Ocean warming enhances malformations, premature hatching, metabolic suppression and oxidative stress in the early life stages of a keystone squid

Projected ocean temperatures impair key proteins used in vision of octopus hatchlings

Global warming is one of the most significant and widespread effects of climate change. While early life stages are particularly vulnerable to increasing temperatures, little is known about the molecular processes that underpin their capacity to adapt to temperature change during early development. Using a quantitative proteomics approach, we investigated the effects of thermal stress on octopus embryos. We exposed Octopus berrima embryos to different temperature treatments (control 19°C, current summer temperature 22°C, or future projected summer temperature 25°C) until hatching. By comparing their protein expression levels, we found that future projected temperatures significantly reduced levels of key eye proteins such as S-crystallin and retinol dehydrogenase 12, suggesting the embryonic octopuses had impaired vision at elevated temperature. We also found that this was coupled with a cellular stress response that included a significant elevation of proteins involved in molecular chaperoning and redox regulation. Energy resources were also redirected away from non-essential processes such as growth and digestion. These findings, taken together with the high embryonic mortality observed under the highest temperature, identify critical physiological functions of embryonic octopuses that may be impaired under future warming conditions. Our findings demonstrate the severity of the thermal impacts on the early life stages of octopuses as demonstrated by quantitative proteome changes that affect vision, protein chaperoning, redox regulation and energy metabolism as critical physiological functions that underlie the responses to thermal stress.

Understanding baseline levels of physiological stress tolerance from excessive exercise in a holobenthic octopus species, Octopus pallidus

Cephalopods receive a great deal of attention due to their socioeconomically important fisheries and aquaculture industries as well their unique biological features. However, basic information about their physiological responses under stress conditions is lacking. This study investigated the impact of a simple stressor, exercise to exhaustion, on the activity levels of antioxidant enzymes and the concentrations of molecules involved in oxidative stress response in the pale octopus (Octopus pallidus). Eight biochemical assays were measured in the humoral (plasma) and cellular (hemocyte) components of O. pallidus haemolymph, the invertebrate analogue to vertebrate blood. Overall, exercise resulted in an increase in activity of plasma catalase (CAT) and glutathione-S-transferase (GST) and the decrease in activity of plasms glutathione reductase (GR). In the hemocytes, the exercise elicited a different response, with a reduction in the activity of superoxide dismutase (SOD), GR, and glutathione peroxidase (GPX) and a reduction in nitric oxide (NO) concentration. Malondialdehyde (MDA) activity was similar in the plasma and haemocytes in control and exercised treatments, indicating that exercise did not induce lipid peroxidation. These results provide an important baseline for understanding oxidative stress in octopus, with exercise to exhaustion serving as a simple stressor which will ultimately inform our ability to detect and understand physiological responses to more complex stressors.

Multigenerational effects of elevated temperature on host-microbiota interactions in the marine water flea Diaphanosoma celebensis exposed to micro- and nanoplastics

Rising ocean temperatures are driving unprecedented changes in global marine ecosystems. Meanwhile, there is growing concern about microplastic and nanoplastic (MNP) contamination, which can endanger marine organisms. Increasing ocean warming (OW) and plastic pollution inevitably cause marine organisms to interact with MNPs, but relevant studies remain sparse. Here, we investigated the interplay between ocean warming and MNP in the marine water flea Diaphanosoma celebensis. We found that combined exposure to MNPs and OW induced reproductive failure in the F2 generation. In particular, the combined effects of OW and MNPs on the F2 generation were associated with key genes related to reproduction and stress response. Moreover, populations of predatory bacteria were significantly larger under OW and MNP conditions during F2 generations, suggesting a potential link between altered microbiota and host fitness. These results were supported by a host transcriptome and microbiota interaction analysis. This research sheds light on the complex interplay between environmental stressors, their multigenerational effects on marine organisms, and the function of the microbiome.

Climate-Change Impacts on Cephalopods: A Meta-Analysis

Aside from being one of the most fascinating groups of marine organisms, cephalopods play a major role in marine food webs, both as predators and as prey, while representing key living economic assets, namely for artisanal and subsistence fisheries worldwide. Recent research suggests that cephalopods are benefitting from ongoing environmental changes and the overfishing of certain fish stocks (i.e., of their predators and/or competitors), putting forward the hypothesis that this group may be one of the few "winners" of climate change. While many meta-analyses have demonstrated negative and overwhelming consequences of ocean warming (OW), acidification (OA), and their combination for a variety of marine taxa, such a comprehensive analysis is lacking for cephalopod molluscs. In this context, the existing literature was surveyed for peer-reviewed articles featuring the sustained (≥24 h) and controlled exposure of cephalopod species (Cephalopoda class) to these factors, applying a comparative framework of mixed-model meta-analyses (784 control-treatment comparisons, from 47 suitable articles). Impacts on a wide set of biological categories at the individual level (e.g., survival, metabolism, behavior, cell stress, growth) were evaluated and contrasted across different ecological attributes (i.e., taxonomic lineages, climates, and ontogenetic stages). Contrary to what is commonly assumed, OW arises as a clear threat to cephalopods, while OA exhibited more restricted impacts. In fact, OW impacts were ubiquitous across different stages of ontogeny, taxonomical lineages (i.e., octopuses, squids, and cuttlefish). These results challenge the assumption that cephalopods benefit from novel ocean conditions, revealing an overarching negative impact of OW in this group. Importantly, we also identify lingering literature gaps, showing that most studies to date focus on OW and early life stages of mainly temperate species. Our results raise the need to consolidate experimental efforts in a wider variety of taxa, climate regions, life stages, and other key environmental stressors, such as deoxygenation and hypoxia, to better understand how cephalopods will cope with future climate change.

