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In light of ongoing climate change, it is increasingly important to know how nutritional requirements of ectotherms are affected by changing temperatures. Here, we analyse the wide thermal response of phosphorus (P) requirements via elemental gross growth efficiencies of Carbon (C) and P, and the Threshold Elemental Ratios in different aquatic invertebrate ectotherms: the freshwater model species Daphnia magna, the marine copepod Acartia tonsa, the marine heterotrophic dinoflagellate Oxyrrhis marina, and larvae of two populations of the marine crab Carcinus maenas. We show that they all share a non-linear cubic thermal response of nutrient requirements. Phosphorus requirements decrease from low to intermediate temperatures, increase at higher temperatures and decrease again when temperature is excessive. This common thermal response of nutrient requirements is of great importance if we aim to understand or even predict how ectotherm communities will react to global warming and nutrient-driven eutrophication.

Species’ responses to climate change may vary considerably among populations. Various response patterns define the portfolio available for a species to cope with and mitigate effects of climate change. Here, we quantified variation in larval survival and physiological rates of Carcinus maenas among populations occurring in distant or contrasting habitats (Cádiz: Spain, Helgoland: North Sea, Kerteminde: Baltic Sea). During the reproductive season, we reared larvae of these populations, in the laboratory, under a combination of several temperatures (15–24 °C) and salinities (25 and 32.5 PSU). In survival, all three populations showed a mitigating effect of high temperatures at lower salinity, with the strongest pattern for Helgoland. However, Cádiz and Kerteminde differed from Helgoland in that a strong thermal mitigation did not occur for growth and developmental rates. For all populations, oxygen consumption rates were driven only by temperature; hence, these could not explain the growth rate depression found at lower salinity. Larvae from Cádiz, reared in seawater, showed increased survival at the highest temperature, which differs from Helgoland (no clear survival pattern), and especially Kerteminde (decreased survival at high temperature). These responses from the Cádiz population correspond with the larval and parental habitat (i.e., high salinity and temperature) and may reflect local adaptation. Overall, along the European coast, C. maenas larvae showed a diversity of responses, which may enable specific populations to tolerate warming and subsidise more vulnerable populations. In such case, C. maenas would be able to cope with climate change through a spatial portfolio effect., Open Access funding enabled and organized by Projekt DEAL. This work is a part of the doctoral dissertation of ZŠ and was supported by Deutsche Forschungsgemeinschaft (Research Training Group 2010: RESPONSE) at the University of Greifswald, in a partnership with the Alfred-Wegener-Institute.

In light of ongoing climate change, it is increasingly important to know how nutritional requirements of ectotherms are affected by changing temperatures. Here, we analyse the wide thermal response of phosphorus (P) requirements via elemental gross growth efficiencies of Carbon (C) and P, and the Threshold Elemental Ratios in different aquatic invertebrate ectotherms such as the freshwater model species Daphnia magna, the marine copepod Acartia tonsa, the marine heterotrophic dinoflagellate Oxyrrhis marina, and larvae of two populations of the marine crab Carcinus maenas. We show that they all share a non-linear cubic thermal response of nutrient requirements. Phosphorus requirements decrease from low to intermediate temperatures, increase at higher temperatures, and decrease again when temperature is excessive. This universality in the thermal response of nutrient requirements is of great importance if we aim to understand or even predict how ectotherm communities will react to global warming and nutrient-driven eutrophication.

Sounds from human activities such as shipping and seismic surveys have been progressively invading natural soundscapes and pervading oceanic ambient sounds for decades. Benthic invertebrates are important ecosystem engineers that continually rework the sediment they live in. Here, we tested how low-frequency noise (LFN), a significant component of noise pollution, affects the sediment reworking activities of selected macrobenthic invertebrates. In a controlled laboratory setup, the effects of acute LFN exposure on the behavior of three abundant bioturbators on the North Atlantic coasts were explored for the first time by tracking their sediment reworking and bioirrigation activities in noisy and control environments via luminophore and sodium bromide (NaBr) tracers, respectively. The amphipod crustacean Corophium volutator was negatively affected by LFN, exhibiting lower bioturbation rates and shallower luminophore burial depths compared to controls. The effect of LFN on the polychaete Arenicola marina and the bivalve Limecola balthica remained inconclusive, although A. marina displayed greater variability in bioirrigation rates when exposed to LFN. Furthermore, a potential stress response was observed in L. balthica that could reduce bioturbation potential. Benthic macroinvertebrates may be in jeopardy along with the crucial ecosystem-maintaining services they provide. More research is urgently needed to understand, predict, and manage the impacts of anthropogenic noise pollution on marine fauna and their associated ecosystems.

