Description: Oceans are experiencing increasing acidification in parallel to a distinct warming trend in consequence of ongoing climate change. Rising seawater temperatures are mediating a northward shift in distribution of Atlantic cod (Gadus morhua), into the habitat of polar cod (Boreogadus saida), that is associated with retreating cold water masses. This study investigates the competitive strength of the co-occurring gadoids under ocean acidification and warming (OAW) scenarios. Therefore, we incubated specimens of both species in individual tanks for 4 months, under different control and projected temperatures (polar cod: 0, 3, 6, 8 °C, Atlantic cod: 3, 8, 12, 16 °C) and PCO2 conditions (390 and 1170 µatm) and monitored growth, feed consumption and standard metabolic rate. Our results revealed distinct temperature effects on both species. While hypercapnia by itself had no effect, combined drivers caused nonsignificant trends. The feed conversion efficiency of normocapnic polar cod was highest at 0 °C, while optimum growth performance was attained at 6 °C; the long-term upper thermal tolerance limit was reached at 8 °C. OAW caused only slight impairments in growth performance. Under normocapnic conditions, Atlantic cod consumed progressively increasing amounts of feed than individuals under hypercapnia despite maintaining similar growth rates during warming. The low feed conversion efficiency at 3 °C may relate to the lower thermal limit of Atlantic cod. In conclusion, Atlantic cod displayed increased performance in the warming Arctic such that the competitive strength of polar cod is expected to decrease under future OAW conditions.

Description: Background: Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO2-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO2 under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience. Results: We found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In B. saida, changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO2, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO2 induced behavioural impairments. In contrast to B. saida, such temperature limitation was not detected in G. morhua; however, at 8 °C, CO2 induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in G.morhua. Further, increased availability of energy-rich substrates was detected under these conditions. Conclusions: Our results indicate a change of GABAergic metabolism in the nervous system of Gadus morhua close to the optimum of the temperature range. Since a former study showed that juvenile G. morhua might be slightly more behaviourally resilient to CO2 at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to B. saida in a future warmer, more acidified polar ocean.

Description: In order to access potential impacts of ocean acidification and warming on the whole-animal performance of polar cod (Boreogadus saida) and Atlantic cod (Gadus morhua), individuals of both species were acclimated to different temperature (polar cod: 0, 3, 6, 8°C; Atlantic cod: 3, 8, 12, 16°C) and PCO2 (390 and 1,170 µatm) scenarios for four months. Wet body weight (BW) (g) and total length (TL) (mm) of each individual were measured before and after the incubation period. Subsequently, the specific growth rate (SGR) (%/day) was calculated. The fish were fed every fourth day. Individual feed consumption (FI) (g) was recorded and used for the calculation of daily feed intake (g/(day*BW)). Growth gain (g) and FI throughout the incubation period were translated into feed conversion efficiency (FCE). After the incubation period, starved fish were placed in a respiration chamber to identify the standard metabolic rate (SMR) (µmol/(min*g)) using intermittent-flow respirometry. Subsequently, the fish were sacrificed for the determination of BW, TL, liver weight (WL) (g), gonad weight (WG) (g), stomach including content (g) and stomach content (g) for the calculation of condition factor (CF), hepatosomatic index (HSI) (%), gonadosomatic index (GSI) (%) and stomach filling (%).

Description: Oceans are experiencing increasing acidification in parallel to a distinct warming trend in consequence of ongoing climate change. Rising seawater temperatures are mediating a northward shift in distribution of Atlantic cod (Gadus morhua), into the habitat of polar cod (Boreogadus saida), that is associated with retreating cold water masses. This study investigates the competitive strength of the co-occurring gadoids under ocean acidification and warming (OAW) scenarios. Therefore, we incubated specimens of both species in individual tanks for 4 months, under different control and projected temperatures (polar cod: 0, 3, 6, 8 °C, Atlantic cod: 3, 8, 12, 16 °C) and PCO2 conditions (390 and 1170 µatm) and monitored growth, feed consumption and standard metabolic rate. Our results revealed distinct temperature effects on both species. While hypercapnia by itself had no effect, combined drivers caused nonsignificant trends. The feed conversion efficiency of normocapnic polar cod was highest at 0 °C, while optimum growth performance was attained at 6 °C; the long-term upper thermal tolerance limit was reached at 8 °C. OAW caused only slight impairments in growth performance. Under normocapnic conditions, Atlantic cod consumed progressively increasing amounts of feed than individuals under hypercapnia despite maintaining similar growth rates during warming. The low feed conversion efficiency at 3 °C may relate to the lower thermal limit of Atlantic cod. In conclusion, Atlantic cod displayed increased performance in the warming Arctic such that the competitive strength of polar cod is expected to decrease under future OAW conditions