Does the egg capsule protect against chronic UV-B radiation? A study based on encapsulated and decapsulated embryos of cuttlefish Sepia officinalis

Although the egg capsule plays a crucial role in the embryonic development of cephalopods, its ability to protect embryos from Ultraviolet (UV) radiation is unknown. Our study evaluated the photoprotection mechanisms of S. officinalis to UV-B radiation and estimated the ability of the black capsule to act as a physical shield against it. Embryos with and without capsule and juveniles were exposed to four experimental UVB conditions for 55 days. The effects of different UVB doses were evaluated in terms of morphological abnormalities and differences in gene expression between each group. We observed that the development might be severely impaired in embryos exposed to UVB without capsule protection, and these effects were time- and UVB-dose-dependent. In addition, we found variations in gene expression levels (light-sensitive, stress response and DNA repair) in different tissues as a function of UVB doses. We suggest a relationship between morphological abnormalities and the limit of molecular regulation. These results suggest that the quantitative differences in expression are essential for defining the survivability of the embryo face to UVB. Thus, we demonstrated that the egg capsule could ensure successful embryonic development of the cuttlefish S. officinalis even at high doses of UVB.

Camouflage and Exploratory Avoidance of Newborn Cuttlefish under Warming and Acidification

Ocean warming and acidification have been shown to elicit deleterious effects on cephalopod mollusks, especially during early ontogeny, albeit effects on behavior remain largely unexplored. This study aimed to evaluate, for the first time, the effect of end-of-the-century projected levels of ocean warming (W; + 3 °C) and acidification (A; 980 µatm pCO₂) on Sepia officinalis hatchlings' exploratory behavior and ability to camouflage in different substrate complexities (sand and black and white gravel). Cuttlefish were recorded in open field tests, from which mobility and exploratory avoidance behavior data were obtained. Latency to camouflage was registered remotely, and pixel intensity of body planes and background gravel were extracted from photographs. Hatching success was lowered under A and W combined (AW; 72.7%) compared to control conditions (C; 98.8%). Motion-related behaviors were not affected by the treatments. AW delayed camouflage response in the gravel substrate compared to W alone. Moreover, cuttlefish exhibited a higher contrast and consequently a stronger disruptive pattern under W, with no changes in background matching. These findings suggest that, although climate change may elicit relevant physiological challenges to cuttlefish, camouflage and mobility of these mollusks are not undermined under the ocean of tomorrow.

How efficient is graphene-based nanocomposite to adsorb Hg from seawater. A laboratory assay to assess the toxicological impacts induced by remediated water towards marine bivalves

Advanced investigations on the use of graphene based nanomaterials have highlighted the capacity of these materials for wastewater treatment. Research on this topic revealed the efficiency of the nanocomposite synthetized by graphene oxide functionalized with polyethyleneimine (GO-PEI) to adsorb mercury (Hg) from contaminated seawater. However, information on the environmental risks associated with these approaches are still lacking. The focus of this study was to evaluate the effects of Hg in contaminated seawater and seawater remediated by GO-PEI, using the species Ruditapes philippinarum, maintained at two different warming scenarios: control (17 °C) and increased (22 °C) temperatures. The results obtained showed that organisms exposed to non-contaminated and remediated seawaters at control temperature presented similar biological patterns, with no considerable differences expressed in terms of biochemical and histopathological alterations. Moreover, the present findings revealed increased toxicological effects in clams under remediated seawater at 22 °C in comparison to those subjected to the equivalent treatment at 17 °C. These results confirm the capability of GO-PEI to adsorb Hg from water with no noticeable toxic effects, although temperature could alter the responses of mussels to remediated seawater. These materials seem to be a promise eco-friendly approach to remediate wastewater, with low toxicity evidenced by remediated seawater and high regenerative capacity of this nanomaterial, keeping its high removal performance after successive sorption-desorption cycles.

Morphological response accompanying size reduction of belemnites during an Early Jurassic hyperthermal event modulated by life history

One of the most common responses of marine ectotherms to rapid warming is a reduction in body size, but the underlying reasons are unclear. Body size reductions have been documented alongside rapid warming events in the fossil record, such as across the Pliensbachian-Toarcian boundary (PToB) event (~ 183 Mya). As individuals grow, parallel changes in morphology can indicate details of their ecological response to environmental crises, such as changes in resource acquisition, which may anticipate future climate impacts. Here we show that the morphological growth of a marine predator belemnite species (extinct coleoid cephalopods) changed significantly over the PToB warming event. Increasing robustness at different ontogenetic stages likely results from indirect consequences of warming, like resource scarcity or hypercalcification, pointing toward varying ecological tolerances among species. The results of this study stress the importance of taking life history into account as well as phylogeny when studying impacts of environmental stressors on marine organisms.

The Role of Temperature on the Impact of Remediated Water towards Marine Organisms

Marine organisms are frequently exposed to pollutants, including trace metals, derived from natural and anthropogenic activities. In order to prevent environmental pollution, different approaches have been applied to remove pollutants from waste water and avoid their discharge into aquatic systems. However, organisms in their natural aquatic environments are also exposed to physico-chemical changes derived from climate change-related factors, including temperature increase. According to recent studies, warming has a negative impact on marine wildlife, with known effects on organisms physiological and biochemical performance. Recently, a material based on graphene oxide (GO) functionalized with polyethyleneimine (PEI) proved to be effective in the remediation of mercury (Hg) contaminated water. Nevertheless, no information is available on the toxic impacts of such remediated water towards aquatic systems, neither under actual nor predicted temperature conditions. For this, the present study assessed the toxicity of seawater, previously contaminated with Hg and remediated by GO-PEI, using the clam species Ruditapes philippinarum exposed to actual and a predicted temperature conditions. The results obtained demonstrated that seawater contaminated with Hg and/or Hg+GO-PEI induced higher toxicity in clams exposed to 17 and 22 °C compared to organisms exposed to remediated seawater at the same temperatures. Moreover, similar histological and biochemical results were observed between organisms exposed to control and remediated seawater, independently of the temperatures (17 and 21 °C), highlighting the potential use of GO-PEI to remediate Hg from seawater without significant toxicity issues to the selected marine species.

