Abiotic conditions in cephalopod (Sepia officinalis) eggs: embryonic development at low pH and high pCO2

Abstract

Low pO 2 values have been measured in the perivitelline fluids (PVF) of marine animal eggs on several occasions, especially towards the end of development, when embryonic oxygen consumption is at its peak and the egg case acts as a massive barrier to diffusion. Several authors have therefore suggested that oxygen availability is the key factor leading to hatching. However, there have been no measurements of PVF pCO 2 so far. This is surprising, as elevated pCO 2 could also constitute a major abiotic stressor for the developing embryo. As a first attempt to fill this gap in knowledge, we measured pO 2 , pCO 2 and pH in the PVF of late cephalopod (Sepia officinalis) eggs. We found linear relationships between embryo wet mass and pO 2 , pCO 2 and pH. pO 2 declined from [12 kPa to less than 5 kPa, while pCO 2 increased from 0.13 to 0.41 kPa. In the absence of active accumulation of bicarbonate in the PVF, pH decreased from 7.7 to 7.2. Our study supports the idea that oxygen becomes limiting in cephalopod eggs towards the end of development; however, pCO 2 and pH shift to levels that have caused significant physiological disturbances in other marine ectothermic animals. Future research needs to address the physiological adaptations that enable the embryo to cope with the adverse abiotic conditions in their egg environment.

Ocean acidification and temperature rise: effects on calcification during early development of the cuttlefish Sepia officinalis

“…Within the egg at the end of development, PVF pO 2 was low due to the metabolic requirements of the growing embryo, as previously demonstrated (Cronin and Seymour 2000;Gutowska and Melzner 2009). In turn, aerobic metabolism produces CO 2 , ultimately resulting in a very high PVF pCO 2 , even in ambient conditions ; this study).…”

“…Measurements were obtained using a 1 mL plastic syringe equipped with fiber optic micro-sensors (optodes, tip diameter 140 µm, Presens GmbH, Regensburg, Germany). Stable PVF pO 2 values were obtained within 10s in the syringe filled with 200-300 µL of PVF (as previously described in Gutowska and Melzner 2009). PVF pH (SWS scale) values were measured in 0.5 mL plastic tubes using a pH electrode (WTW Mic and WTW pH340i pH meter), with stable values reached within 1min.…”

“…Due to the egg case serving as a diffusion barrier for respiratory gases (CO 2 , O 2 ), embryos are exposed to low PVF pO 2 (pO 2 < 6 kPa, Cronin andSeymour 2000, Gutowska and and to high pCO 2 in turn (pCO 2 > 0.4 kPa i.e. > 2000-4000 µatm, Gutowska and Melzner 2009). PVF is also slightly hypertonic when compared to seawater (de Leersnyder and Lemaire 1972), which enables the characteristic egg swelling process (Cronin and Seymour 2000).…”

The dynamic nitric oxide pattern in developing cuttlefish Sepia officinalis

“…In this regard, the presence of Naþ/Kþ-ATPase has been reported in the internal transportactive epithelium of the gills in S. officinalis (Hu et al, 2010;Donaubauer, 1981). The functioning of this pump in late embryos is of great importance in regulating acid-base disturbances due to high pCO 2 and low pH values detected inside the egg capsule as hatching approaches (Gutowska and Melzner, 2009;Gutowska et al, 2010). Considering that NO has been reported to affect Naþ/Kþ-ATPase activity in the Atlantic salmon (Ebbesson et al, 2005), a possibility remains that in Sepia NO may act on this pump and further colocalization studies will be necessary to prove this hypothesis.…”

Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods

“…On the opposite site this egg capsule constitutes a diffusion barrier for gases such as O 2 and CO 2 , with diffusion coefficients of 10-20 % to that of pure seawater, leading to increasing hypoxic and hypercapnic conditions inside the egg along embryogenesis 49,51,52 (Fig. 1A).…”