Description: The impact of a realistic warming scenario on the metabolic physiology of early cephalopod (squid Loligo vulgaris and cuttlefish Sepia officinalis) life stages was investigated. During exposure to the warming conditions (19 °C for the western coast of Portugal in 2100), the increase in oxygen consumption rates throughout embryogenesis was much steeper in squid (28-fold increase) than in cuttlefish (11-fold increase). The elevated catabolic activity–accelerated oxygen depletion within egg capsules, which exacerbated metabolic suppression toward the end of embryogenesis. Squid late-stage embryos appear to be more impacted by warming via metabolic suppression than cuttlefish embryos. At all temperature scenarios, the transition from encapsulated embryos to planktonic paralarvae implied metabolic increments higher than 100 %. Contrary to the nektobenthic strategy of cuttlefish newborns, the planktonic squid paralarvae rely predominantly on pulsed jet locomotion that dramatically increases their energy requirements. In the future, hatchlings will require more food per unit body size and, thus, feeding intake success will be crucial, especially for squid with high metabolic rates and low levels of metabolic reserves.

Description: Little is known about the capacity of early life stages to undergo hypercapnic and thermal acclimation under the future scenarios of ocean acidification and warming. Here, we investigated a comprehensive set of biological responses to these climate change-related variables (2°C above winter and summer average spawning temperatures and ΔpH=0.5 units) during the early ontogeny of the squid Loligo vulgaris. Embryo survival rates ranged from 92% to 96% under present-day temperature (13–17°C) and pH (8.0) scenarios. Yet, ocean acidification (pH 7.5) and summer warming (19°C) led to a significant drop in the survival rates of summer embryos (47%, P〈0.05). The embryonic period was shortened by increasing temperature in both pH treatments (P〈0.05). Embryo growth rates increased significantly with temperature under present-day scenarios, but there was a significant trend reversal under future summer warming conditions (P〈0.05). Besides pronounced premature hatching, a higher percentage of abnormalities was found in summer embryos exposed to future warming and lower pH (P〈0.05). Under the hypercapnic scenario, oxygen consumption rates decreased significantly in late embryos and newly hatched paralarvae, especially in the summer period (P〈0.05). Concomitantly, there was a significant enhancement of the heat shock response (HSP70/HSC70) with warming in both pH treatments and developmental stages. Upper thermal tolerance limits were positively influenced by acclimation temperature, and such thresholds were significantly higher in late embryos than in hatchlings under present-day conditions (P〈0.05). In contrast, the upper thermal tolerance limits under hypercapnia were higher in hatchlings than in embryos. Thus, we show that the stressful abiotic conditions inside the embryo's capsules will be exacerbated under near-future ocean acidification and summer warming scenarios. The occurrence of prolonged embryogenesis along with lowered thermal tolerance limits under such conditions is expected to negatively affect the survival success of squid early life stages during the summer spawning period, but not winter spawning.

Description: The combined effects of future ocean acidification and global warming on the hypoxia thresholds of marine biota are, to date, poorly known. Here, we show that the future warming and acidification scenario led to shorter embryonic periods, lower survival rates and the enhancement of premature hatching in the cuttlefish Sepia officinalis. Routine metabolic rates increased during the embryonic period, but environmental hypercapnia significantly depressed pre-hatchling's energy expenditures rates (independently of temperature). During embryogenesis, there was also a significant rise in the carbon dioxide partial pressure in the perivitelline fluid (PVF), bicarbonate levels, as well as a drop in pH and oxygen partial pressure (pO2). The critical partial pressure (i.e. hypoxic threshold) of the pre-hatchlings was significantly higher than the PVF oxygen partial pressure at the warmer and hypercapnic condition. Thus, the record of oxygen tensions below critical pO2 in such climate scenario indicates that the already harsh conditions inside the egg capsules are expected to be magnified in the years to come, especially in populations at the border of their thermal envelope. Such a scenario promotes untimely hatching and smaller post-hatching body sizes, thus challenging the survival and fitness of early life stages.