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translocation and exposure experiments were statistically analysed with ANOVA Sokal and Rohlf, 1995 by the Systat programme Wilkinson, 1988.
3. Results
In the preliminary experiment, the measured parameters of the translocated animals, i.e., weight index Fig. 2, copper concentrations Fig. 3, glycogen content Fig. 4, free
amino acid composition Fig. 5, and the stress indicator taurine glycine ratio Fig. 5,
3
Fig. 2. The weight-index mg of dry tissue weight DW cm ; average and standard error, N 5 10 of translocated clams in the preliminary experiments at the beginning of the translocation 17 April, 1991 from
Dortsman 5 Do, and 1 month after 15 May, in comparison to the endemic local specimens sampled at 15 MaySo 5 Somme, Se 5 Seine, BdV5 Baie des Veys, Lo 5 Loire.
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91
Fig. 3. The copper concentration mg g DW; average and standard error, N 5 10 of translocated clams in the preliminary experiments at the beginning of, and 1 month after, translocation in comparison to the endemic
local specimens dates and abbreviations as in Fig. 2.
strongly resembled the values found in the specimens from the local populations within 1 month mid April to mid May.
The animals translocated in May 1996 to Arcachon and Bidasoa were recovered in August in original densities hardly empty shells found, and in November 1996 and
February 1997 in low densities many empty shells. In May 1997 no animals were recovered. It is not known whether the animals emigrated from the translocation plot,
died or were eaten. At Grevelingen higher densities were found till the end of the experiment May 1997.
The weight-index weight per volume and glycogen content of clams changed significantly with season and between stations ANOVA, P , 0.01. From August 1996
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Fig. 4. The glycogen concentration [ DW; average and standard error, N 5 2 two groups of ten animals] of translocated clams in the preliminary experiments at the beginning of, and 1 month after, translocation in
comparison to the endemic local specimens dates and abbreviations as in Fig. 2.
to February 1997 the weight-index and glycogen decreased at the translocation stations and at the station of origin Fig. 6. The index was always the lowest, and the decrease
of the index strongest, at the Southern stations Arcachon and Bidasoa. In Grevelingen the weight-index started to increase again from February 1997; in Paulina from May
1997 no data available on Arcachon and Bidasoa. There was no significant difference in weight between specimens kept for 1 month in the laboratory at the higher
temperature M-hi or at the lower temperature M-loANOVA, P 5 0.10.
The respiration rate of the clams was higher at the higher test-temperature Fig. 7; ANOVA on all data combined: P , 0.01. Yet, the animals that were kept only 1 month
in the laboratory at the testing temperature M-lo and M-hi showed in the summer to be able to acclimatize their respiration. Therefore, it can make rather a difference if animals
from territories with a different temperature regime, as such from the Netherlands and South France, are compared to each other at one fixed temperature. A Southern
population will be acclimatized to a higher ambient field temperature and thus will experience a fixed test temperature as being relatively lower than clams from a Northern
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93
Fig. 5. The free amino acid concentration DW, and taurine glycine ratio used as a stress indicator [averages and standard error, N 5 3 three groups of ten animals] of translocated clams in the preliminary
experiments at the beginning of, and 1 month after, translocation in comparison to the endemic local specimens dates and abbreviations as in Fig. 2.
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3
Fig. 6. Weight-index dry tissue weight per volume 5 mg DW cm ; average and standard error, N 5 20 and glycogen content DW; average and standard error, N 5 2, two groups of ten animals, for M-lo and M-hi
N 5 1 group of ten animals of clams kept in the translocation experiment Pau 5 Paulina, Arc 5 Arcachon, Bid 5 Bidasoa, Gre 5 Grevelingen, M-lo 5 Mesocosm-laboratory low-temperature 108C, winter 38C, M-hi 5
Mesocosm-laboratory high temperature 208C, winter 108C; the clams from the mesocosm-laboratory were kept for 1 month before measuring the respiration already at the testing temperature, and thus could
acclimatize, yet with a low level of food.
station. Because of such, the results were also re-arranged according to the difference between ambient and testing temperatures Fig. 8. The respiration of the clams from
Paulina was remarkably stable around 0.6 ml O h g DW during all seasons when
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95
Fig. 7. Respiration rate ml O g DW h of clams kept in the translocation experiment in the field or in the
2
laboratory experiment abbreviations as in Fig. 6.
tested at ambient temperatures, with slightly lower respiration 0.4 ml O h g DW at
2
lower temperatures, and higher respiration 0.8 ml O h g DW at higher temperatures
2
Fig. 8. The respiration of specimens translocated to Arcachon, Bidasoa, and Grevelingen
differed significantly from those at Paulina Table 1. Yet, the difference, as well as the
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Fig. 8. Respiration rate of clams. Same data as in Fig. 7, but now arranged into groups with regard to difference between test temperature and ambient field temperature T normal 5 test temperature was , 38C
lower or higher than ambient temperature, T low 5 test temperature was . 38C lower than ambient temperature, T high 5 test temperature was . 38C higher than ambient temperature abbreviations as in Fig.
6.
sign of the difference i.e., being more or less, changed with the season Table 1. During summer the respiration of the translocated clams was 25–50 higher than of
those at Paulina Fig. 8; August. In contrast to this, during winter the respiration of
H . Hummel et al. J. Exp. Mar. Biol. Ecol. 251 2000 85 –102
97 Table 1
Significance of the differences in respiration rate ml O h g DW between clams kept at Paulina and those
2
translocated to other stations 5 effect of station, between seasons at a station 5 effect of season, and the interaction of differences [indicating changes in the sign of differences between stations throughout the seasons
a
5 effect of stationseason Effect of
Difference between Paulina and Bidasoa
Arcachon Grevelingen
Mesocosm Station
– StationSeason
– Season
– –
–
a
ANOVA: P , 0.05, P , 0.01, –, not significant.
clams at Arcachon and Grevelingen decreased to a much lower level than the controls at Paulina Fig. 8; November, February. Whereas at Bidasoa the respiration at ambient
temperatures remained as in Paulina stable, yet at a higher level. In the laboratory, the animals that were allowed to acclimatize during 1 month, the respiration in winter
decreased as did that of the translocated specimens at Arcachon and Grevelingen Fig. 8.
In the test with different sediment and water types, the weight index and glycogen content of the clams did not differ between treatments Fig. 9; ANOVA, P . 0.05. The
respiration was higher at the higher test temperatures ANOVA, P , 0.01. A significant difference in the respiration rate occurred also in case water from the different stations
was used Fig. 9; ANOVA, P , 0.05, with a consistently higher respiration in the clams exposed to water from Bidasoa.
4. Discussion
