maenas (intertidal zone) and Segonzacia mesatlantica - Station ...

5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 205
zone and the average experienced ionic concentrations must be quite close to those of deep-sea water
on the whole.
Measured organic ions levels are high compared to shallow water species. The observed range for
L-lactate concentration is similar to those for other decapods, but a high basal level is evidenced by the
average value of 4 mM even in normoxia acclimations. This indicates that a basal level of anaerobic
metabolism may be triggered at all times in S. mesatlantica. Values of 5.57 ± 1.07 mM lactate were
recorded for freshly caught B. thermydron and 3.47 ± 0.5 mM in 24-48h maintained individuals (Sanders
et Childress, 1992), showing that high basal levels of lactate are found also for this hydrothermal
vent crab. The maximum observed value of 12 mM for S. mesatlantica is inferior to the 31.1 mM
found in hypoxic B. thermydron (Chausson, 2001), but this could be due to a hypoxia not severe enough
in our study. Higher levels could possibly be detected in tougher conditions. For urate levels, a
very high variability was observed between individuals. Urate levels measured in hydrothermal vent
crustaceans are generally high. The highest values measured here are well above those observed for
shallow water species and were always found in acclimated crabs, whatever the condition was. Urate
is a typical modulator present under stress in decapods (Bridges, 2001) ; the urate response to acclimation
indicates that the repressurization process in itself can be a stress, maybe due to the rapid rise
of pressure. This calls for control experiments with progressive increase of the pressure.
The hemolymph protein content is high for S. mesatlantica, as observed for other hydrothermal
crustacean species. This results in a higher oxyphoric capacity of the blood since hemocyanin is the
main protein present, as in other brachyurans/decapods. For an average value of 117 µg/µl Hc for S.
mesatlantica, the oxyphoric capacity is 1.56 mM O 2 compared to 0.97 mM O 2 for Carcinus maenas
(average value of 73 µg/µl Hc for 32 individuals, personal observation). A very high variabwility was
observed between individuals as in other species. The hemocyanin content is in contradiction with
previous results from Chausson (Chausson et al., 2004). In this study, a high protein concentration was
also observed but only 30 % of protein was identified as hemocyanin. Our results are in accordance
with the protein content but not on the hemocyanin content. Since the authors could not detect other
protein by FPLC, we hypothesize that the difference comes from the determination of hemocyanin
content in the previous study.
Hemocyanin structure
As previously described by Chausson and Sanglier (Sanglier et al., 2003, Chausson et al., 2004),
S. mesatlantica presents a typical decapod hemocyanin structure comprised mainly of dodecamers
and hexamers of ˜75 kDa subunits. The subunit diversity observed here is higher than previously described
with 8 major subunits and 8 minor subunits detected by denaturing ESI-MS. Only 4 subunits