Potential impacts of climate change on cephalopods in a highly productive region (Northwest Pacific): Habitat suitability and management.

Cephalopods occupy a mid-trophic level in marine ecosystems and are vital both ecologically and as fishery resources. However, under the pressure of climate change and fishing, the sustainability of cephalopod resources requires reasonable management. This study aims to study climate change and fishing impacts on the common economic cephalopod species habitats using species distribution models. We take the northwest Pacific Ocean region as an example, which stands out as a significant region for cephalopod production around the world. Results found that the habitats of cephalopods are moving to higher latitudes or deeper waters (Bohai Sea, mid-bottom Yellow Sea, or the Okinawa Trough waters) under climate change. Additionally, these regions are currently under lower fishing pressure, which suggests that species migration might mitigate the effects of warming and fishing. This study provides the large-scale assessment of the distribution range of cephalopods affected by climate change coping with fishing pressure in the northwest Pacific Ocean. By identifying climate refuges and key fishing grounds, we underscore the importance of this information for managing cephalopod resources in the context of climate adaptation and sustainable fishing practices.

Observational evidence of egg guarding in wild European squid.

It is accepted that loliginids, like other squid, deposit their eggs in crevices on the seabed and then abandon them. In this work, we present observational evidence of egg guarding behavior in wild European squid, Loligo vulgaris. While monitoring a squid spawning crevice at night in Spain, a large mass of squid eggs was located and filmed 17 times during 42 days, until hatching. A male and a female of L. vulgaris were filmed in front of the crevice. The same male was filmed guarding the eggs on consecutive days. In the presence of the divers, male and female alternated their approaches to the crevice repeatedly touching and flushing the egg clusters. This guarding behavior differs from the reproductive habits assumed for the European squid and could represent the first evidence of egg guarding by a male in cephalopods.

Antimicrobial and cytotoxic activities of flavonoid and phenolics extracted from Sepia pharaonis ink (Mollusca: Cephalopoda).

BACKGROUND: Several studies have been reported previously on the bioactivities of different extracts of marine molluscs. Therefore, we decided to evaluate the cytotoxic and antimicrobial activities of S. pharaonis ink as a highly populated species in the Red Sea. We extracted the flavonoids from the ink and analyzed their composition. Then we evaluated systematically the cytotoxic and antimicrobial properties of this extract. A pharmacokinetic study was also conducted using SwissADME to assess the potential of the identified flavonoids and phenolic compounds from the ink extract to be orally active drug candidates. RESULTS: Cytotoxic activity was evaluated against 5 cell lines (MCF7, Hep G2, A549, and Caco2) at different concentrations (0.4 µg/mL, 1.6 µg/mL, 6.3 µg/mL, 25 µg/mL, 100 µg/mL). The viability of examined cells was reduced by the extract in a concentration-dependent manner. The highest cytotoxic effect of the extract was recorded against A549 and Hep G2 cancer cell lines cells with IC50 = 2.873 and 7.1 µg/mL respectively. The mechanistic analysis by flow cytometry of this extract on cell cycle progression and apoptosis induction indicated that the extract arrests the cell cycle at the S phase in Hep G2 and MCF7, while in A549 cell arrest was recorded at G1 phase. However, it causes G1 and S phase arrest in Caco2 cancer cell line. Our data showed that the extract has significant antimicrobial activity against all tested human microbial pathogens. However, the best inhibitory effect was observed against Candida albicans ATCC 10,221 with a minimum inhibitory concentration (MIC) of 1.95 µg/mL. Pharmacokinetic analysis using SwissADME showed that most flavonoids and phenolics compounds have high drug similarity as they satisfy Lipinski's criteria and have WLOGP values below 5.88 and TPSA below 131.6 Å2. CONCLUSION: S. pharaonis ink ethanolic extract showed a promising cytotoxic potency against various cell lines and a remarkable antimicrobial action against different pathogenic microbial strains. S. pharaonis ink is a novel source of important flavonoids that could be used in the future in different applications as a naturally safe and feasible alternative of synthetic drugs.