Description: Within consortium 4 of BIOACID II, we examine effects of ocean warming and acidification (OWA) on different cod species: Polar cod, Boreogadus saida, and Atlantic cod, Gadus morhua. Species distribution as well as population structure of both are reported to be already changing, mainly driven by warming of water masses in their natural habitats. Shifts of G. morhua into higher latitudes will increasingly interact/interfere with populations of B. saida in Arctic waters. However, it is unclear, by which dynamics and how fast the intersecting area of both species will alter during the next decades, which could even lead to extinction of the cold-adapted native species. Within this work package stock distribution patterns are monitored by means of population genetic analyses of hundreds of samples collected from the beginning in the early nineties of the last century until today to assess the current situation and to project future species occurrences. Complementary to these studies is the physiological characterization of each species by means of incubation experiments. These are used to qualify their robustness/vulnerability to future conditions in the northern oceans on multiple levels of organization, i.e. at whole animal down to the molecular level, studying energy budgets and metabolic regulation as well as effects of OWA on different life stages (work packages 4.1 – 4.7). At first, specimens of B. saida have been under study to evaluate critical levels of OWA. Animals caught this January in the Barents Sea north of Norway were brought to Bremerhaven and incubated for 3 months under different CO2 and temperature combinations. During the incubation period, growth data (WP 4.1) and behavioural patterns (WP 4.6) were collected. Furthermore, samples were taken to monitor the total energy budget (EB) (WP 4.1), cellular and mitochondrial energy budget (WP 4.2) as well as for molecular studies of marker metabolites (WP 4.6) and transcriptomic analyses (this work package, 4.3). In parallel, we set up the basis for comparative protein and DNA sequence analyses for both species by constructing normalized cDNA libraries, which were sequenced with Illumina MiSeq (paired end). In total, sequencing output consists of 3.8 and 2.5 Gbp for B. saida and G. morhua, respectively. Transcripts were assembled using Trinity providing approx. 16k protein sequences for each species with an intersecting sequence amount of 14,843 orthologs. The latter will be analyzed for differences in amino acid usage and codon usage by large-scale comparison. Our working hypothesis is that the different habitat conditions have left adaptational signatures in codon and amino acid usage, which reflect different plasticities for acclimation in both species at the molecular level. Moreover, we would expect the regulation of functional genes in the transcriptomes to be differing, due to different critical thresholds of environmental factors and due to the different evolutionary pressures on metabolic genes. Consensus sequences of both library assemblies are used to build a compact Gadus spec. microarray matching sequence identities of both species to equal amounts. This array will be used to monitor long-term effects of different treatments on the transcriptome of B. saida and will provide an application that will also be used for samples of the planned incubation of specimens of G. morhua in 2014. Together with the collected physiological parameters, population genetics and transcriptomic data will provide an integrated picture of species fitness, critical thresholds of environmental conditions as well as consequences of synergistic effects caused by elevated temperature and high CO2 concentrations.

Description: The non-Antarctic Notothenioidei families, Bovichtidae, Pseudaphritidae and Eleginopsidae, diverged early from the main notothenioid lineage. They are important in clarifying the early evolutionary processes that triggered notothenioid evolution in the Antarctic. The early-diverged group represents 8% of all notothenioid species and never established themselves on the Antarctic shelf. Most attention has been paid to the Antarctic notothenioids and their limited physiological tolerance to climate change and increased temperatures. In this review, we discuss key life history traits that are characteristic of the non-Antarctic early-diverged notothenioid taxa as well as the genetic resources and population differentiation information available for this group. We emphasise the population fitness and dynamics of these species and indicate how resource management and conservation of the group can be strengthened through an integrative approach. Both Antarctic waters and the non-Antarctic regions face rapid temperature rises combined with strong anthropogenic exploitation. While it is expected that early-diverged notothenioid species may have physiological advantages over high Antarctic species, it is difficult to predict how climate changes might alter the geographic range, behaviour, phenology and ultimately genetic variability of these species. It is possible, however, that their high degree of endemism and dependence on local environmental specificities to complete their life cycles might enhance their vulnerability.

Description: Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO2-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO2 under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience.

Description: Oceans are experiencing increasing acidification in parallel to a distinct warming trend in consequence of ongoing climate change. Rising seawater temperatures are mediating a northward shift in distribution of Atlantic cod (Gadus morhua), into the habitat of polar cod (Boreogadus saida), that is associated with retreating cold water masses. This study investigates the competitive strength of the co-occurring gadoids under ocean acidification and warming (OAW) scenarios. Therefore, we incubated specimens of both species in individual tanks for 4 months, under different control and projected temperatures (polar cod: 0, 3, 6, 8 °C, Atlantic cod: 3, 8, 12, 16 °C) and PCO2 conditions (390 and 1170 µatm) and monitored growth, feed consumption and standard metabolic rate. Our results revealed distinct temperature effects on both species. While hypercapnia by itself had no effect, combined drivers caused nonsignificant trends. The feed conversion efficiency of normocapnic polar cod was highest at 0 °C, while optimum growth performance was attained at 6 °C; the long-term upper thermal tolerance limit was reached at 8 °C. OAW caused only slight impairments in growth performance. Under normocapnic conditions, Atlantic cod consumed progressively increasing amounts of feed than individuals under hypercapnia despite maintaining similar growth rates during warming. The low feed conversion efficiency at 3 °C may relate to the lower thermal limit of Atlantic cod. In conclusion, Atlantic cod displayed increased performance in the warming Arctic such that the competitive strength of polar cod is expected to decrease under future OAW conditions.