Cantabrian Sea Research Articles

Changes in the Climate Comfort of the Coast of Spain (1940-2022)

The Spanish coastal regions register specific climatic conditions due to the combination of mild temperatures with little variation throughout the year, high relative humidity and the influence of maritime storms. In summer, the climatic comfort conditions are excessively hot, especially on the Mediterranean coast of Spain. Understanding these conditions and analysing the temporal evolution of recent decades, as well as regional differences, is fundamental for future summer tourism planning in the coming decades. This study analyses the principal 37 coastal tourist hubs of Spain grouped into 10 large regions (the Atlantic, Cantabrian, Mediterranean coasts, and the two archipelagos of the Balearic and Canary Islands). Daily data drawn from the ERA-5 (Copernicus) atmospheric reanalysis from 1940 to 2022 have been used (mean air temperature, mean relative humidity, and mean wind speed), with which the Climate Comfort Index has been calculated (CCI) by González (1998). The results show a significant reduction of the CCI in all the coastal areas analyzed, being more relevant in winter (-0.10 decade). The decrease in the index implies a decrease in cold thresholds and an expansion of comfort throughout the study area, especially in the central Mediterranean and Cantabrian Sea. For its part, in summer, the most important decreases (-0.07 and -0.08 / decade) show an increase in the most important climatic discomfort on the Cantabrian Coast – Euskal Kostaldea and on the Costa Brava-El Garraf, with a significant intensification and expansion temporary thermal sensation of heat. In other coastal sectors, in recent years, the climatic thresholds of heat and extreme heat have been reached for the first time.

Late Triassic to present-day tectono-thermal history of the coastal part of the Asturian basin: Implications for hydrocarbon exploration and for the North-Iberian margin evolution

The Asturian Basin, situated on the North Iberian margin, is a Permian-Mesozoic extensional basin developed over a Variscan Palaeozoic basement, subsequently inverted during the Cenozoic Alpine orogeny. The compilation of cartographic, structural, biostratigraphic and vitrinite reflectance data collected in a Late Triassic-Jurassic succession, excellently exposed along the Cantabrian Sea coast, has allowed us to gain insight into the Mesozoic and Cenozoic tectono-thermal history of this basin. The oldest recorded event occurred in Middle-Late Jurassic times and consisted of uplift, development of a large syncline, and normal faulting accompanied by circulation of hydrothermal fluids along the faults. The basin emersion caused an angular unconformity, together with a change in the sedimentary environment that passed from marine to continental. A second event, whose age was probably Late Jurassic-Early Cretaceous, was responsible for extensional reactivation of previous normal faults accompanied by a weaker fault-related hydrothermal episode. In Cenozoic (Eocene-Miocene) times, as a consequence of the Alpine orogeny some of the previous faults were reactivated as reverse and/or strike-slip faults, and folds developed. Here we analyse which structures were active during each event, their relationship with the hydrothermal fluids, the control they exerted on the hydrocarbon generation, and how the large-scale models proposed for this portion of the North Iberian margin fit the onshore field observations, in particular regarding the structural position of the Asturian Basin within the Iberian Plate Mesozoic rifts and the role of the Ventaniella Fault.

Habitat preferences of Phycis blennoides (Pisces: Gadiformes): environmental factors and fishing-related ontogenic deepening

Phycis blennoides is a component of the ecosystem of the Atlantic waters of northern Spain and a species of commercial interest for fisheries in this region. However, little is known about the distribution of this species. The present study analyses the relationships between different environmental and spatial variables and distribution of P. blennoides. Biological (presence-absence, abundance, biomass and total length) and environmental data were collected from a bottom trawl survey carried out off the northern coast of Spain. These data were used in 2-step generalised additive models to examine both the relative significance of physical factors in influencing P. blennoides distribution and to generate density distribution maps. Additionally, the role of fishing effort on P. blennoides body size distribution with depth was analysed. Geospatial analyses showed that changes in annual abundance did not influence physical habitat preference. Most of the variation in spatial distribution was explained by the sampling position and depth. The analyses showed that P. blennoides exhibited habitat preferences in the waters of Galicia and the Cantabrian Sea, with higher values of presence, abundance and biomass on the upper slope and on fine-grained sediment bottoms. P. blennoides biomass increased with depth, probably due to the increased mean size of individuals with depth. Modelling results suggest that the observed ontogenetic deepening appears to be mainly driven by the life history strategy of the species, but is also reinforced by fishing effort.

