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.

Non-contact robotic manipulation of floating objects: exploiting emergent limit cycles

The study of non-contact manipulation in water, and the ability to robotically control floating objects has gained recent attention due to wide-ranging potential applications, including the analysis of plastic pollution in the oceans and the optimization of procedures in food processing plants. However, modeling floating object movements can be complex, as their trajectories are influenced by various factors such as the object's shape, size, mass, and the magnitude, frequency, and patterns of water waves. This study proposes an experimental investigation into the emergence ofrobotically controlled limit cycles in the movement of floating objects within a closed environment. The objects' movements are driven by robot fins, and the experiment plan set up involves the use of up to four fins and variable motor parameters. By combining energy quantification of the system with an open-loop pattern generation, it is possible to demonstrate all main water-object interactions within the enclosed environment. A study using dynamic time warping around floating patterns gives insights on possible further studies.

Cephalopod Susceptibility to Asphyxiation via Ocean Incalescence, Deoxygenation, and Acidification

Squids are powerful swimmers with high metabolic rates despite constrained oxygen uptake and transport. They have evolved novel physiological strategies for survival in extreme environments that provide insight into their susceptibility to asphyxiation under anthropogenic ocean incalescence (warming), deoxygenation, and acidification. Plasticity of ecological and physiological traits, in conjunction with vertical and latitudinal mobility, may explain their evolutionary persistence and ensure their future survival.

The Evolution and Development of Cephalopod Chambers and Their Shape

The Ammonoidea is a group of extinct cephalopods ideal to study evolution through deep time. The evolution of the planispiral shell and complexly folded septa in ammonoids has been thought to have increased the functional surface area of the chambers permitting enhanced metabolic functions such as: chamber emptying, rate of mineralization and increased growth rates throughout ontogeny. Using nano-computed tomography and synchrotron radiation based micro-computed tomography, we present the first study of ontogenetic changes in surface area to volume ratios in the phragmocone chambers of several phylogenetically distant ammonoids and extant cephalopods. Contrary to the initial hypothesis, ammonoids do not possess a persistently high relative chamber surface area. Instead, the functional surface area of the chambers is higher in earliest ontogeny when compared to Spirula spirula. The higher the functional surface area the quicker the potential emptying rate of the chamber; quicker chamber emptying rates would theoretically permit faster growth. This is supported by the persistently higher siphuncular surface area to chamber volume ratio we collected for the ammonite Amauroceras sp. compared to either S. spirula or nautilids. We demonstrate that the curvature of the surface of the chamber increases with greater septal complexity increasing the potential refilling rates. We further show a unique relationship between ammonoid chamber shape and size that does not exist in S. spirula or nautilids. This view of chamber function also has implications for the evolution of the internal shell of coleoids, relating this event to the decoupling of soft-body growth and shell growth.

Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods

Cephalopods have evolved complex sensory systems and an active lifestyle to compete with fish for similar resources in the marine environment. Their highly active lifestyle and their extensive protein metabolism has led to substantial acid-base regulatory abilities enabling these organisms to cope with CO2 induced acid-base disturbances. In convergence to teleost, cephalopods possess an ontogeny-dependent shift in ion-regulatory epithelia with epidermal ionocytes being the major site of embryonic acid-base regulation and ammonia excretion, while gill epithelia take these functions in adults. Although the basic morphology and excretory function of gill epithelia in cephalopods were outlined almost half a century ago, modern immunohistological and molecular techniques are bringing new insights to the mechanistic basis of acid-base regulation and excretion of nitrogenous waste products (e.g. NH3/NH4 (+)) across ion regulatory epithelia of cephalopods. Using cephalopods as an invertebrate model, recent findings reveal partly conserved mechanisms but also novel aspects of acid-base regulation and nitrogen excretion in these exclusively marine animals. Comparative studies using a range of marine invertebrates will create a novel and exciting research direction addressing the evolution of pH regulatory and excretory systems.

Ultra-fast escape maneuver of an octopus-inspired robot

We design and test an octopus-inspired flexible hull robot that demonstrates outstanding fast-starting performance. The robot is hyper-inflated with water, and then rapidly deflates to expel the fluid so as to power the escape maneuver. Using this robot we verify for the first time in laboratory testing that rapid size-change can substantially reduce separation in bluff bodies traveling several body lengths, and recover fluid energy which can be employed to improve the propulsive performance. The robot is found to experience speeds over ten body lengths per second, exceeding that of a similarly propelled optimally streamlined rigid rocket. The peak net thrust force on the robot is more than 2.6 times that on an optimal rigid body performing the same maneuver, experimentally demonstrating large energy recovery and enabling acceleration greater than 14 body lengths per second squared. Finally, over 53% of the available energy is converted into payload kinetic energy, a performance that exceeds the estimated energy conversion efficiency of fast-starting fish. The Reynolds number based on final speed and robot length is [Formula: see text]. We use the experimental data to establish a fundamental deflation scaling parameter [Formula: see text] which characterizes the mechanisms of flow control via shape change. Based on this scaling parameter, we find that the fast-starting performance improves with increasing size.

