Northern Iberian Research Articles

Weight–length relationships, weight conversion factors and somatic indices from two stocks of black anglerfish (Lophius budegassa) and white anglerfish (L. piscatorius) in north-eastern Atlantic waters

Weight–length relationships, weight conversion factors and somatic indices are presented from a decade (2006 to 2015) for two stocks of Lophius budegassa and L.piscatorius in northern Iberian Atlantic waters (ICES Div. VIIIc–IXa2) and in Celtic Sea, south-western Ireland and Porcupine Bank (Div. VIIb,c,h,j,k). A total of 3298 L.budegassa and 7219 L.piscatorius were sampled from commercial landings and research surveys. Total length (Lt), total weight (Wt), “commercial” weight (Wgl) and “scientific” weight (Wg) were obtained. The parameters (a, b) in the power relationships weight–length for combined sexes in L.budegassa were: 0.020, 2.916; 0.017, 2.929; 0.017, 2.922 for Wt, Wgl and Wg respectively in Div. VIIIc–IXa2; 0.025, 2.841; 0.013, 2.984; 0.013, 2.971 in Div. VIIb,c,h,j,k. For L.piscatorius: 0.025, 2.853; 0.020, 2.868; 0.024, 2.861 in Div. VIIIc–IXa2; 0.027, 2.826; 0.023, 2.825; 0.023, 2.816 in Div. VIIb,c,h,j,k. Significant differences between stocks were found in both species. The conversion factors between total and gutted weight in L.budegassa were: 1.186, 1.236 for Wgl and Wg respectively in Div. VIIIc–IXa2; 1.187, 1.233 in Div. VIIb,c,h,j,k. For L.piscatorius: 1.181, 1.241 in Div. VIIIc–IXa2; 1.210, 1.262 in Div. VIIb,c,h,j,k. The parameters can be used in the process of annual assessment of the state of each stock. Gonadosomatic index (GSI), hepatosomatic index (HSI) and Le Cren’s condition factor, indicators of reproductive and nutritional status, were seasonally analyzed and compared between sexes and stocks. Significant better condition and higher GSI and HSI were found in females. In Div. VIIb,c,h,j,k better condition was found for both species and higher GSI for L.piscatorius. The analysis throughout the year of GSI and HSI for L.budegassa showed seasonality in liver growth previous to spawn and corroborated the spawning season from January to June in VIIIc–IXa2. The parameters obtained were compared with previous ones from these and others Lophiiformes, showing common patterns.

Development of a fish-based index to assess the ecological status of oceanic-temperate streams in the Northern Iberian Peninsula

Development of a fish-based index to assess the ecological status of oceanic-temperate streams in the Northern Iberian Peninsula

Contribution of spatially explicit models to climate change adaptation and mitigation plans for a priority forest habitat

Climate change will impact forest ecosystems, their biodiversity and the livelihoods they sustain. Several adaptation and mitigation strategies to counteract climate change impacts have been proposed for these ecosystems. However, effective implementation of such strategies requires a clear understanding of how climate change will influence the future distribution of forest ecosystems. This study uses maximum entropy modelling (MaxEnt) to predict environmentally suitable areas for cork oak (Quercus suber) woodlands, a socio-economically important forest ecosystem protected by the European Union Habitats Directive. Specifically, we use two climate change scenarios to predict changes in environmental suitability across the entire geographical range of the cork oak and in areas where stands were recently established. Up to 40 % of current environmentally suitable areas for cork oak may be lost by 2070, mainly in northern Africa and southern Iberian Peninsula. Almost 90 % of new cork oak stands are predicted to lose suitability by the end of the century, but future plantations can take advantage of increasing suitability in northern Iberian Peninsula and France. The predicted impacts cross-country borders, showing that a multinational strategy, will be required for cork oak woodland adaptation to climate change. Such a strategy must be regionally adjusted, featuring the protection of refugia sites in southern areas and stimulating sustainable forest management in areas that will keep long-term suitability. Afforestation efforts should also be promoted but must consider environmental suitability and land competition issues.

33. Verdeospesoa mire (Basque Country, Northern Iberian Peninsula, Spain)

The Verdeospesoa mire is located in the Basque Mountains (Basque Country, Northern Iberian Peninsula, Spain) on the western slopes of the Gorbeia Mountain (43° 03ʹ 18ʺ N, 2° 51ʹ 41ʺ W, 1015 m above...

