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Anthropogenic CO2 is acidifying the ocean, but knowledge of the carbonate properties underlying these dynamics in coastal oceans is lacking. Here, the authors reveal spatial distribution patterns and variability in carbonate chemistry along North America’s coasts.

Body size is hypothesised to be a major determinant of β-diversity in passively-dispersing marine organisms. Here, Villarino et al. show that plankton body size determines rates of dispersal along marine currents, with shorter dispersal and higher species spatial turnover in larger organisms.

Space-based observations offer unique capabilities for studying spatial and temporal dynamics of the upper ocean inorganic carbon cycle and, in turn, supporting research tied to ocean acidification (OA). Satellite sensors measuring sea surface temperature, color, salinity, wind, waves, currents, and sea level enable a fuller understanding of a range of physical, chemical, and biological phenomena that drive regional OA dynamics as well as the potentially varied impacts of carbon cycle change on a broad range of ecosystems. Here, we update and expand on previous work that addresses the benefits of space-based assets for OA and carbonate system studies. Carbonate chemistry and the key processes controlling surface ocean OA variability are reviewed. Synthesis of present satellite data streams and their utility in this arena are discussed, as are opportunities on the horizon for using new satellite sensors with increased spectral, temporal, and/or spatial resolution. We outline applications that include the ability to track the biochemically dynamic nature of water masses, to map coral reefs at higher resolution, to discern functional phytoplankton groups and their relationships to acid perturbations, and to track processes that contribute to acid variation near the land-ocean interface.

By analyzing otolith microchemistry, we examined the use of freshwater and marine environments by brown trout Salmo trutta L. that spawn in the Swedish River Emån and migrate to the Baltic Sea. We estimated the time juveniles spent in freshwater and the number of times the fish returned to freshwater, presumably to spawn. Twenty-six percent of the fish migrated to sea by 1 year of age. However, 13% spent less than one year in the river. Most brown trout (48%) migrated to the sea between 1 and 2 years of age. On average, brown trout, which averaged 4.4 years in age (range 3–6 years), returned to freshwater 2.3 times, and there was an inverse relationship between time spent in freshwater after hatching and the number of visits to freshwater. Our results do not support the classical life history pattern, where brown trout spend one or more years in freshwater before migrating to the sea. Here, we found evidence that part of the population leaves freshwater during their first year. While the cause for precocial migration in the River Emån is not known, our results from this permanently flowing river do not support the idea proposed for other Baltic Sea populations, where the risk of drought has been suggested to be the cause.

Changes in the number, structure, and function of mitochondria during the early life stages of animals can play an important role for an organism’s metabolic rate, growth, and health. Previous studies have shown that juvenile brown trout (Salmo trutta) subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced metabolic rate. The aim of this study was to explore if embryonic temperature affects the mitochondria content of young brown trout and as such explains the previously found differences in metabolic rates. Here, we optimize a quantitative PCR (qPCR) method for the mitochondria cytochrome c oxidase subunit I gene, and then use the method as a proxy for mitochondrial DNA content. We hypothesize that young trout subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduced mitochondrial DNA content. To test this hypothesis, we subjected brown trout to either control ambient (4.4 ± 1.5 °C) or elevated temperatures (7.1 ± 0.6 °C) during embryogenesis. Subsequently, we extracted DNA from liver and white muscle tissue of juvenile brown trout from the two different incubation temperature treatments and successively optimized qPCR for mitochondrial DNA. We found that the amount of mitochondria DNA in liver tissue was 18 times higher than in white muscle tissue, but there was no significant difference in mitochondria content in liver or muscle tissue between brown trout exposed to elevated and ambient control temperatures during embryogenesis. We conclude that reduced metabolic rate is not likely associated with mitochondria DNA content. We also suggest that qPCR is a simple and cost-effective method to quantify mitochondria DNA in frozen and partly degraded tissue from different treatment groups and a useful proxy for identification of differences in mitochondria number.

Climate warming is a serious threat to many organisms, such as cold-adapted ectotherms [...]

Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salmonids, LILT is close to 0 and UILT is between 20 and 30 °C. UILT and LILT are influenced by the acclimation temperature. Thermal tolerance is affected by fish size and ambient oxygen content, which decreases with increasing temperature. Standard metabolic rate (SMR), the energy required to maintain essential functions, increases with temperature, whereas maximum metabolic rate (MMR) increases with temperature until reaching a peak (pejus). Then, it decreases gradually to zero, i.e., the upper critical limit (TCrit). Aerobic scope (AS = MMR-SMR) reaches its maximum at the pejus temperature. Metabolic rates and aerobic scope can be modified by temperatures that the fish experiences during embryogenesis and possibly also as larvae and young fry. At maximum feeding, maximum growth increases to a point at or below the pejus temperature. The optimum temperature for growth decreases with reduced food intake and increased body size. As for metabolic rate, the growth rate is influenced by the temperature during embryonic development. In a warmer climate, adult body size is expected to decrease chiefly because of a younger age at maturity. Parental fish retained at a higher temperature during maturation produce larger eggs, and this change in egg size may also be transferred to next-generation offspring. Furthermore, embryogenesis in warmer water leads to larger gonad and egg sizes at maturity. Water temperature influences locomotion, foraging and migratory activity. In a warmer climate, juveniles migrate to the sea earlier in spring. In addition, higher embryo temperature leads to delayed return of adult salmon from the ocean. Thus, temperature affects life history traits of salmonid fishes, partly as a direct effect on metabolic rates and food consumption and partly induced as a phenotypically plastic effect. The phenotypically plastic response may preadapt offspring to perform better in the expected future thermal environment.

