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Remote sensing observations from satellites and global biogeochemical models have combined to revolutionize the study of ocean biogeochemical cycling, but comparing the two data streams to each other and across time remains challenging due to the strong spatial-temporal structuring of the ocean. Here, we show that the Wasserstein distance provides a powerful metric for harnessing these structured datasets for better marine ecosystem and climate predictions. The Wasserstein distance complements commonly used point-wise difference methods such as the root-mean-squared error, by quantifying differences in terms of spatial displacement in addition to magnitude. As a test case, we consider chlorophyll (a key indicator of phytoplankton biomass) in the northeast Pacific Ocean, obtained from model simulations, in situ measurements, and satellite observations. We focus on two main applications: (i) comparing model predictions with satellite observations, and (ii) temporal evolution of chlorophyll both seasonally and over longer time frames. The Wasserstein distance successfully isolates temporal and depth variability and quantifies shifts in biogeochemical province boundaries. It also exposes relevant temporal trends in satellite chlorophyll consistent with climate change predictions. Our study shows that optimal transport vectors underlying the Wasserstein distance provide a novel visualization tool for testing models and better understanding temporal dynamics in the ocean.

Simple Summary: Otoliths, which are calcium carbonate structures found in the inner ears of fish, can be used to describe the use of freshwater and saltwater habitats during the lifespan of fish. This is performed by looking at the ratio of strontium to calcium along the radius of an otolith, where a high ratio indicates the use of saltwater and a low ratio indicates the use of freshwater. We studied brown trout (Salmo trutta L.) from the Swedish River Emån. We found that most brown trout, as expected, spent the first 1–2 years of their lives in freshwater before migrating to the Baltic Sea. We also found that 13% spent considerably less than one year in the river, which was not expected based on classical life history patterns for brown trout. In addition, we found that brown trout, which ranged from 3 to 6 years of age, returned to freshwater 2.3 times, and the amount of time spent in freshwater after hatching was negatively related to the number of visits to freshwater. Previous studies have explained that precocial migration occurs when there is a risk of drought. This explanation cannot apply to the permanently flowing River Emån. 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. [ABSTRACT FROM AUTHOR]

Temperature during egg incubation and early development influences later life stages of fishes, potentially influencing survival. Throughout its distribution, Atlantic salmon (Salmo salar Linnaeus, 1758) have experienced population declines, and in view of ongoing global warming, we tested if temperature during the earliest developmental stages modified body shape and fin size when temperatures averaged 2.6 vs. 5.6 [degrees]C. This temperature difference simulates increases predicted in climate change scenarios. Based on previous studies, we hypothesized that salmon originating from eggs subjected to cold incubation temperatures would have slimmer bodies and larger pectoral and dorsal fins than salmon from eggs that experienced warmer temperatures. After hatching, the juveniles were raised for 1 year under identical temperatures, after which we measured their body shape and fin areas. We found no support for our hypothesis regarding body shape. Indeed, we found the opposite, with cold-incubated salmon having deeper bodies than warm-incubated salmon. For fin size, the pectoral fins of cold-incubated salmon were larger than for warm-incubated salmon as predicted, but there was no difference in dorsal fin size. These results suggest that global warming may lead to altered body shape and fin size, possibly affecting swimming performance, and thus raise questions about the ecological consequences of the changes. Key words: ectotherm, phenotypic plasticity, morphology, global warming, incubation temperature, Salmo salar, Atlantic salmon. La temperature durant l'incubation des oeufs et le developpement precoce influence les etapes subsequentes du cycle biologique des poissons et pourrait influencer leur survie. A la grandeur de son aire de repartition, le saumon atlantique (Salmo salar Linnaeus, 1758) a connu des baisses demographiques et, etant donne le rechauffement planetaire en cours, nous avons verifie si la temperature durant les toutes premieres etapes du developpement modifie la forme du corps et la taille des nageoires quand les temperatures moyennes sont de 2,6 et 5,6 [degrees]C. Cette difference de temperatures simule des augmentations predites par differents scenarios de changements climatiques. A la lumiere d'etudes anterieures, nous avons postule que les saumons issus d'oeufs assujettis a de basses temperatures d'incubation auraient des corps plus elances et de plus grandes nageoires pectorales et dorsales que les saumons issus d'oeufs incubes a des temperatures plus elevees. Apres leur eclosion, des poissons juveniles ont ete eleves pendant une annee a des temperatures identiques, apres quoi nous avons mesure la forme de leur corps et l'aire de leurs nageoires. Nous n'avons trouve aucun appui pour notre hypothese concernant la forme du corps. C'est en fait le contraire que nous avons constate, les saumons incubes a basse temperature presentant des corps plus hauts que les saumons incubes a temperature plus elevee. En ce qui concerne la taille des nageoires, les nageoires pectorales des saumons incubes a basse temperature etaient plus grandes que celles des saumons incubes a temperature elevee, conformement aux predictions, mais les nageoires dorsales ne presentaient aucune difference. Ces resultats indiqueraient que le rechauffement planetaire pourrait mener a la modification de la forme du corps et de la taille des nageoires, ce qui pourrait avoir une incidence sur la performance de nage, et ils soulevent des questions concernant les consequences ecologiques de ces changements. [Traduit par la Redaction] Mots-cles : ectotherme, plasticite phenotypique, morphologie, rechauffement planetaire, temperature d'incubation, Salmo salar, saumon atlantique., Introduction Increased temperature mediated by global warming represents a type of environmental stress with potentially large impacts on the earth's biota (Milligan et al. 2009; Bellard et al. 2012; Paaijmans [...]