Three new species of Spiralix (Burgosia) (Gastropoda, Moitessieriidae) from the northern Iberian Peninsula

Three new species of Spiralix (Burgosia) (Gastropoda, Moitessieriidae) from the northern Iberian Peninsula

The Basque farmhouses of Zelaa and Maiz Goena: New dendrochronology-based findings about the evolution of the built heritage in the northern Iberian Peninsula

The Basque farmhouse, a characteristic building type for north-western Spain, is an architectural solution that allows the combined management of different rural activities. In addition to providing living quarters and a space for a cider press these farmhouses were designed to function as, among others, stable, barn and warehouse. They were often owned and managed by one family, with no links to ecclesiastic organizations. Architectural studies have established that these buildings first were constructed at the end of the 15th century without previous local precedent. This places their initial construction in a calm and relatively secure period, when the wars between the aristocratic lineages which had started in 1418, and which had resulted in assaults, looting and fires, had come to an end. The timing of their first occurrence has led to the interpretation that they represent a building tradition imported from the North. Dendrochronological research initially confirmed their late fifteenth-century origin. However recent restoration work in two previously undocumented farmhouses at Ezkio and Lazkao (Gipuzkoa territory) has enabled a reassessment of this interpretation. The architectural analysis of these buildings shows that their construction plans, which are quite similar, deviates from the general plan according to which the majority of Basque farmhouses were built. The newly identified model, wholly executed in wood with the exception of the roof covering, is based on the repetition of frames and bays. Together these generate the volume of the building, which is larger than the volume of other farmhouses. We collected a total of 81 oak (Quercus sp.) samples from both farmhouses and using Basque chronology ARAB9 as a reference established that these represent trees that were cut down in the spring of 1445 and in 1453 respectively. Since construction most likely took place within a few years after the trees were felled, this indicates that Basque farmhouses began to be constructed decades earlier than expected. At that time wars still raged in the Basque Country. If it is true that the political situation determined the degree of diffusion of non-indigenous architectural concepts in this region, the new findings can be interpreted as supporting the hypothesis that Basque farmhouses reflect a regionally-developed building tradition.

Analysis of geographic and orographic influence in Spanish monthly precipitation

ABSTRACTPrecipitation is a major concern in water resources studies. Being a main variable, the inefficiency of historical ground network, particularly at higher altitudes where precipitation and runoff augmentations are expected, constitutes a major drawback. This work analyses the competence of Spanish historical precipitation network and explores the physiographic influence of elevation and orientation at a national scale. The usefulness of slopes is also explored. Nearly 12 000 monthly precipitation series recorded from the 19th century until the hydrological year 2004/2005 over a high‐resolution topographic map (200 m) of Spanish territory are used. Comparable statistics and precipitation lapse rates are managed once a completion of gaps is accomplished. Then, Spanish yearly rates range from 0.3 to 1.2 mm m−1, reaching 1.5 mm m−1 in Northern Iberian Peninsula, diminishing at highest altitudes.Conclusions address the inefficiency and uncertainties revealed by historical ground networks as well as the variable relationship existing between precipitation and physiographic parameters, such as altitude and orientation.

Lateglacial to Late Holocene palaeoclimatic and palaeoenvironmental reconstruction of El Mirador cave (Sierra de Atapuerca, Burgos, Spain) using the small-mammal assemblages

El Mirador is a cave in the Sierra de Atapuerca (northern Iberian Peninsula) that contains 27 archaeological layers from the Lateglacial to the Late Holocene. A total of 4436 small-mammal remains have been analysed from these layers, and 19 taxa have been identified (three insectivores, seven chiropters and nine rodents). The palaeoenvironmental reconstruction based on a small-mammal analysis suggests that the entire sequence is dominated by a woodland landscape. Our climatic analysis characterises the climate in terms of an evolution from a cool and arid period in the Pleistocene layers (16,000 to 14,000calyr BP), probably related to Heinrich Event 1, to humid conditions and temperatures similar to nowadays in the Holocene layers in general. In MIR23 and MIR22 (7300 to 6800calyr BP) we detect an increase in temperature to levels above current values and an important decrease in rainfall. These climatic characteristics could be related to the end of the African Humid Period. Moreover, a short, slightly cooler event is registered in MIR11 (ca. 6300 to 5900calyr BP), coinciding with a change in the economic pattern in El Mirador. The results obtained on the basis of small-mammal studies are compared with multiproxy terrestrial data (pollen, charcoal, phytoliths, geochemistry, large mammals) and the Greenland ice-core record, as well as various other core records closer to the coasts of the Iberian Peninsula (MD95-2042, MD99-2331, MD95-2043 and SMP02-3). These comparisons show the agreement of the palaeoenvironmental and palaeoclimatic results with all the previous multiproxy and core-record data.

