Northern cod species risk loss of spawning habitat if global warming exceeds 1.5 ° C

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Abstract

Rapid climate change in the northeastern Atlantic and the Arctic is threatening some of the world's largest fish populations. The impacts of warming and acidification could become accessible through mechanism-based risk badessments and future quality projections of habitat. We show that ocean acidification results in shrinking of embryonic thermal ranges, thereby determining whether spawning habitats are appropriate as a vital life-cycle bottleneck for two abundant cod species. The embryonic tolerance ranges badociated with climate simulations reveal that CO2 shows [Representative Concentration Pathway (RCP) 8.5] deteriorate the suitability of the current spawning habitat for Atlantic cod (Gadus morhua) and polar cod (Boreogadus saida) by 2100. Moderate warming (RCP4.5) can avoid dangerous climate impacts on Atlantic cod, but leaves few spawning areas for more vulnerable Atlantic cod, which also loses benefits an ocean covered with ice. Emissions following RCP2.6, however, confirm that habitat suitability for both species is virtually unchanged, suggesting that risks are minimized if warming is maintained "below 2 ° C". C, or 1.5 ° C, as promised by the Paris Agreement.

INTRODUCTION

Ocean Warming and Acidification (OWA), driven by undiluted CO2 emissions, should limit the survival and reproduction of many marine organisms (1). Existing knowledge implies that the physiological limits of the early stages of life history define the species' vulnerability to OWA (2). Studies on the most adverse impact scenarios are important to raise public awareness of risks and to gain acceptance by society of the risk reduction policy (3). However, it is even more important to identify the emission pathways required to minimize the risk of impact and to locate potential refuge habitats for endangered species that should be given priority for conservation (1–3). However, risk badessments based on mechanisms that integrate vulnerable life stages and their specific habitat needs into a scenario scenario are barely available, especially for marine species living in arctic regions (4, 5).

The subarctic and arctic seas surrounding northern Europe (Iceland Sea, Norwegian Sea, East Greenland Sea and Barents Sea) are expected to experience higher rates of global warming, acidification and sea ice loss. than most other marine areas of the Earth (6). These oceanic regions, previously known as the Norden Seas (7) – are populated by highly productive fish populations, most of which undertake annual migrations to specific spawning grounds (4). The biophysical characteristics of suitable spawning habitat favor early life survival and dispersal to appropriate growth areas (p.24).8). Since fish embryos are often more sensitive to environmental changes than later stages of life (2), embryo tolerance may be a fundamental constraint to the quality of spawning habitat. For example, thermal tolerance ranges that are narrower in fish embryos than in other stages of development may be a biogeographic constraint (8) and is probably explained by the incomplete development of cardiovascular systems and other homeostatic systems (9). Ocean acidification caused by high concentration of CO in the aquatic environment2 levels can exacerbate the disturbance of homeostasis (ten), thus reducing the thermal range (2, 11) and possibly reduce the ability of the spawning habitat by harming the survival of the eggs.

Atlantic cod and Arctic cod are key members of the high northern latitudes fish fauna, but their thermal affinity and spawning preferences differ (4, 5). Atlantic cod is a "thermal generalist" that occupies temperate to arctic waters between -1.5 and 20 ° C (12). Polar cod, on the other hand, is a "heat specialist" endemic to the High Arctic and is rarely found at temperatures above 3 ° C (13). Due to overlapping temperature ranges between the juvenile and adult life stages, both species coexist during their summer migrations of food (14). In winter and spring, however, spawning occurs in separate locations with different water temperatures and sea ice conditions (Fig. 1). Since Atlantic cod prefer warmer waters (3 to 7 ° C) than polar cod (-1 to 2 ° C), the latter species is considered particularly vulnerable to climate change (5, 14). In addition, another indirect threat to polar cod breeding is the predicted loss of sea ice, which serves as a nursery habitat for larvae and juveniles in spring and summer (5).

Fig. 1 Distribution patterns of Atlantic cod and Arctic cod in the Norden seas.

(A) Atlantic cod; (B) Polar cod. Populations of both species breed in winter and spring (Atlantic cod: March to May, polar cod: December to March) in specific areas (species, spawning habitats, shaded areas in blue) with temperature conditions and characteristic sea ice (Atlantic cod: 3 ° to 7 ° C, open water, polar cod: -1 ° to 2 ° C, closed sea ice cover). Green arrows indicate the dispersion of eggs and larvae caused by dominant surface currents. In summer, the feeding areas (shaded areas in green) of both species overlap partially, for example around Svalbard, which marks the northernmost distribution limit of Atlantic cod. The red symbols indicate the origin of the animals (breeding adults) used in this study. The distribution maps were redrawn after (4, 13, 33). NEW, northeastern waters polynya; FJL, Franz-Joseph-Land; New Zealand, Novaya Zemlya.

Concentrations of Atlantic and polar cod spawners – often including several million individuals – are important resources for humans and other marine predators. For example, the Norwegian Atlantic cod fishery alone generates an annual income of 800 million US dollars (15), while polar cod is an essential food for many marine birds and mammals (5). The estimation of the evolution of the quality of the spawning habitat for these focal species is therefore of great socio-ecological importance (4). Functional responses of embryos to OWAs incorporated into habitat models can help identify risks and spatial benefits under different emission scenarios, including the goal of limiting global warming to 1.5 ° C above pre-industrial levels (16).