FELASA Working Group report: Capture and transport of live cephalopods - recommendations for scientific purposes.

On 1 January 2013, research using cephalopod molluscs, from hatchlings to adults, became regulated within Directive 2010/63/EU. There are significant difficulties in captive breeding in the great majority of currently utilised species. Thus, scientific research relies upon the use of wild-caught animals. Furthermore, live cephalopods are shared and transported between different stakeholders and laboratories across Europe and other continents. Despite existing European and national legislation, codes, guidelines and reports from independent organisations, a set of recommendations specifically addressing the requirements for the capture and transport of animals belonging to this taxon are missing. In addition, although training and development of competence for all people involved in the supply chain are essential and aim to ensure that animals do not suffer from pain, distress or lasting harm, the requirements for those capturing and transporting wild cephalopods have not been considered. This Working Group reviewed the current literature to recognise scientific evidence and the best practice, and compiled a set of recommendations to provide guidance on the 'techniques' to be used for the capture and transport of live cephalopods for their use in scientific procedures. In addition, we propose to (a) develop standardised approaches able to assess recommended methods and objectively quantify the impact of these processes on animals' health, welfare and stress response, and (b) design a training programme for people attaining the necessary competence for capture and transportation of live cephalopods, as required by Directive 2010/63/EU.

Embryonic development of a centralised brain in coleoid cephalopods.

The last common ancestor of cephalopods and vertebrates lived about 580 million years ago, yet coleoid cephalopods, comprising squid, cuttlefish and octopus, have evolved an extraordinary behavioural repertoire that includes learned behaviour and tool utilization. These animals also developed innovative advanced defence mechanisms such as camouflage and ink release. They have evolved unique life cycles and possess the largest invertebrate nervous systems. Thus, studying coleoid cephalopods provides a unique opportunity to gain insights into the evolution and development of large centralised nervous systems. As non-model species, molecular and genetic tools are still limited. However, significant insights have already been gained to deconvolve embryonic brain development. Even though coleoid cephalopods possess a typical molluscan circumesophageal bauplan for their central nervous system, aspects of its development are reminiscent of processes observed in vertebrates as well, such as long-distance neuronal migration. This review provides an overview of embryonic coleoid cephalopod research focusing on the cellular and molecular aspects of neurogenesis, migration and patterning. Additionally, we summarize recent work on neural cell type diversity in embryonic and hatchling cephalopod brains. We conclude by highlighting gaps in our knowledge and routes for future research.

Climate change consequences on the systemic heart of female Octopus maya: oxidative phosphorylation assessment and the antioxidant system.

There is evidence that indicates that temperature modulates the reproduction of the tropical species Octopus maya, through the over- or under-expression of many genes in the brain. If the oxygen supply to the brain depends on the circulatory system, how temperature affects different tissues will begin in the heart, responsible for pumping the oxygen to tissues. The present study examines the impact of heat stress on the mitochondrial function of the systemic heart of adult O. maya. The mitochondrial metabolism and antioxidant defense system were measured in the systemic heart tissue of female organisms acclimated to different temperatures (24, 26, and 30°C). The results show that acclimation temperature affects respiratory State 3 and State 4o (oligomycin-induced) with higher values observed in females acclimated at 26°C. The antioxidant defense system is also affected by acclimation temperature with significant differences observed in superoxide dismutase, glutathione S-transferase activities, and glutathione levels. The results suggest that high temperatures (30°C) could exert physical limitations on the circulatory system through the heart pumping, affecting nutrient and oxygen transport to other tissues, including the brain, which exerts control over the reproductive system. The role of the cardiovascular system in supporting aerobic metabolism in octopus females is discussed.

HOST SWITCHING IN DICYEMIDS (PHYLUM DICYEMIDA).

