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Kelp forests are critical marine ecosystems that provide habitat and ecological services, as well as economic benefits. However, kelp forests worldwide are facing multiple pressures, including climate change and human activities. In this study, we investigated whether recruitment success, an infrequently recorded variable in kelp monitoring studies, was affected in degraded kelp reefs where adult golden kelps (Laminaria ochroleuca) were persistently absent due to fish consumption. We conducted a three-year seasonal monitoring of kelp recruits and juveniles in both healthy and degraded kelp reefs in northwest Spain. Our findings reveal a decline in spring kelp recruitment over time on degraded reefs, while it remained stable on healthy reefs. The results indicate that continued herbivory pressure can decrease kelp recruitment, suggesting the potential exhaustion of kelp stand resilience. Altogether, our study highlights the importance of biotic interactions, such as herbivory, in understanding changes in kelp forest dynamics. Moreover, it emphasizes the significance of including recruitment in kelp forest assessments as an indicator of resilience

The 2007 flora “Green Seaweeds of Britain and Ireland” did not present the molecular data underpinning the Ulvaceae treatment, mostly ITS sequences. Subsequently, names have changed as type material of Ulva species is sequenced and intensive sampling with DNA barcoding adds new European species. To update the Ulvaceae, we systematically sampled from 2007 to 2021, identifying specimens using various molecular markers alongside DNA from type material of four species. We show here that Ulva gigantea , based on rbc L, tuf A and ITS sequences of its holotype, is assigned to Ulva compressa , as is the lectotype of Ulva curvata . Ulva gigantea sensu GenBank and Ulva pseudocurvata are conspecific. The correct name is U. pseudocurvata based on rbc L sequences of the lectotype. Two species of monostromatic Ulvaceae were included in the 2007 flora, but we show that both of them and all earlier British monostromatic collections represent Ulvaria splendens , a species originally described from Alaska. Analysis of two rbc L amplicons of the Ulva sordida lectotype shows that it is conspecific with Ulvaria splendens . Our first genuine collections of Ulvaria obscura from SW England and SW Wales correspond to topotype material from the Bay of Biscay, recent samples from Galicia and unpublished tuf A sequences from Britanny.

Molecular analyses, in combination with morphological studies, provide invaluable tools for delineating red algal taxa. However, molecular datasets are incomplete and taxonomic revisions are often required once additional species or populations are sequenced. The small red alga Conferva parasitica was described from the British Isles in 1762 and then reported from other parts of Europe. Conferva parasitica was traditionally included in the genus Pterosiphonia (type species P. cloiophylla in Schmitz and Falkenberg 1897), based on its morphological characters, and later transferred to Symphyocladia and finally to Symphyocladiella using molecular data from an Iberian specimen. However, although morphological differences have been observed between specimens of Symphyocladiella parasitica from northern and southern Europe they have yet to be investigated in a phylogenetic context. In this study, we collected specimens from both regions, studied their morphology and analyzed rbcL and cox1 DNA sequences. We determined the phylogenetic position of a British specimen using a phylogenomic approach based on mitochondrial and plastid genomes. Northern and southern European populations attributed to S. parasitica represent different species. Symphyocladiella arecina sp. nov. is proposed for specimens from southern Europe, but British specimens were resolved as a distant sister lineage to the morphologically distinctive Amplisiphonia, so we propose the new genus Deltalsia for this species. Our study highlights the relevance of using materials collected close to the type localities for taxonomic reassessments, and showcases the utility of genome-based phylogenies for resolving classification issues in the red algae.

Species identification in red algae poses significant challenges when relying solely on morphological characteristics. Consequently, the absence of molecular information often conceals misidentifications, cryptic diversity and introduced cryptic species. Within the genus Lophocladia, species have traditionally been delineated based on subtle morphological traits. Lophocladia trichoclados and Lophocladia lallemandii have been extensively documented in warm and temperate coastal regions, with the latter recognized as an invasive species in the Mediterranean. However, the molecular relationship between these species remains unexplored. To address this gap, a comprehensive taxonomic reevaluation of Lophocladia was conducted in the NE Atlantic, Mediterranean Sea and Red Sea. Through combined molecular and morphological analyses of 75 specimens, two distinct taxa of Lophocladia were identified within the study area. Sequences of the rbcL plastid gene unequivocally demonstrated that L. lallemandii and L. trichoclados are conspecific. Consequently, we propose the synonymization of L. lallemandii with L. trichoclados, which has nomenclatural priority. We report L. kuetzingii, a potentially introduced species from Australia, for the first time in the Macaronesian region of the North Atlantic. This finding underscores the importance of expanding red algal DNA datasets, as such efforts significantly enhance our ability to detect and discern introduced species. Additionally, this research highlights the existence of taxonomic uncertainties surrounding introduced species, even among those already classified as invasive.