Here, we evaluate the embryonic heat tolerance ranges under osteoarthritis in Atlantic cod and polar cod. Oxygen consumption rate (MO2) eye stage embryos and larval morphometry at hatch provide a better understanding of the energy constraints imposed by OWA. The suitability of spawning habitat has been mapped in the Norden Seas under various representative pathways of concentration (RCP) by linking egg survival data to climate simulations of Phase 5 of the model intercrop comparison project. coupled (CMIP5). PCRs badume either "no greenhouse gas mitigation" (RCP8.5), "intermediate mitigation" (RCP4.5), or "strong attenuation" (RCP2.6). The latter scenario was developed with the aim of limiting the increase in global mean surface temperature (average soil and sea surface) to less than 2 ° C compared to the 1850 reference period. -1900 and provides a first estimate of the consequences of maintaining global warming at "well below 2 ° C, or even 1.5 ° C", as indicated in the Paris Agreement (16).

RESULTS

Embryo oxygen consumption (MO2) increased with increasing temperature but stabilized or decreased at warmer temperatures (cod ≥ 9 ° C, polar cod ≥ 4.5 ° C, Fig. 2 A and B), which combined with increased mortality under these conditions (Fig. 3), indicating severe heat stress. Embryos acclimated to lower temperatures (<9 ° / 4.5 ° C) and higher Pco2 (partial pressure of CO2) consumed about 10% more oxygen compared to those raised under control Pco2. This trend reversed during warming, indicating that the additional oxygen and energy requirements badociated with osteoarthritis conditions can not be met at extremely high temperatures, resulting in a decrease in the upper thermal limit of maintenance. metabolic. Higher energy requirements under elevation Pco2 may result from the cumulative costs of increased regulation of acid-base, protein turnover and damage repair (9, ten). Energy allocation to life support functions should be prioritized over growth (17), as evidenced by the CO2– and reductions in hatch size at hatching induced by warming (Fig 2, C to F and Fig S2). The relative decrease in body surface area free from larval yellow due to Pco2 average of 10% for Atlantic cod (P < 0.001) and 13% for polar cod (P < 0.001), the smaller larvae hatching at the hottest temperature (Fig 2, C and D, and Table S1). Reductions in larval body size and dry weight (Fig 2, E and F, and Table S1) are in line with CO2induced by the reallocation of energy away from growth, also observed in other species of fish (18).

Fig. 2 Effects of elevation Pco2 rate of oxygen consumption depending on the temperature (MO2) and the growth of Atlantic cod embryos and polar cod embryos (right).

(A and B) MO2 was measured in embryos at the ocular stage (image). Symbols are means (± SEM represented as bars, not = 6 or 4). Performance curves (rows) are based on not = 28 data points. The dark and light shades indicate credible Bayesian confidence intervals of 90 and 95%, respectively. (C and re) Body area without larval eggs at hatch was badessed as an indicator of somatic growth and resource use (yolk). Overlaid boxed charts with individual values ​​indicate the 25th, 50th, and 75th percentiles; whiskers have 95% confidence intervals. (D) The size of the samples was not sufficient at 6 ° C as most individuals died or did not hatch well. (E and F) The offsets between the regression lines (with 95% confidence intervals) indicate a CO value2differences in size-weight relationships of newly hatched larvae (image). The individuals were pooled through temperature treatments (E: 0 ° to 12 ° C, F: 0 ° to 3 ° C). (A to F) Main effects of temperature, Pco2, or their interaction (T * Pco2) are indicated by a black ★, while the orange ★ represents a significant level of CO2 effects in heat treatments (Tukey's post hoc test, not = 6 or 4 per treatment). See Table S1 for more details on statistical tests. N.a., not available.

Fig. 3 Effects of elevation Pco2 on temperature-dependent egg survival in Atlantic cod and polar cod.

(A) Atlantic cod; (B) Polar cod. The symbols represent means (± SEM represented in the form of bars, not = 6). The thermal performance curves (TPC, lines) of each species are based on not = 36 data points. The dark and light shades indicate credible Bayesian confidence intervals of 90 and 95%, respectively. CTPs were extrapolated to temperatures below zero by incorporating the frost tolerance thresholds of the literature (Materials and Methods). Main effects of temperature, Pco2, or their interaction (T * Pco2) are indicated by a black ★, while the orange ★ represents a significant level of CO2 effects in heat treatments (Tukey's post hoc test, not = 6 or 4 per treatment). See Table S1 for more details on statistical tests.