The historical demise of Pinus nigra forests in the Northern Iberian Plateau (south‐western Europe)

Summary Pinus nigra Arn. forests dominated over extensive areas of the Northern Iberian Plateau (Spain) during the Holocene, but a strong decline during the historical period (c. 1300–700 cal. bp) led to the present fragmented populations. This demise has been generally attributed to land‐use changes or climate, but the specific roles of disturbance regimes such as fire variability and grazing on the long‐term are not fully understood yet. We combine multi‐proxy palaeoecological data (fossil pollen, spores, conifer stomata, microscopic and macroscopic charcoal) together with quantitative analyses (ordination and peak detection) from a high‐resolution sedimentary sequence (Tubilla del Lago, 900 m a.s.l.) to assess the causes of pine forests demise. A new microscopic charcoal record from an additional sequence (Espinosa de Cerrato, 885 m a.s.l.) is used to assess burning and pine decline at a more regional (100‐km radius) scale. Pinus nigra forests could cope with drought and fire regime variability (FRI = 110–500 years), with forest recovery taking c. 100–200 years after fires. Only at 1300–1200 cal. bp a long‐lasting irrecoverable demise of P. nigra forests occurred when human‐induced fires together with arable and pastoral farming became widespread in the area. Subsequently, Quercus woodlands expanded in the remnant patchy pinewoods. This vegetation shift was primarily caused by three particularly important fire episodes in less than a century (c. 1300–1200 cal. bp). Synthesis. Pinus nigra forests have shown a millennial resilience to the natural fire regime of the Northern Iberian Plateau that was characterized by relatively frequent small‐moderate fires and rare high‐intensity fires. However, frequent human‐caused crown fires and the onset of intensive farming caused their demise over an extensive area. Ongoing land‐use abandonment in the Iberian mountains could promote the occurrence of high‐intensity, severe fires due to the rapid build‐up of high fuel loads. Forest management could mimic the natural fire regime by periodically reducing fuel loads for a transitional period until natural disturbance variability is fully restored, thus preserving these relict native plant communities.

Distribution of dead wood volume and mass in mediterranean Fagus sylvatica L. forests in Northern Iberian Peninsula. Implications for field sampling inventory

Aim of study: The aim of this study was to 1) estimate the amount of dead wood in managed beech (Fagus sylvatica L.) stands in northern Iberian Peninsula and 2) evaluate the most appropriate volume equation and the optimal transect length for sampling downed wood.Area of study: The study area is the Aralar Forest in Navarra (Northern Iberian Peninsula).Material and methods: The amount of dead wood by component (downed logs, snags, stumps and fine woody debris) was inventoried in 51 plots across a chronosequence of stand ages (0-120 years old).Main results: The average volume and biomass of dead wood was 24.43 m3 ha-1 and 7.65 Mg ha-1, respectively. This amount changed with stand development stage [17.14 m3 ha-1 in seedling stage; 34.09 m3 ha-1 inpole stage; 22.54 m3 ha-1 in mature stage and 24.27 m3 ha-1 in regular stand in regeneration stage], although the differences were not statistically significant for coarse woody debris. However, forest management influenced the amount of dead wood, because the proportion of mass in the different components and the decay stage depended on time since last thinning. The formula based on intersection diameter resulted on the smallest coefficient of variation out of seven log-volume formulae. Thus, the intersection diameter is the preferred method because it gives unbiased estimates, has the greatest precision and is the easiest to implement in the field.Research highlights: The amount of dead wood, and in particular snags, was significantly lower than that in reserved forests. Results of this study showed that sampling effort should be directed towards increasing the number of transects, instead of increasing transect length or collecting additional piece diameters that do not increase the accuracy or precision of DWM volume estimation.Keywords: snags; downed logs; stumps; fine woody debris; beech; line intersect sampling.