A new threat to the European marine environment: The exotic polyclad flatworm Postenterogonia orbicularis (Schmarda, 1859)

Harbours and marinas are optimal places for the detection of the arrival of Non-Indigenous Species (NIS) in the early stages of introduction. Marine traffic serves as a route for species movement among different regions, while the species settlement in the ports is facilitated due to habitat degradation. Among NIS, polyclads flatworms are active hunters of bivalves, posing a threat to recipient environments and aquaculture. They can either use their pharynx and mucus to penetrate the mussels and oysters, or enter molluscs while they filter, making the management of the species difficult. In this regard, this work aims to report the first morphological and molecular identification of a new NIS polyclad native to the Pacific Ocean in Europe, specifically in the Ría de Avilés and the Gijón Port (North of Spain, Cantabrian Sea, Bay of Biscay). The occurrence of mature ovigerous specimens and the collection of specimens of various sizes from different times of the year, evidence a reproductively-active population in the area. The external morphological characters, as the ruffled pharynx and the cephalic eyes, and the internal ones, as the male copulatory apparatus, fit with the description of Postenterogonia orbicularis. The phylogenetic analysis based on the mitochondrial COI marker, placed the studied specimens from Avilés and Gijón (Spain) and the recently described species Idiostylochus tortuosus from Arcachon Bay (France) within the P. orbicularis clade (Ilyplanidae family). Therefore, our results suggest that I. tortuosus may be a synonym of the New Zealander P. orbicularis. Finally, we discuss the possible ecological impacts of its introduction and provide some management recommendations for controlling its influx in the recipient environments.

Phenotypic response of a geographically expanding species, Scomber colias: Clues in the fish otolith shape

During the last decades, there has been a growing interest in the Atlantic chub mackerel, Scomber colias, owing to its northward expansion across the East Atlantic Ocean. This trend has been observed from regions of higher abundance off northwest Africa to the waters of the Atlantic Iberian and the Mediterranean Sea. Changes in abundance and spatial distribution of Atlantic chub mackerel have been previously studied and various theoretical models have been proposed to elucidate the changes in its abundance and biomass. However, within this fishing context, only a limited number of studies have attempted to understand how this species has responded at both the individual and population levels to the changing environmental conditions. The phenotypic variability of 1660 individuals of S. colias collected from the Canary Islands, Madeira, the Cantabrian Sea and the Central-Northern Mediterranean Sea was examined, with a specific focus on otolith shape. We identified six morphotypes classified into two groups and associated to the four analyzed regions. Despite of the occurrence of shared phenotypes in varying proportions among the different fishing grounds, this classification might be explained by the adaptation of certain morphotypes to specific environmental conditions and the migratory behavior of this species. The morphotypes M1-M5 were more abundant in the warmer waters of Madeira-Canary Islands region and M6 in the colder waters of Ligurian-Cantabrian. It is plausible that the former set may represent resident contingents, while morphotypes M2-M3 and M4 are likely to exhibit migratory behavior. Therefore, we suggest a complex metapopulation structure, where different contingents coexist.

Deep-Sea Ophiuroids (Echinodermata; Ophiuroidea) from the Avilés Canyon System: Seven New Records for the Spanish North Atlantic Marine Subdivision

The Avilés Canyon System (ACS) is located in the southern Bay of Biscay (northern Spain, Cantabrian Sea). It has been declared a Site of Community Importance (SCI: C ESZZ12003) within the Natura 2000 Network and recognized as a Vulnerable Marine Ecosystem (VME). This area is included in the North Atlantic Marine Subdivision (NAMD). The present study reviews ophiuroid fauna collected during the INDEMARES–ACS project and compares the new findings with previous studies using the Official Spanish Checklist (“Inventario Español de Especies Marinas”) to update our knowledge on the diversity and distribution of these species. During the surveys carried out within the LIFE + INDEMARES–Avilés Canyon System project (2010–2012), a total of 7413 specimens belonging to 45 ophiuroid species were collected from 50 stations in a depth range between 266 and 2291 m. The most frequent species was Ophiactis abyssicola (M. Sars, 1861). Comparing the identified species with public datasets, seven species should be considered as new records for NAMD: Ophiocten centobi Paterson, Tyler & Gage, 1982, Amphiura borealis (G.O. Sars, 1872), Amphiura fragilis Verrill, 1885, Ophiochondrus armatus (Koehler, 1907), Ophiosabine parcita (Koehler, 1906), Ophiophrixus spinosus (Storm, 1881), Ophiotreta valenciennesi (Lyman, 1879). Furthermore, one species has expanded its bathymetric range: Ophiosabine parcita (Koehler, 1906).

