Intracapsular oxygen availability is one of the main factors affecting embryo development of marine gastropod species with encapsulation. This is because the low solubility and diffusion rate of O2 in water, plus the low oxygen diffusion rate that the capsule wall presents, reduces oxygen inside capsules. In addition, temperature affects embryo development inside capsules through its effect on embryo metabolic rate and oxygen availability. In spite of both factors being highly correlated and that a synergic effect on embryo development may be expected, there are few studies evaluating temperature and intracapsular oxygen availability simultaneously. In this work we evaluated the role of the capsule wall of the marine gastropod Chorus giganteus as a barrier for oxygen diffusion and its interaction with temperature affecting intracapsular oxygen availability and embryonic development. For that, we cultivated capsules in seawater at three different temperatures, 9, 12 and 15°C, for a time to complete embryo development. Oxygen level was measured inside capsules with and without embryos, and outside capsules at all temperatures. The number of capsules successfully hatched at the end of the experiment, and early and late embryo mortality were recorded. Finally, we measured embryo metabolic rate at the three different temperatures assayed. We found that embryo mortality and abnormal morphological development were more frequent at higher temperatures. Intracapsular oxygen availability decreases at higher temperatures in capsules with and without embryos. These results may be explained by an increase in the total intracapsular embryo metabolic rate (per capsule) with temperature and an inadequate oxygen diffusion rate from seawater through the capsule wall and intracapsular fluid to the embryonic cells. Our findings suggest that encapsulation is constrained at high temperatures in C. giganetus affecting significantly its reproductive success. This may have important consequences in a scenario of global warming.
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