Description: Until now, it is not known how the antioxidant and digestive enzymatic machinery of fish early life stages will change with the combined effects of future ocean acidification and warming. Here we show that high pCO2 (~1600 μatm) significantly decreased metabolic rates (up to 27.4 %) of flatfish larvae, Solea senegalensis, at both present (18 °C) and warmer temperatures (+4 °C). Moreover, both warming and hypercapnia increased the heat shock response and the activity of antioxidant enzymes, namely catalase (CAT) and glutathione S-transferase (GST), mainly in post-metamorphic larvae (30 dph). The lack of changes in the activity of CAT and GST of pre-metamorphic larvae (10 dph) seems to indicate that earlier stages lack a fully-developed antioxidant defense system. Nevertheless, the heat shock and antioxidant responses of post-metamorphic larvae were not enough to avoid the peroxidative damage, which was greatly increased under future environmental conditions. Digestive enzymatic activity of S. senegalensis larvae was also affected by future predictions. Hypercapnic conditions led to a decrease in the activity of digestive enzymes, both pancreatic (up to 26.1 % for trypsin and 74.5 % for amylase) and intestinal enzymes (up to 36.1 % for alkaline phosphatase) in post-metamorphic larvae. Moreover, the impact of ocean acidification and warming on some of these physiological and biochemical variables (namely, lower OCR and higher HSP and MDA levels) were translated into larvae performance, being significantly correlated with decreased larval growth and survival or increased incidence of skeletal deformities. The increased vulnerability of flatfish early life stages under future ocean conditions is expected to potentially determine recruitment and population dynamics in marine ecosystems.

Description: Early life stages of many marine organisms are being challenged by climate change, but little is known about their capacity to tolerate future ocean conditions. Here we investigated a comprehensive set of biological responses of larvae of two commercially important teleost fishes, Sparus aurata (gilthead seabream) and Argyrosomus regius (meagre), after exposure to future predictions of ocean warming (+4 °C) and acidification (ΔpH = 0.5). The combined effect of warming and hypercapnia elicited a decrease in the hatching success (by 26.4 and 14.3 % for S. aurata and A. regius, respectively) and larval survival (by half) in both species. The length for newly-hatched larvae was not significantly affected, but a significant effect of hypercapnia was found on larval growth. However, while S. aurata growth was reduced (24.8–36.4 % lower), A. regius growth slightly increased (3.2–12.9 % higher) under such condition. Under acidification, larvae of both species spent less time swimming, and displayed reduced attack and capture rates of prey. The impact of warming on these behavioural traits was opposite but less evident. While not studied in A. regius, the incidence of body malformations in S. aurata larvae increased significantly (more than tripled) under warmer and hypercapnic conditions. These morphological impairments and behavioural changes are expected to affect larval performance and recruitment success, and further influence the abundance of fish stocks and the population structure of these commercially important fish species. However, given the pace of ocean climate change, it is important not to forget that species may have the opportunity to acclimate and adapt.

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 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.