Paralytic Shellfish Toxins in Mollusks from Galicia Analyzed by a Fast Refined AOAC 2005.06 Method: Toxicity, Toxin Profile, and Inter-Specific, Spatial, and Seasonal Variations.

Paralytic shellfish poisoning is an important concern for mollusk fisheries, aquaculture, and public health. In Galicia, NW Iberian Peninsula, such toxicity has been monitored for a long time using mouse bioassay. Therefore, little information exists about the precise toxin analogues and their possible transformations in diverse mollusk species and environments. After the change in the European PSP reference method, a refinement of the Lawrence method was developed, achieving a 75% reduction in chromatogram run time. Since the beginning of 2021, when this refinement Lawrence method was accredited under the norm UNE-EN ISO/IEC 17025, it has been used in the area to determine the toxin profiles and to estimate PSP toxicity in more than 4500 samples. In this study, we have summarized three years of monitoring results, including interspecific, seasonal, and geographical variability of PSP toxicity and toxin profile. PSP was detected in more than half of the samples analyzed (55%), but only 4.4% of the determinations were above the EU regulatory limit. GTX1,4 was the pair of STX analogs that produced the highest toxicities, but GTX2,3 was found in most samples, mainly due to the reduction of GTX1,4 but also by the higher sensitivity of the method for this pair of analogs. STX seems to be mainly a product of biotransformation from GTX2,3. The studied species (twelve bivalves and one gastropod) accumulated and transformed PSP toxins to a different extent, with most of them showing similar profiles except for Spisula solida and Haliotis tuberculata. Two seasonal peaks of toxicity were found: one in spring-early summer and another in autumn, with slightly different toxin profiles during outbreaks in relation to the toxicity during valleys. In general, both the total toxicity and toxin profiles of the southernmost locations were different from those in the northern part of the Atlantic coast and the Cantabrian Sea, but this general pattern is modified by the PSP history of some specific locations.

The best defense is a good offense: Anti-predator behavior of the common octopus (Octopus vulgaris) against conger eel attacks.

We present the description of defensive behavior in wild Octopus vulgaris against conger eel (Conger conger) attacks based on three video sequences recorded by recreational SCUBA divers in the eastern Atlantic off the coast of Galicia (NW Spain) and in the Cantabrian Sea (NW Spain). These records document common traits in defensive behavior: (1) the octopuses enveloped the conger eel's head to obscure its view; (2) they covered the eel's gills in an attempt to suffocate it; (3) they released ink; (4) the octopuses lost some appendages because of the fight. In the third video, the octopus did not exhibit the defensive behavior described in the first two videos due to an inability to utilize its arms in defense, and the conger eel's success in capturing octopuses is discussed. Additionally, both the cost that the octopus could face by losing some arms during the fight and whether the experience it acquires can be an advantage for future encounters are analyzed. The defensive behavior exhibited by octopuses in this study highlights their ability to survive in a hostile environment and serves as an example of the extensive repertoire of anti-predator strategies employed by these cephalopods.

Estimating spatial variability of baseline isoscapes from fish isotopic signatures at the community level