Offshore human activities lead to increasing amounts of underwater noise in coastal and shelf environments, which may affect commercially-important benthic invertebrate groups like the re-stocked Helgoland European lobster (Homarus gammarus) in the German Bight (North Sea). It is crucial to understand the impact tonal low-frequency noises, like maritime transport and offshore energy operations, may have on substrate choice and lobsters' behavior to assess potential benefits or bottlenecks of new hard-substrate artificial offshore environments that become available. In this study, we investigated the full factorial effect of a tonal low-frequency noise and predator presence on young-of-year (YOY) European lobsters' in a diurnal and nocturnal experiment. Rocks and European oyster shells (Ostrea edulis) were offered as substrate to YOY lobsters for 3 h. Video recordings (n = 134) allowed the identification of lobsters' initial substrate choice, diel activity and key behaviors (peeking, shelter construction, exploration and hiding). To ensure independence, YOY lobsters in the intermolt stage were randomly selected and assigned to the experimental tanks and used only once. We provide the first evidence that stressors alone, and in combination, constrain YOY lobsters' initial substrate choice towards rocks. During nighttime, the joint effect of exposure to a constant low-frequency noise and predator presence decreased antipredator behavior (i.e., hiding) and increased exploration behavior. Noise may thus interfere with YOY lobsters' attention and decision-making processes. This outcome pinpoints that added tonal low-frequency noise in the environment have the potential to influence the behavior of early-life stages of European lobsters under predator pressure and highlights the importance of including key benthic invertebrates' community relationships in anthropogenic noise risk assessments. Among others, effects of noise must be taken into consideration in plans involving the multi-use of any offshore area for decapods’ stock enhancement, aquaculture, and temporary no-take zones.

Oxygen Minimum Zones prevail in most of the world’s oceans and are particularly extensive in Eastern Boundary Upwelling Ecosystems such as the Humboldt and the Benguela upwelling systems. In these regions, euphausiids are an important trophic link between primary producers and higher trophic levels. The species are known as pronounced diel vertical migrators, thus facing different levels of oxygen and temperature within a 24 h cycle. Declining oxygen levels may lead to vertically constrained habitats in euphausiids, which consequently will affect several trophic levels in the food web of the respective ecosystem. By using the regulation index (RI), the present study aimed at investigating the hypoxia tolerances of different euphausiid species from Atlantic, Pacific as well as from Polar regions. RI was calculated from 141 data sets and used to differentiate between respiration strategies using median and quartile (Q) values: low degree of oxyregulation (0.25 < RI median < 0.5); high degree of oxyregulation (0.5 < RI median < 1; Q1 > 0.25 or Q3 > 0.75); and metabolic suppression (RI median, Q1 and Q3 < 0). RI values of the polar (Euphausia superba, Thysanoessa inermis) and sub-tropical (Euphausia hanseni, Nyctiphanes capensis, and Nematoscelis megalops) species indicate a high degree of oxyregulation, whereas almost perfect oxyconformity (RI median ≈ 0; Q1 < 0 and Q3 > 0) was identified for the neritic temperate species Thysanoessa spinifera and the tropical species Euphausia lamelligera. RI values of Euphausia distinguenda and the Humboldt species Euphausia mucronata qualified these as metabolic suppressors. RI showed a significant impact of temperature on the respiration strategy of E. hanseni from oxyregulation to metabolic suppression. The species’ estimated hypoxia tolerances and the degree of oxyconformity vs. oxyregulation were linked to diel vertical migration behavior and the temperature experienced during migration. The results highlight that the euphausiid species investigated have evolved various strategies to deal with different levels of oxygen, ranging from species showing a high degree of oxyconformity to strong oxyregulation. Neritic species may be more affected by hypoxia, as these are often short-distance-migrators and only adapted to a narrow range of environmental conditions.

