A . Bennett et al. J. Exp. Mar. Biol. Ecol. 242 1999 1 –20
7
2.6. Statistical analyses Analysis of variance ANOVA analyses were conducted using the software STAT-
GRAPHICS Plus 2.0. Values of P , 0.05 were considered to be significant. When ANOVA differences were significant, the Fisher’s Least Significant Difference, LSD, a
posteriori multiple range test was used to detect differences among effects. A 2 3 3 3 9 repeated measures ANOVA design was used to detect significant differences among
sediment type, snail type, PAH concentration, and time effects in the microcosm experiment. Regressions and correlations were determined using both STATGRAPHICS
Plus 2.0 and SigmaPlot 1.02 software.
3. Results
3.1. Microcosm sediments and L. irrorata PAH concentrations in the Low-PAH sediment treatments ranged from 0.1 to 0.2 ppm
Fig. 2, whereas PAH concentrations in the High-PAH sediments were significantly higher P , 0.05 and ranged from 5 to 18 ppm Fig. 2b. A loss of PAHs in both High-
and Low-PAH sediments was observed between Days 28 and 60 and was consistent across all three of the High-PAH treatments.
Relative abundances of PAHs in the High-PAH sediments Fig. 3 reflect PAH concentrations normalized to the most abundant PAH isomer Steinhauer and Boehm,
1992. When examining the relative abundances of certain PAH groups with a variety of molecular weights the proportion of HMW PAHs increased with time in High-PAH
sediments. In High-PAH sediments, Low-Exposure and High-Exposure snail treatments had similar trends in low molecular weight LMW and HMW PAH relative abundances
within each sediment treatment throughout the duration of the experiment Fig. 3. The relative abundances of PAHs in Low-PAH sediments had a broader and more evenly
distributed range of molecular weights than High-PAH sediments data not shown.
Initial Day 0 C:N ratios were significantly higher P , 0.0001 in Low-PAH sediments 60.966.03 than in High-PAH sediments 19.861.71, Table 1. The C:N
ratios of sediments in the three Low-PAH sediment treatments all declined significantly P , 0.02 over the course of the experiment, with some sporadic changes in treatments
involving snails Table 1. The C:N ratios of the Low-PAH sediments on Day 60 were similar to the initial C:N ratios of the High-PAH sediments. There were no significant
changes in the C:N ratios of High-PAH sediments over the 60 days Table 1.
High-PAH sediments had a significantly higher initial Day 0 concentration of
21
chlorophyll-a 65.3064.01 mg g dry sed. than did the Low-PAH sediments
21
2.0960.22 mg g dry sed. , P , 0.0001 Fig. 4. Chlorophyll-a concentrations
21
declined to below 10 mg g dry sed. in all of the High-PAH sediment treatments by Day
12 of the experiment and remained below this level for the remainder of the experiment. Chlorophyll-a concentrations in Low-PAH sediments also declined from Day 0 2.09 mg
21 21
g dry sed. to Day 12 a range of 0.004 to 0.06 mg g dry sed. . Chlorophyll-a concentrations in the Low-PAH sediment treatments increased over the final 16 days of
8 A
. Bennett et al. J. Exp. Mar. Biol. Ecol. 242 1999 1 –20
Fig. 2. Changes in total PAH concentrations over a 60-day interval in Low-PAH A and High-PAH B microcosm sediments collected from Pass Fourchon, LA. Error bars indicate one standard deviation.
21
the experiment up to a range of 0.30 to 2.05 mg g dry sed. by Day 60, particularly in
the treatment without L . irrorata.
Total phaeopigment concentrations total phaeophytins and phaeophorbides increased above initial Day 0 levels in all treatments over the early stages Days 4 and 12 in
Low-PAH sediments and Day 4 in High-PAH sediments of the microcosm experiment Figs. 5 and 6. Total phaeopigment concentrations peaked at Day 4 in treatments with
High-PAH sediments. Phaeophytin-a concentrations peaked at Day 12 in Low-PAH sediments. Total phaeophorbide concentrations in Low-PAH sediments without L
.
A . Bennett et al. J. Exp. Mar. Biol. Ecol. 242 1999 1 –20
9
Fig. 3. Relative abundances of specific PAHs and PAH groups in High-PAH sediment treatments with No Snails A, Low-Exposure snails B, and High-Exposure snails C of the microcosm experiment. Napth 5
napthalene, Phenan 5 phenanthrene,
Dibenzo 5 dibenzothiophene, Fluoran 5 fluoranthene,
Benzan 5 benzanthracene,
Benzobf 5 benzobfluoranthene, Benzokf 5 benzokfluoranthene,
Benzoap 5 benzoapyrene.
irrorata peaked at Day 12 and on Day 28 in Low-PAH treatments with L . irrorata.
Phaeophorbides were not detectable in Low-PAH treatments from Day 36 throughout the remainder of the experiment.
Fucoxanthin increased significantly P , 0.0001 over the final 24 days of the
10 A
. Bennett et al. J. Exp. Mar. Biol. Ecol. 242 1999 1 –20 Table 1
Changes in carbon:nitrogen ratios over 60-day interval in Low-PAH and High-PAH microcosm sediments collected from Pass Fourchon, LA; error bars indicate one standard deviation
Day C:N in Low-PAH sediment
C:N in High-PAH sediment Without
With With
Without With
With snails
Low-Exposure High-Exposure
snails Low-Exposure
High-Exposure snails
snails snails
snails 60.8666.03
60.8666.03 60.8666.03
19.7961.71 19.7961.71
19.7961.71 28
18.6365.30 73.95656.72
17.4862.68 54.89632.62
49.73648.83 20.0062.98
60 19.2960.21
17.4160.58 15.9462.49
77.98663.20 19.0567.55
30.1361.66
experiment in the treatments with Low-PAH sediments without L . irrorata Fig. 7.
Fucoxanthin, zeaxanthin, and chlorophyll-a showed the same rapid decay in High-PAH sediments within the first ten days of the experiment Figs. 4, 7 and 8. Fucoxanthin
2
concentrations were significantly correlated with chlorophyll-a r 5 0.82 in all treatments throughout the duration of the microcosm experiment data not shown.
Zeaxanthin was rarely detected in Low-PAH sediments Fig. 8. Zeaxanthin con- centrations in High-PAH sediments did not change significantly from Day 28 to Day 60,
and did not show any significant differences due to the presence of L
. irrorata Fig. 8. In all four treatments containing snails, L
. irrorata experienced weight loss over the course of the 60 days of the microcosm experiment Fig. 9. High-Exposure snails
preexposed to High-PAH concentrations experienced more total wet weight loss over the 60 day period than did Low-Exposure snails collected from Low-PAH sediments.
In all treatments L . irrorata experienced some weight gain during the early stages of the
experiment Fig. 9. This weight gain occurred consistently earlier in the High-Exposure snails than in Low-Exposure snails. We were not able to detect significant differences in
PAH concentrations in whole animal tissues collected from Low-Exposure and High- Exposure snails at the beginning and end of the experiment due to the high variability
high standard deviations in replicate concentrations.
4. Discussion