One of the main limitations in the application of stable isotopes to marine trophic ecology is obtaining a reliable baseline upon which to calculate isotopic enrichment. Isotopic baselines are variable in space and time, influenced by several environmental factors such as terrestrial runoff, oceanic currents or primary production, and thus, investigating their patterns of variability is essential to gain confidence in the estimates of trophic position based on isotopic signatures. We here propose a multispecies and multitrophic approach to study baseline isoscapes for nitrogen (δ15N) and carbon (δ13C), which we test on the demersal community of the Northwestern Iberian Peninsula. Using a set of 372 isotopic data of 11 demersal fish species sampled during autumn, we modelled the spatial variability of the isotopic baseline (for δ15N and δ13C separately) by removing the biological effect of species identity and individual length. Using the residuals of these models, which represent the isotopic baseline anomalies, we investigated the effect of environmental variables in driving the observed spatial patterns. Our results identify clear and consistent spatial patterns for the δ13C isotopic baseline. This isoscape achieved the lowest values in the westernmost part of the study area (Galician coast) increasing towards the east (Cantabrian Sea). This spatial pattern was mostly driven by primary production and organic matter in the sediment, reflecting the influence of upwelling intensity in the δ13C isotopic baseline over the study area. Baseline isotopic anomalies of δ15N, on the other hand, did not show clear spatial patterns, suggesting that for this isotopic baseline spatial patterns at the regional scale might not be as consistent. Our study brings forward the potential of multispecies isotopic data for approximating the environmental isotopic baselines for the whole ecosystem.

The thermal journey of macroalgae: Four decades of temperature-induced changes in the southeastern Bay of Biscay

Global warming is triggering significant shifts in temperate macroalgal communities worldwide, favoring small, warm-affinity species over large canopy-forming, cold-affinity species. The Cantabrian Sea, a region acutely impacted by climate change, is also witnessing this shift. This study delved into the impacts of increasing sea surface temperature on the subtidal macroalgal communities in the southeastern Bay of Biscay over the last four decades, by using data from the years 1982, 2007, 2014, and 2020. We found that temperature has shaped the community structure, with warm-affinity species steadily displacing their cold-affinity counterparts. Notably, new communities exhibited a profusion of smaller algal species, explaining the observed increased biodiversity within the area. In the last period investigated (2014–2020), we observed a partial recovery of the communities, coinciding with cooler sea surface temperatures. Shallow algal communities were more reactive to temperature variations than deeper communities, possibly associated with higher exposure to increased temperatures. Our study offered insights into the intricate relationship between the changes in ocean temperature and algal species in the southeastern Bay of Biscay, shedding light on the ongoing ecological shifts in this region.

High compositional and functional similarity in the microbiome of deep-sea sponges.

Sponges largely depend on their symbiotic microbes for their nutrition, health, and survival. This is especially true in high microbial abundance (HMA) sponges, where filtration is usually deprecated in favor of a larger association with prokaryotic symbionts. Sponge-microbiome association is substantially less understood for deep-sea sponges than for shallow water species. This is most unfortunate, since HMA sponges can form massive sponge grounds in the deep sea, where they dominate the ecosystems, driving their biogeochemical cycles. Here, we assess the microbial transcriptional profile of three different deep-sea HMA sponges in four locations of the Cantabrian Sea and compared them to shallow water HMA and LMA (low microbial abundance) sponge species. Our results reveal that the sponge microbiome has converged in a fundamental metabolic role for deep-sea sponges, independent of taxonomic relationships or geographic location, which is shared in broad terms with shallow HMA species. We also observed a large number of redundant microbial members performing the same functions, likely providing stability to the sponge inner ecosystem. A comparison between the community composition of our deep-sea sponges and another 39 species of HMA sponges from deep-sea and shallow habitats, belonging to the same taxonomic orders, suggested strong homogeneity in microbial composition (i.e. weak species-specificity) in deep sea species, which contrasts with that observed in shallow water counterparts. This convergence in microbiome composition and functionality underscores the adaptation to an extremely restrictive environment with the aim of exploiting the available resources.

Spatial and seasonal variability of picoplankton abundance and growth rates in the southern Bay of Biscay

Autotrophic and heterotrophic picoplankton play fundamental roles in marine food webs and biogeochemical cycles. However, their growth responses have seldom been jointly assessed, including many temperate regions such as the Bay of Biscay. There, previous studies have shown their relevance in carbon fluxes. We describe here the spatio-temporal variability of the abundances and growth rates of the picoplanktonic groups routinely distinguished by flow cytometry (Synechococcus and Prochlorococcus cyanobacteria, two groups of differently sized picoeukaryotes and two groups of heterotrophic bacteria distinguished by their relative nucleic acid content) in the central Cantabrian Sea (S Bay of Biscay). To that end, from February to December 2021 we collected surface water on 5 occasions from 6 stations distributed along the S Bay of Biscay (6-3°W) and incubated it after removing protistan grazers in order to determine their dynamics along the seasonal cycle as well as the inshore-offshore and the west-east gradients. Seasonal variations in initial and maximum abundances generally matched previous knowledge of the region but growth rates were more variable, with Prochlorococcus and high nucleic acid (HNA) bacteria showing the maximum values (up to 2 d−1) while negative growth was observed in one third of Synechococcus incubations. Temporal differences generally overrode differences along the inshore-offshore gradient in trophic status while in situ and maximum abundances of most of the groups generally decreased towards the east following the increase in stratification and lower nutrient availability. Responses to stratification suggest Prochlorococcus and low nucleic acid (LNA) cells may prevail among autotrophic and heterotrophic bacteria, respectively, in a warmer ocean.