Thermal stability vs. variability: Insights in oxidative stress from a eurytolerant fish

Climate change will increase the frequency, intensity, and duration of heatwaves. This thermal volatility will challenge to the oxidative homeostasis of aquatic ectotherms through many temperature-dependent environmental factors. In this study, we examined the effects of chronic exposure of sheepshead minnows (Cyprinodon variegatus) to multiple thermal regimes on the oxidative physiology of white muscle in these eurytolerant fish. The thermal treatments included stable (15 °C and 30 °C) and cycling regimes (between 21 and 29 °C at 6, 8 and 10-h intervals). The effect of these thermal treatments on oxidative stress during an acute thermal challenge (12 h at 32 °C) was also examined. Enzymatic activity of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), scavenging capacities of hydroxyl and peroxyl radicals, and lipid peroxidation (LPO) damage were quantified. We found no differences between or across treatments in any of the enzymatic antioxidants or LPO damage. We found that peroxyl radical scavenging was greatest at the peak of the 8- and 10-h thermal cycles. Peroxyl scavenging after an acute thermal challenge was greater than before the challenge for the steady 15 °C and 8-h cycle treatments, greater before the acute challenge for the steady 30 °C and 6-h cycle, and equivalent in the 10-h cycle. These findings demonstrate that even the most tolerant of marine ectotherms must engage oxidative defenses when presented with thermal variability and heighten concerns about the impact of climate change on less tolerant species.

Antagonistic Interactions and Clutch-Dependent Sensitivity Induce Variable Responses to Ocean Acidification and Warming in Squid (Doryteuthis pealeii) Embryos and Paralarvae

Ocean acidification (OA) and warming seas are significant concerns for coastal systems and species. The Atlantic longfin squid, Doryteuthis pealeii, a core component of the Northwest Atlantic trophic web, has demonstrated impacts, such as reduced growth and delayed development, under high chronic exposure to acidification (2200 ppm), but the combined effects of OA and warming have not been explored in this species. In this study, D. pealeii egg capsules were reared under a combination of several acidification levels (400, 2200, and 3500 ppm) and temperatures (20 and 27°C). Hatchlings were measured for a range of metrics [dorsal mantle length (DML), yolk sac volume (YV), malformation, and hatching success] in three trials over the 2016 breeding season (May – October). Although notable resistance to stressors was seen, highlighting variability within and between clutches, reduced DML and malformation of the embryos occurred at the highest OA exposure. Surprisingly, increased temperatures did not appear to exacerbate OA impacts, although responses were variable. Time to hatching, which increased with acidification, decreased much more drastically under warming and, further, decreased or removed delays caused by acidification. Hatching success, while variable by clutch, showed consistent patterns of greater late stage loss of embryos under acidification and greater early stage loss under warming, highlighting the potential difference in timing between these stressors for this system, i.e., that acidification stress builds up and causes impacts over time within the egg capsule as the embryos grow and respire. High OA-exposed hatchlings from the warmer conditions often showed reduced impacts compared to those reared in ambient temperatures. This may be due to the increased developmental rate and subsequently reduced OA exposure time of embryos in the higher temperature treatment. These results indicate a substantive potential plasticity to multiple stressors during the embryonic development of this species of squid, but do not predict how this species would fare under these future ocean scenarios.

Mercury in Juvenile Solea senegalensis: Linking Bioaccumulation, Seafood Safety, and Neuro-Oxidative Responses under Climate Change-Related Stressors

Mercury (Hg) is globally recognized as a persistent chemical contaminant that accumulates in marine biota, thus constituting an ecological hazard, as well as a health risk to seafood consumers. Climate change-related stressors may influence the bioaccumulation, detoxification, and toxicity of chemical contaminants, such as Hg. Yet, the potential interactions between environmental stressors and contaminants, as well as their impacts on marine organisms and seafood safety, are still unclear. Hence, the aim of this work was to assess the bioaccumulation of Hg and neuro-oxidative responses on the commercial flat fish species Solea senegalensis (muscle, liver, and brain) co-exposed to dietary Hg in its most toxic form (i.e., MeHg), seawater warming (ΔT°C = +4 °C), and acidification (pCO2 = +1000 µatm, equivalent to ΔpH = −0.4 units). In general, fish liver exhibited the highest Hg concentration, followed by brain and muscle. Warming enhanced Hg bioaccumulation, whereas acidification decreased this element’s levels. Neuro-oxidative responses to stressors were affected by both climate change-related stressors and Hg dietary exposure. Hazard quotient (HQ) estimations evidenced that human exposure to Hg through the consumption of fish species may be aggravated in tomorrow’s ocean, thus raising concerns from the seafood safety perspective.

Embryonic canalization and its limits-A view from temperature

Many animals are able to produce similar offspring over a range of environmental conditions. This property of the developmental process has been termed canalization-the channeling of developmental pathways to generate a stable outcome despite varying conditions. Temperature is one environmental parameter that has fundamental effects on cell physiology and biochemistry, yet developmental programs generally result in a stable phenotype under a range of temperatures. On the other hand, there are typically upper and lower temperature limits beyond which the developmental program is unable to produce normal offspring. This review summarizes data on how development is affected by temperature, particularly high temperature, in various animal species. It also brings together information on potential cell biological and developmental genetic factors that may be responsible for developmental stability in varying temperatures, and likely critical mechanisms that break down at high temperature. Also reviewed are possible means for studying temperature effects on embryogenesis and how to determine which factors are most critical at the high-temperature limits for normal development. Increased knowledge of these critical factors will point to the targets of selection under climate change, and more generally, how developmental robustness in varying environments is maintained.

Effect of a gradually increasing temperature on the behavioural and physiological response of juvenile Hippocampus erectus: Thermal preference, tolerance, energy balance and growth

The physiological and behavioural responses of ectotherms to temperature is strongly dependent on the individuals' previous thermal history. Laboratory based studies investigating the mechanisms of thermoregulation in marine ectotherms, however, rarely consider key temporal elements of thermal exposure, such as the rate at which temperature changes. We tested the hypothesis that juvenile seahorses, Hippocampus erectus, from a tropical coastal lagoon in Yucatan, Mexico, would exhibit variations in physiological and behavioural descriptors of thermoregulation when submitted to contrasting regimes during 30 days: temperature constant at 25 °C (C 25); gradually increasing 1 °C every 5 days from 25 to 30 °C (GI 25-30); and constant at 30 °C (C 30). Immediately after exposure, critical maximum temperature, thermal preference, oxygen consumption, partial energy balance, growth rate and survival of seahorses were measured. Seahorses exposed to GI 25-30 showed a significantly higher critical thermal maxima (37.8 ± 0.9 °C), preference (28.7 ± 0.4 °C), growth (1.10 ± 0.49%) and survival (97.6%) than those exposed to C 30 (36.5 ± 1, 29.4 ± 0.3 °C, 0.48 ± 0.32%, 73.8%, respectively). Both high temperature regimes induced metabolic depression, but ramping resulted in a greater amount of energy assimilated (278.9 ± 175.4 J g^-1 day^-1) and higher energy efficiency for growth (89.8%) than constant exposure to 30 °C (115.4 ± 63.4 J g^-1 day^-1, 65.3%, respectively). Gradually increasing temperature allowed physiological mechanisms of thermal adjustment to take place, reflecting the capacity of juvenile H. erectus to respond to environmental change. Despite its advantage, this capacity is limited in time, since the cumulative effect of thermal exposure affected metabolic performance, eventually compromising survival. The study of seahorse response to thermal variations in the context of ocean warming needs to consider the temporal elements of thermal exposure to foresee its vulnerability under future scenarios.