The introduction of new non-indigenous species (NIS) in Spanish marine waters is addressed under Descriptor 2 of the European Union’s Marine Strategy Framework Directive. National baseline inventories of NIS have been compiled and updated for the three subregions (Western Mediterranean Sea, WMED; Bay of Biscay–Iberian Coast, ABI; Macaronesia, AMA) with data from 1800 to 2021. An overall of 574 species were identified with an alien, cryptogenic, crypto-expanding, or debatable status, mostly invertebrates (~65%) and primary producers (~22%). Of 412 alien species, 80.51% were reported in ABI, 67.82% in WMED, and 66.67% in AMA. Cryptogenic species are more abundant in the WMED (25.25%), compared to AMA (19.77%) and ABI (18.46%). ABI harbors more established species (62.56%) than AMA (45.2%) and WMED (43.56%), contrary to casual records (AMA 31.64%, WMED 23.76%, ABI 13.85%). Invasive species are more abundant (14.36%) in WMED. The ‘transport-stowaway’ pathway accounted for 142 (79.33%), 123 (67.58%), and 169 (85.21%) records in WMED, ABI, and AMA, respectively. The second most common pathway was ‘transport-contaminant’ related to mariculture (~10% of the total), prevalently in ABI with 42 species (23.08%). The Canary Islands stand out for species introduced through oil platforms from throughout the world. ‘Unaided’ was a relevant pathway of secondary introduction into the WMED, particularly of Lessepsian species progressing westwards. Temporal trends in newly introduced species show similar behavior among subregions.

Cryptic diversity is common among marine macroalgae, with molecular tools leading to the discovery of many new species. To assign names to these morphologically similar species, the type and synonyms have to be examined, and if appropriate, new species must be described. The turf-forming red alga Polysiphonia scopulorum was originally described from Rottnest Island, Australia, and subsequently widely reported in tropical and temperate coasts based on morphological identifications. A recent study of molecular species delineation revealed a complex of 12 species in Australia, South Africa, and Europe. These species are placed in a taxonomically unresolved lineage of the tribe Polysiphonieae. The aim of this study was to resolve the genus- and species-level taxonomy of this complex and related species using molecular and morphological information. Three morphologically indistinguishable species of the complex were found at the type locality of P. scopulorum, preventing a straightforward assignment of the name to any of the molecular lineages. Therefore, we propose a molecularly characterized epitype. Polysiphonia caespitosa is reinstated for the only species found in its type locality in South Africa. We describe seven new species. Only one species of the complex can be morphologically recognized, with the other eight species indistinguishable based on morphometric analysis. The studied complex, together with another seven species currently placed in Polysiphonia and two Bryocladia species, formed a clade distinct from Polysiphonia sensu stricto. Based on observations of Bryocladia cervicornis (the generitype), we describe our seven new species in the genus Bryocladia and transfer another nine species from Polysiphonia to Bryocladia.

Effective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are

Species of flora and fauna occurring in the west of Ireland and south-west Europe, known as Lusitanian elements, constitute a puzzling case of isolated populations of uncertain origin. Here we studied the population genetic structure of the heather Erica mackayana in Ireland and northern Spain and compared it with its widespread close relative Erica tetralix using single nucleotide polymorphisms (SNPs). We reconstructed phylogenetic relationships using maximum likelihood (ML), inferred population genetic structure using cluster assignment and principal component analysis, and estimated population genetic diversity. The cluster analysis and ML phylogenetic tree showed a geographical pattern for E. tetralix supporting a post-glacial migration from Iberia to Ireland. In contrast, Irish populations of E. mackayana were supported in independent clades in the phylogenetic tree and shared clusters with Iberian populations in the structure analysis, and FST values were lower among Irish and Spanish populations than among Irish ones. This suggests that Irish populations of E. mackayana are the result of recent multiple independent introductions from its native area in northern Spain, probably assisted by humans. However, the origin of the largest Irish population at Roundstone Bog is unclear and should be further investigated. Postglacial, long-distance dispersal is the most plausible explanation for Lusitanian species distribution in Ireland.