The blue crab Callinectes sapidus is a widespread ectothermic species that supports large fisheries. Physiology of temperate and subtropical populations of blue crabs are well studied; however, a lack of information exists on tropical populations. Given the low locomotion capabilities of C. sapidus adult blue crabs, natural selection should favor traits that shape a particular thermal niche reflected through tolerance modulation to dissolved oxygen. This study was designed to evaluate the thermal window and hypoxia sensitivity of the blue crab population in the southern Gulf of Mexico. The effect of acclimation temperatures from 20 °C to 34 °C on thermal preference (TP), critical thermal limits (CT), and thermal metabolic scope (TMS) was assessed in normoxia. Metabolic rate regulation over partial oxygen (pO2) pressure gradient was evaluated through oxygen consumption measurements at different degrees of acute hypoxia. Callinectes sapidus was observed tending to specialize towards higher temperatures, showing a mean TP from 26 °C to 33 °C. The lowest performance of aerobic pathways was observed at the coldest regimes and the highest at the warmest ones with mean TMS value being 35 % greater at 34 °C than 20 °C. Patterns for metabolic regulation were dependent on the interaction between environmental temperature and dissolved oxygen, in which the interval from 29 °C to 34 °C provoked a 50 % reduction in oxygen consumption when exposed to ∼20% air saturation levels. The results obtained showed that blue crabs distributed in the southern Gulf of Mexico could be close to their oxygen-temperature tolerance limits, which has important implications when climate change effects on species re-distribution is considered.

Offshore wind farms (OWF) are bound to increase as a mitigation strategy to reduce the emission of greenhouse gases, it is crucial to address all of their potential impacts on key ecosystem components in detail. Especially, the chronic effect of noise created during OWF turbine operations (duration 20-25 years) must be understood. As sensitive receptors cover the whole body of crustaceans to detect their surroundings, those low frequency noises may disrupt basic ecological (prey detection and predator avoidance) and physiological (metabolism) functions. Here we present an investigation designed to understand the joint effect of noise and increased temperature on copepod. The pelagic copepod Acartia tonsa is commonly used as a proxy for a range of fundamental processes that relate to marine planktonic crustaceans. Given that higher temperatures increase metabolic demands, the experiment was conducted at three different temperature levels (18, 21, 24°C) combined with silent and noise treatments. We assessed the combined effects on energetic balance, and oxidative stress indicators. The outputs of the project will provide important information on the potential impact of low-frequency noise on marine invertebrate key organisms with implications for secondary production and ecosystem functioning.

Data on the impact of environmental pollution on the homeostasis of sea turtles remains scarce, particularly in the Southern Gulf of Mexico. As many municipalities along the coastline of the Yucatan Peninsula do not rely on a waste treatment plant, these organisms could be particularly vulnerable. We searched for relationships between the presence of organochlorine pesticides (OCP) and the level of several oxidative and pollutant stress indicators of the hawksbill sea turtle (Eretmochelys imbricata) during the 2010 nesting season at Punta Xen (Campeche, Mexico). Of the 30 sampled sea turtles, endosulfans, aldrin related (aldrin, endrin, dieldrin, endrin ketone, endrin aldehyde) and dichlorodiphenyldichloroethylene (DDT) families were detected in 17, 21 and 26, respectively. Significant correlation existed between the size of sea turtles with the concentration of methoxychlor, cholinesterase activity in plasma and heptachlors family, and catalase activity and hexachlorohexane family. Cholinesterase activity in washed erythrocytes and lipid peroxidation were positively correlated with glutathione reductase activity. Antioxidant enzyme actions seem adequate as no lipids damages were correlated with any OCPs. Future studies are necessary to evaluate the effect of OCPs on males of the area due to the significant detection of methoxychlor, which target endocrine functioning and increases its concentration with sea turtles size.