Distinct Bleaching Resilience of Photosynthetic Plastid-Bearing Mollusks Under Thermal Stress and High CO2 Conditions

The impact of temperature on photo-symbiotic relationships has been highly studied in the tropical reef-forming corals but overlooked in less charismatic groups such as solar-powered sacoglossan sea slugs. These organisms display one of the most puzzling symbiotic features observed in the animal kingdom, i.e., their mollusk-plastid association, which enables them to retain photosynthetic active chloroplasts (i.e., kleptoplasts) retrieved from their algae feed sources. Here we analyze the impact of thermal stress (+4°C) and high pCO2 conditions (ΔpH = 0.4) in survival, photophysiology (i.e., bleaching, photosynthetic efficiency, and metabolism) and stress defense mechanisms (i.e., heat shock and antioxidant response) of solar-powered sacoglossan sea slugs, from tropical (Elysia crispata) and temperate (E. viridis) environments. High temperature was the main factor affecting the survival of both species, while pH only affected the survival of the temperate model. The photobiology of E. viridis remained stable under the combined scenario, while photoinhibition was observed for E. crispata under high temperature and high pCO2. In fact, bleaching was observed within all tropical specimens exposed to warming (but not in the temperate ones), which constitutes the first report where the incidence of bleaching in tropical animals hosting photosynthetic symbionts, other than corals, occurs. Yet, the expulsion of kleptoplasts by the tropical sea slug, allied with metabolic depression, constituted a physiological response that did not imply signs of vulnerability (i.e., mortality) in the host itself. Although the temperate species revealed greater heat shock and antioxidant enzyme response to environmental stress, we argue that the tropical (stenotherm) sea slug species may display a greater scope for acclimatization than the temperate (eurytherm) sea slug. E. crispata may exhibit increased capacity for phenotypic plasticity by increasing fitness in a much narrower thermal niche (minimizing maintenance costs), which ultimately may allow to face severe environmental conditions more effectively than its temperate generalist counterpart (E. viridis).

Predicted 2100 climate scenarios affects growth and skeletal development of tambaqui (Colossoma macropomum) larvae

Climate changes driven by greenhouse gas emissions have been occurring in an accelerated degree, affecting environmental dynamics and living beings. Among all affected biomes, the Amazon is particularly subjected to adverse impacts, such as temperature rises and water acidification. This study aimed to evaluate the impacts of predicted climate change on initial growth and development of an important Amazonian food fish, the tambaqui. We analyzed growth performance, and monitored the initial osteogenic process and the emergence of skeletal anomalies, when larvae were exposed to three climate change scenarios: mild (B1, increase of 1.8°C, 200 ppm of CO2); moderate (A1B, 2.8°C, 400 ppm of CO2); and drastic (A2, 3.4°C, 850 ppm of CO2), in addition to a control room that simulated the current climatic conditions of a pristine tropical forest. The exposure to climate change scenarios (B1, A1B, and A2) resulted in low survival, especially for the animals exposed to A2, (24.7 ± 1.0%). Zootechnical performance under the B1 and A1B scenarios was higher when compared to current and A2, except for condition factor, which was higher in current (2.64 ± 0.09) and A1B (2.41 ± 0.14) scenarios. However, skeletal analysis revealed higher incidences of abnormalities in larvae exposed to A1B (34.82%) and A2 (39.91%) scenarios when compared to current (15.38%). Furthermore, the bone-staining process revealed that after 16 days posthatch (7.8 ± 0.01 mm total length), skeletal structures were still cartilaginous, showing no mineralization in all scenarios. We concluded that tambaqui larvae are well-adapted to high temperatures and may survive mild climate change. However, facing more severe climate conditions, its initial development may be compromised, resulting in high mortality rates and increased incidence of skeletal anomalies, giving evidence that global climate change will hamper tambaqui larvae growth and skeletal ontogeny.

Accumulation, elimination and neuro-oxidative damage under lanthanum exposure in glass eels (Anguilla anguilla)

Rare earth elements (REEs) comprise elements from lanthanum to lutetium that together with yttrium and scandium are emergent contaminants of critical importance for numerous groundbreaking environmental technologies. Transfer to aquatic ecosystems is expected to increase, however, little information is known about their potential impacts in marine biota. Considering the endangered conservation status of the European eel (Anguilla anguilla) and the vulnerability of early fish life stages to contaminants, we exposed glass eels, through water, to an environmentally relevant concentration (120 ng.L^-1) of lanthanum (La) for 7 days (plus 7 days of depuration). The aim was to study the accumulation and elimination of La in eel's body and subsequent quantification of acetylcholinesterase (AchE), lipid peroxidation and antioxidant enzymatic machinery. Accumulation peaked after 72 h-exposure to La, decreasing afterwards, even in continuous exposure. Accumulation was higher in the viscera, followed by the skinless body and ultimately in the head, possibly as a protective mechanism to cope with La neurotoxicity. A significant increase in AChE activity was observed in La-exposed glass eels, suggesting that La³⁺ may inhibit the binding of acetylcholine. A depression in lipid peroxidation was registered under La exposure, possibly indicating that La³⁺ may play physiological activities and functions as a free radical scavenger. Catalase activity was significantly inhibited in La-exposed glass eels after 72 h, indicating that the availability of La may induce physiological impairment. The quantification of Glutathione S-Transferase activity revealed no differences between control and La-exposed organisms. Further investigation is needed towards understanding the biological effects of REEs.