Invasive species have been a focus of concern in recent decades, becoming more problematic due to the cumulative impacts of climate change. Understanding the interactions among stress factors is essential to anticipate ecosystems' responses. Hereby, robust modeling frameworks must be able to identify the environmental drivers of invasion and forecast the current and future of their potential distribution. These studies are essential for the management of invasions and to be prepared for the future we are facing. Here we demonstrate that taxonomic misidentifications may lead to absolutely erroneous predictions, by using as an example one of the worst invasive species in the Mediterranean Sea (Lophocladia lallemandii), which has been misidentified for three decades and now is correctly identified. Consequently, and bearing in mind overall trends in species misidentification due to the loss of taxonomic expertise and the presence of cryptic species, among others, attempts to understand and predict species involved in invasion processes must always first consider taxonomic studies.

Introduced seaweeds and undescribed species often remain undetected because marine regional floras are as yet poorly understood. DNA sequencing facilitates their detection, but databases are incomplete, so their improvement will continue to lead the discovery of these species. Here we aim to clarify the taxonomy of two turf-forming red algal Australian species that morphologically resemble the European Aphanocladia stichidiosa. We also aim to elucidate whether either of these species could have been introduced in Europe or Australia. We studied their morphology, analyzed 17 rbcL sequences of European and Australian specimens, examined their generic assignment using a phylogeny based on 24 plastid genomes, and investigated their biogeography using a taxon-rich phylogeny including 52 rbcL sequences of species in the Pterosiphonieae. The rbcL sequences of one of the Australian species were identical to A. stichidiosa from Europe, considerably expanding its known distribution. Unexpectedly, our phylogenetic analyses resolved this species in the Lophurella clade rather than in Aphanocladia and the new combination L. stichidiosa is proposed. The other Australian species is described as L. pseudocorticata sp. nov. Although L. stichidiosa was originally described in the Mediterranean ca. 70 years ago, our phylogenetic analyses placed it in a lineage restricted to the southern hemisphere, showing that it is native to Australia and introduced to Europe. This study confirms that further work using molecular tools is needed to characterize seaweed diversity, especially among the poorly explored algal turfs, and showcases the usefulness of phylogenetic approaches to uncover introduced species and to determine their native ranges.

The analysis of biological and ecological traits has a long history in evolutionary and ecological research. However, trait data are often scattered and standardised terminology that transcends taxonomic and biogeographical context are generally missing. As part of the development of a global trait database of marine species, we collated trait information for European seaweeds and structured the data within the standardised framework of the World Register of Marine Species (WoRMS). We collected 45175 trait records for 21 biologically and ecologically relevant traits of seaweeds. This resulted in a trait database for 1745 European seaweed species of which more than half (56%) of the records were documented at the species level, while the remaining 44% were documented at a higher taxonomic level and subsequently inherited at lower levels. The trait database for European seaweeds will serve as a foundation for future research on diversity and evolution of seaweeds and their responses to global changes. The data will contribute to developing detailed trait-based ecosystem models and will be an important tool to inform marine conservation policies. The data are publicly accessible through the AlgaeTraits portal, 10.14284/574 (AlgaeTraits, 2022).