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. [ABSTRACT FROM AUTHOR]

The consistency of the global declining trend of Atlantic salmon (Salmo salar) populations suggests that climate-driven reduced survival and growth at sea are the main driving factors. The southernmost populations have experienced the greatest declines, consistent with harsher conditions in natal fresh waters. We analyzed temporal trends in Spanish Atlantic salmon, important food organisms at sea, and climatic variables in the breeding (fresh water) and feeding (marine) salmon areas from 1950 onwards to elucidate drivers of declining patterns. Salmon abundance dropped abruptly in 1970-1971, plausibly linked to widespread overfishing coincident with incipient changes in the marine food webs and freshwater hydrology. A major regime shift in biophysical conditions throughout the North Atlantic salmon feeding grounds occurred in 1986-1987, driven by the concurrence of an abrupt acceleration in the anthropogenic warming trend and the warm phase of the Atlantic Multidecadal Oscillation. This regime shift may be the proximate cause of the collapse of Spanish salmon observed in 1988-1989, which kept declining in parallel to trends of ever-increasing ocean and freshwater temperatures, decreasing river flows, and poorer marine trophic conditions. La coherence de la tendance planetaire a la baisse des populations de saumon atlantique (Salmo salar) porte a croire que les reductions de la survie et de la croissance en mer causees par le climat en sont les principaux facteurs. Les populations les plus meridionales ont subi les plus grandes baisses, ce qui concorde avec des conditions plus difficiles dans les eaux douces natales. Nous avons analyse les tendances dans le temps du saumon atlantique espagnol, d'importants organismes lui servant de nourriture en mer et de variables climatiques dans ses aires de reproduction (en eau douce) et d'alimentation (en mer) a partir de 1950, afin de cerner les causes de ces declins. L'abondance du saumon a chute abruptement en 1970-1971, cette baisse etant plausiblement liee a la coincidence d'une surpeche repandue et de modifications emergentes aux reseaux trophiques marins et a l'hydrologie des cours d'eau douce. Un important changement du regime de conditions biophysiques dans toutes les aires d'alimentation du saumon dans l'ocean Atlantique Nord s'est produit en 1986-1987, cause par la cooccurrence d'une acceleration soudaine du rechauffement d'origine anthropique et de la phase chaude de l'oscillation atlantique multidecennale. Ce changement de regime pourrait etre la cause proximale de l'effondrement du saumon espagnol observe en 1988-1989, qui s'est poursuivi parallelement a des tendances d'augmentation continue des temperatures de l'eau de mer et de l'eau douce, de diminution des debits des rivieres et de deterioration des conditions trophiques marines. [Traduit par la Redaction], Introduction Current climate change is a main driver of the biodiversity loss that will not only increase but also accelerate global and local extinctions (Urban 2015). Specifically, both marine and [...]