Molecular and biological studies of nonindigenous and extremely rare fish species from the western Baltic reported from the Pomeranian Bay (southwest Baltic Proper)

W ięcaszek B., P anicz R., E ljasik P., Tański A., B ushra A. 2023. Molecular and biological studies of nonindigenous and extremely rare fish species from the western Baltic reported from the Pomeranian Bay (southwest Baltic Proper). Folia Biologica (Kraków) 71: 181-194. Water inflows from the North Sea to the Baltic Sea are recognized as a significant factor influencing the diversity of fish species in the region. In this report, we present findings on three newly discovered fish species (Solea solea, Merluccius merluccius, and Limanda limanda) and the presence of species that were previously seldom observed in the Pomeranian Bay and the associated oligohaline waters of Szczecin Lagoon. These fishes were incidentally captured during monitoring surveys of commercially important fish species. Species identification relied on partial sequences of cytochrome c oxidase subunit I (COI), cytochrome b (cytb), and rhodopsin (rho) genes, as well as morphometric diagnostic characteristics. Upon comparing the obtained sequences with GenBank records, it was revealed that the sequences for Merluccius merluccius (rho, GenBank acc. no. OM737733) and Chelidonichthys lucerna (cytb, GenBank acc. no. OM737734) constitute new DNA barcodes. The majority of sequences obtained in our study matched those available in GenBank for fishes inhabiting the North Sea, suggesting spatial and temporal linkages between the two seas. The remaining sequences exhibited similarity to data from the Cantabrian Sea, the coasts of France, and the Norwegian Sea. The study results, in conjunction with information on the inflows of saline waters and data from previous studies on reported fish occurrences, indicate that the bycatch species could serve as potential bioindicators of environmental changes in the study area.

Techno-economic assessment of potential zones for offshore wind energy: A methodology

This work presents a methodology for the techno-economic assessment and comparison of potential zones for the development of offshore wind energy. The methodology is illustrated through a case study in North Spain, using the high-potential zones designated by the Spanish government. The main elements considered include the bathymetry (water depths), energy production and total working hours based on the wind climate, maintenance windows based on the wave climate, and distance to selected port facilities that can accommodate the installation and operational and maintenance phases of an offshore wind farm. An interesting dichotomy arises moving from west to east along N Spain – energy production and working hours decrease, but maintenance windows increase. Given that both aspects play a role in the costs of an offshore wind project, pondering them adequately is crucial, and the selection of a particular zone for development may depend on project-specific cost models. Water depths may preclude the installation of bottom-fixed structures in certain areas; importantly, they may also represent a constraint for the deployment of certain floating concepts, particularly in the high-potential zones of the Cantabrian Sea. Finally, ports capable of servicing the offshore wind farms are identified and distances to all high-potential zones, calculated. By examining the unique properties of the high-potential zones, this methodology, which can be applied to other regions of interest for offshore wind, provides valuable insights into the advantages and challenges of offshore wind development at each site and thereby contributes to informed decision-making.