The introduction of new non-indigenous species (NIS) in Spanish marine waters is addressed under Descriptor 2 of the European Union’s Marine Strategy Framework Directive. National baseline inventories of NIS have been compiled and updated for the three subregions (Western Mediterranean Sea, WMED; Bay of Biscay–Iberian Coast, ABI; Macaronesia, AMA) with data from 1800 to 2021. An overall of 574 species were identified with an alien, cryptogenic, crypto-expanding, or debatable status, mostly invertebrates (~65%) and primary producers (~22%). Of 412 alien species, 80.51% were reported in ABI, 67.82% in WMED, and 66.67% in AMA. Cryptogenic species are more abundant in the WMED (25.25%), compared to AMA (19.77%) and ABI (18.46%). ABI harbors more established species (62.56%) than AMA (45.2%) and WMED (43.56%), contrary to casual records (AMA 31.64%, WMED 23.76%, ABI 13.85%). Invasive species are more abundant (14.36%) in WMED. The ‘transport-stowaway’ pathway accounted for 142 (79.33%), 123 (67.58%), and 169 (85.21%) records in WMED, ABI, and AMA, respectively. The second most common pathway was ‘transport-contaminant’ related to mariculture (~10% of the total), prevalently in ABI with 42 species (23.08%). The Canary Islands stand out for species introduced through oil platforms from throughout the world. ‘Unaided’ was a relevant pathway of secondary introduction into the WMED, particularly of Lessepsian species progressing westwards. Temporal trends in newly introduced species show similar behavior among subregions.

Effective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are

Parasitic red algae are an interesting system for investigating the genetic changes that occur in parasites. These parasites have evolved independently multiple times within the red algae. The functional loss of plastid genomes can be investigated in these multiple independent examples, and fine-scale patterns may be discerned. The only plastid genomes from red algal parasites known so far are highly reduced and missing almost all photosynthetic genes. Our study assembled and annotated plastid genomes from the parasites Janczewskia tasmanica and its two Laurencia host species (Laurencia elata and one unidentified Laurencia sp. A25) from Australia and Janczewskia verruciformis, its host species (Laurencia catarinensis), and the closest known free-living relative (Laurencia obtusa) from the Canary Islands (Spain). For the first time we show parasitic red algal plastid genomes that are similar in size and gene content to free-living host species without any gene loss or genome reduction. The only exception was two pseudogenes (moeB and ycf46) found in the plastid genome of both isolates of J. tasmanica, indicating potential for future loss of these genes. Further comparative analyses with the three highly reduced plastid genomes showed possible gene loss patterns, in which photosynthetic gene categories were lost followed by other gene categories. Phylogenetic analyses did not confirm monophyly of Janczewskia, and the genus was subsumed into Laurencia. Further investigations will determine if any convergent small-scale patterns of gene loss exist in parasitic red algae and how these are applicable to other parasitic systems.

Alexandrium minutum blooms generally occur in semi-enclosed sites such as estuaries, harbours and lagoons, where enhanced stratification, restricted circulation and accumulation of resting cysts in the sediment set suitable habitat conditions for the proliferation of this paralytic shellfish poisoning toxigenic species. In the Galician Rías Baixas (NW Iberian Peninsula), according to weekly time-series between 1994 and 2020, blooms of A. minutum were recurrent in small, shallow estuarine bays inside the Rías de Vigo and Pontevedra, but rarely detected, and if so at low concentrations, out of these environments. However, from May to July 2018 it developed as usual in the small inner bays but then spread over both Rías (Vigo and Pontevedra) causing discoloured waters during one month and prolonged harvesting closures. Meteorological conditions during that period (rains / runoff higher than climatological averages, sustained temperature increment and oscillating wind pattern –i.e., series of upwelling-relaxation cycles), fostered optimal circumstances for the development of that extensive and massive proliferation: strong vertical stratification and the alternation of retention and dispersion processes. Simulations from a particle tracking model portrayed the observed bloom development phases: onset and development inside a small inner bay; transport within the surface layer, from these sites towards the interior parts of the Ría; and dispersion all over the embayment. Seedbeds with high concentrations of resting cysts were detected several months after the bloom, which may have favoured flourishment of A. minutum in the following two years, markedly in 2020. The present work contributes to the general understanding of the dynamics of harmful algal blooms (HABs), from which surveillance indicators of the state of marine ecosystems and their evolution can be derived. We hypothesize that the intensity and frequency of A. minutum proliferations in the Galician Rías could