Egg survival decreased outside the preferred spawning temperatures of Atlantic cod (≤ 0 ° C and ≥ 9 ° C) and polar cod (≥ 3 ° C), particularly under the influence of Pco2 (Fig. 3 and Table S1). As a result, our results confirm that embryonic tolerance ranges represent a significant constraint on the thermal spawning niche of Atlantic cod and polar cod. CO2The mortalities induced at their optimal spawning temperature were less pronounced for Atlantic cod (6 ° C, Fig. 3A) than for polar cod (0 ° to 1.5 ° C, Fig. 3B). This observation corresponds to the variation of CO2 sensitivity reported by earlier studies of early life fish and having tested the effects of OWA only under optimal temperature conditions (18). However, both species experienced a level of CO2decline due to egg survival at their respective warming threshold (-48% at 9 ° C for Atlantic cod and -67% at 3 ° C for polar cod). Increased thermal sensitivity of embryos under projected Pco2 levels of thermal tolerance and therefore the breeding niche of the species (2). As a result, the spatial extent of heat-sensitive spawning habitat for Atlantic cod and polar cod may not only move to higher latitudes due to warming, but may also contract in the near future. because of the OWA.

Compared to the (known) contemporary spawning grounds of Atlantic cod and polar cod in the study area (blue areas of Figure 1, yellow dashed areas in Figure 4), our baseline simulations (1985-2004 ) suggest that spawning occurs exclusively in optimal thermal range of development of the embryo [>90% potential egg survival (PES), Fig. 4]. However, the thermally suitable spawning habitat area (SEP> 90%) is larger than the area where spawning actually occurs. For example, despite suitable temperatures, no cod spawning is currently observed in the northeastern Barents Sea (19), indicating that the quality of spawning habitat also depends on factors other than temperature. Mechanisms that prevent areas from breeding may include aberrant egg and larval dispersal, unfavorable feeding conditions, and predation pressure (8, 19).

Fig. 4 Appropriateness (basic) of spawning habitat for Atlantic cod and Arctic cod in the Norden Seas.

(A) Atlantic cod; (B) Polar cod. The suitability of the spawning habitat is expressed in PES (% PES, color code) by combining the experimental survival data (Fig. 3) with the temperature fields of WOA13 (1 ° × 1 °, 50 m continental shelf) for the reference period 1984-2005. Values ​​are averaged over spawning seasons (Atlantic cod: March to May, polar cod: December to March) and are referenced to locations where spawning has been documented.[Zonesenpointillésjaunes([Yellowdashedareas([zonesenpointillésjaunes([yellowdashedareas(13, 33)]. The spatial extent of thermally adapted spawning habitat (PES> 90%) is generally larger than "spawning habitat realized" as other limiting factors are not taken into account. account. The dashed magenta lines indicate the respective seasonal positions of the sea ice edge (defined as areas with ice concentrations> 70%, note that the edge of the sea ice varies slightly between species due to different spawning seasons).

By 2100, relentless animal production areas (RCP8.5) are expected to result in a substantial decline in PES at the main spawning sites of both species (Fig. 5, A to C). For Atlantic cod, SEPs are expected to decline around Iceland (-10 to -40%) and the Faroe Islands (-20 to -60%) and the entire Norwegian coast ( -20 to -60%), including the most important ones. spawning grounds of the Lofoten archipelago (at 68 ° N, Fig. 5A). In turn, large areas of the shelf off Svalbard and the northeastern Barents Sea will become more suitable (PSE, +10 to + 60%) due to warming and decreasing ice cover However, the potential habitat gains in the North are limited by the reduced cold tolerance of Atlantic cod embryos under osteoarthritic conditions and, possibly, by seabirds. unknown limiting factors (see above). Under RCP4.5, the thermal benefits (PSE, +20 to + 60%) of the northeastern Barents Sea largely offset the PSE reductions of Atlantic cod in some southern spawning grounds. (eg Faroe Islands: -10 to -40%) (between Svalbard, Franz Josef Land and Novaya Zemlya, Fig. 5, D and F).

Fig. 5 Spawning habitat change conducive to the heat of Atlantic cod (left) and polar cod (right) in the Norden seas as part of the PRC.

(A at C) RCP8.5: OWA unchanged. (re at F) RCP4.5: Intermediate warming (no acidification envisaged). (g at I) RCP2.6: Global warming below 2 ° C (no acidification envisaged). The maps show the evolution of PES between the reference period (1985-2004, Atlantic cod spawning season: March to May, polar cod spawning season: December to March, see Figure 3). ) and the median of the multi-model CMIP5 projections (seasonal sea surface temperature, 0 to 50 m (see Materials and Methods) for the end of this century (2081-2100). areas (cells, 1 ° × 1 °) with great uncertainty (in other words, the shift of the PES in this cell is smaller than the overall dispersion of the CMIP5, see Materials and Methods) The dashed magenta lines represent sea ice pack positions during the species-specific spawning period (defined as areas with ice concentrations> 70%) (C, F, and I). each card, the values ​​(change of PES) of individual cells are summarized by e kernel density stimulations, the width corresponding to the relative occurrence of values. Boxplots represent the 25th, 50th and 75th percentiles; the ends of the whiskers mark the intervals of 95%.

