Results of analyses of genetic diversity and phylogeography for polar cod Boreogadus saida in the Pacific Arctic are presented. Analyses leverage polymorphism of Cyt b and COI gene fragments obtained from samples in the Russian Arctic, as well as samples available in open databases. According to these markers, although polar cod demonstrates high haplotype diversity, our results suggest no clear population structure within the Russian Arctic, the Beaufort Sea, and the North Atlantic. This may be explained by the peculiarities of the life cycle of polar cod, particularly oceanographic mechanisms related to the mixing of pelagic eggs and the dispersal of early juveniles by currents and their movement following ice drift within the open waters of the studied area. Results are presented within the context and consideration of existing hypotheses of the origin of the common ancestor of Boreogadus, Arctogadus and Gadus, hypotheses of the divergence of these genera, the formation of the modern range of polar cod and the causes of the genetic diversity of its mitochondrial DNA. We also provide a reconstruction of the evolution of mitochondrial lineages of polar cod, according to one of the possible scenarios of its evolutionary history.
The results of extensive research over four decades (1983-2024) investigating the spatial and depth distributions, catch per unit effort (CPUE) dynamics, and basic biological characteristics of the understudied mud skate Bathyraja taranetzi throughout its range are presented for the first time. Data used in this study were collected from Russian bottom trawl surveys and supplemented by publicly available databases. Regions with the densest aggregations of mud skate were identified in the waters along the eastern slope of the Bering Sea, off the Aleutian Islands, and in Pacific waters off southeastern Kamchatka and the northern Kuril Islands. The species was most abundant in these areas at depths between 201 and 400 m. Individual total length (TL) ranged from 11.3 to 74 cm, with the majority between 46 and 65 cm. The average TL of females was 1.8 cm larger and the average body weight was 0.17 kg greater than that of males. In the timeframe of these data, a considerable increase in the catch rate of mud skates was observed in most parts of their range. In Russian waters, CPUE initially decreased from 1985 until the early 2000s and then began to increase, while in US waters CPUE increased until 2010, after which catches began to decline.
Climate warming has impacted the Chukchi Sea resulting in reduced sea ice extent and increased water transport through the Bering Strait. This study explores the effect of recent warming by using 11 years (2010-2020) of estimated biomass data for two dominant copepods (Calanus glacialis and Pseudocalanus spp.). C. glacialis biomass declined in response to diminishing ice extent and Pseudocalanus spp. biomass increased as transport from the Bering Sea increased. Pseudocalanus spp. estimated biomass (4.61 & times; 108 kg) was four times greater than that of C. glacialis (1.13 & times; 108 kg) during the year with the lowest sea ice extent and highest transport (2019). In contrast, C. glacialis estimated biomass (1.02 & times; 109 kg) was 17 times greater than Pseudocalanus spp. (6.0 & times; 107kg) in the year with the highest sea ice extent and lowest transport (2012). The ratio of C. glacialis biomass to total biomass decreased while the same ratio for Pseudocalanus spp. increased over time. The northern Chukchi Sea had the highest C. glacialis biomass in most years; however, significant C. glacialis biomass was observed in the southern Chukchi Sea in years with greater ice extent. During warm periods, C. glacialis biomass increased in the southern Chukchi, whereas Pseudocalanus spp. were primarily located in the southern Chukchi Sea and had equal or greater biomass than C. glacialis. Shifts in biomass towards smaller, lower lipid copepod species have the potential to impact Arctic ecosystem structure and function, specifically impacting the trophic efficiency of energy transfer in the ecosystem.
The eastern Indian Ocean (IO) is a poorly characterized oligotrophic region influenced by the Indonesian Throughflow (ITF), with limited data on nutrient uptake and microbial community structure. We conducted depth-resolved measurements of nitrate and ammonium uptake, primary production and carbon-based biomasses of pico, nano and microplankton in waters overlying the Argo Abyssal Plain, downstream of the ITF. Our findings revealed picoplankton dominance of biomass, notably by Prochloroccus and heterotrophic bacteria. Primary production and phytoplankton specific growth rates declined with increasing depth (similar to 4-fold) to the deep chlorophyll maximum (DCM), suggesting that light limitation occurred at the DCM. Ammonium uptake exceeded nitrate uptake by similar to 15-fold, peaking in the upper euphotic zone, indicating strong nutrient recycling. Nitrate uptake was highest at the DCM, where phytoplankton and heterotrophic bacteria biomass increased. Nighttime nitrate uptake and a low median f-ratio (similar to 0.05) emphasizes the importance of nutrient recycling in this region. Our study enhances our understanding of nitrogen cycling, microbial community structure, and productivity in the Argo Basin, offering a valuable baseline for assessing future changes in oligotrophic ocean productivity.
In the Humboldt Current System, recurrent episodes of ocean warming drive large shifts in the abundance and accessibility of small pelagic prey, with widespread consequences for seabird populations. For Humboldt penguins (Spheniscus humboldti, HUPE), this threat is magnified given the recent reduction of one of its historically most important colonies, Punta San Juan (PSJ). We evaluated the influence of local warming events on the HUPE adult population at PSJ from 2012 to 2024 at two temporal resolutions, monthly and interannually. We estimated monthly average sea surface temperature (SST) values from 2012 to 2024 within the HUPE foraging range off PSJ as a proxy of local fluctuations in environmental conditions (source: MODIS). We then used GLMs at a monthly resolution to estimate SST association with two HUPE population parameters: adult population and reproductive success (ratio of chicks/adults). Reproductive success declined during the warm period of 2015, increased following the onset of cooler conditions in 2018, peaked in 2021-2022 during a particularly cold phase, and declined again in 2023-2024 as temperatures rose. Therefore, our study shows that the reproductive success of HUPE had an immediate response to SST trends (negative association) explaining the decrease in breeding failure with increased SST. In contrast, the adult population continuously decreased from 2016 until 2024 despite colder conditions between 2018 and 2022. Results highlight the complexity of HUPE response to SST anomalies as well as contrasting results when evaluated at monthly or interannual resolutions. We found differences between short-term reproductive responses (i.e. breeding failure) and long term demographic responses (i.e. adult dispersal or mortality). We recommend future studies to elucidate how rapidly changing climate scenarios can affect trophic food webs and other HUPE demographics, such as survival, in synergy with other potential threats (e.g. fishery pressure) at different temporal and spatial scales.