Research in marine Spanish waters are focused on several actions to achieve an effectively management on protected areas, with the active participation of the stakeholders and research as basic tools for decision-making. Among these actions, there is one about the knowledge and control on NIS. One of its objectives is the creation of NIS factsheets, which are going to be added to the National Marine Biodiversity Geographical System (GIS) providing complementary information about taxonomic classification, common names, taxonomic synonyms, species illustrations, identification morphological characters, habitat in the native and introduced regions, biological and ecological traits, GenBank DNA sequences, world distribution, first record and evolution in the introduced areas, likely pathways of introduction, effects in the habitats and interaction with native species, and potential management measures to apply. The database will also provide data for (1) the European online platforms, (2) the environmental assessment for the Descriptor 2 (D2-NIS) of the EU Marine Strategy Framework Directive (MSFD), as well as (3) supporting decisions made by stakeholders. It is the result of extensive collaboration among scientist, manager’s and citizen science in the Spanish North-Atlantic, South-Atlantic, Gibraltar Strait-Alboran, Levantine-Balearic and Canary Islands marine divisions, providing an updated overview of the spatial distribution of relevant extended and invasive NIS of recent and established NIS introduced by maritime transport and aquaculture pathways, as well as on cryptogenic or native species in expansion due to the climatic water warming trend.

The toxic dinoflagellate Alexandrium minutum generally proliferates in semi-enclosed sites such as estuaries, harbours and lagoons, where stratification, restricted circulation and accumulation of resting cysts set suitable conditions for its development. In the Galician Rías (NW Iberian Peninsula), its blooms follow also this pattern. They are recurrent in small, shallow estuarine bays inside the Rías, but rarely detected, and if so in minor amount, out of these areas. However, a massive proliferation of A. minutum from June to July 2018 in the Rías Baixas (Vigo and Pontevedra) changed this picture. The bloom initiated in semi-enclosed waters, as previously described for this species, but thereafter spread to the whole embayments where persisted more than one month. It generated a noticeable red tide with disperse patches that became heavily concentrated inside the port of Vigo. During that period shellfish harvesting closures and paralytic shellfish toxins in certain marine invertebrates and fish were reported for the first time in Spain. Meteorological conditions (higher than usual rains/runoff, sustained temperature increment and oscillating wind pattern promoting a series of upwelling-relaxation cycles) fostered optimal circumstances for the outbreak of A. minutum: strong vertical stratification and the alternation of retention and dispersion processes. Simulations from a particle tracking model portrayed the observed bloom development phases: onset, transport within the surface layer towards the interior parts of the Ría of Vigo, and dispersion all over the embayment. High concentrations of resting cysts were detected several months after the bloom, which may have favoured flourish of A. minutum in the following years, markedly in 2020.

Species discovery is facilitated by the application of molecular tools and the exploration of poorly studied habitats. Recent surveys in Bafa Lake, Turkey, which experienced a transition from oligo- to mesohaline conditions during the last 40 years, led to the finding of two species of the genera Lophosiphonia and Polysiphonia. Our molecular and morphological study showed that one of the species corresponded to L. obscura, while the other differs from previously described Polysiphonia species and is proposed as P. sukatarii sp. nov. The new species differs from related congeners by a rbcL sequence divergence ≥5.8% and is morphologically distinguished by having four pericentral cells and trichoblasts arranged several segments apart. Lophosiphonia obscura, and its closely related species L. hemisphaerica comb. nov. and L. boldii comb. nov., have been previously found in similar habitats in Europe and Atlantic North America. Along with its record from Bafa Lake, P. sukatarii sp. nov. has been discovered in open shore algal turfs from the Canary Islands, suggesting that it is a euryhaline species with probably a wide distribution. Our work highlights that poorly studied habitats still harbour undiscovered species and additional surveys are necessary to acquire a more comprehensive understanding of the macroalgal diversity.

The present study adds 19 species (15 Rhodophyta, one Chlorophyta and three Ochrophyta) to the Azorean marine macroalgal flora, increasing the current total of species recorded in this region to 521 (349 Rhodophyta, 76 Chlorophyta and 96 Ochrophyta), and showing that this isolated island group supports a relatively rich marine macroalgal flora. Some species fall within their known overall distributional range, whereas other found here represent a northern or southern extension to their known distribution in the Atlantic. Three species (Antithamnionella elegans, Gymnophycus hapsiphorus and Scytosiphon dotyi) are probable introductions to the Azores, whereas Melanothamnus pseudoforcipatus has an uncertain status. Six of the newly reported species were found as components of the intertidal algal turf samples, which justifies the need for continuing to examine turf samples as new discoveries can be anticipated.