Polar cod are likely to experience the most dramatic losses of spawning habitat south of Svalbard and Novaya Zemlya (PSE, -40 to -80%, RCP8.5, Figure 5B). In addition, polar cod will lose most of its habitats under ice, with the exception of a small refuge on the eastern Greenland Plateau (Figure 5B). Even non-osteoarthritic warming (RCP4.5, Fig. 5, E and F) will significantly reduce habitat suitability for polar cod spawning off Svalbard (PES, -20 to -60%) and Novaya Zemlya (PES, -10 to -40%). The widespread loss of sea ice in the RCP8.5 and RCP4.5 scenarios could indirectly affect the reproductive success of polar cod, as it protects breeding adults from predation and serves as habitat for fish. feeding in the early stages of life (5). Limiting global warming to about 1.5 ° C above pre-industrial levels (ie, the median temperature of RCP2.6) could not only minimize the reductions in PES in the current spawning two species up to less than 10% (Figure 5, Figure 1). at I) but also maintain some sea ice cover.

DISCUSSION

Our projections suggest that the impacts of egg survival on egg survival and subsequent changes in the quality of spawning habitat may be the main determinants of climate-dependent constraints on Atlantic cod and polar cod. Current results support the hypothesis that thermal tolerance ranges and embryonic habitats of both species are compressed by the progressive OWA method (2). Our results also support the idea that unmitigated climate change poses an existential threat to cold-adapted species such as polar cod (20), although we have identified cold refuges for this species in the High Arctic. Atlantic cod can follow the shift of its thermal optimum towards the poleward pole, eventually leading to the establishment of this commercially important species in areas where polar cod is currently dominant. The parallel decline in habitat quality off Iceland and the Norwegian coast (RCP8.5) implies that by 2100 spawning south of the Arctic Circle (at southern Lofoten, for example) may no longer be possible. The potential movement of commercially important fish stocks across management boundaries and exclusive economic zones poses major challenges not only to national fishermen and environmental advocates.5), but also to international organizations and regulations, which aim to avoid over-exploitation, resource conflicts and degradation of early Arctic ecosystems (4, 21).

However, if global warming is limited to 1.5 ° C above pre-industrial levels, it is unlikely that changes in thermal fitness of current spawning habitats will exceed critical Atlantic cod thresholds. and polar cod. Residual risks can be further reduced as both species can potentially adapt to climate change, either by (i) changes in the timing and / or location of spawning in current areas (22) or ii) through transgenerational processes that improve physiological tolerance (23). The uncertainties in our results are also related to (iii) the reliability and resolution of CMIP5 climate projections (24).

First, the time window for spawning in the North is limited at the end of the winter-spring due to the extreme seasonality of light and the badociated primary production (food for planktonic larvae) at high latitudes ( > 60 ° N) (22). It is therefore unlikely that significant changes in spawning phenology occur in this region. Spawning expansions to the north during historical and ongoing warming periods are well documented, particularly for Atlantic cod, which expanded its spawning activity to West Svalbard in the 1930s (25). However, the main spawning grounds (the Lofoten Archipelago for the Barents Sea population, for example) have always been occupied in past centuries, probably because of the favorable combination of biotic and abiotic maximize recruitment success (8, 22). After spawning, dispersal of eggs and larvae to appropriate growth areas – sometimes hundreds of kilometers – plays an important role in terms of connectivity throughout the life cycle and rebuilding populations (8). Spawning at other locations (as required by RCP8.5 for both species and RCP4.5 for polar cod) could disrupt connectivity and thus increase the risk of advective losses and recruitment failure (8). As a result, success in establishing new spawning habitat will largely depend on a number of factors, in addition to egg survival (prey availability, predation pressure, and connectivity), all of which are difficult to predict. to predict (2, 22).

Second, our results badume that embryonic tolerance ranges are constant across populations and generations (ie, there is no evolutionary change in this century) . These hypotheses are supported by experimental data[Parexempledestempératuresoptimalessimilairespourledéveloppementdesœufschezdifférentespopulationsdemorue([EgsimilartemperatureoptimaforeggdevelopmentamongdifferentAtlanticcodpopulations([parexempledestempératuresoptimalessimilairespourledéveloppementdesœufschezdifférentespopulationsdemorue([egsimilartemperatureoptimaforeggdevelopmentamongdifferentAtlanticcodpopulations(26see also fig. S1]as well as by field observations[Parexempledéplacementcohérentverslenorddelafraiedelamorueenréponseauréchauffementprécédent/outstanding([Egconsistentnorthwardshiftofcodspawningactivityinresponsetoprevious/ongoingwarming([parexempledéplacementcohérentverslenorddelafraiedelamorueenréponseauréchauffementprécédent/encours([egconsistentnorthwardshiftofcodspawningactivityinresponsetoprevious/ongoingwarming(17)]and phylogenetic badyzes of the evolution of thermal tolerance in sea fish[Parexemplevariationdelatolérancethermiquedemoinsde01°Cparmilliond&#39;years([Eg<01°Cchangeinthermaltoleranceper1millionyears([Parexemplevariationdelatolérancethermiquedemoinsde01°Cparmilliond'années([eg<01°Cchangeinthermaltoleranceper1millionyears(27)]. Transgenerational plasticity (TGP) can promote short-term adaptation to environmental change through non-genetic inheritance (eg, maternal transmission) (23). However, contrary to TGP theory, experiments on Atlantic cod suggest that egg viability is altered at similar levels of warming if females are exposed to heat during gonad maturation (28). This example of negative TGP corresponds to the majority (57%) of TGP studies in fish that observed neutral (33%) or negative (24%) responses (29). Given the limited capacity for short-term adaptation, it is very likely that species must abandon their traditional habitats as soon as the physiological limits are exceeded (2). As a result, our results identify not only the high-risk areas, but also the potential refuge habitats that should be prioritized for the implementation of marine reserves.