Grazing exclusion unleashes competitive plant responses in Iberian Atlantic mountain grasslands

AbstractQuestionsDoes the absence of equalizing mechanisms after cessation of grazing unleash strong above‐ground competitors to create large patches in the community? Do these competitive intraspecific aggregations displace and exclude other species, thereby reducing species diversity?LocationAtlantic grasslands, Aralar Natural Park, Basque Country, Northern Iberian Peninsula.MethodsLarge herbivores were experimentally excluded from three sites (50 m × 50 m exclusion fences) during 9 yr in a productive semi‐natural grassland system with a long history of grazing, using adjacent grazed plots as experimental controls. Sampling was carried out by systematically placing 100 quadrats (0.5 m × 0.5 m) in each of the six plots. Floristic composition and abundance, as well as eight hydrological and chemical soil properties, were measured in each quadrat. The spatial structures created by competitive species were analysed usingRDAin conjunction with Moran's eigenvector maps, and soil variables were simultaneously included in the analyses, thus disentangling the structures likely created by niche effects. Competitive exclusion was further determined using linear regressions between species richness and abundance of competitive species.ResultsGrazing exclusion unleashed competitive species such asFestuca microphyllaandAgrostis capillaris, which became dominant in the exclusion plots and created large spatial patches. Furthermore, a negative linear relationship, consistent across exclusion plots, was observed between species richness and abundance of competitive species, indicating that strong above‐ground competitors outcompeted other species when herbivores were excluded. However, the outcome of grazing exclusion across sites depended to some extent on local environmental conditions (niche effects).ConclusionsThis work confirms that the powerful equalizing mechanism of disturbance by herbivores is crucial for species co‐existence in productive grasslands. However, important differences observed in environmental effects across sites suggest that, even in highly productive grasslands, plant traits and local environmental characteristics (niche effects) do matter for species co‐existence.

Radiometric, isotopic, and petrographic evidence of changing interglacials over the past 550,000 years from six stalagmites from the Serra do Courel in the Cordillera Cantábrica of northwestern Spain

Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation.Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers' results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.

The first herders in the upper Ebro basin at Los Husos II (Álava, Spain): microarchaeology applied to fumier deposits

Fumier deposits are the product of the recurrent use of caves and rock shelters for stabling livestock and the periodic burning of the resulting dung. Their chronologies in the Mediterranean area extend from Neolithic times up to the Bronze Age, but they are scarce in or absent from Iron Age sites. The study of these deposits has provided important information to better understand past livestock and husbandry practices. The archaeological site of Los Husos II, Alava, in the upper Ebro basin, Spain, dating to 6,990–6,770 cal bp, represents one of the earliest pieces of evidence for animal domestication in the Basque Country. The Ebro basin is particularly important, since this was the main route by which the Neolithic economic system spread from the Mediterranean coast to the northern Iberian Peninsula and the western Pyrenees. We present here the results of the study of the fumier deposits from the Neolithic Levels IV to IX of Los Husos II, through analyses of phytoliths, faecal spherulites and ash pseudomorphs. The main goal was to discover the ways in which Neolithic populations in this region adapted these new practices and carried out their activities. The results indicate a constant pattern of keeping animals throughout the study period. The principal component of the livestock diet consisted of wild grasses from the vicinity. The presence of grass inflorescences suggests a diet rich in summer grass. In addition to grasses, dicotyledonous plants were also indicated, both through phytoliths and ash pseudomorphs. Faecal spherulites from herbivores were also noted in the samples and together with phytoliths and ash pseudomorphs they give important information regarding the formation processes of the studied deposits.