The detection of invasive species is commonly challenging in marine environments, often related with the insufficient taxonomic knowledge of the local diversity. Using DNA sequences in diversity surveys and their phylogenetic analysis can assist us to clarify the native or introduced origin of some species. We applied this approach to study the red algae Aphanocladia stichidiosa. It was originally described in the Mediterranean (1955), later recorded in Portugal (1960), the Canary Islands (1986), the northwestern Spain (1990) and the Azores (2012). Unexpectedly, our diversity surveys in Australia revealed its presence in Victoria in 2015, finding that European and Australian specimens had identical DNA sequences (rbcL gene) and suggesting that it is introduced in one of the regions. Phylogenetic analysis resolved A. stichidiosa in a highly supported clade with species restricted to the southern hemisphere, mainly from Australia. Accordingly, we conclude that A. stichidiosa is native from Australia, although it has never been recorded there before, and that it represents a relatively old introduction in Europe. In both native and introduced regions, it is frequent in algal turfs, a type of assemblage composed by a carpet of small, morphologically similar species whose identification is often difficult. The type of growth of this species explains the absence of previous records in Australia, where the number of taxonomists studying this assemblage is lower than in Europe. Sequential reports of A. stichidiosa in different European regions suggest that it is expanding its distribution, as well as its abundance is increasing. The invasive character of this species needs to be determined yet, and its small size should not lead to underestimate its potential harmfulness. In the current context, in which kelp forests are globally declining and algal turfs are expanding, this species might play a relevant role in the transformation of the European marine ecosystems.

Prokaryotes play an important role in biogeochemical cycling in marine ecosystems, but little is known about their diversity and composition, and it’s even less understood how they may contribute to the ecological functioning of highly variable coastal areas affected by upwelling. Between May 2016 and May 2018, we carried out 26 one-day samplings in the temperate northwestern Iberian upwelling system to investigate the temporal patterns of variability for prokaryotic abundance, diversity and community composition by combining flow cytometry and 16S RNA high- throughput sequencing. A marked seasonality was found for prokaryotic abundance, peaking during summer upwelling and relaxation season (≈May to September), when extracellular release of organic matter from phytoplanktonic blooms is a significant process, and decreasing in downwelling events (≈October to April). Those downwelling conditions, characterized by deeper mixed layers and a homogeneous water column, favored a higher abundance of the archaeal groups, Marine Group II (Euryarchaeota) and Nitrosopelagicus (Thaumarchaeota), as well as of Marinimicrobia bacterium (SAR406 clade) and the group Bacteria_Others. By contrast, upwelling and relaxation conditions characterized by enhanced vertical stratification and hydrographic variability, included a community generally less diverse with core-phylotypes (occurring > 75% of the samples) proliferating, i.e. Flavobacteriaceae (Bacteroidetes), Chloroplast (C

The number of newly described species has increased since the addition of molecular data to taxonomic studies, revealing that species considered widely distributed by morphological and anatomical studies are often comprised of complexes of several distinct species. This study reports on a new turf-forming species of Digenea from the Greater Caribbean (South Florida and eastern Cuba), previously identified as D. simplex based on morpho-anatomical characters, but shown through DNA sequences to be a distinct species. Digenea nana sp. nov. is characterized by its small brush appearance, small dimensions (2.5 cm high and 0.6 mm wide), long determinate branches reaching 15 mm in length (its most striking feature) and 11–12 pericentral cells. Digenea nana is distinct from all its congeners, showing sequence divergences of 3.5–5.0% in COI-5P and 1.7–2.7% in rbcL. The species resolved as sister to D. rafaelii (genetic distance of about 3.5% and 1.7% in COI-5P and rbcL respectively) from Pacific Mexico, and can be easily distinguished by morpho-anatomical characters. Digenea nana is the seventh species in the genus worldwide. Given the presumed wide distribution of D. simplex, based solely on morpho-anatomy, and the number of cryptic and pseudo-cryptic species recently described, further integrative molecular and morpho-anatomical studies are likely to reveal new taxa.