Temperature is recongnised as the main factor controlling the species fitness and performance. Naturally, the thermal preferences (TP) of aquatic organisms obtained in controlled conditions have been used to relate physiological performance with field data since they are a good proxy to the fundamental niche. Literature suggests that dispersal capabilities, biological interactions, acclimatisation, adaptation, among others might play a role in species distribution; thus, in reality, species are usually occupying a realized thermal niche (RTN). Therefore, this study was designed to inquire into the following questions: Are the TP of tropical aquatic ectotherms found in laboratory conditions similar to their RTN? Can TP be validated with occurrences in the wild? To answer these questions, this study compared the TP obtained from previously published works with the RTN of the crabs Callinectes similis and C. sapidus, the fishes Centropomus undecimalis and Ocyurus chrysurus, the lobster Panulirus argus, and the octopus Octopus maya obtained from occurrences from 1693documents. When RTN values were tested against the TPs obtained in laboratory, no significant differences were found for fish species (P > 0.05); in contrast, differences for the benthic invertebrates were reported (P

The abundance of the alien, Indo-Pacific damselfish Neopomacentrus cyanomos on an oil-loading platform in the southwest Gulf of Mexico indicates that widely distributed platforms could facilitate the expansion of its geographic range across the western and northern fringes of the Gulf. From there it likely will spread to other areas of the Greater Caribbean. The lionfish example demonstrates that it eventually happens, and can do so rapidly. Reduced temperature effects on the physiology of this species were examined to better predict its survivability in the northern Gulf during winter, when sea surface temperatures fall as low as 15 °C along the coast. Overall, our results show that when the degree of experimental temperature decline was large and rapid, no compensation occurred and the stress response observed mostly reflected cellular processes that minimized damage. Integrated biomarker response values were significantly different between fish rapidly exposed to colder vs. warmer temperatures (declines of −4 °C each day, from 26 to 14 °C), reflected in higher values of blood metabolites and routine metabolic rates observed in fish exposed to 14 and 18 °C respectively, and lower activity of all enzymes, lower protein carbonylation, and higher oxidative damage to lipids in fish exposed to 14 °C. While the physiological proxies responded to minimize damage during the rapid-decrease experiment, the same proxies reflected the consequences of compensation when fish were thermally challenged after a 45 days acclimation at 18 °C. In this case, lower values of blood metabolites and high antioxidant levels and indicators of damages underpinned its pejus lower range. Based on the results of the present work, it seems clear that low winter SSTs in the northern Gulf will slow down the colonization of the inshore area of N. cyanomos . We suggest that the use of physiological cellular stress markers on specimens acquired at the beginning of an invasion should be implemented in new standardized experimental protocols, including both rapid increases/decreases of temperature and post-acclimation temperature challenges, to assess the invasiveness potential of aquatic species such as this.

Freezing, dehydration, salinity variations, hypoxia or anoxia are some of the environmental constraints that many organisms must frequently endure. Organisms adapted to these stressors often reduce their metabolic rates to maximize their chances of survival. However, upon recovery of environmental conditions and basal metabolic rates, cells are affected by an oxidative burst that, if uncontrolled, leads to (oxidative) cell damage and eventually death. Thus, a number of adapted organisms are able to increase their antioxidant defenses during an environmental/functional hypoxic transgression; a strategy that was interpreted in the 1990s as a “preparation for oxidative stress” (POS). Since that time, POS mechanisms have been identified in at least 83 animal species representing different phyla including Cnidaria, Nematoda, Annelida, Tardigrada, Echinodermata, Arthropoda, Mollusca and Chordata. Coinciding with the 20th anniversary of the postulation of the POS hypothesis, we compiled this review where we analyze a selection of examples of species showing POS-mechanisms and review the most recent advances in understanding the underlying molecular mechanisms behind those strategies that allow animals to survive in harsh environments. Fil: Giraud Billoud, Maximiliano German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; Argentina Fil: Rivera Ingraham, Georgina A.. Laboratoire Environnement de Petit Saut, Hydreco-Guyane; Guayana Francesa Fil: Moreira, Daniel C.. Universidade do Brasília; Brasil Fil: Burmester, Thorsten. Universitat Hamburg; Alemania Fil: Castro Vazquez, Alfredo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; Argentina Fil: Carvajalino Fernández, Juan M.. Universidade do Brasília; Brasil Fil: Dafre, Alcir. Universidade Federal de Santa Catarina; Brasil Fil: Niu, Cuijuan. Beijing Normal University; China Fil: Tremblay, Nelly. Alfred Wegener Institute for Polar and Marine Research, Helgoland; Alemania Fil: Paital, Biswaranjan. University of Agriculture and Technology; India Fil: Rosa, Rui. Universidade de Lisboa, Lisboa; Portugal Fil: Storey, Janet M.. Carleton University; Canadá Fil: Vega, Israel Aníbal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histología y Embriología de Mendoza Dr. Mario H. Burgos; Argentina Fil: Zhang, Wenyi. Beijing Normal University; China Fil: Yepiz Plascencia, Gloria. Centro de Investigacion En Alimentacion y Desarrollo; México Fil: Zenteno Savin, Tania. Centro de Investigaciones Biológicas del Noroeste; México Fil: Storey, Kenneth B.. Carleton University; Canadá Fil: Hermes Lima, Marcelo. Universidade do Brasília; Brasil