Fish energy budget under ocean warming and flame retardant exposure

Climate change and chemical contamination are global environmental threats of growing concern for the scientific community and regulatory authorities. Yet, the impacts and interactions of both stressors (particularly ocean warming and emerging chemical contaminants) on physiological responses of marine organisms remain unclear and still require further understanding. Within this context, the main goal of this study was to assess, for the first time, the effects of warming (+ 5 °C) and accumulation of a polybrominated diphenyl ether congener (BDE-209, brominated flame retardant) through dietary exposure on energy budget of the juvenile white seabream (Diplodus sargus). Specifically, growth (G), routine metabolism (R), excretion (faecal, F and nitrogenous losses, U) and food consumption (C) were calculated to obtain the energy budget. The results demonstrated that the energy proportion spent for G dominated the mode of the energy allocation of juvenile white seabream (56.0-67.8%), especially under the combined effect of warming plus BDE-209 exposure. Under all treatments, the energy channelled for R varied around 26% and a much smaller percentage was channelled for excretion (F: 4.3-16.0% and U: 2.3-3.3%). An opposite trend to G was observed to F, where the highest percentage (16.0 ± 0.9%) was found under control temperature and BDE-209 exposure via diet. In general, the parameters were significantly affected by increased temperature and flame retardant exposure, where higher levels occurred for: i) wet weight, relative growth rate, protein and ash contents under warming conditions, ii) only for O:N ratio under BDE-209 exposure via diet, and iii) for feed efficiency, ammonia excretion rate, routine metabolic rate and assimilation efficiency under the combination of both stressors. On the other hand, decreased viscerosomatic index was observed under warming and lower fat content was observed under the combined effect of both stressors. Overall, under future warming and chemical contamination conditions, fish energy budget was greatly affected, which may dictate negative cascading impacts at population and community levels. Further research combining other climate change stressors (e.g. acidification and hypoxia) and emerging chemical contaminants are needed to better understand and forecast such biological effects in a changing ocean.

The Current State of Cephalopod Science and Perspectives on the Most Critical Challenges Ahead From Three Early-Career Researchers

Here, three researchers who have recently embarked on careers in cephalopod biology discuss the current state of the field and offer their hopes for the future. Seven major topics are explored: genetics, aquaculture, climate change, welfare, behavior, cognition, and neurobiology. Recent developments in each of these fields are reviewed and the potential of emerging technologies to address specific gaps in knowledge about cephalopods are discussed. Throughout, the authors highlight specific challenges that merit particular focus in the near-term. This review and prospectus is also intended to suggest some concrete near-term goals to cephalopod researchers and inspire those working outside the field to consider the revelatory potential of these remarkable creatures.

Effects of water warming and acidification on bioconcentration, metabolization and depuration of pharmaceuticals and endocrine disrupting compounds in marine mussels (Mytilus galloprovincialis)

Warming and acidification are expected impacts of climate change to the marine environment. Besides, organisms that live in coastal areas, such as bivalves, can also be exposed to anthropogenic pollutants like pharmaceuticals (PhACs) and endocrine disrupting compounds (EDCs). In this study, the effects of warming and acidification on the bioconcentration, metabolization and depuration of five PhACs (sotalol, sulfamethoxazole, venlafaxine, carbamazepine and citalopram) and two EDCs (methylparaben and triclosan) were investigated in the mussel species (Mytilus galloprovincialis), under controlled conditions. Mussels were exposed to warming and acidification, as well as to the mixture of contaminants up to 15.7 μg L^-1 during 20 days; followed by 20 days of depuration. All contaminants bioconcentrated in mussels with levels ranging from 1.8 μg kg^-1 dry weight (dw) for methylparaben to 12889.4 μg kg^-1 dw for citalopram. Warming increased the bioconcentration factor (BCF) of sulfamethoxazole and sotalol, whereas acidification increased the BCF of sulfamethoxazole, sotalol and methylparaben. In contrast, acidification decreased triclosan levels, while both stressors decreased venlafaxine and citalopram BCFs. Warming and acidification facilitated the elimination of some of the tested compounds (i.e. sotalol from 50% in control to 60% and 68% of elimination in acidification and warming respectively). However, acidification decreased mussels' capacity to metabolize contaminants (i.e. venlafaxine). This work provides a first insight in the understanding of aquatic organisms' response to emerging contaminants pollution under warming and acidification scenarios.

Ocean acidification dampens physiological stress response to warming and contamination in a commercially-important fish (Argyrosomus regius)

Increases in carbon dioxide (CO₂) and other greenhouse gases emissions are changing ocean temperature and carbonate chemistry (warming and acidification, respectively). Moreover, the simultaneous occurrence of highly toxic and persistent contaminants, such as methylmercury, will play a key role in further shaping the ecophysiology of marine organisms. Despite recent studies reporting mostly additive interactions between contaminant and climate change effects, the consequences of multi-stressor exposure are still largely unknown. Here we disentangled how Argyrosomus regius physiology will be affected by future stressors, by analysing organ-dependent mercury (Hg) accumulation (gills, liver and muscle) within isolated/combined warming (ΔT=4°C) and acidification (ΔpCO₂=1100μatm) scenarios, as well as direct deleterious effects and phenotypic stress response over multi-stressor contexts. After 30days of exposure, although no mortalities were observed in any treatments, Hg concentration was enhanced under warming conditions, especially in the liver. On the other hand, elevated CO₂ decreased Hg accumulation and consistently elicited a dampening effect on warming and contamination-elicited oxidative stress (catalase, superoxide dismutase and glutathione-S-transferase activities) and heat shock responses. Thus, potentially unpinned on CO₂-promoted protein removal and ionic equilibrium between hydrogen and reactive oxygen species, we found that co-occurring acidification decreased heavy metal accumulation and contributed to physiological homeostasis. Although this indicates that fish can be physiologically capable of withstanding future ocean conditions, additional experiments are needed to fully understand the biochemical repercussions of interactive stressors (additive, synergistic or antagonistic).