Metabolic suppression during protracted exposure to hypoxia in the jumbo squid, Dosidicus gigas, living in an oxygen minimum zone

The jumbo squid, Dosidicus gigas, can survive extended forays into the oxygen minimum zone (OMZ) of the Eastern Pacific Ocean. Previous studies have demonstrated reduced oxygen consumption and a limited anaerobic contribution to ATP production, suggesting the capacity for substantial metabolic suppression during hypoxic exposure. Here we provide a more complete description of energy metabolism and explore the expression of proteins indicative of transcriptional and translational arrest that may contribute to metabolic suppression. We demonstrate a suppression of total ATP demand under hypoxic conditions (1% oxygen, PO2 = 0.8 kPa) in both juveniles (52%) and adults (35%) of the jumbo squid. Oxygen consumption rates are reduced to 20% under hypoxia relative to air-saturated controls. Concentrations of Arg-P and ATP declined initially, reaching a new steady state (~30% of controls) after the first hour of hypoxic exposure. Octopine began accumulating after the first hour of hypoxic exposure, once Arg-P breakdown resulted in sufficient free arginine for substrate. Octopine reached levels near 30 mmoles g-1 after 3.4 h of hypoxic exposure. Succinate did increase through hypoxia but contributed minimally to total ATP production. Glycogenolysis in mantle muscle presumably serves to maintain muscle functionality and balance energetics during hypoxia. We provide evidence that post-translational modifications on histone proteins and translation factors serve as a primary means of energy conservation and that select components of the stress response are altered in hypoxic squids. Reduced ATP consumption under hypoxia serves to maintain ATP levels, prolong fuel store use and minimize the accumulation of acidic intermediates of anaerobic ATP generating pathways during prolonged diel forays into the OMZ. Metabolic suppression likely limits active, daytime foraging at depth in the core of the OMZ, but confers an energetic advantage over competitors that must remain in warm, oxygenated surface waters. Moreover, capacity for metabolic suppression provides habitat flexibility as oxygen minimum zones expand due to climate change.

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.

Energy homeostasis as an integrative tool for assessing limits of environmental stress tolerance in aquatic invertebrates

Energy balance is a fundamental requirement of stress adaptation and tolerance. We explore the links between metabolism, energy balance and stress tolerance using aquatic invertebrates as an example and demonstrate that using key parameters of energy balance (aerobic scope for growth, reproduction and activity; tissue energy status; metabolic rate depression; and compensatory onset of anaerobiosis) can assist in integrating the effects of multiple stressors and their interactions and in predicting the whole-organism and population-level consequences of environmental stress. We argue that limitations of both the amount of available energy and the rates of its acquisition and metabolic conversions result in trade-offs between basal maintenance of a stressed organism and energy costs of fitness-related functions such as reproduction, development and growth and can set limit to the tolerance of a broad range of environmental stressors. The degree of stress-induced disturbance of energy balance delineates transition from moderate stress compatible with population persistence (pejus range) to extreme stress where only time-limited existence is possible (pessimum range). It also determines the predominant adaptive strategy of metabolic responses (energy compensation vs. conservation) that allows an organism to survive the disturbance. We propose that energy-related biomarkers can be used to determine the conditions when these metabolic transitions occur and thus predict ecological consequences of stress exposures. Bioenergetic considerations can also provide common denominator for integrating stress responses and predicting tolerance limits under the environmentally realistic scenarios when multiple and often variable stressors act simultaneously on an organism. Determination of bioenergetic sustainability at the organism's level (or lack thereof) has practical implications. It can help identify the habitats and/or conditions where a population can survive (even if at the cost of reduced reproduction and growth) and those that are incapable of supporting viable populations. Such an approach will assist in explaining and predicting the species' distribution limits in the face of the environmental change and informing the conservation efforts and resource management practices.