Sexual maturation and reproduction influence the status of a number of physiological processes and consequently the ecology and behavior of cephalopods. Using Octopus mimus as study model, the present study was focused on the changes in biochemical composition that take place during gonadal maturation of octopus females and its consequences in embryo and hatchlings characteristics, putting special attention to energetic metabolites, digestive enzymes, and antioxidant defense mechanisms. To do that, a total of 32 adult females of Octopus mimus were sampled during ovarian maturation and the biochemical composition (metabolites and digestive enzymes) of digestive gland (DG) and ovaries (only metabolites) were followed during physiological and functional maturation. Levels of protein (Prot), triacyl glycerol (TG), cholesterol (Chol), glucose (Glu) and glycogen (Gly) were evaluated. In DG also the activity of alkaline and acidic enzymes was measured. Simultaneously, groups of eggs coming form mature females were also sampled along development, and metabolites (Prot, TG, Glu, Gly, TG, Chol), digestive enzymes activity (Lipases, alkaline and acidic), antioxidant defence mechanisms and radical oxygen species (ROS) were evaluated. Results obtained showed that ovarium is a site for reserve of some nutrients for reproduction. Presumably, TG where stored at the beginning of the maturation processes followed by Chol, both at the same time were energetically supported by Glu, derived from Gly following gluconeogenic pathways. Also, was observed that embryos during organogenesis nutrients and enzymes (metabolic, digestive and REDOX system) where maintained without significant changes and in a low activity. Results obtained in the present study shows that that activity could be not energetically costly. In contrast, was observed that during the embryo growth there were mobilization of nutrients and activation of the metabolic and digestive enzymes, joint with increments in consumption of yolk and glycogen, and reduction in molecules associated with oxidative stress, allowing paralarvae hatch with the antioxidant defence mechanisms ready to support the ROS production.

Histophagous ciliates of the genus Pseudocollinia cause epizootic events that kill adult female krill (Euphausiacea), but their mode of transmission is unknown. We compared 16S rRNA sequences of bacterial strains isolated from stomachs of healthy krill Nyctiphanes simplex specimens with sequences of bacterial isolates and sequences of natural bacterial communities from the hemocoel of N. simplex specimens infected with P. brintoni to determine possible transmission pathways. All P. brintoni endoparasitic life stages and the transmission tomite stage (outside the host) were associated with bacterial assemblages. 16S rRNA sequences from isolated bacterial strains showed that Photobacterium spp. and Pseudoalteromonas spp. were dominant members of the bacterial assemblages during all life phases of P. brintoni and potential pathobionts. They were apparently unaffected by the krill's immune system or the histophagous activity of P. brintoni. However, other bacterial strains were found only in certain P. brintoni life phases, indicating that as the infection progressed, microhabitat conditions and microbial interactions may have become unfavorable for some strains of bacteria. Trophic infection is the most parsimonious explanation for how P. brintoni infects krill. We estimated N. simplex vulnerability to P. brintoni infection during more than three-fourths of their life span, infecting mostly adult females. The ciliates have relatively high prevalence levels (albeit at