Third, the CMIP5 climate projections include uncertainties (24). To some extent, these uncertainties can be reduced and evaluated by taking into account the results of several models (see Materials and Methods). Nearshore habitats are poorly represented in current global climate models (24). The reliability of climate impact projections in these areas could be improved in future studies, as elegantly as possible using global multiresolution oceanic models with unstructured meshes (30).

In light of embryonic intolerance to OWA, we show that with unrestricted greenhouse gas emissions, large areas currently used for spawning will be less able to recruit Atlantic cod and cod. potentially cascading effects on Arctic food webs and related ecosystem services (4, 5). However, our results also highlight that mitigation measures, as provided for in the Paris Agreement, can mitigate the effects of climate change on both species. Since the current CO2 emission trajectories give 1% chance to limit global warming to 1.5 ° C above pre-industrial levels (31), our results call for immediate emission reductions under scenarios consistent with 1.5 ° C warming to avoid irreversible damage to ecosystems in the Arctic and elsewhere.

MATERIALS AND METHODS

spawners

Atlantic cod were fished by longline gear in the southern Barents Sea (Tromsøflaket: 70 ° 28'00 "N, 18 ° 00'00" E) in March 2014. Fish roe were transported to the Marine Aquaculture Center (Nofima AS, Tromsø, Norway) and held in a continuous flow tank (25 m3) under ambient light, salinity [34 practical salinity units (PSU)]and temperature conditions (5 ° ± 0.5 ° C). Polar cod were caught at Kongsfjorden (West Svalbard: 78 ° 95'02 "N, 11 ° 99'84" N) by trawling in January 2014. Selected fish were retained in continuous flow ponds (0 , 5 m3) and transferred to the Karvikå Aquaculture Research Station (NOFIMA, Norwegian Arctic University, ITU, Tromsø). At the station, the fish were kept in a continuous flow tank (2 m3) at 3 ° ± 0.3 ° C water temperature (34 PSU) and complete darkness. In both experiments, the gametes used for in vitro fertilization were obtained by band spawning. not = 13 (polar cod: 12) males and not = 6 females (Table S2).

Fertilization protocol

All fertilizations were done within 30 minutes after stripping. Chaque lot d’oeufs a été divisé en deux et fertilisé à l’aide d’eau de mer filtrée et stérilisée aux ultraviolets (UV) (34 UPE) préalablement ajustée à la température de maintien du stock reproducteur (morue atlantique: 5 ° C; morue polaire: 3 ° C) et deux Pco2 terms[contrôle[control[contrôle[controlPco2: 400 μatm, pH(Échelle libre) 8,15; high Pco2: 1100 μatm, pHF 7.77]. Un protocole de fertilisation sèche normalisé avec des aliquotes de laitance de not = 3 hommes ont été utilisés pour maximiser le succès de la fécondation (32).

Succès de la fertilisation

Le succès de la fertilisation a été évalué dans des sous-échantillons (3 × 100 œufs par lot et Pco2 traitement), qui ont été incubés dans des boîtes de Pétri scellées jusqu&#39;au stade 8/16 cellules (morue: 12 heures à 5 ° C; morue polaire: 24 heures à 3 ° C) et photographiés sous stéréomicroscope pour évaluation ultérieure (tableau S3 ). Ces images ont également été utilisées pour déterminer le diamètre moyen des œufs d&#39;un lot d&#39;œufs (30 œufs par lot, tableau S3).

Configuration de l&#39;incubation

Selon les saisons de frai, les deux expériences pourraient être menées de manière consécutive avec le même dispositif expérimental en 2014 (morue polaire: de février à avril; morue de l&#39;Atlantique: d&#39;avril à mai). Œufs fécondés soit au contrôle, soit au maximum Pco2 ont été maintenus à la CO respective2 traitement et incubation jusqu&#39;à éclosion à cinq températures différentes (morue de l&#39;Atlantique: 0 °, 3 °, 6 °, 9 ° et 12 ° C; morue polaire: 0 °, 1,5 °, 3 °, 4,5 ° et 6 ° C) . Les plages de température ont été choisies pour couvrir les préférences de frai de la morue franche (3 ° à 7 ° C) (33) et la morue polaire (≤2 ° C) (13) et les scénarios de réchauffement prévus pour la région concernée. Chaque groupe de traitement d&#39;un lot d&#39;oeufs a été subdivisé en deux incubateurs stagnants (20 incubateurs par femme, 120 dans chaque expérience). Afin de ne pas biaiser les estimations de la survie, un seul des deux incubateurs a été utilisé pour évaluer la survie de l&#39;œuf (et la morphométrie larvaire à l&#39;éclosion), tandis que des sous-échantillons étaient nécessaires pour le traitement embryonnaire. MO2 les mesures ont été prises à partir du deuxième incubateur.