The Digestive Tract of Cephalopods: a Neglected Topic of Relevance to Animal Welfare in the Laboratory and Aquaculture

Maintenance of health and welfare of a cephalopod is essential whether it is in a research, aquaculture or public display. The inclusion of cephalopods in the European Union legislation (Directive 2010/63/EU) regulating the use of animals for scientific purposes has prompted detailed consideration and review of all aspects of the care and welfare of cephalopods in the laboratory but the information generated will be of utility in other settings. We overview a wide range of topics of relevance to cephalopod digestive tract physiology and their relationship to the health and welfare of these animals. Major topics reviewed include: (i) Feeding cephalopods in captivity which deals with live food and prepared diets, feeding frequency (ad libitum vs. intermittent) and the amount of food provided; (ii) The particular challenges in feeding hatchlings and paralarvae, as feeding and survival of paralarvae remain major bottlenecks for aquaculture e.g., Octopus vulgaris; (iii) Digestive tract parasites and ingested toxins are discussed not only from the perspective of the impact on digestive function and welfare but also as potential confounding factors in research studies; (iv) Food deprivation is sometimes necessary (e.g., prior to anesthesia and surgery, to investigate metabolic control) but what is the impact on a cephalopod, how can it be assessed and how does the duration relate to regulatory threshold and severity assessment? Reduced food intake is also reviewed in the context of setting humane end-points in experimental procedures; (v) A range of experimental procedures are reviewed for their potential impact on digestive tract function and welfare including anesthesia and surgery, pain and stress, drug administration and induced developmental abnormalities. The review concludes by making some specific recommendations regarding reporting of feeding data and identifies a number of areas for further investigation. The answer to many of the questions raised here will rely on studies of the physiology of the digestive tract.

Response of antioxidant enzymes in Mythimna separata (Lepidoptera: Noctuidae) exposed to thermal stress

The oriental army worm Mythimna separata (Lepidoptera: Noctuidae) is a migratory pest in Eastern Asia and China. Seasonal high temperatures in Southern China and low temperatures in Northern China are pressures favouring the annual migration of this species, while cold tolerance determines the northern limit of its overwintering range. A number of physiological stress responses occur in insects as a result of variations in temperature. One reaction to thermal stress is the generation of reactive oxygen species (ROS), which can be harmful by causing oxidative damage. The time-related effects (durations of 1, 4 and 7 h) of thermal stress treatments of M. separata at comparatively low (5, 10, 15 and 20°C) and high (30, 35, 40 and 45°C) temperatures on the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POX) and glutathione S-transferases (GSTs), and total antioxidant capacity (T-AOC) were determined. Thermal stress resulted in significant elevation of the activities of SOD, CAT and GSTs, indicating that these enzymes contribute to defence mechanisms counteracting oxidative damage caused by an increase in ROS. However, at high-temperatures, POX and T-AOC were also found to contribute to scavenging ROS. Our results also indicate that extreme temperatures lead to elevated ROS production in M. separata. The present study confirms that thermal stress can be responsible for oxidative damage. To overcome such stress, antioxidant enzymes play key roles in diminishing oxidative damage in M. separata.

Indirect effects of climate changes on cadmium bioavailability and biological effects in the Mediterranean mussel Mytilus galloprovincialis

Despite the great interest in the consequences of climate change on the physiological functioning of marine organisms, indirect and interactive effects of rising temperature and pCO₂ on bioaccumulation and responsiveness to environmental pollutants are still poorly explored, particularly in terms of cellular mechanisms. According to future projections of temperature and pH/pCO₂, this study investigated the main cellular pathways involved in metal detoxification and oxidative homeostasis in Mediterranean mussels, Mytilus galloprovincialis, exposed for 4 weeks to various combinations of two levels of pH/pCO₂ (8.2/∼400 μatm and 7.4/∼3000 μatm), temperature (20 and 25 °C), and cadmium addition (0 and 20 μg/L). Bioaccumulation was increased in metal exposed organisms but it was not further modulated by different temperature and pH/pCO₂ combinations. However, interactions between temperature, pH and cadmium had significant effects on induction of metallothioneins, responses of the antioxidant system and the onset of oxidative damages, which was tissue dependent. Multiple stressors increased metallothioneins concentrations in the digestive gland revealing different oxidative effects: while temperature and cadmium enhanced glutathione-dependent antioxidant protection and capability to neutralize peroxyl radicals, the metal increased the accumulation of lipid peroxidation products under acidified conditions. Gills did not reveal specific effects for different combinations of factors, but a general stress condition was observed in this tissue after various treatments. Significant variations of immune system were mainly caused by increased temperature and low pH, while co-exposure to acidification and cadmium enhanced metal genotoxicity and the onset of permanent DNA damage in haemocytes. Elaboration of the whole biomarker data in a cellular hazard index, corroborated the synergistic effects of temperature and acidification which increased the toxicological effects of cadmium. The overall results confirmed that climate change could influence ecotoxicological effects of environmental contaminants, highlighting the importance of a better knowledge of cellular mechanisms to understand and predict responsiveness of marine organisms to such multiple stressors.

Development of Embryonic Market Squid, Doryteuthis opalescens, under Chronic Exposure to Low Environmental pH and [O2]

The market squid, Doryteuthis opalescens, is an important forage species for the inshore ecosystems of the California Current System. Due to increased upwelling and expansion of the oxygen minimum zone in the California Current Ecosystem, the inshore environment is expected to experience lower pH and [O2] conditions in the future, potentially impacting the development of seafloor-attached encapsulated embryos. To understand the consequences of this co-occurring environmental pH and [O2] stress for D. opalescens encapsulated embryos, we performed two laboratory experiments. In Experiment 1, embryo capsules were chronically exposed to a treatment of higher (normal) pH (7.93) and [O2] (242 μM) or a treatment of low pH (7.57) and [O2] (80 μM), characteristic of upwelling events and/or La Niña conditions. The low pH and low [O2] treatment extended embryo development duration by 5-7 days; embryos remained at less developed stages more often and had 54.7% smaller statolith area at a given embryo size. Importantly, the embryos that did develop to mature embryonic stages grew to sizes that were similar (non-distinct) to those exposed to the high pH and high [O2] treatment. In Experiment 2, we exposed encapsulated embryos to a single stressor, low pH (7.56) or low [O2] (85 μM), to understand the importance of environmental pH and [O2] rising and falling together for squid embryogenesis. Embryos in the low pH only treatment had smaller yolk reserves and bigger statoliths compared to those in low [O2] only treatment. These results suggest that D. opalescens developmental duration and statolith size are impacted by exposure to environmental [O2] and pH (pCO2) and provide insight into embryo resilience to these effects.