Dicyemids (phylum Dicyemida) are the most common and most characteristic endosymbionts in the renal sacs of benthic cephalopod molluscs: octopuses and cuttlefishes. Typically, 2 or 3 dicyemid species are found in a single specimen of the host, and most dicyemids have high host specificity. Host-specific parasites are restricted to a limited range of host species by ecological barriers that impede dispersal and successful establishment; therefore, phylogenies of interacting groups are often congruent due to repeated co-speciation. Most frequently, however, host and parasite phylogenies are not congruent, which can be explained by processes such as host switching and other macro-evolutionary events. Here, the history of dicyemids and their host cephalopod associations were studied by comparing their phylogenies. Dicyemid species were collected from 8 decapodiform species and 12 octopodiform species in Japanese waters. Using whole mitochondrial cytochrome c oxidase subunit 1 (COI) sequences, a phylogeny of 37 dicyemid species, including 4 genera representing the family Dicyemidae, was reconstructed. Phylogenetic trees derived from analyses of COI genes consistently suggested that dicyemid species should be separated into 3 major clades and that the most common genera, Dicyema and Dicyemennea, are not monophyletic. Thus, morphological classification does not reflect the phylogenetic relationships of these 2 genera. Divergence (speciation) of dicyemid species seems to have occurred within a single host species. Possible host-switching events may have occurred between the Octopodiformes and Decapodiformes or within the Octopodiformes or the Decapodiformes. Therefore, the mechanism of dicyemid speciation may be a mixture of host switching and intra-host speciation. This is the first study in which the process of dicyemid diversification involving cephalopod hosts has been evaluated with a large number of dicyemid species and genera.

Understanding the response of the Western Mediterranean cephalopods to environment and fishing in a context of alleged winners of change.

Increasing impacts of both fisheries and climate change have resulted in shifts in the structure and functioning of marine communities. One recurrent observation is the rise of cephalopods as fish recede. This is generally attributed to the removal of main predators and competitors by fishing, while mechanistic evidence is still lacking. In addition, climate change may influence cephalopods due to their high environmental sensitivity. We aim to unveil the effects of different anthropogenic and environmental drivers at different scales focusing on the cephalopod community of the Western Mediterranean Sea. We investigate several ecological indicators offering a wide range of information about their ecology, and statistically relating them with environmental, biotic and fisheries drivers. Our results highlight non-linear changes of indicators along with spatial differences in their responses. Overall, the environment drivers have greater effects than biotic and local human impacts with contrasting effects of temperature across the geographic gradient. We conclude that cephalopods may be impacted by climate change in the future while not necessary through positive warming influence, which should make us cautious when referring to them as generalized winners of current changes.

Detection and quantification of biogenic amines in cephalopod using dansyl chloride pre-column derivatization-HPLC and their production.

The accurate detection of biogenic amines (BAs) is an important means of ensuring the quality and safety of cephalopod seafood products. In this study, the pre-column derivatization of high-performance liquid chromatography (HPLC) was optimized using dansyl chloride (Dns-Cl) to detect BAs in octopus, cuttlefish, and squid. The reasons for the formation of BAs were investigated by assessing their decarboxylase activity and the rates of decomposition. The findings demonstrated that using Dns-Cl to optimize pre-column derivatization enabled the separation of nine different BAs. The detection limits ranged from 0.07 to 0.25 mg/L, and the results exhibited a high level of linearity (R2 ≥ 0.997). The decarboxylase activity and biodegradation rate positively correlated with the formation of BAs at temperatures below 0°C. Notably, the decarboxylase activity of octopus, cuttlefish, and squid exhibited a significant increase with prolonged storage time, and formyltransferase and carbamate kinase may be the key decarboxylase in cephalopod products. These findings serve as a valuable reference for further investigations into the mechanisms behind BAs production and the development of control technologies for BAs in cephalopod products. This study has successfully demonstrated the effectiveness of the Dns-Cl pre-column derivatization-HPLC method in accurately and efficiently detecting BAs in octopus, cuttlefish, and squid. Moreover, it highlights the influence of decarboxylase content and biodegradation rate on the formation of BAs. Importantly, this method can serve as a reference for detecting BAs in various seafood products.