Ventilation rates and activity levels of juvenile jumbo squids under metabolic suppression in the oxygen minimum zones

The Humboldt (jumbo) squid, Dosidicus gigas, is a part-time resident of the permanent oxygen minimum zone (OMZ) in the Eastern Tropical Pacific and, thereby, it encounters oxygen levels below its critical oxygen partial pressure. To better understand the ventilatory mechanisms that accompany the process of metabolic suppression in these top oceanic predators, we exposed juvenile D. gigas to the oxygen levels found in the OMZ (1% O2, 1kPa, 10ºC) and measured metabolic rates, activity cycling patterns, swimming mode, escape-jet (burst) frequency, mantle contraction frequency and strength, stroke volume and oxygen extraction efficiency. In normoxia, the metabolic rates varied between 14 to 29 µmol O2 g (ww)-1 h-1, depending on the level of activity. The mantle contraction frequency and strength was linearly correlated and increased significantly with activity level. Additionally, an increased stroke volume and ventilatory volume per minute were observed, followed by a mantle hyperinflation process during high activity periods. Squid metabolic rates dropped more than 75% during exposure to hypoxia. Maximum metabolic rates were not achieved under such conditions and the metabolic scope was significantly decreased. Hypoxia changed the relationship between mantle contraction strength and frequency from linear to polynomial with increasing activity indicating that, under hypoxic conditions, the jumbo squid primarily increases the strength of mantle contraction and does not regulate its frequency. Under hypoxia, jumbo squids also showed a larger inflation period (reduced contraction frequency) and decreased relaxed mantle diameters (shortened diffusion pathways), which optimize oxygen extraction efficiency (up to 82%/34%, without/with consideration of 60% potential skin respiration). Additionally, they breathe “deeply”, with more powerful contractions and enhanced stroke volume. This deep-breathing behavior allows them to display a stable ventilatory volume per min, and explains the maintenance of the squid’s cycling activity under such O2 conditions. During hypoxia, the respiratory cycles were shorter in length but increased in frequency. This was accompanied by an increase in the number of escape-jets during active periods and a faster switch between swimming modes. In late hypoxia (onset ~170±10 min), all the ventilatory processes were significantly reduced and followed by a lethargic state, a behavior that seems closely associated with the process of metabolic suppression and enables the squid to extend its residence time in the OMZ.

Critical oxygen levels and metabolic suppression in oceanic oxygen minimum zones

The survival of oceanic organisms in oxygen minimum zones (OMZs) depends on their total oxygen demand and the capacities for oxygen extraction and transport, anaerobic ATP production and metabolic suppression. Anaerobic metabolism and metabolic suppression are required for daytime forays into the most extreme OMZs. Critical oxygen partial pressures are, within a range, evolved to match the minimum oxygen level to which a species is exposed. This fact demands that low oxygen habitats be defined by the biological response to low oxygen rather than by some arbitrary oxygen concentration. A broad comparative analysis of oxygen tolerance facilitates the identification of two oxygen thresholds that may prove useful for policy makers as OMZs expand due to climate change. Between these thresholds, specific physiological adaptations to low oxygen are required of virtually all species. The lower threshold represents a limit to evolved oxygen extraction capacity. Climate change that pushes oxygen concentrations below the lower threshold (∼0.8 kPa) will certainly result in a transition from an ecosystem dominated by a diverse midwater fauna to one dominated by diel migrant biota that must return to surface waters at night. Animal physiology and, in particular, the response of animals to expanding hypoxia, is a critical, but understudied, component of biogeochemical cycles and oceanic ecology. Here, I discuss the definition of hypoxia and critical oxygen levels, review adaptations of animals to OMZs and discuss the capacity for, and prevalence of, metabolic suppression as a response to temporary residence in OMZs and the possible consequences of climate change on OMZ ecology.

Localization of ion-regulatory epithelia in embryos and hatchlings of two cephalopods

The tissue distribution and ontogeny of Na(+)/K(+)-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na(+)/K(+)-ATPase with the polyclonal antibody alpha (H-300) raised against the human alpha1-subunit of Na(+)/K(+)-ATPase. Na(+)/K(+)-ATPase immunoreactivity was observed in several tissues (gills, pancreatic appendages, nerves), exclusively located in baso-lateral membranes lining blood sinuses. Furthermore, large single cells in the gill of adult L. vulgaris specimens closely resembled Na(+)/K(+)-ATPase-rich cells described in fish. Immunohistochemical observations indicated that the amount and distribution of Na(+)/K(+)-ATPase in late cuttlefish embryos was similar to that found in juvenile and adult stages. The ion-regulatory epithelia (e.g., gills, excretory organs) of the squid embryos and paralarvae exhibited less differentiation than adults. Na(+)/K(+)-ATPase activities for whole animals were higher in hatchlings of S. officinalis (157.0 +/- 32.4 micromol g (FM) (-1) h(-1)) than in those of L. vulgaris (31.8 +/- 3.3 micromol g (FM) (-1) h(-1)). S. officinalis gills and pancreatic appendages achieved activities of 94.8 +/- 18.5 and 421.8 +/- 102.3 micromol(ATP) g (FM) (-1) h(-1), respectively. High concentrations of Na(+)/K(+)-ATPase in late cephalopod embryos might be important in coping with the challenging abiotic conditions (low pH, high pCO(2)) that these organisms encounter inside their eggs. Our results also suggest a higher sensitivity of squid vs. cuttlefish embryos to environmental acid-base disturbances.

Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator

By the end of this century, anthropogenic carbon dioxide (CO(2)) emissions are expected to decrease the surface ocean pH by as much as 0.3 unit. At the same time, the ocean is expected to warm with an associated expansion of the oxygen minimum layer (OML). Thus, there is a growing demand to understand the response of the marine biota to these global changes. We show that ocean acidification will substantially depress metabolic rates (31%) and activity levels (45%) in the jumbo squid, Dosidicus gigas, a top predator in the Eastern Pacific. This effect is exacerbated by high temperature. Reduced aerobic and locomotory scope in warm, high-CO(2) surface waters will presumably impair predator-prey interactions with cascading consequences for growth, reproduction, and survival. Moreover, as the OML shoals, squids will have to retreat to these shallower, less hospitable, waters at night to feed and repay any oxygen debt that accumulates during their diel vertical migration into the OML. Thus, we demonstrate that, in the absence of adaptation or horizontal migration, the synergism between ocean acidification, global warming, and expanding hypoxia will compress the habitable depth range of the species. These interactions may ultimately define the long-term fate of this commercially and ecologically important predator.

Locomotion by Abdopus aculeatus (Cephalopoda: Octopodidae): walking the line between primary and secondary defenses

Speeds and variation in body form during crawling, bipedal walking, swimming and jetting by the shallow-water octopus Abdopus aculeatus were compared to explore possible interactions between defense behaviors and biomechanics of these multi-limbed organisms. General body postures and patterns were more complex and varied during the slow mode of crawling than during fast escape maneuvers such as swimming and jetting. These results may reflect a trade-off between predator deception and speed, or simply a need to reduce drag during jet-propelled locomotion. Octopuses swam faster when dorsoventrally compressed, a form that may generate lift, than when swimming in the head-raised posture. Bipedal locomotion proceeded as fast as swimming and can be considered a form of fast escape (secondary defense) that also incorporates elements of crypsis and polyphenism (primary defenses). Body postures during walking suggested the use of both static and dynamic stability. Absolute speed was not correlated with body mass in any mode. Based on these findings the implications for defense behaviors such as escape from predation, aggression, and 'flatfish mimicry' performed by A. aculeatus and other octopuses are discussed.

Temperature-dependent oxygen extraction from the ventilatory current and the costs of ventilation in the cephalopod Sepia officinalis

Earlier work found cuttlefish (Sepia officinalis) ventilatory muscle tissue to progressively switch to an anaerobic mode of energy production at critical temperatures (T (c)) of 7.0 and 26.8 degrees C. These findings suggested that oxygen availability limits thermal tolerance. The present study was designed to elucidate whether it is the ventilatory apparatus that sets critical temperature thresholds during acute thermal stress. Routine metabolic rate (rmr) rose exponentially between 11 and 23 degrees C, while below (8 degrees C) and above (26 degrees C) this temperature range, rmr was significantly depressed. Ventilation frequency (f (V)) and mean mantle cavity pressure (MMP) followed an exponential relationship within the entire investigated temperature range (8-26 degrees C). Oxygen extraction from the ventilatory current (EO(2)) decreased in a sigmoidal fashion with temperature, falling from > 90% at 8 degrees C to 32% at 26 degrees C. Consequently, ventilatory minute volume (MV(V)) increased by a factor of 20 from 7 to 150% body weight min(-1) in the same temperature interval. Increases in MMP and MV(V) resulted in ventilatory muscle power output (P (out)) increasing by a factor of > 80 from 0.03 to 2.4 mW kg(-1) animal. Nonetheless, costs for ventilatory mechanics remain below 1.5% rmr in the natural thermal window of the population (English Channel, 9-17 degrees C), owing to very low MMPs of < 0.05 kPa driving the ventilatory stream, and may maximally rise to 8.6% rmr at 26 degrees C. Model calculations suggest that the ventilatory system can maintain high arterial PO(2) values of > 14 kPa over the entire temperature interval. We therefore conclude that the cuttlefish ventilation system is probably not limiting oxygen transfer during acute thermal stress. Depression of rmr, well before critical temperatures are being reached, is likely caused by circulatory capacity limitations and not by fatigue of ventilatory muscle fibres.