Unlike decapod crustaceans of commercial interest, the krill defense system and its response to parasites and pathogens is virtually unknown. Histophagous ciliates of the genus Pseudocollinia interact with at least 7 krill species in the northeastern Pacific. Although they can cause epizootic events, the physiology of the histophagous ciliate-host interaction and krill (host) defenses remain unknown. From 1 oceanographic survey along the southwestern coast of the Baja California Peninsula near Bahía Magdalena and 2 in the Gulf of California, we investigated parasitoid-host physiological responses (fatty acid and oxidative stress indicators) of the subtropical krill Nyctiphanes simplex infected with the ciliate P. brintoni. All life stages of P. brintoni were associated with opportunistic bacterial assemblages that have not been explicitly investigated in other Pseudocollinia species (P. beringensis, P. oregonensis, and P. similis). Parasitoid ciliates exclusively infected adult females, which showed increased lipid content during gonad development. As the infection progressed, omega-3 eicosapentaenoic and docosahexaenoic fatty acids, which may act as energy sources to produce high numbers of ciliate transmission stages, were quickly depleted. Antioxidant enzymes, components of the crustacean defense system, varied throughout infection, but without inhibiting Pseudocollinia infection, i.e. higher levels of lipid oxidative damage were detected in late stages of infection. The ineffective response of the krill antioxidant defense system against histophagous ciliates and the bacteria associated with the ciliates suggests that Pseudocollinia ciliates are functionally analogous to krill predators and may have a strong influence on the population dynamics of krill.

Sexual maturation and reproduction influence the status of a number of physiological processes and consequently the ecology and behaviour of cephalopods. UsingOctopus mimusas a study model, the present work was focused in the changes in biochemical compound and activity that take place during gonadal maturation of females and its consequences in embryo and hatchlings characteristics. To do that, a total of 31 adult females ofO. mimuswere sampled to follow metabolites (ovaries and digestive gland) and digestive enzyme activities (alkaline and acidic proteases) during physiological and functional maturation. Levels of protein (Prot), triacylglyceride (TG), cholesterol (Chol), glucose (Glu), and glycogen (Gly) were evaluated. Groups of eggs coming from mature females were also sampled along development and after hatching (paralarvae of 1 and 3 days old) to track metabolites (Prot, TG, Glu, Gly, TG, Chol), digestive enzymes activity (Lipase, alkaline proteases, and acidic proteases), and antioxidant/detoxification defence indicators with embryos development. Based on the data obtained, we hypothesized that immature females store Chol in their ovaries, probably from the food they ingested, but switch to TG reserves at the beginning of the maturation processes. At the same time, results suggest that these processes were energetically supported by Glu, obtained probably from Gly breakdown by gluconeogenic pathways. Also, was observed that embryos metabolites and enzyme activities (digestive and antioxidant/detoxification enzymes) where maintained without significant changes and in a low activity during the whole organogenesis, meaning that organogenesis is relatively not energetically costly. In contrast, after organogenesis, a mobilization of nutrients and activation of the metabolic and digestive enzymes was observed, together with increments in consumption of yolk and Gly, and reduction in lipid peroxidation. Derived from our results, we also have the hypothesis that reactive oxygen species (ROS) were produced during the metabolic processes that occurs in ovarian maturation. Those ROS may be in part transferred to the egg provoking a ROS charge to the embryos. The elimination of ROS in embryos started when the activity of the heart and the absorption of the yolk around stages XIV and XV were evident. Altogether, these processes allowed the paralarvae to hatch with buffered levels of ROS and with the antioxidant defence mechanisms ready to support further ROS production derived from paralarvae higher life stage requirements (feeding and metabolic demands).

Vertical distribution and abundance of three numerically dominant krill species (Nyctiphanes simplex, Nematoscelis difficilis, and Euphausia eximia) were surveyed in the Gulf of California to understand the role of oxidative stress in their daily vertical migration (DVM) and zoogeographic patterns. Superoxide radical production, lipid peroxidation, and antioxidant enzyme activities were analyzed from krill collected with stratified nets from the surface down to 200 m during January, July, and October 2007. The upper boundary of the oxygen minimum zone (OMZ) was significantly shallower during October than during January. N. simplex was always distributed above the hypoxic layers, mostly in coastal upwelling areas. Ne. difficilis and E. eximia were relatively abundant during January, but detected mostly during their ascending migration. N. simplex was the most sensitive species to high temperatures and low oxygen concentrations, showing evidence of oxidative stress during summer (100 times more lipid peroxidation and 30 times more antioxidant enzyme activities than in winter). Ne. difficilis had higher glutathione peroxidase activity than N. simplex, which could facilitate its larger DVM. Low abundance of Ne. difficilis at 100 m during summer suggests that high temperature was also an environmental limiting factor. Oxidative stress indicators could explain the absence of N. simplex and Ne. difficilis in the eastern tropical Pacific and the ability of E. eximia to live in the OMZ and the eastern tropical Pacific. The latter had higher superoxide radical production and smaller lipid peroxidation during October. This suggests that E. eximia antioxidant enzyme activities are enough to avoid oxidative damage when exposed to hypoxic conditions during DVM.