The microbe-dissolved organic matter (DOM) interactions include microbial uptake and DOM reworking and release, affecting the composition of the heterogeneous DOM pool. In turns, this distinct DOM composition can select for microbial assemblages. We investigated the diversity of microbial (both Bacteria and Archaea) communities (combining Illumina tag sequencing of 16S rRNA gen -amplicon sequencing variants, ASVs- and metagenomics) and the chemodiversity of dissolved organic molecules (extracted by solid phase extraction and analyzed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, FT-ICR-MS) in the Eastern North Atlantic Ocean off the Galician coast (43oN, 9o-15oW). Sampling ranged from 100 m to 5000 m, thereby encompassing a wide variety of water masses with contrasting origins and different aging. Applying diversity ecological metrics to both organic compounds and ASVs, we found that microbial diversity and richness were negatively correlated with DOM concentration and chemo-diversity. Besides, our results demonstrated the link between this trend and water mass aging, which enhances biosphere taxonomic diversity but reduces molecular variety. DOM diversity, decreasing along the water mass aging gradient, would likely reflect the persistence of the most refractory molecules, generated as by- product of the DOM degradation by microbes. In two PCoAs based on the metagenomic data, combined PCoA axis 1 and PCoA axis 2, explained the 80% and 20% of the microbial gene ́s structural variability among water masses. The oldest water masses, originated at high latitudes, such as NADW and LDW, were associated to higher abundance of genes involved in metabolism of aromatic compound. Intermediate waters such as ENACWst were related to sulphur/iron/phosphorous metabolism related genes. Surface waters were linked to genes involved in photosynthesis, autotrophy and cell division. Taken together, the observed increase of DOM homogenization along water mass aging was

[EN] Syngnathid fishes (Actinopterygii, Syngnathidae), including seahorses and pipefishes, are flagship vulnerable species highly associated with seaweed and seagrass habitats. Our multidisciplinary study provides the first insights for syngnathid populations in Atlantic Islands of Galicia (Cíes Archipelago, Atlantic Ocean) and Cabrera Archipelago (Mediterranean Sea) Spanish National Parks. Syngnathid fishes were collected on several sites in the first year of the study, and habitat characteristics were also determined. From the results achieved, a further two-years monitoring was performed seasonally in selected sites. The fishes were analyzed for size, weight, sex and sexual maturity, stable isotope signatures and genetics. Epifauna and gut contents were also analyzed for further dietary assessment of syngnathids. Diversity and abundances were generally low, with four species (including seahorses) identified in the Atlantic Islands of Galicia National Park and five (only pipefishes) at Cabrera National Park. Syngnathids from both national parks differed in size, isotopic values and prey regime. Syngnathids preferred less exposed sites in macroalgal assemblages (Atlantic) or Cymodocea meadows (Mediterranean). Population characteristics in the Atlantic Islands of Galicia National Park suggests that syngnathids mainly comprise breeders that migrate seasonally, with preference for less exposed sites on shallow complex rocky-sandy substrates covered by macroalgae. Prey preferences would rely mainly on the consumption of copepods and gammarids. In the Mediterranean, syngnathids were likely limited by the depth of the studied sites, showing preference for Cymodocea meadows over Posidonia, and for the capture of a wider range of prey compared to the Atlantic populations. Borrón (Atlantic) and Es Burri (Mediterranean) would be preferential sites to undertake conservations plans for syngnathids. Several research topics are suggested for further management of syngnathids pop, [ES] Los signátidos (Actinopterygii, Syngnathidae) son una familia de peces que incluye caballitos de mar y peces pipa. Se trata de especies vulnerables estrechamente asociadas a las comunidades vegetales. Este estudio multidisciplinar en signátidos es el primero realizado en los Parques Nacionales Marítimo-Terrestres de las Islas Atlánticas de Galicia (Archipiélago de Cíes, Atlántico) y del Archipiélago de Cabrera (Mediterráneo). En el primer año de estudio, se estudiaron los signátidos en diversas zonas de ambos parques nacionales, así como las características de sus hábitats. Los resultados alcanzados permitieron establecer zonas preferentes para la realización de un estudio bianual posterior. En los peces capturados se determinaron las siguientes características: talla, peso, sexo y madurez sexual, isótopos estables y características genéticas. También se analizó la epifauna y los contenidos digestivos para determinar preferencias alimentarias. La diversidad y las abundancias fueron reducidas, con cuatro y cinco especies identificadas en el Atlántico y Mediterráneo, respectivamente, con presencia de caballitos de mar solo en la vertiente atlántica. Se observaron diferencias importantes en los signátidos de ambas zonas en lo relacionado con talla, valores isotópicos y preferencias alimentarias, Los signátidos atlánticos mostraron preferencia por zonas someras menos expuestas en hábitats macroalgales complejos arenoso-rocosos, con preferencia por el consumo de gammáridos y copépodos. Las especies del mediterráneo estuvieron mejor representadas en praderas de Cymodocea comparado con las de Posidonia, con una mayor variedad de fuentes alimenticias que en el atlántico, dependiendo de la especie. Las zonas de mayor interés, de cara a futuros planes de conservación, fueron Borrón (Atlántico) y Es Burri (Mediterráneo). Se proponen diversas actuaciones para el estudio futuro de las poblaciones estudiadas