A new Late Pleistocene non-anthropogenic vertebrate assemblage from the northern Iberian Peninsula: Artazu VII (Arrasate, Basque Country)

Late Pleistocene palaeontological sites without human intervention are limited in the Cantabrian region, and even more so those with a good state of preservation and rich biodiversity. A new vertebrate fossiliferous locality discovered at Kobate Quarry (Arrasate, northern Iberian Peninsula) is presented in this article. This site, in which remains of 40 different vertebrate taxa were accumulated, acted as a natural trap. The preliminary vertebrate faunal list includes five amphibian taxa, four reptiles, seven species of birds and 24 mammalian taxa. While small mammals are represented by 13 small mammal taxa (seven in the Order Rodentia, five in the Order Eulipotyphla, and one in the Order Chiroptera), the large mammal fauna comprises eleven species, including ungulates and carnivores. The palaeoecology inferred from this faunal assemblage suggests the existence of large forested areas with some grassland and a watercourse nearby, within a notably warm and humid climate. These palaeoenvironmental conditions, combined with AMS and AAR results carried out in macrofaunal bone samples, suggest that the deposit from Artazu VII would be located in the first half of the Late Pleistocene, in the Marine Isotope Stage (MIS) 5c.

Neanderthal settlement in central Iberia: Geo-archaeological research in the Abrigo del Molino site, MIS 3 (Segovia, Iberian Peninsula)

The Abrigo del Molino archaeological site is located in the valley of the Eresma river, near Segovia in central Spain. It consists of a shallow cave of fluvio-karstic origin, which has been completely filled with detrital deposits. Geo-archaeological interpretation of the genesis of these deposits differentiates three groups: a lower group with sandy loams and fine sands interbedded with pebble and gravel layers, deposited respectively by palaeofloods and slope contributions; a middle group with massive silt and grain-supported boulders, formed by alternating contributions from the overlying slope, karst mudflows and rockfalls from the shelter roof; and an upper group of silt cemented by carbonates, final backfill alteration and degradation of the host rock. The techno-typological characteristics of the lithic assemblage confirm the existence of Mousterian levels at the site, and optically stimulated luminescence (OSL) dating of these levels obtains an age range of 31–60 ka for the detrital deposits, presenting the occupation by Neanderthal groups for the first time in karstic environments in the northern Iberian plateau, the southern part of the Duero basin.

8000 years of vegetation history in the northern Iberian Peninsula inferred from the palaeoenvironmental study of the Zalama ombrotrophic bog (Basque‐Cantabrian Mountains, Spain)

This paper focuses on pollen, spores, non‐pollen palynomorphs (NPPs) and certain geochemical elements from the ombrotrophic blanket bog of Zalama (Basque‐Cantabrian Mountains, northern Iberian Peninsula), with the support of a robust chronology based on 17 AMS 14C dates. The main results related to the last 8000 years show that, during the early middle Holocene, pines and deciduous forests were the most extensive tree formations. At the beginning of the succession, pines reach 44%, showing regional presence, whereas after 7600 cal. a BP, deciduous forests were particularly abundant. From c. 6500 cal. a BP the pollen diagram constructed from our samples shows the first anthropogenic evidence, linked with the new economic practices related to the Neolithic of the Basque‐Cantabrian Mountains. From 3300 cal. a BP the expansion of Fagus sylvatica is particularly clear, and has since then become one of the dominant forest species in this region. We also discuss the Holocene evolution of other noteworthy plant communities in southwestern Europe, such as Taxus baccata, Juglans and shrublands.

Are we able to affect the population structure of an invasive species through culling? A case study of the attempts to control the American mink population in the Northern Iberian Peninsula

The American mink (Neovison vison) is a semi-aquatic mustelid from North America that is considered an invasive species in many countries. Due to its reported damage to native species, efforts are often undertaken to eradicate or control these mink populations. The aims of this study were to describe the demographic structures of three mink populations subjected to different culling intensities, to detect possible variations in these structures caused by trapping and to identify possible efficient indicators of trapping efforts. From 1998 to 2011, a total of 1306 American mink collected during official culling operations in three different Spanish areas were submitted for study. We sexed the carcasses and removed a canine tooth from each animal during the post-mortem procedures. The incremental cementum lines of the teeth were used for age estimation. No evidence of age structure changes was detected in any population. The proportion of individuals in each sex and age class remained constant over time, suggesting that despite control efforts, the age structure remained stable over the study period. The population with the highest culling intensity has the highest sub-adult/adult ratio (1.51), and the catch per unit effort in this area was lower in the second part of the period, which is a possible indicator of reduced density. Age structure and sub-adult ratio might be useful indicators of successful trapping efforts. The results from this study could be useful for decision-making in conservation of native species and management of mink populations.

