are not adversely impacted.

We thank Lawrence Davis, Donald Gruber, and Nathan Cook for their assistance in sampling. We are especially appreciative of the efforts of Randall Cummings, COE, in coordinating and overseeing all the diving activities. The Portland District COE funded the research and conducted the sediment analyses.

Table of Contents

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Dawley, E. M., R. D. Ledgerwood, T. H. Blahm, C. W. Sims, J. T. Durkin, R. A. Kirn, A. E. Rankis, G. E. Monan, and F. J. Ossiander. 1986. Migrational characteristics, biological observations, and relative survival of juvenile salmonids entering the Columbia River estuary, 1966-1983. Report to Bonneville Power Administration, Contract DE-A179-84BP39652, 256 p. (Available from Bonneville Power Administration, Division of Fish and Wildlife-PJ, P.O. Box 3621, Portland, OR 97208.)

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Emmett, R. L., G. T. McCabe, Jr., T. C. Coley, R. J. McConnell, and W. D. Muir. 1986. Benthic sampling in Cathlamet Bay, Oregon--1984. Report to U.S. Army Corps of Engineers, Contract DACW57-84-F-0384, 11 p. plus appendices. (Available from Northwest Fisheries Science Center, 2725 Montlake Blvd. E., Seattle, WA 98112.)

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Sanborn, H. R. 1975. Benthic infauna observed at five sites in the Columbia River from August 1973 to July 1974. Report to U.S. Army Corps of Engineers and Columbia River Fish. Prog. Office (Nat. Mar. Fish. Serv.), 21 p. (Available from Northwest Fisheries Science Center, 2725 Montlake Blvd. E., Seattle, WA 98112.)

U.S. Army Corps of Engineers. 1991. Federal navigation projects: Columbia River maintenance disposal plan, main and side channels downstream of Bonneville Dam. Navigation Branch, Operations Division, Portland District, U.S. Army Corps of Engineers, Portland, OR, 161 p.

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