Initialement, tous les incubateurs (volume, 1000 ml) ont été remplis avec de l’eau de mer filtrée (0,2 µm) et stérilisée aux UV (34 UPE) adaptée au traitement de fertilisation respectif et garnie d’œufs à la flottabilité positive. En ce qui concerne l&#39;apport en oxygène dans un incubateur stagnant, il est important de s&#39;badurer que les œufs disposent de suffisamment d&#39;espace pour se disposer en une seule couche sous la surface de l&#39;eau. Nous avons donc ajusté la quantité d’œufs par incubateur (morue atlantique: ~ 300 à 500; morue polaire: ~ 200 à 300) en fonction des différences de taille d’œufs entre la morue atlantique (~ 1,45 mm) et la morue polaire (~ 1,65 mm). Les incubateurs chargés ont ensuite été placés dans des bains d’eau de mer à thermostat différent (volume 400 litres) afin d’badurer un changement de température en douceur à l’intérieur de l’incubateur. Les incubateurs transparents à fond conique ont été scellés avec un couvercle en mousse de polystyrène pour empêcher le CO2 dégazage et fluctuations de température. Selon les régimes de lumière naturelle, les œufs de morue de l’Atlantique recevaient une lumière tamisée au rythme quotidien de 8 heures de lumière / 16 heures d’obscurité, et les œufs de morue polaire étaient maintenus dans l’obscurité, à l’exception d’une exposition à la lumière faible lors de la manipulation. Toutes les 24 heures, 90% du volume d&#39;eau de chaque incubateur étaient remplacés par de l&#39;eau de mer filtrée (0,2 µm) et stérilisée aux UV pour éviter l&#39;appauvrissement en oxygène. Une soupape de sortie a été installée au bas des incubateurs pour drainer l’eau de mer d’œufs morts, qui perdent leur flottabilité et descendent au fond. Chaque bain d’eau de mer contenait deux réservoirs de 60 litres qui ont été utilisés pour régler l’eau de mer à la température et au volume correspondants. Pco2 conditions. Les températures de l&#39;eau à l&#39;intérieur des bains d&#39;eau étaient contrôlées par des thermostats et enregistrées automatiquement toutes les 15 minutes (± 0,1 ° C) via un ordinateur d&#39;aquarium multicanaux (IKS-Aquastar, IKS Systems, Allemagne). Futur Pco2 les conditions ont été établies par injection de CO pur2 gaz dans les réservoirs immergés de 60 litres à chaque température. Un système de retour multicbad (IKS-Aquastar), connecté à des sondes de pH individuelles (IKS-Aquastar) et à des électrovannes, a été utilisé pour contrôler le pH de l&#39;eau et Pco2 valeurs. the Pco2 des réservoirs a été mesurée in situ avant chaque échange d’eau par infrarouge Pco2 sonde (Vaisala GMP 343, compensation manuelle de la température, précision ± 5 μatm; Vaisala, Finlande). La sonde était équipée d’un appareil de lecture MI70 et d’une pompe d’aspiration reliée à une membrane de dégazage (G541, Liqui-Cel, 3M, USA) pour mesurer Pco2 dans l&#39;air équilibré aux gaz de l&#39;eau dissous (34). L’étalonnage en usine a été confirmé par des mesures de l’eau de mer préalablement barbotée avec un mélange de gaz technique (1000 µat2 dans l&#39;air, Air Liquide, Allemagne). Avant l&#39;échange quotidien d&#39;eau, les valeurs de pH des réservoirs étaient mesurées avec une électrode de pH de laboratoire à trois décimales près (Mettler Toledo InLab Routine Pt 1000 avec compensation de température, Mettler Toledo, Suisse), qui était connectée à un WTW 3310 pH mètre. Un étalonnage en deux points avec des tampons NBS (National Bureau of Standards) a été effectué quotidiennement. Convertir le NBS en échelle de concentration de protons libres pour le pH de l’eau de mer (35), l’électrode a été étalonnée avec des tampons d’eau de mer tris-HCl (36), qui ont été acclimatés à la température d’incubation correspondante avant chaque mesure. Les valeurs de pH de l’eau de mer se rapportent à l’échelle de pH libre (pHF) tout au long de ce manuscrit. Les paramètres de l’eau de mer sont résumés à la fig. S3.

Survie des œufs

La mortalité des oeufs a été enregistrée sur une base de 24 heures jusqu&#39;à ce que tous les individus à l&#39;intérieur d&#39;une couveuse soient morts ou éclos (fig. S4). Une fois l&#39;éclosion commencée, les larves nageant librement ont été collectées le matin, euthanasiées avec une surdose de méthanesulfonate de tricaine (MS-222) et comptées après un examen visuel des déformations morphologiques au stéréomicroscope. L&#39;incidence des difformités larvaires a été quantifiée par le pourcentage de nouveau-nés présentant de graves déformations du sac vitellin, du crâne ou de la colonne vertébrale. La survie des œufs a été définie comme le pourcentage de larves viables non formées qui ont éclos depuis le nombre initial d’œufs fécondés (fig. S5). La proportion d&#39;œufs fécondés dans un incubateur a été estimée à partir du succès moyen de fécondation du lot d&#39;œufs respectif (tableau S3).

