S. Zielinski et al., Metabolic performance of the squid Lolliguncula brevis (Cephalopoda) during hypoxia: an analysis of the critical P-O2, J EXP MAR B, 243(2), 2000, pp. 241-259
Citations number
54
Categorie Soggetti
Aquatic Sciences
Journal title
JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY
Brief squid Lolliguncula brevis are regularly exposed to fluctuating oxygen
levels in their shallow coastal environment. To assess hypoxia resistance,
animals were exposed for two hours to ambient oxygen partial pressures (P-
O2) between 19.3 kPa (normoxia) and 6.6 kPa (34.2% air saturation) at 20+/-
1 degrees C. In a second set of experiments, the animals were subjected to
a low P-O2 Of 2.8+/-0.3 kPa (14.5+/-1.6% air saturation) for 15 to 60 min.
Subsequently, metabolic, energy and acid-base status were analysed in the m
antle tissue. Onset of anaerobic metabolism was observed between 9.4 and 7.
9 kPa (48.7 and 40.9% air saturation), reflecting the critical oxygen tensi
on for this species. The formation of octopine and acetate indicates a simu
ltaneous onset of anaerobic metabolism in both the cytosol and the mitochon
dria during progressive hypoxia. Concomitantly, an intracellular acidosis d
eveloped. During exposure to oxygen partial pressures between 19.3 and 6.6
kPa, aerobic and anaerobic processes were sufficient to maintain energy sta
tus in the mantle musculature. No significant changes in ATP and phospho-L-
arginine (PLA) concentrations were observed. In contrast, both ATP and PLA
levels declined significantly after 15 min at an ambient P-O2 of 2.8+/-0.3
kPa. Concomitantly, the Gibb's free energy change of ATP hydrolysis fell to
a minimum value of about -44 kJ.mol(-1), a level suggested to reflect limi
ting energy availability for cellular ATPases. These results indicate that
hypoxia at 2.8 kPa (14.5% air saturation) rapidly takes Lolliguncula brevis
to the limits of performance. However, it is probably capable of withstand
ing longer periods of moderate hypoxia close to 50% air saturation (9.7 kPa
), enabling the squids to cope with oxygen fluctuations in their shallow es
tuarine environment or to dive into hypoxic waters by use of their economic
jetting strategy. Nonetheless, the critical P-O2 is considered to be high
compared to other hypoxia tolerant animals, an observation likely related t
o the high metabolic rate of these squids. (C) 2000 Elsevier Science B.V. A
ll rights reserved.