The best defense is a good offense: Anti-predator behavior of the common octopus (Octopus vulgaris) against conger eel attacks.

We present the description of defensive behavior in wild Octopus vulgaris against conger eel (Conger conger) attacks based on three video sequences recorded by recreational SCUBA divers in the eastern Atlantic off the coast of Galicia (NW Spain) and in the Cantabrian Sea (NW Spain). These records document common traits in defensive behavior: (1) the octopuses enveloped the conger eel's head to obscure its view; (2) they covered the eel's gills in an attempt to suffocate it; (3) they released ink; (4) the octopuses lost some appendages because of the fight. In the third video, the octopus did not exhibit the defensive behavior described in the first two videos due to an inability to utilize its arms in defense, and the conger eel's success in capturing octopuses is discussed. Additionally, both the cost that the octopus could face by losing some arms during the fight and whether the experience it acquires can be an advantage for future encounters are analyzed. The defensive behavior exhibited by octopuses in this study highlights their ability to survive in a hostile environment and serves as an example of the extensive repertoire of anti-predator strategies employed by these cephalopods.

Husbandry and methodology for assessing learning and memory in the juvenile life stage of octopus.

The purpose of this project was to use modified methodology and new approaches to determine whether the California two-spotted octopus (Octopus bimaculoides) shows evidence of higher cognitive function as juveniles. This species' cognitive ability was assessed in ∼4 month old octopus using a food preference test and a learning test (ability to recognize a habitat created from 3D printed rocks and navigate to its hidden food source). Methods for determining associative learning for this species were developed. In addition, potential enhancements to future O. bimaculoides husbandry and study design are discussed.•Enrichment and care methodology for juvenile cephalopods from hatchling to juvenile•In the article we discuss new approaches for studying associative learning, spatial learning, and food preference that can be adapted for various species of cephalopods, and the usage of 3D printing as a habitat re-creation tool in aquaria•We introduce histology methodology for observing and comparing brain development in juvenile cephalopods.

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.

Octopus vulgaris Exhibits Interindividual Differences in Behavioural and Problem-Solving Performance.

By presenting individual Octopus vulgaris with an extractive foraging problem with a puzzle box, we examined the possible correlation between behavioural performances (e.g., ease of adaptation to captive conditions, prevalence of neophobic and neophilic behaviours, and propensity to learn individually or by observing conspecifics), biotic (body and brain size, age, sex) and abiotic (seasonality and place of origin) factors. We found more neophilic animals showing shorter latencies to approach the puzzle box and higher probability of solving the task; also, shorter times to solve the task were correlated with better performance on the individual learning task. However, the most neophilic octopuses that approached the puzzle box more quickly did not reach the solution earlier than other individuals, suggesting that strong neophilic tendency may lead to suboptimal performance at some stages of the problem-solving process. In addition, seasonal and environmental characteristics of location of origin appear to influence the rate of expression of individual traits central to problem solving. Overall, our analysis provides new insights into the traits associated with problem solving in invertebrates and highlights the presence of adaptive mechanisms that promote population-level changes in octopuses' behavioural traits.

Unusual Evolution of Cephalopod Tryptophan Indole-Lyases.

