C .-Y. Horng, G.L. Taghon J. Exp. Mar. Biol. Ecol. 242 1999 41 –57
47
effect of phenanthrene concentration using a particle preference model modified after Self and Jumars 1988:
2
LOR 5 a 1 b log D 1 c log
D 1 d C 1
e s
d
s d
10 10
phenanthrene
where D is the mean test particle diameter, C is the concentration of
phenanthrene
phenanthrene in sediment, and e is the residual error. Self and Jumars 1988 used
geometric mean diameter within a size interval to represent the mean size of the particles within that size range. The use of the geometric mean presumes a lognormal size
distribution, which is largely true for natural sediments. For this selectivity experiment, the glass bead mixture was made from four types of bead stocks, each distributed in a
rather narrow range about 20 mm. The size distributions within every 15-mm wide size category may not be continuous and lognormal. Therefore, the mean size of particles for
each size interval was estimated by pooling all size data collected from ambient sediments and fecal pellets, and then averaging every single particle within the size
range for the mean. The mean diameters for ,15, 15–30, 30–45, 45–60, 60–75, 75–90, and 90–105-mm intervals were 12.7, 20.7, 39.1, 51.3, 64.1, 86.6, and 94.2 mm,
respectively. The method of least-squares was used to determine the values of the coefficients a, b, c, and d in the multiple curvilinear model. The most preferred particle
size and its variance were estimated as in Self and Jumars 1988.
3. Results
3.1. Particle selection on natural sediments All four sediment had high, similar concentrations of total C and total N Table 1.
Protein concentrations were also similar in the sediments from Sippewissett Marsh, Schooner Creek, and Barnegat Bay; Piles Creek sediment had lower protein. There were
obvious differences in the concentrations of the measured PAHs, reflecting the expected patterns based on location of the sampling sites.
The size–frequency distributions of ingested particles and available particles were not significantly different p .0.9 for Sippewissett Marsh, Schooner Creek, and Barnegat
Bay sediments, but were significantly different p ,0.001 for the Piles Creek treatment Fig. 1. The adjusted residuals in the Sippewissett Marsh, Schooner Creek, and
Barnegat Bay treatments were mostly within the 5 deviation from zero and indicated
Table 1
a
Total C, total N, protein, and PAH concentrations in natural sediments
21 21
21 21
Sediment C mg g
N mg g Protein mg g
PAH mg g Sippewissett Marsh
50.1 0.12 4.78 0.24
2.68 0.11 0.08 0.03
Schooner Creek 45.7 0.19
4.48 0.32 2.67 0.12
0.83 0.09 Barnegat Bay
41.6 0.22 4.35 0.07
2.94 0.20 5.40 0.56
Piles Creek 44.6 0.45
3.32 0.09 1.61 0.07
31.1 5.34
a
Means S.D. based on three replicate analyses.
48 C
.-Y. Horng, G.L. Taghon J. Exp. Mar. Biol. Ecol. 242 1999 41 –57
Fig. 1. Size–frequency distributions of available dashed lines and ingested solid lines particles in selection experiment with four natural sediments. The p values indicate probability that the two distributions are
equivalent G-test.
no selection for particles ,100 mm Fig. 2. The very smallest particles of Piles Creek sediment a few micrometers in diameter were selected for, and the larger particles were
ingested indiscriminately. There was no evidence that the size of worms affected particle selection Fig. 3.
3.2. Effect of phenanthrene on particle selection Phenanthrene concentrations in the spiked sediments were only about 10 of the
target concentrations Table 2. Some phenanthrene was probably lost during the rinsing
21
procedure. Phenanthrene is relatively soluble in water 1290 mg l ; Mackay and Shiu,
1977 and much of it could have been lost by desorption. The amounts of phenanthrene were, however, comparable to the levels in natural sediments from several sites Table
2. Worms preferentially fed on small particles and avoided larger particles in all
treatments Fig. 4. The adjusted residuals showed a strong selection for ,30 mm particles and against .90 mm particles Fig. 5.
C .-Y. Horng, G.L. Taghon J. Exp. Mar. Biol. Ecol. 242 1999 41 –57
49
Fig. 2. Adjusted residuals for comparison of frequency of particles ingested to frequency of particles available in selection experiment with four natural sediments. The regions enclosed by dashed lines are the 5 deviates
from no selection.
Multiple regression analysis indicated no significant contribution of phenanthrene
21
concentration at levels up to 13 mg g to the quadratic model for particle selection
Table 3. The model was improved by a mere 0.1 with the addition of phenanthrene concentration. No significant difference in median size of ingested beads among
treatments ANOVA, F 51.47, p .0.2 also indicated that particle selection was
5,24
independent of phenanthrene concentration over the range used in these experiments. Because the ANOVA Table 3 indicated that the quadratic model could not explain the
data completely lack of fit, p ,0.001, we can only conclude that there was insufficient evidence to reject the null hypothesis of no effect of phenanthrene on particle selection.
2
The coefficient of determination r for the regression, on the other hand, indicated that the quadratic model accounted for a reasonable amount 78 of the variability in the
data Fig. 6. Assuming this model was valid to describe the particle preference of Capitella sp. I, a most preferred particle size of 16.764.16 S.D. mm was derived.
Selection of particles larger than 63 mm the boundary between silt and sand decreased sharply Fig. 6. Again, there was no evidence that worm size affected particle selection
Fig. 3.
50 C
.-Y. Horng, G.L. Taghon J. Exp. Mar. Biol. Ecol. 242 1999 41 –57
Fig. 3. Median diameter of ingested particles versus body size of Capitella sp. I in selection experiments with four natural sediments Si, Sippewissett Marsh; S, Schooner Creek; B, Barnegat Bay; P, Piles Creek and with
glass bead–sediment mixtures numbers refer to treatments.
Table 2 Concentration of phenanthrene in experimental sediments and field sediments collected from coastal sites in
a
New Jersey and New York
21
Sediment Concentration mg g
Target concentration Particle selection experiment
Treatment 1 0.07 0.03
Treatment 2 0.15 0.02
1 Treatment 3
0.67 0.03 5
Treatment 4 1.16 0.13
10 Treatment 5
4.81 0.04 50
Treatment 6 13.0 0.16
100 Field sediments
Barnegat Bay 0.35 0.05
b
Arthur Kill main channel 0.65 0.16
Piles Creek 0.89 0.18
b
Newtown Creek, East River 9.33 0.85
a
Means S.D. based on three replicates.
b
Data from Horng 1998.
C .-Y. Horng, G.L. Taghon J. Exp. Mar. Biol. Ecol. 242 1999 41 –57
51
Fig. 4. Size distributions of available particles dashed lines and ingested particles solid lines in selection experiment with glass bead–sediment mixtures spiked with phenanthrene. The p values indicate probability
that the two distributions are equivalent G-test.
4. Discussion