Interbrood period, gonad development, and total lipid content throughout the oogenesis and spermatogenesis processes of the subtropical euphausiid Nyctiphanes simplex were studied. Specimens were collected during six oceanographic cruises in Bahía Magdalena (March, July, and December 2004) and in the Gulf of California (November 2005 and January and July 2007). Females attained first spawning when ~7.5 mm total length (>52 days old). Histological evidence indicates that N. simplex females have group-synchronous ovaries, able to produce four broods per gonadic cycle, since ovigerous females develop simultaneously in three and four distinct substages (Oc1, Oc2, Oc3, and Oc4) in their gonads. Once females mature, as shown by pale pink gonads, they may reabsorb their gonads in 10 days. Embryonic development in the ovigerous sac last

To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZ), respiratory response and stress experiments combining hypoxia/reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current system (HCS, Chilean coast), and the Northern California Current system (NCCS, Oregon). Euphausia mucronata from the HCS shows oxyconforming pO2-dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a “high oxygen stress” for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba maintain respiration rates constant down to low critical pO2 values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. Temperate krill species had higher SOD (superoxide dismutase) values in winter than in summer, which relate to higher winter metabolic rate (E. pacifica). In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7°C above their typical temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4°C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2°C). In this season, experimental warming by +4°C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.

Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (artificial neural network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2 = 0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2 = 0.563) and DoY (r2 = 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modeling.

International audience; Antarctic krill Euphausia superba (hereafter `krill') occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has in creased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of climate change on krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of krill. Although some of these changes can have positive effects on krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval krill, is probably the population parameter most susceptible to climate change. Predicting changes to krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved. [GRAPHICS] .

Vertical and horizontal distributions of the subtropical euphausiid juvenile and adult Nyctiphanes simplex were mapped from samples collected during winter and summer 2007 in the Gulf of California, Mexico. During winter, wide-ranging high densities occurred in most of the Gulf of California. Densities decreased considerably during summer, with only at few locations having high densities. N. simplex made short daily vertical migrations of 50 m, clearly avoiding layers with temperatures >20 °C. In both seasons, N. simplex occurred above the low-oxygen layer (23 °C. Seasonal brood size and reproductive effort were estimated for both sides of the Baja California Peninsula under ship board experiments as a proxy of the relative effect of seasonal environmental conditions for euphausiid reproduction. Experiments were done during March, July, and December 2004 at the entrance to Bahía Magdalena and its westward continental shelf and in November 2005 and January and July 2007 in the Gulf of California. Contrary to broadcast-spawning euphausiids, N. simplex, a sac-spawning euphausiid, has a significant association of the brood size as a function of the total length of females. N. simplex produces an average brood of 52 eggs female-1 (range 5-116 eggs female-1) with a estimated total fecundity of 936 eggs female-1 in a life span (360-1337 eggs female-1), of which about 8% of its carbon weight is released per spawn, significantly higher than estimates of previous studies. In Bahía Magdalena, broods contained more embryos in March and July 2004 than in December 2004 when temperatures increased to >23 °C. In the Gulf of California, broods had higher numbers of embryos in November and July than in January 2007, suggesting that N. simplex has an out-of-phase reproductive season on both coasts of the peninsula. Reproductive investment effort was larger in the Gulf of California than in Bahía Magdalena, where females generated up to 18.3% of their weight in their broods, primarily by brood sizes produced from females between 10-12 mm total length that were particularly fecund during November and July.