Incorporating seed fate into plant–frugivore networks increases interaction diversity across plant regeneration stages

Plant–animal mutualistic interactions, such as pollination and seed dispersal, affect ecosystem functioning by driving plant population dynamics. However, little is known of how the diversity of interactions in these mutualistic networks determines plant regeneration dynamics. To fill this gap, interaction networks should not only account for the number of seeds dispersed by animals, but also for seed fate after dispersal. Here, we compare plant–animal networks at both the seed dispersal and seedling recruitment stage to evaluate how interaction diversity, represented by different network metrics, changes throughout the process of plant regeneration. We focused on a system with six species of frugivorous birds and three species of fleshy‐fruited trees in the temperate secondary forest of the Cantabrian Range (northern Iberian Peninsula). We considered two plant cohorts corresponding to two fruiting years showing strong differences in fruit and frugivore abundance. Seed dispersal interactions were estimated from a spatially‐explicit, field‐validated model predicting tree and bird species‐specific seed deposition in different microhabitats. These interactions were further transformed into interactions at the seedling recruitment stage by accounting for plant‐ and microhabitat‐specific seed fates estimated from field sampling. We found that network interaction diversity varied across plant regeneration stages and cohorts, both in terms of the evenness and the number of paired interactions. Tree–bird interactions were more evenly distributed across species pairs at the recruitment stage than at the seed deposition stage, although some interactions disappeared in the seed‐to‐seedling transition for one plant cohort. The variations in interaction diversity were explained by between‐plant differences in post‐dispersal seed fate and in inter‐annual fruit production, rather than by differences between frugivores in seed deposition patterns. These results highlight the need for integrating plant traits and disperser quality to predict the functional outcome of plant–animal mutualistic networks.

Optimal management of Pinus pinea stands when cone and timber production are considered

Pinus pinea is one of the most important tree species in the Mediterranean region due to the economic value of its edible seeds called “pinones”. Timber also represents an important source of income from this species. Generally, P. pinea stands have been managed to maximize either timber or seed production, optimization of the joint production of both products being rare. The difficulty in optimizing seed or joint production is the highly stochastic masting habit of P. pinea. The aim of the present study was to find the optimal management of P. pinea stands from the economic point of view when both seed and timber production are considered. A growth and yield model was employed to simulate the dynamics of P. pinea stands of the northern Iberian Peninsula. The novelty of the study is the implementation of a cone yield model that is able to predict expected cone harvests and seed yields when masting is stochastic. The model was linked with an optimization algorithm to obtain optimal schedules for two different stands. The results showed that seed production of P. pinea in the northern plateau of the Iberian Peninsula may increase the soil expectation value by more than 300 % in dense stands and 200 % in sparse stands. When seed yields were considered, rotation lengths were longer and thinnings were delayed. The results were highly sensitive to cone prices and discount rates.

Vertical distribution of major photosynthetic picoeukaryotic groups in stratified marine waters.

Photosynthetic picoeukaryotes (PPEs) are fundamental contributors to oceanic primary production and form diverse communities dominated by prymnesiophytes, chlorophytes, pelagophytes and chrysophytes. Here, we studied the vertical distribution of these major groups in two offshore regions of the northern Iberian Peninsula during summer stratification. We performed a fine-scale vertical sampling (every ∼2 m) across the DCM and used fluorescence in situ hybridization (FISH) to determine the PPE composition and to explore the possible segregation of target groups in the light, nutrient and temperature gradients. Chlorophytes, pelagophytes and prymnesiophytes, in this order of abundance, accounted for the total PPEs recorded by flow cytometry in the Avilés canyon, and for more than half in the Galicia Bank, whereas chrysophytes were undetected. Among the three detected groups, often the prymnesiophytes were dominant in biomass. In general, all groups were present throughout the water column with abundance peaks around the DCM, but their distributions differed: pelagophytes were located deeper than the other two groups, chlorophytes presented two peaks and prymnesiophytes exhibited surface abundances comparable to those at the DCM. This study offers first indications that the vertical distribution of different PPE groups is heterogeneous within the DCM.