Tryptophan indole-lyase (TIL), a pyridoxal-5-phosphate-dependent enzyme, catalyzes the hydrolysis of L-tryptophan (L-Trp) to indole and ammonium pyruvate. TIL is widely distributed among bacteria and bacterial TILs consist of a D2-symmetric homotetramer. On the other hand, TIL genes are also present in several metazoans. Cephalopods have two TILs, TILα and TILß, which are believed to be derived from a gene duplication that occurred before octopus and squid diverged. However, both TILα and TILß individually contain disruptive amino acid substitutions for TIL activity, and neither was active when expressed alone. When TILα and TILß were coexpressed, however, they formed a heterotetramer that exhibited low TIL activity. The loss of TIL activity of the heterotetramer following site-directed mutagenesis strongly suggests that the active heterotetramer contains the TILα/TILß heterodimer. Metazoan TILs generally have lower kcat values for L-Trp than those of bacterial TILs, but such low TIL activity may be rather suitable for metazoan physiology, where L-Trp is in high demand. Therefore, reduced activity may have been a less likely target for purifying selection in the evolution of cephalopod TILs. Meanwhile, the unusual evolution of cephalopod TILs may indicate the difficulty of post-gene duplication evolution of enzymes with catalytic sites contributed by multiple subunits, such as TIL.

Predicting the effects of spatiotemporal modifications of muscle activation on the tentacle extension in squid.

Squid use eight arms and two slender tentacles to capture prey. The muscular stalks of the tentacles are elongated approximately 80% in 20-40 ms towards the prey, which is adhered to the terminal clubs by arrays of suckers. Using a previously developed forward dynamics model of the extension of the tentacles of the squid Doryteuthis pealeii (formerly Loligo pealeii), we predict how spatial muscle-activation patterns result in a distribution of muscular power, muscle work, and kinetic and elastic energy along the tentacle. The simulated peak extension speed of the tentacles is remarkably insensitive to delays of activation along the stalk, as well as to random variations in the activation onset. A delay along the tentacle of 50% of the extension time has only a small effect on the peak extension velocity of the tentacle compared with a zero-delay pattern. A slight delay of the distal portion relative to the proximal has a small positive effect on peak extension velocity, whereas negative delays (delay reversed along stalk) always reduce extension performance. In addition, tentacular extension is relatively insensitive to superimposed random variations in the prescribed delays along the stalk. This holds in particular for small positive delays that are similar to delays predicted from measured axonal diameters of motor neurons. This robustness against variation in the activation distribution reduces the accuracy requirements of the neuronal control and is likely due to the non-linear mechanical properties of the muscular tissue in the tentacle.

High-level RNA editing diversifies the coleoid cephalopod brain proteome.

Coleoid cephalopods (octopus, squid and cuttlefish) have unusually complex nervous systems. The coleoid nervous system is also the only one currently known to recode the majority of expressed proteins through A-to-I RNA editing. The deamination of adenosine by adenosine deaminase acting on RNA (ADAR) enzymes produces inosine, which is interpreted as guanosine during translation. If this occurs in an open reading frame, which is the case for tens of thousands of editing sites in coleoids, it can recode the encoded protein. Here, we describe recent findings aimed at deciphering the mechanisms underlying high-level recoding and its adaptive potential. We describe the complement of ADAR enzymes in cephalopods, including a recently discovered novel domain in sqADAR1. We further summarize current evidence supporting an adaptive role of high-level RNA recoding in coleoids, and review recent studies showing that a large proportion of recoding sites is temperature-sensitive. Despite these new findings, the mechanisms governing the high level of RNA recoding in coleoid cephalopods remain poorly understood. Recent advances using genome editing in squid may provide useful tools to further study A-to-I RNA editing in these animals.

Improving the biological realism of predator-prey size relationships in food web models alters ecosystem dynamics.

Body-size relationships between predators and prey exhibit remarkable diversity. However, the assumption that predators typically consume proportionally smaller prey often underlies size-dependent predation in ecosystem models. In reality, some animals can consume larger prey or exhibit limited changes in prey size as they grow larger themselves. These distinct predator-prey size relationships challenge the conventional assumptions of traditional size-based models. Cephalopods, with their diverse feeding behaviours and life histories, offer an excellent case study to investigate the impact of greater biological realism in predator-prey size relationships on energy flow within a size-structured ecosystem model. By categorizing cephalopods into high and low-activity groups, in line with empirically derived, distinct predator-prey size relationships, we found that incorporating greater biological realism in size-based feeding reduced ecosystem biomass and production, while simultaneously increasing biomass stability and turnover. Our results have broad implications for ecosystem modelling, since distinct predator-prey size relationships extend beyond cephalopods, encompassing a wide array of major taxonomic groups from filter-feeding fishes to baleen whales. Incorporating a diversity of size-based feeding in food web models can enhance their ecological and predictive accuracy when studying ecosystem dynamics.

