Respiration of the eggs of the giant cuttlefish Sepia apama

On the roofs of subtidal crevices, the giant cuttlefish (Sepia apama) of southern Australia lays clutches of lemon-shaped eggs which hatch after 3 to 5 mo. Diffusion of oxygen through the capsule and chorion membrane to the perivitelline fluid and embryo was modelled using the equation V˙ _O2 = G _O2(P _O2out−P _O2in), where V˙ _O2 = rate of oxygen consumption, G _O2 = oxygen conductance of the capsule, and P _O2 values = oxygen partial pressures across the capsule. During development, V˙ _O2 rose exponentially as the embryo grew, reaching 5.5 μl h⁻¹ at hatching. Throughout development, the capsule dimensions enlarged by absorption of water into the perivitelline space, increasing G _O2 by a combination of increasing surface area, and decreasing thickness of the capsule. These processes maintained P _O2in high enough to allow unrestricted V˙ _O2 until shortly before hatching. Diffusion limitation of respiration in hatching-stage embryos was demonstrated by (1) increased embryonic V˙ _O2 when P _O2out was experimentally raised, (2) greater V˙ _O2 of resting individuals immediately after hatching, and (3) reduced V˙ _O2 of hatchlings at experimental P _O2 levels higher than P _O2in before hatching. Thus, low P _O2in may be the stimulus to hatch. Potential problems of diffusive gas-exchange are mitigated by the relatively low incubation temperature (12 °C), which may be a factor limiting the distribution of the species to cool, southern waters. Received: 14 August 1999 / Accepted: 24 January 2000