Allometry of thermal limitation in the cephalopod Sepia officinalis

Cuttlefish (Sepia officinalis) routine metabolic rate was determined in response to acute thermal changes at a rate of 1 °C h− 1 for a variety of animal sizes (15–496 g wet mass, laboratory reared at 15 °C). In a thermal frame of 11 to 23 °C, oxygen consumption rates (MO2, in μmol O2 g− 1 min− 1) were observed to rise with increasing temperature (T, in °C) and to decline with increasing body mass (m, in g), according to the formula: ln MO2 = − 3.3 + 0.0945T − 0.215 ln m (R2 = 0.93). Outside the above thermal window, animals were not able to increase MO2 at similar rates, indicating a beginning oxygen limitation of metabolism. Large animals (> 100 g body mass) already displayed lower than expected MO2 values at 8 and 26 °C, while smaller animals (15 g wet mass) were characterized by a wider thermal window (MO2 values deviated from expected rates at 5 and 29 °C).Morphometric data of cuttlefish mantle skin area was obtained to discuss size — related effects of skin respiration potential on thermal tolerance. Cuttlefish growth was observed to be isometric, as constant ‘Vogel numbers’ of 4.2 indicated (animal body masses: 11 to 401 g). In the same mass range, specific mantle surface area declined three-fold from 10.7 (0.24) (means ± SD) to 3.3 (0.52) cm2 g− 1. Thus, increased thermal tolerance in smaller animals may be enabled by a higher skin respiration potential due to higher specific skin surface areas. An elevated fraction of MO2 provided by means of skin respiration in small animals could relieve the cardiovascular system, which previously has been found a major limiting component during acute thermal stress in cuttlefish.