Effects of Environmental Enrichment on the Behavior of Octopus vulgaris in a Recirculating Aquaculture System.

Octopus vulgaris is a commercially valuable species. It is overexploited in the natural environment and is considered to be an innovative species for aquaculture. However, large-scale farming is generally designed only based on economic requirements, disregarding any form of enrichment that induces the natural behavior of aquatic species. Although many studies have shown the influence of environmental enrichment on terrestrial vertebrates, fish, and cephalopod mollusks, information on the effect of environmental enrichment on the body patterns of O. vulgaris is limited. Therefore, in this study, we assessed how different environmental conditions (Basic vs. Enriched) affect sub-adults of O. vulgaris kept in recirculation systems, through qualitative-quantitative studies of the main body patterns and their potential application in the commercial production of this species. The results indicated that octopuses kept in the enriched environment showed several body patterns and gained a significantly higher weight than those kept in the basic environment. The body patterns displayed by the individuals kept in the basic environment were similar to those exhibited under situations of hostility and inter/intra-specific conflict. Hence, the environment of octopuses needs to be enriched, especially for the large-scale production of this species.

A chromosome-level reference genome for the common octopus, Octopus vulgaris (Cuvier, 1797).

Cephalopods are emerging animal models and include iconic species for studying the link between genomic innovations and physiological and behavioral complexities. Coleoid cephalopods possess the largest nervous system among invertebrates, both for cell counts and brain-to-body ratio. Octopus vulgaris has been at the center of a long-standing tradition of research into diverse aspects of cephalopod biology, including behavioral and neural plasticity, learning and memory recall, regeneration, and sophisticated cognition. However, no chromosome-scale genome assembly was available for O. vulgaris to aid in functional studies. To fill this gap, we sequenced and assembled a chromosome-scale genome of the common octopus, O. vulgaris. The final assembly spans 2.8 billion basepairs, 99.34% of which are in 30 chromosome-scale scaffolds. Hi-C heatmaps support a karyotype of 1n = 30 chromosomes. Comparisons with other octopus species' genomes show a conserved octopus karyotype and a pattern of local genome rearrangements between species. This new chromosome-scale genome of O. vulgaris will further facilitate research in all aspects of cephalopod biology, including various forms of plasticity and the neural machinery underlying sophisticated cognition, as well as an understanding of cephalopod evolution.

Assessing juvenile swordfish (Xiphias gladius) diet as an indicator of marine ecosystem changes in the northwestern Mediterranean Sea.

To preserve marine biodiversity, we need reliable early warning indicators that inform changes in marine ecosystems. As reliable samplers of mid-trophic level communities, studying the trophodynamics of large pelagic fish can contribute to monitoring these changes. Here, we combined stomach content and stable isotope analyses to reconstruct the diet of juvenile swordfish (Xiphias gladius) in the northwestern Mediterranean Sea, in a time-lapse of almost a decade (2012 and 2020). Overall, our study showed that swordfish fed on a wide range of fish and cephalopod species from both pelagic and demersal habitats. A dietary shift towards increasing consumption of cephalopods and decreasing consumption of Gadiformes had been observed between 2012 and 2020. Stable isotope approaches revealed that gelatinous organisms were also important prey, particularly for smaller-sized swordfish. We underline the importance of combining multiple and complementary approaches to better reconstruct the diet of generalist species. Our findings highlight the generalist and opportunistic diet of Mediterranean swordfish, which makes them good candidates for monitoring changes in the ecosystem.