Respirométrie

Taux de consommation d&#39;oxygène (MO2) des embryons au stade œil (avec une pigmentation oculaire à 50%, fig. S4) ont été mesurés dans des chambres respiratoires fermées à température contrôlée (OXY0 41 A, Collotec Meßtechnik GmbH, Allemagne). Les chambres à double paroi ont été connectées à un thermostat à circulation pour ajuster la température de la chambre de respiration à la température d’incubation correspondante des œufs. Les mesures ont été effectuées en triple avec 10 à 20 œufs de chaque combinaison femelle et traitement. Les œufs ont été placés dans la chambre avec un volume de 1 ml d’eau de mer stérilisée ajustée à la température correspondante. Pco2 traitement. Un microstireur magnétique (3 mm) a été placé sous les œufs en suspension pour éviter la stratification de l&#39;oxygène dans la chambre de respiration. The change in oxygen saturation was detected by micro-optodes (fiber-optic microsensor, flat broken tip, diameter: 140 μm, PreSens GmbH, Germany) connected to a Microx TX3 (PreSens GmbH, Germany). Recordings were stopped as soon as the oxygen saturation declined below 80% air saturation. Subsequently, the water volume of the respiration chamber and wet weight of the measured eggs (gww) were determined by weighing (±1 mg). Oxygen consumption was expressed as[nmolO[nmolO[nmolO[nmolO2 (gww * min)−1]and corrected for bacterial oxygen consumption (<5%) and optode drift, which was determined by blank measurements before and after three successive egg respiration measurements.

Larval morphometrics

Subsamples of 10 to 30 nonmalformed larvae from each female and treatment combination were photographed for subsequent measurements of larval morphometrics (standard length, yolk-free body area, total body area, and yolk sac area) using Olympus image badysis software (Stream Essentials, Olympus, Tokyo, Japan). Only samples obtained from the same daily cohort (during peak hatch at each temperature treatment) were used for statistical comparison. After being photographed, 10 to 20 larvae were freeze dried to determine individual dry weights (±0.1 μg, XP6U Micro Comparator, Mettler Toledo, Columbus, OH, USA). Replicates with less than 10 nonmalformed larvae were precluded from statistical badyses.

Statistical badysis

Statistics were conducted with the open source software R, version 3.3.3 (www.r-project.org). Linear mixed effect models[package“lme4”([package“lme4”([package“lme4”([package“lme4”(37)]were used to badyze data on egg survival and MO2. In each case, we treated different levels of temperature and Pco2 as fixed factors and included “female” (egg batch) as a random effect. Differences in larval morphometrics (yolk-free body area, total body area, dry weight, standard length, and yolk sac area) were determined by multifactorial badysis of covariance. These models were run with temperature and Pco2 as fixed factors and egg diameter as a covariate. Levene’s and Shapiro-Wilk methods confirmed normality and homoscedasticity, respectively. The package “lsmeans” (38) was used for pairwise comparisons (P values were adjusted according to Tukey’s post hoc test method). All data are presented as means (± SEM) and statistical tests with P < 0.05 were considered significant. Results are summarized in table S1.

Curve fitting

Generalized additive models[package“mgcv”([package“mgcv”([package“mgcv”([package“mgcv”(39)]were used to fit temperature-dependent curves of successful development building on egg survival and MO2. This method has the benefit of avoiding a priori badumptions about the shape of the performance curve, which is crucial in badessing the impact of elevated Pco2 on thermal sensitivity. “Betar” and “Gaussian” error distributions were used for egg survival and MO2 data, respectively. To avoid overfitting, the complexity of the curve (i.e., the number of degrees of freedom) was determined by penalized regression splines and generalized cross-validation (39). Models of egg survival were constrained at thermal minima because eggs of cold-water fish can survive subzero temperatures far below any applicable in rearing practice. Following Niehaus et al. (40), we forced each model with artificial zero values (not = 6) based on absolute cold limits from the literature. These limits were set to −4°C for Atlantic cod (41) and −9°C for Polar cod baduming similar freezing resistance, as reported for another ice-badociated fish species from Antarctica (42).

Spawning habitat maps

Fitted treatment effects on normalized egg survival data (fig. S6A; raw data are shown in Fig. 3) were linked to climate projections for the Seas of Norden to infer spatially explicit changes in the maximum PES under different RCPs. That is, the treatment fits were evaluated for gridded upper-ocean water temperatures (monthly averages) bilinearly interpolated to a horizontal resolution of 1° × 1° and a vertical resolution of 10 m. To account for species-specific reproduction behavior, we first constrained each map according to spawning seasonality and depth preferences reported for Atlantic cod[MarchtoMay50to400m([MarchtoMay50to400m([MarchtoMay50to400m([MarchtoMay50to400m(33)]and Polar cod[DecembertoMarch5to400m([DecembertoMarch5to400m([DecembertoMarch5to400m([DecembertoMarch5to400m(13)]. As both species produce pelagic eggs that immediately ascend into the upper mixed layer if spawned at greater depths (13, 33), we further limited the eligible depth range to the upper 50 m. PES at a given latitude and longitude was then estimated from the calculations by selecting the value at the depth of maximum egg survival (at 0 to 50 m depth). Egg dispersal was not considered since the major bulk of temperature- and acidification-related mortality occurs during the first week of development (fig. S4).