Prior stress by marine heatwaves and micro-habitat fragmentation drive the colonisation of epifaunal assemblages in marine forests

Macroalgae species of the genus Cystoseira s.l. (Fucales, Phaeophyceae) and genera Cystoseira, Ericaria, and Gongolaria are habitat-forming species from temperate areas characterised by their high productivity and associated biodiversity. These key species are declining worldwide due to multiple anthropogenic and biotic pressures, such as habitat loss or climate change-related effects. These impacts are leading to local/regional extinctions of marine forests and increasing their fragmentation and isolation. Discrete extreme temperature events in the ocean, known as marine heatwaves (MHWs), are emerging as threats to marine systems in many areas of the planet due to climate change. We analysed 74 yr of daily sea surface temperature data on the occurrence of MHWs in the Cantabrian Sea (northern Iberian Peninsula), finding a clear increase in their frequency, duration and intensity in the last 20 yr. We also performed a 10 d mesocosm experiment to assess how MHWs affect fragmented and non-fragmented patches of Ericaria selaginoides. After this experiment, the experimental patches were deployed in a tidal rock pool for 10 d to detect effects on composition and structure of associated epifaunal assemblages. Mesocosm experiment results showed how the biomass, productivity and oxygen consumption of E. selaginoides significantly decreased as MHW intensity increased. Field deployment revealed that abundance, composition and structure of the epifaunal assemblages were significantly affected by the interaction of prior stress by MHWs and patch fragmentation. Overall, our results showed how a canopy-forming macroalga is affected by extreme temperature events and, consequently, having effects on the colonisation of epifauna according to the level of microhabitat fragmentation with potential implications for the conservation of these endangered systems.

Impact of critical eddy diffusivity on seasonal bloom dynamics of Phytoplankton in a global set of aquatic environments

The intensity of eddy diffusivity and the spatial average of water velocity at the depths of the water column in oceans and lakes play a fundamental role in phytoplankton production and phytoplankton and zooplankton biomass, and community composition. The critical depth and intensity of turbulent mixing within the water column profoundly affect phytoplankton biomass, which depends on the sinking characteristic of planktonic algal species. We propose an Nutrient-Phytoplankton-Zooplankton (NPZ) model in 3D space with light and nutrient-limited growth in a micro-scale ecological study. To incorporate micro-scale observation of phytoplankton intermittency in bloom mechanism in stationary as well as oceanic turbulent flows, a moment closure method has been applied in this study. Experimental observations imply that an increase in turbulence is sometimes ecologically advantageous for non-motile planktonic algae. How do we ensure whether there will be a bloom cycle or whether there can be any bloom at all when the existing phytoplankton group is buoyant, heavier, motile, or non-motile? To address these questions, we have explored the effects of critical depth, the intensity of eddy diffusivity, spatial average of water velocity, on the concentration as well as horizontal and vertical distribution of phytoplankton and zooplankton biomass using a mathematical model and moment closure technique. We quantify a critical threshold value of eddy diffusivity and the spatial average of water velocity and observe the corresponding changes in the phytoplankton bloom dynamics. Our results highlight the importance of eddy diffusivity and the spatial average of water velocity on seasonal bloom dynamics and also mimic different real-life bloom scenarios in Mikawa Bay (Japan), Tokyo Bay (Japan), Arakawa River (Japan), the Baltic Sea, the North Atlantic Ocean, Gulf Alaska, the North Arabian Sea, the Cantabrian Sea, Lake Nieuwe Meer (Netherlands) and several shallower lakes.

Taxonomic status of deep-sea sharks Deania calceus and D. hystricosa (Centrophoridae)

The taxonomic status and identification of the deep-sea sharks of the genus Deania have been controversial mainly due to morphological similarities between some of its species. The aim of this work was to update the taxonomic status of Deania hystricosa (and other putative species, such as D. calceus and D. profundorum) and the validity as a true taxa using specimens from the Atlantic (East-Central and Southeast) and the North Atlantic (Cantabrian Sea) as determined by analysis of sequences of COI and 16 S rRNA genes and comparative analysis of meristics of skin on different body parts. Traditionally, individuals of the genus Deania, including D. hystricosa, D. quadrispinosa, D. calceus and D. profundorum, were classified according to the length of the denticle crown. In our study, this character was found to be significantly dependent on the sexual maturity stage or length of the individual and the area of the body where the denticles were taken. Here, 23 individuals of these species were caught during campaigns carried out in the Atlantic Ocean (East-Central and Southeast) and in the North Atlantic (Cantabrian Sea), in order to be analysed for the mitochondrial genes 16 S ribosomal RNA (16 S rRNA) and cytochrome oxidase subunit I (COI). Phylogenetic analysis of concatenated sequences showed two clearly differentiated groups: one consisting of the species D. profundorum, and the other one consisting of the species belonging to D. calceus and D. hystricosa. The genetic differences measured between D. profundorum group and calceus-hystricosa group (3.9%) were within the range of congeneric species, whereas those differences obtained between D. calceus and D. hystricosa (0.2%) were within the range of intraspecific variation of any of the 3 species analyzed. These results suggest that D. calceus and D. hystricosa are synonyms.