Guidelines for the Care and Welfare of Cephalopods in Research -A consensus based on an initiative by CephRes, FELASA and the Boyd Group

This paper is the result of an international initiative and is a first attempt to develop guidelines for the care and welfare of cephalopods (i.e. nautilus, cuttlefish, squid and octopus) following the inclusion of this Class of ∼700 known living invertebrate species in Directive 2010/63/EU. It aims to provide information for investigators, animal care committees, facility managers and animal care staff which will assist in improving both the care given to cephalopods, and the manner in which experimental procedures are carried out. Topics covered include: implications of the Directive for cephalopod research; project application requirements and the authorisation process; the application of the 3Rs principles; the need for harm-benefit assessment and severity classification. Guidelines and species-specific requirements are provided on: i. supply, capture and transport; ii. environmental characteristics and design of facilities (e.g. water quality control, lighting requirements, vibration/noise sensitivity); iii. accommodation and care (including tank design), animal handling, feeding and environmental enrichment; iv. assessment of health and welfare (e.g. monitoring biomarkers, physical and behavioural signs); v. approaches to severity assessment; vi. disease (causes, prevention and treatment); vii. scientific procedures, general anaesthesia and analgesia, methods of humane killing and confirmation of death. Sections covering risk assessment for operators and education and training requirements for carers, researchers and veterinarians are also included. Detailed aspects of care and welfare requirements for the main laboratory species currently used are summarised in Appendices. Knowledge gaps are highlighted to prompt research to enhance the evidence base for future revision of these guidelines.

Oxidative Stress and Digestive Enzyme Activity of Flatfish Larvae in a Changing Ocean

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.

Temperature experienced during incubation affects antioxidant capacity but not oxidative damage in hatchling red-eared slider turtles (Trachemys scripta elegans)

Our understanding of how oxidative stress resistance phenotypes are affected by the developmental environment is limited. One component of the developmental environment, which is likely central to early life oxidative stress among ectothermic and oviparous species, is that of temperature. We investigated how incubation temperature manipulations affect oxidative damage and total antioxidant capacity (TAC) in red-eared slider turtle (Trachemys scripta elegans) hatchlings. First, to determine if temperature fluctuations elicit oxidative stress, eggs from clutches were randomly assigned to either a constant (29.5°C) or daily fluctuating temperature incubation (28.7±3°C) treatment. Second, to assess the effect of temperature fluctuation frequency on oxidative stress, eggs were incubated in one of three fluctuating incubation regimes; 28.7±3°C fluctuations every 12 (Hyper), 24 (Normal), or 48 hours (Hypo). Third, we tested the influence of average incubation temperature by incubating eggs in a daily fluctuating incubation temperature regime with a mean temperature of 26.5°C (Low), 27.1°C (Medium), or 27.7°C (High). Although the accumulation of oxidative damage in hatchlings was unaffected by any thermal manipulation, TAC was affected by both temperature fluctuation frequency and average incubation temperature. Individuals incubated with a low frequency of temperature fluctuations had reduced TAC, while incubation at a lower average temperature was associated with enhanced TAC. These results indicate that while sufficient to prevent oxidative damage, TAC is influenced by developmental thermal environments, potentially due to temperature mediated changes in metabolic rate. The observed differences in TAC may have important future consequences for hatchling fitness and overwinter survival.

Defective skeletogenesis and oversized otoliths in fish early stages in a changing ocean

Early life stages of many marine organisms are being challenged by rising seawater temperature and CO₂ concentrations, but their physiological responses to these environmental changes still remain unclear. In the present study, we show that future predictions of ocean warming (+4°C) and acidification (ΔpH=0.5 units) may compromise the development of early life stages of a highly commercial teleost fish, Solea senegalensis. Exposure to future conditions caused a decline in hatching success and larval survival. Growth, metabolic rates and thermal tolerance increased with temperature but decreased under acidified conditions. Hypercapnia and warming amplified the incidence of deformities by 31.5% (including severe deformities such as lordosis, scoliosis and kyphosis), while promoting the occurrence of oversized otoliths (109.3% increase). Smaller larvae with greater skeletal deformities and larger otoliths may face major ecophysiological challenges, which might potentiate substantial declines in adult fish populations, putting in jeopardy the species' fitness under a changing ocean.

Differential impacts of ocean acidification and warming on winter and summer progeny of a coastal squid (Loligo vulgaris)

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.

Cephalopods in neuroscience: regulations, research and the 3Rs

Cephalopods have been utilised in neuroscience research for more than 100 years particularly because of their phenotypic plasticity, complex and centralised nervous system, tractability for studies of learning and cellular mechanisms of memory (e.g. long-term potentiation) and anatomical features facilitating physiological studies (e.g. squid giant axon and synapse). On 1 January 2013, research using any of the about 700 extant species of "live cephalopods" became regulated within the European Union by Directive 2010/63/EU on the "Protection of Animals used for Scientific Purposes", giving cephalopods the same EU legal protection as previously afforded only to vertebrates. The Directive has a number of implications, particularly for neuroscience research. These include: (1) projects will need justification, authorisation from local competent authorities, and be subject to review including a harm-benefit assessment and adherence to the 3Rs principles (Replacement, Refinement and Reduction). (2) To support project evaluation and compliance with the new EU law, guidelines specific to cephalopods will need to be developed, covering capture, transport, handling, housing, care, maintenance, health monitoring, humane anaesthesia, analgesia and euthanasia. (3) Objective criteria need to be developed to identify signs of pain, suffering, distress and lasting harm particularly in the context of their induction by an experimental procedure. Despite diversity of views existing on some of these topics, this paper reviews the above topics and describes the approaches being taken by the cephalopod research community (represented by the authorship) to produce "guidelines" and the potential contribution of neuroscience research to cephalopod welfare.