Oceanic conditions were expressed as climatological averages of water temperatures, sea-ice concentrations, and the pH of surface water. Our observational baseline is represented by monthly water temperatures[WOA13([WOA13([WOA13([WOA13(43)]and sea-ice concentrations[HadISST([HadISST([HadISST([HadISST(44)], averaged from 1985 to 2004, and by pH values averaged over the period 1972–2013[GLODAPv2([GLODAPv2([GLODAPv2([GLODAPv2(45, 46)]. Simulated ocean climate conditions were expressed as 20-year averages of monthly seawater temperatures and sea-ice concentrations and of 20-year averages of annual pH values of surface water. End-of-century projections were derived from climate simulations for 2081–2100 carried out in CMIP5 (45). We considered only those 10 ensemble members (see table S4) that provide data on each of the relevant parameters (water temperature, sea ice, and pH) under RCP8.5, RCP4.5, and RCP2.6 (47). Projected pH values and temperatures are shown in fig. S6 (E to L). To account for potential model biases, we diagnosed for each of the 10 CMIP5 models the differences between simulations and observations for the baseline period and subtracted these anomalies from the CMIP5-RCP results for 2081–2100. For 2081–2100, we considered the CMIP5-RCPs ensemble median of maximum PES and badessed the uncertainty of PES at a given location by defining a signal-to-noise ratio that relates the temporal change in PES between 2081–2100 and 1985–2004 (ΔPES) to the median absolute deviation (MAD) of results for 2081–2100. Model results are not robust where the temporal change in PES is smaller than the ensemble spread, i.e., ΔPES/MAD < 1. PES calculations for scenarios RCP2.6 and RCP4.5 were carried out for Pco2 = 400 μatm. The effect of elevated Pco2 (1100 μatm) on PES was only considered under scenario RCP8.5.

SUPPLEMENTARY MATERIALS

Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaas8821/DC1

Fig. S1 Thermal niches of adult Atlantic cod and Polar cod.

Fig. S2 Treatment effects on larval morphometrics at hatch.

Fig. S3. Water quality measurements.

Fig. S4. Effects of temperature and Pco2 on daily mortality rates of Atlantic cod and Polar cod.

Fig. S5. Effects of temperature and Pco2 on embryonic development of Atlantic cod and Polar cod.

Fig. S6. Spawning habitat maps for Atlantic cod and Polar cod are based on experimental egg survival data and climate projections under different emission scenarios.

Table S1. Summary table for statistical badyses conducted on data presented in Figs. 2 and 3 of the main text and in figs. S1 and S5.

Table S2. Length and weight of female and male Atlantic cod and Polar cod used for strip spawning and artificial fertilization.

Table S3. Mean egg diameter and fertilization success of egg batches (±SD, not = 3) produced by different females (not = 6).

Table S4. List of CMIP5 models that met the requirements for this study (for details, see the “Spawning habitat maps” section in the main text).

References (48–55)

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is do not for commercial advantage and provided the original work is properly cited.

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Acknowledgments: We acknowledge the support of S. Hardenberg, E. Leo, M. Stiasny, C. Clemmensen, G. Göttler, F. Mark, and C. Bridges. Special thanks are dedicated to the staff of the Tromsø Aquaculture Research Station and the Centre for Marine Aquaculture. Funding: Funding was received from the research program BIOACID [Biological Impacts of Ocean Acidification by the German Federal Ministry of Education and Research (BMBF), FKZ 03F0655B to H.-O.P. and FKZ 03F0728B to D.S.]. Funding was also received from AQUAculture infrastructures for EXCELlence in European fish research (AQUAEXCEL, TNA 0092/06/08/21 to D.S.). F.T.D., M.B., H.-O.P., and D.S. were supported by the PACES (Polar Regions and Coasts in a Changing Earth System) program of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). Previous and additional support from grants POLARIZATION (Norwegian Research Council grant no. 214184 to J.N.) and METAFISCH (BMBF grant no. FZK01LS1604A to H.-O.P. and F.T.D.) are also acknowledged. Author contributions: F.T.D. and D.S. devised the study and designed the experiments. F.T.D. conducted the experiments. J.N., V.P., and A.M. provided equipment and facility infrastructure. F.T.D. badyzed the experimental data. M.B. badyzed climate data and generated habitat maps. F.T.D. drafted the manuscript. F.T.D., D.S., M.B., and H.-O.P. wrote the manuscript. J.N., V.P., and A.M. edited the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors. The experimental data supporting the findings of this study are available from PANGEA (https://doi.org/10.1594/PANGAEA.868126), a member of the ICSU World Data System.

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