Alexandrium minutum blooms generally occur in semi-enclosed sites such as estuaries, harbours and lagoons, where enhanced stratification, restricted circulation and accumulation of resting cysts in the sediment set suitable habitat conditions for the proliferation of this paralytic shellfish poisoning toxigenic species. In the Galician Rías Baixas (NW Iberian Peninsula), according to weekly time-series between 1994 and 2020, blooms of A. minutum were recurrent in small, shallow estuarine bays inside the Rías de Vigo and Pontevedra, but rarely detected, and if so at low concentrations, out of these environments. However, from May to July 2018 it developed as usual in the small inner bays but then spread over both Rías (Vigo and Pontevedra) causing discoloured waters during one month and prolonged harvesting closures. Meteorological conditions during that period (rains / runoff higher than climatological averages, sustained temperature increment and oscillating wind pattern –i.e., series of upwelling-relaxation cycles), fostered optimal circumstances for the development of that extensive and massive proliferation: strong vertical stratification and the alternation of retention and dispersion processes. Simulations from a particle tracking model portrayed the observed bloom development phases: onset and development inside a small inner bay; transport within the surface layer, from these sites towards the interior parts of the Ría; and dispersion all over the embayment. Seedbeds with high concentrations of resting cysts were detected several months after the bloom, which may have favoured flourishment of A. minutum in the following two years, markedly in 2020. The present work contributes to the general understanding of the dynamics of harmful algal blooms (HABs), from which surveillance indicators of the state of marine ecosystems and their evolution can be derived. We hypothesize that the intensity and frequency of A. minutum proliferations in the Galician Rías could

The microbe-dissolved organic matter (DOM) interactions include microbial uptake and DOM reworking and release, affecting the composition of the heterogeneous DOM pool. In turns, this distinct DOM composition can select for microbial assemblages. We investigated the diversity of microbial (both Bacteria and Archaea) communities (combining Illumina tag sequencing of 16S rRNA gen -amplicon sequencing variants, ASVs- and metagenomics) and the chemodiversity of dissolved organic molecules (extracted by solid phase extraction and analyzed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, FT-ICR-MS) in the Eastern North Atlantic Ocean off the Galician coast (43oN, 9o-15oW). Sampling ranged from 100 m to 5000 m, thereby encompassing a wide variety of water masses with contrasting origins and different aging. Applying diversity ecological metrics to both organic compounds and ASVs, we found that microbial diversity and richness were negatively correlated with DOM concentration and chemo-diversity. Besides, our results demonstrated the link between this trend and water mass aging, which enhances biosphere taxonomic diversity but reduces molecular variety. DOM diversity, decreasing along the water mass aging gradient, would likely reflect the persistence of the most refractory molecules, generated as by- product of the DOM degradation by microbes. In two PCoAs based on the metagenomic data, combined PCoA axis 1 and PCoA axis 2, explained the 80% and 20% of the microbial gene ́s structural variability among water masses. The oldest water masses, originated at high latitudes, such as NADW and LDW, were associated to higher abundance of genes involved in metabolism of aromatic compound. Intermediate waters such as ENACWst were related to sulphur/iron/phosphorous metabolism-related genes. Surface waters were linked to genes involved in photosynthesis, autotrophy and cell division. Taken together, the observed increase of DOM homogenization along water mass aging was