Plicopurpura patula and Monoplex parthenopeus (Gastropoda: Caenogastropoda): New evidence of the tropicalization of the Bay of Biscay (NE Atlantic)

Recent changes in climate and oceanographic conditions have been affecting the dynamics and composition of species communities worldwide, increasing the occurrence of tropical-subtropical species within a specific biogeographic area. This phenomenon defined as tropicalization is occurring in the Cantabrian Sea (Bay of Biscay), a transitional zone between two different regions of the North Atlantic. In this study we present new records of the tropical-subtropical gastropod species Plicopurpura patula and Monoplex parthenopeus in the European Atlantic, which constitute their northernmost distribution in the Atlantic Ocean to date. We provide a detailed characterization of both species, combining morphological and molecular features. Finally, supported by provided evidence and justification, we propose both species as two new potential bioindicators of the tropicalization phenomenon in the North Atlantic waters.

Pleistocene river diversions caused by large landslides in the western Pyrenees (Oria River drainage basin, N Spain)

AbstractRiver‐blocking landslides exert a deep impact on mountain range landscapes and the organization of catchments. A blocked river diverted to another watershed modifies both original and transferred drainage networks both up‐ and downstream. Using western Pyrenees examples, a geological and geomorphic framework with diagnostic criteria to detect river diversion by landslides is presented, including the identification of elbows of diversion, eroded divides, beheaded underfit rivers, diverted overfit rivers, reversed river segments and the landslides at fault. Some landslides caused the formation of lakes that overflowed upstream at catchment divide segments with elevations lower than those of blocking landslide tops. Unravelling the presence of fan deltas at distinct sites/elevations of palaeolake shores contributed as well to identification of river damming and later diversion episodes. Reconstruction of the sedimentary organization of river palaeovalleys and of their associated fluvial terraces and palaeoriver channels (some currently submerged by the Cantabrian Sea), along with the reconstruction of river profiles, analysis of bedrock and morphology of watershed divides, identify seven river diversions caused by landslides and 14 additional slides that variably constrained river basin dynamics in the area studied. The diverting slides have current areas between 0.06 and 12.3 km2 (thus including giant examples), thicknesses up to 300 m and translational–rotational rupture surfaces usually with low dip angles (3.5–12.3°). A combination of relative dating methods and published absolute ages suggests that diversion events occurred during the Quaternary. This study shows that river diversion by landslides can be significant in mountainous areas of moderate relief.

Long distance dispersal and oceanographic fronts shape the connectivity of the keystone sponge Phakellia ventilabrum in the deep northeast Atlantic

Little is known about dispersal in deep-sea ecosystems, especially for sponges, which are abundant ecosystem engineers. Understanding patterns of gene flow in deep-sea sponges is essential, especially in areas where rising pressure from anthropogenic activities makes difficult to combine management and conservation. Here, we combined population genomics and oceanographic modelling to understand how Northeast Atlantic populations (Cantabrian Sea to Norway) of the deep-sea sponge Phakellia ventilabrum are connected. The analysis comprised ddRADseq derived SNP datasets of 166 individuals collected from 57 sampling stations from 17 different areas, including two Marine Protected Areas, one Special Area of Conservation and other areas with different levels of protection. The 4,017 neutral SNPs used indicated high connectivity and panmixis amongst the majority of areas (Ireland to Norway), spanning ca. 2,500-km at depths of 99–900 m. This was likely due to the presence of strong ocean currents allowing long-distance larval transport, as supported by our migration analysis and by 3D particle tracking modelling. On the contrary, the Cantabrian Sea and Roscoff (France) samples, the southernmost areas in our study, appeared disconnected from the remaining areas, probably due to prevailing current circulation patterns and topographic features, which might be acting as barriers for gene flow. Despite this major genetic break, our results suggest that all protected areas studied are well-connected with each other. Interestingly, analysis of SNPs under selection replicated results obtained for neutral SNPs. The relatively low genetic diversity observed along the study area, though, highlights the potential fragility of this species to changing climates, which might compromise resilience to future threats.