72 S
.D. Roast et al. J. Exp. Mar. Biol. Ecol. 245 2000 69 –81
correction for any residual weight change. Absorption efficiency was calculated using the equation:
A 5 F 2 E 4 [1 2 E 3 F ] where: A5absorption efficiency, F 5ash-free fraction of food source, and E 5ash-free
fraction of faeces Conover, 1966. 2.4. Experimental protocol
Egestion rates and absorption efficiencies were investigated at salinities 1, 10, 20 and
30‰ and temperatures 5, 10 and 158C within the range experienced by N
. integer in the estuarine environment Roast et al., 1998b. Salinities were prepared by diluting
filtered 10 mm seawater with tap water de-chlorinated by aeration for 24 h. All experiments were carried out in a Sanyo MLR-350HT growth cabinet with pro-
grammable temperature 60.18C and photoperiod. Test vessels were placed in the cabinet 2 h prior to the addition of mysids to allow the water temperature to equilibrate
with cabinet temperature. Experimental vessels were aerated constantly with filtered, compressed air. Experiments were run for 16 h overnight, with the cabinet lighting
programmed to synchronize with the natural photoperiod [16 h light 8 h dark with dawn and dusk sequence i.e. gradual increase and decrease of light intensity]. During the
experiment, mysids were, therefore, exposed to 4 h light 8 h dark 4 h light. All mysids were adults of similar size 1261 mm from the anterior margin of the rostrum to the tip
of the telson; ovigerous females were excluded. A total of 18 experiments was run at each temperature salinity combination using nine mysids of each gender.
2.5. Statistical treatment of results Two-way analysis of variance ANOVA was applied to egestion rate data to
determine the significance of temperature, salinity or gender effects and to establish factor interactions. Multiple linear regression analysis determined how egestion rates
differed with temperature, salinity and gender.
3. Results
3.1. Effect of temperature on egestion rates At most salinities, Neomysis integer egestion rates increased significantly with
increasing temperature Fig. 1 [ANOVA, f 5401 male and 328 female, d.f.52, p ,0.01]. The relationship was not simple, however, as temperature interacted sig-
nificantly with salinity to affect faecal production [ANOVA, f 53.42 male and 5.94 female, d.f.56, p ,0.01]. At salinities between 1–20‰, egestion rates were most
sensitive to temperature change between 5 and 108C, compared with mysids at 30‰ where egestion rates were affected most by temperature change between 10 and 158C.
Temperature coefficients Q indicated there were no obvious differences in tempera-
10
S .D. Roast et al. J. Exp. Mar. Biol. Ecol. 245 2000 69 –81
73
Fig. 1. Effect of temperature on the egestion rate of Neomysis integer at various salinities numbers correspond to salinity, ‰. n 59 for each temperature salinity combination. Data are means with 95
confidence intervals.
ture sensitivities for egestion rates over a wide salinity range or between males and females Table 1.
3.2. Effect of salinity Generally, faecal production increased significantly with increasing salinity [ANOVA,
f 539.3 male and 47.9 female, d.f.53, p ,0.01] Fig. 2. As salinity interacted significantly with temperature see previous section, the relationship between these two
variables was complex. At 58C, faecal production increased as salinity was increased from 20 to 30‰, but at 10 and 158C, faecal production decreased at 30‰; this effect
Table 1 Temperature coefficients Q for the faecal production of male and female Neomysis integer at various
10
salinities n 59 for each temperature salinity combination Gender
Salinity ‰ Q
value
10
Male 1
2.10 10
2.35 20
2.17 30
1.91 Female
1 1.88
10 2.06
20 2.09
30 1.91
74 S
.D. Roast et al. J. Exp. Mar. Biol. Ecol. 245 2000 69 –81
Fig. 2. Effect of salinity on the egestion rate of Neomysis integer at various temperatures numbers correspond to temperature, 8C. n 59 for each temperature salinity combination. Data are means with 95 confidence
intervals.
was significant only at 108C Fig. 2 95 confidence intervals, p ,0.05. Thus, egestion rates at 10 and 30‰ were not significantly different at 108C or 158C for males
95 confidence intervals, p .0.05, whereas they were significantly different at 58C 95 confidence intervals, p ,0.05.
3.3. Effect of gender At each temperature salinity combination, there was no significant difference between
male and female egestion rates Figs. 1 and 2 95 confidence intervals, p .0.05, and no significant interaction between gender and either temperature ANOVA, f 51.45,
d.f.52, p .0.05 or salinity ANOVA, f 50.09, d.f.53, p .0.05.
3.4. Combined effects of temperature, salinity and gender Multiple linear regression analysis revealed that temperature, salinity and gender
affected the egestion rate of N . integer according to the equation:
E 5 0.0061 1 0.0022T 1 0.0003S 2 0.0005G
21 21
where: E 5egestion rate mg faeces mg dry wt. h
, T 5temperature 8C, S 5salinity
‰ and G 5score for gender males50, females51. The positive coefficients for temperature and salinity confirm that faecal production increased with increasing
temperature and salinity [multiple linear regression, t 529.7 temperature and 10.5 salinity, d.f.52 temperature and 3 salinity, p ,0.01]. The negative coefficient value
S .D. Roast et al. J. Exp. Mar. Biol. Ecol. 245 2000 69 –81
75 Table 2
a
Effect of temperature and salinity on the food absorption efficiency of male and female Neomysis integer Gender
Temperature Salinity
Food value Faeces value
Absorption 8C
‰ F
E efficiency
Male 5
1 0.080
0.054 0.344
10 0.089
0.060 0.347
20 0.079
0.053 0.343
30 0.091
0.061 0.346
10 1
0.079 0.053
0.347 10
0.083 0.056
0.341 20
0.082 0.055
0.344 30
0.082 0.055
0.349 15
1 0.084
0.056 0.349
10 0.091
0.061 0.352
20 0.083
0.056 0.347
30 0.080
0.054 0.350
Female 5
1 0.082
0.056 0.338
10 0.081
0.054 0.347
20 0.083
0.056 0.341
30 0.082
0.055 0.349
10 1
0.080 0.054
0.344 10
0.079 0.053
0.347 20
0.082 0.055
0.349 30
0.082 0.055
0.344 15
1 0.083
0.056 0.347
10 0.082
0.055 0.349
20 0.081
0.055 0.340
30 0.083
0.056 0.347
a
Data for each temperature salinity combination are pooled from nine replicates. F 5ash-free fraction of sediment, E 5ash-free fraction of faeces.
for gender implies that male egestion rates were faster than those of females, however, this was not significant multiple linear regression, t 5 20.91, d.f.51, p .0.05.
3.5. Absorption efficiencies There were no obvious increases in absorption efficiency with increased temperature
or salinity Table 2. Absorption efficiency of females appeared to be more variable than males Table 2, but this could not be confirmed due to pooled data preventing statistical
analyses.
4. Discussion