Abstract The projected climate change and increase in thermal conditions in northern latitudes over the next 60 yr has the potential to alter the metabolic scope and potential fitness of aquatic ectotherms. Here, we experimentally tested if elevated egg incubation temperature affected metabolic scope in juvenile brown trout (Salmo trutta) as a phenotypically plastic response. Cohorts of brown trout from anadromous and resident crosses were raised through embryogenesis in either natural river temperatures (cold) or elevated (+3°C, warm) temperatures until they could feed exogenously. The standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope (AS = MMR − SMR) of juveniles from four anadromous‐resident crosses and from both incubation temperatures were tested at 13°C. We found that metabolic measures (SMR, MMR, AS) were lower in warm than cold‐incubated fish. There was no difference in the metabolic rates of fish from different anadromous‐resident crosses. The results of this experiment are consistent with the countergradient variation hypothesis (CGV) in which phenotypic variation, in this case variation in metabolic rates, is inversely related to thermal conditions, originally proposed in relation to altitudinal or latitudinal gradients. While previous studies have related CGV to genetic differences between populations, our study shows that thermal differences encountered at the embryonic stage can produce a phenotypic pattern consistent with CGV. It is difficult to predict the consequences of these metabolic changes in a future warmer climate, as lower metabolic rates indicate that brown trout will probably expend less energy, but a reduced aerobic scope may counteract this affect, limiting their ability as a top predator and in escaping predators. Our results suggest that there are mechanisms used to adjust to elevated water temperature that can be initiated during embryogenesis. Given that there were no differences among crosses, it is likely that temperature‐induced differences are the result of plastic responses.

Abstract Wild Atlantic salmon (Salmo salar) are in decline over the entire distribution area, and populations are enhanced by supportive breeding. Parental fish are sampled in rivers, crossed and the offspring reared in hatcheries until smolting when released, ready for ocean migration. Naturally reproducing salmon entering the River Imsa from the ocean were monitored from 1976 through 2013, and since 1982, supportive breeders spawning in the river were also monitored. The supportive breeders were first‐generation salmon, reared for 1—2 years in a hatchery before being released at the mouth of the river so they could migrate to sea (i.e., sea‐ranching). Wild and sea‐ranched salmon live in the ocean for 1—2 years before they return to the river for spawning. In years when only wild adults were present, mean number of smolts produced per 100 m2 river area and female breeder was 0.47. When there were 5% wild females, the mean production was only 0.088 (19%). The gradual decrease in offspring production with decreasing proportion of wild females (r2 = .41) indicates that the reduced offspring production was caused by inferior spawning behavior of hatchery females or reduced survival of their offspring in nature. Previous experimental evidence suggests that wild males fertilize the eggs of wild but also hatchery females. It is discussed how epigenetic effects caused by hatchery environments influence the developing juveniles, lead to phenotypic changes that may reduce their fitness in nature even after free ranging for a year or more in the ocean before they return and spawn.

The precision of growth estimates based on fish scales often remains uncertain because of withinindividual variation in scale size and scale patterns, and also due to measurement errors. Based on scale readings of Atlantic salmon, we show that errors decreased with number of times and number of scales read per fish. The annual number of scale circuli was not constant, but positively correlated with annual specific growth rates. Number of circuli deposited after the last winter correlated positively with sampling date. There was no significant relationship between mean inter-circuli distance and the total circuli number during the first and second year at sea. For growth estimation in scientific studies, we recommend the use of 4-5 scales per fish. Consideration should be given to both circuli number and inter-circuli distances when estimating growth rate instead of relying on inter-circuli distances only.

Two individuals of thinlip grey mullet Liza ramada were collected in a southern Norwegian brook (58° 22’ N, 8° 37’ E) on 12th September 2007. The fish were 8.7 and 9.0 cm in total length, 6 and 7 g in total mass, and most probably in their first year of life. The nearest known spawning area of the species is south of the English Channel, meaning that they had probably moved at least 900 km across the North Sea during their first growth season. To our knowledge, this is the first published observation of the catadromous thinlip grey mullet from a Scandinavian freshwater course.

Sea ranched hatchery-reared smolts of Atlantic salmon originating from the Rivers Imsa and Lone in Norway and Neva in USSR were released in the River Akerselv, in 1985 and 1987. Both 1+ and 2+ smolts were released into the river which had been empty of fish due to heavy pollution from the middle of the 19th century to the beginning of the l980ies. The Norwegian salmon migrated to sea and left the Oslofjord shortly after release. The Neva salmon, on the other hand, stayed in the Oslofjord during the summer after release, and many turned up as maturing adults the first autumn after release. Few recaptures were made the following summer as grilse. The reported recapture-rate varied between 7.1 and 19.1% of the number of smolts released. Few fish strayed to other rivers; those that did entered nearby rivers. Mean weight of grilse produced from 2+ smolts, reflecting differences in size at release. Reported yields per 1000 smolts released varied between 77.5 and 138.4 kg, it was lowest for 2+ Lone smolts and highest for 2+ Neva smolts. These figures are gross underestimates when taking tagging and handling mortality and non-reported tags into consideration.