Effects of thermal stress on lipid peroxidation and antioxidant enzyme activities of the predatory mite, Neoseiulus cucumeris (Acari: Phytoseiidae)

Changes in temperature are known to cause a variety of physiological stress responses in insects and mites. Thermal stress responses are usually associated with the increased generation of reactive oxygen species (ROS), resulting in oxidative damage. In this study, we examined the time-related effect (durations for 1, 2, 3, and 5 h) of thermal stress conditions-i.e., relatively low (0, 5, 10, and 15 °C) or high (35, 38, 41, and 44 °C) temperatures-on the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), glutathione S-transferases (GSTs), and total antioxidant capacity (T-AOC) of the predatory mite Neoseiulus cucumeris. Also the lipid peroxidation (LPO) levels of the predatory mite were measured under thermal stress conditions. The results confirmed that thermal stress results in a condition of so-called oxidative stress and the four antioxidant enzymes play an important role in combating the accumulation of ROS in N. cucumeris. CAT and POX activity changed significantly when the mites were exposed to cold and heat shock, respectively. The elevated levels of SOD and GSTs activity, expressed in a time-dependent manner, may have an important role in the process of antioxidant response to thermal stress. However, the levels of LPO in N. cucumeris were high, serving as an important signal that these antioxidant enzyme-based defense mechanisms were not always adequate to counteract the surplus ROS. Thus, we hypothesize that thermal stress, especially extreme temperatures, may contribute much to the generation of ROS in N. cucumeris, and eventually to its death.

Transitions during cephalopod life history: the role of habitat, environment, functional morphology and behaviour

Cephalopod life cycles generally share a set of stages that take place in different habitats and are adapted to specific, though variable, environmental conditions. Throughout the lifespan, individuals undertake a series of brief transitions from one stage to the next. Four transitions were identified: fertilisation of eggs to their release from the female (1), from eggs to paralarvae (2), from paralarvae to subadults (3) and from subadults to adults (4). An analysis of each transition identified that the changes can be radical (i.e. involving a range of morphological, physiological and behavioural phenomena and shifts in habitats) and critical (i.e. depending on environmental conditions essential for cohort survival). This analysis underlines that transitions from eggs to paralarvae (2) and from paralarvae to subadults (3) present major risk of mortality, while changes in the other transitions can have evolutionary significance. This synthesis suggests that more accurate evaluation of the sensitivity of cephalopod populations to environmental variation could be achieved by taking into account the ontogeny of the organisms. The comparison of most described species advocates for studies linking development and ecology in this particular group.

Developmental and physiological challenges of octopus (Octopus vulgaris) early life stages under ocean warming

The ability to understand and predict the effects of ocean warming (under realistic scenarios) on marine biota is of paramount importance, especially at the most vulnerable early life stages. Here we investigated the impact of predicted environmental warming (+3 °C) on the development, metabolism, heat shock response and antioxidant defense mechanisms of the early stages of the common octopus, Octopus vulgaris. As expected, warming shortened embryonic developmental time by 13 days, from 38 days at 18 °C to 25 days at 21 °C. Concomitantly, survival decreased significantly (~29.9 %). Size at hatching varied inversely with temperature, and the percentage of smaller premature paralarvae increased drastically, from 0 % at 18 °C to 17.8 % at 21 °C. The metabolic costs of the transition from an encapsulated embryo to a free planktonic form increased significantly with warming, and HSP70 concentrations and glutathione S-transferase activity levels were significantly magnified from late embryonic to paralarval stages. Yet, despite the presence of effective antioxidant defense mechanisms, ocean warming led to an augmentation of malondialdehyde levels (an indicative of enhanced ROS action), a process considered to be one of the most frequent cellular injury mechanisms. Thus, the present study provides clues about how the magnitude and rate of ocean warming will challenge the buffering capacities of octopus embryos and hatchlings' physiology. The prediction and understanding of the biochemical and physiological responses to warmer temperatures (under realistic scenarios) is crucial for the management of highly commercial and ecologically important species, such as O. vulgaris.

Cephalopods as vectors of harmful algal bloom toxins in marine food webs

Here we summarize the current knowledge on the transfer and accumulation of harmful algal bloom (HAB)-related toxins in cephalopods (octopods, cuttlefishes and squids). These mollusks have been reported to accumulate several HAB-toxins, namely domoic acid (DA, and its isomers), saxitoxin (and its derivatives) and palytoxin (and palytoxin-like compounds) and, therefore, act as HAB-toxin vectors in marine food webs. Coastal octopods and cuttlefishes store considerably high levels of DA (amnesic shellfish toxin) in several tissues, but mainly in the digestive gland (DG)--the primary site of digestive absorption and intracellular digestion. Studies on the sub-cellular partitioning of DA in the soluble and insoluble fractions showed that nearly all DA (92.6%) is found in the cytosol. This favors the trophic transfer of the toxins since cytosolic substances can be absorbed by predators with greater efficiency. The available information on the accumulation and tissue distribution of DA in squids (e.g., in stranded Humboldt squids, Dosidicus gigas) is scarcer than in other cephalopod groups. Regarding paralytic shellfish toxins (PSTs), these organisms accumulate them at the greatest extent in DG >> kidneys > stomach > branchial hearts > posterior salivary glands > gills. Palytoxins are among the most toxic molecules identified and stranded octopods revealed high contamination levels, with ovatoxin (a palytoxin analogue) reaching 971 μg kg⁻¹ and palytoxin reaching 115 μg kg⁻¹ (the regulatory limit for PlTXs is 30 μg kg⁻¹ in shellfish). Although the impacts of HAB-toxins in cephalopod physiology are not as well understood as in fish species, similar effects are expected since they possess a complex nervous system and highly developed brain comparable to that of the vertebrates. Compared to bivalves, cephalopods represent a lower risk of shellfish poisoning in humans, since they are usually consumed eviscerated, with exception of traditional dishes from the Mediterranean area.

Lower hypoxia thresholds of cuttlefish early life stages living in a warm acidified ocean

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.

Adverse effects of ocean acidification on early development of squid (Doryteuthis pealeii)

Anthropogenic carbon dioxide (CO₂) is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form aragonite cuttlebones and statoliths, are of concern because of the central role they play in many ocean ecosystems and because of their importance to global fisheries. Atlantic longfin squid (Doryteuthis pealeii), an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae) under ambient and elevated CO₂ concentrations in replicated experimental trials. Animals raised under elevated pCO₂ demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO₂-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.