NE Atlantic Ocean Research Articles

Morphosedimentary evolution of the Belgica Mound Drift: Controls on contourite depositional system development in association with cold-water coral mounds

Small-scale contourite drift is an important component of continental margins that can record information about complex oceanographic processes. The Belgica Mound Drift is one example of a small-scale contourite drift. It is formed under the influence of cold-water coral (CWC) mounds and represents one of the most distal contouritic expressions influenced by the Mediterranean Outflow Water (MOW) in the NE Atlantic Ocean. Three distinct evolutionary stages have been identified from new high-resolution pseudo-3D reflection seismic data, each associated with a significant change in paleoceanography, affecting both bottom-current intensity and sediment input. The pre-drift stage (Pliocene–Early Pleistocene) corresponds to the regional RD1 erosive event, which was caused by the reintroduction of the MOW in the Porcupine Seabight, creating a distinct paleotopography that will influence all ensuing sedimentary processes. The second stage (Early Pleistocene–Middle Pleistocene) is the contourite drift inception in two distinct centres of growth, strongly steered by topographic obstacles such as the CWC mounds. During the third and final stage (Middle Pleistocene–present day), the contourite drift is developed under a more stable but less dynamic environment, characterised by more continuous and mounded aggradational stratification. The final stage of the contourite drift is related to the Middle Pleistocene Transition, with a spatially variable reduction in the MOW-related bottom currents and sediment input. The spatial and temporal evolution of this drift shows that its present-day morphology is controlled by the location of initial growth. Evolving moat morphology indicates that the intensity of the bottom currents generally increases during the drift evolution.This research presents a crucial paradigm for advancing our knowledge of elucidating the complexities of smaller-sized contourite systems in diverse oceanic environments.

Rising temperatures, falling fisheries: causes and consequences of crossing the tipping point in a small-pelagic community

Global change has profound effects on marine species, communities, and ecosystems. Among these impacts, small pelagics have emerged as valuable indicators for detecting regime shifts in fish stocks. They exhibit swift responses to changes in ocean variables, including decreased abundances, accelerated juvenile growth rates, early maturation, and reduced adult sizes in warm waters. However, each pelagic species occupies a unique local ecological niche, that reflects the sum of all environmental conditions. Consequently, their responses to environmental changes manifest in distinct ways. We explore here how global change affects small pelagics in the Madeira Archipelago (NE Atlantic Ocean) at (i) community level, by studying the effects of climate change over a 40-year (1980–2019) period on small pelagic landings, and (ii) population level, by studying the effects on the life-history traits of the two most abundant species, Scomber colias and Trachurus picturatus. Our study demonstrated that anomalies in the Sea Surface Temperature and the North Atlantic Oscillation caused a regime shift within the small pelagic community. Both environmental predictors explained 88.9% of the community landings oscillations. S. colias appears to exhibit a relatively more favorable adaptive response to climate change compared to T. picturatus. Understanding the species-specific ecological responses of small pelagic fish to global change is crucial for effective management and conservation efforts in the face of ongoing environmental scenarios.Graphical abstract

Prorocentrum canariense sp. nov., a case of pseudo-cryptic speciation in the cosmopolitan dinoflagellate P. compressum (Prorocentrales, Dinophyceae).

The planktonic dinoflagellate Prorocentrum compressum is widespread in warm and temperate seas. A strain identified as P. cf. compressum BEA 0681B isolated from the island of Gran Canaria, NE Atlantic Ocean, showed a divergence in rDNA/ITS phylogenies with respect to P. compressum. The Canarian strain was oval, with an average length-to-width ratio of 1.35, smooth thecal surface with less than 150 thecal pores, including oblique pores, sometimes with a bifurcated opening. In contrast, P. compressum was rounder, with a length-to-width ratio < 1.2, with reticulate-foveate ornamentation and 200-300 pores per valve. We propose Prorocentrum canariense sp. nov. These species clustered as the most early-branching lineage in the clade Prorocentrum sensu stricto. Although this clade mainly contains planktonic species, the closer relatives were the benthic species P. tsawwassenense and P. elegans. Interestingly, P. compressum and P. canariense sp. nov. are widely distributed in temperate and warm seas without an apparent morphological adaptation to planktonic life. The formation of two concentric hyaline mucilaginous walls could contribute to this success. We discuss the use of Prorocentrum bidens to solve the nomenclature issue of P. compressum that was described citing a diatom as basionym.

Epifaunal Communities in Floating Buoys on Gran Canaria (Canary Islands, NE Atlantic Ocean)

Ocean sprawl has become increasingly prevalent in marine environments. Artificial substrates, notably floating structures like buoys, have gained significant attention in recent years. They serve as valuable models for future studies aimed at understanding and mitigating the impacts of anthropogenic activities on marine ecosystems. We studied the epifauna from buoys at six different locations on the northern and southern coasts of the island of Gran Canaria (Canary Is., NE Atlantic Ocean). A total of 12,130 individuals belonging to 57 species were collected. The abundance of individuals was higher in the northern area, whereas the species richness was higher in the southern area. The n-MDS showed significant differences between localities, with Las Alcaravaneras being separated from the remaining ones. These dissimilarities were due to the differences in the abundances of the amphipods P. gammaroides and A. rubricata. The orientation was a pivotal factor in structuring these associated communities in floating buoys. As a preliminary approach, high biodiversity and species richness were observed in these buoys; hence, they have a high potential to be used as bioindicators of human disturbance.

The remarkable parallels between the North East Atlantic and Arctic regions

Geological understanding of the NE Atlantic and Arctic regions has increased greatly over the last two decades, revealing remarkable similarities. Continental extension in both regions onset during pausing or cessation of adjacent orogenies – the Verkhoyansk-Chukotka and Alpine orogenies – which relaxed compressional stresses and permitted extension. Severe extension accompanied by high-volume magmatism did not onset abruptly but was the culmination of long-term, regional tectonic and magmatic unrest. It was complex and piecemeal, with extension and volcanism occurring along multiple axes simultaneously, a process still ongoing in Iceland today. Large Igneous Province emplacement did not drive breakup but occurred as a consequence of continental extension. The High Arctic Large Igneous Province did not progress to breakup. As a result, much of the Arctic Ocean is floored by hyper-extended continental crust overlain by seaward-dipping reflectors. This crust resembles the passive margins of the NE Atlantic. The Alpha-Mendeleev Rise in the Arctic Ocean is a double-sided passive margin underlain by hyper-extended continental crust draped with seaward-dipping reflectors. A similar structure has been proposed for the Greenland-Iceland-Faroe Ridge. If correct, present-day volcanism in Iceland is building SDRs today. Up to ∼50% of the NE Atlantic Ocean oceanward of the continental shelves is likely underlain by at least some continental crust. For the Arctic Ocean this figure is ∼80%. Similar structures are found elsewhere, including the Madagascar Channel, the NW Indian Ocean, and the South Atlantic. These new ideas suggest promising directions of future study including assessing the true extent of continental crust in the oceans globally.

Revision of deep-water species in Granulina (Gastropoda: Granulinidae) from Mauritania and Western Sahara

Empty shells (thanatocoenoses) have been reviewed of species in the genus Granulina (Gastropoda: Granulinidae) from the lower shelf and upper bathyal zones off Mauritania and Western Sahara. We encountered nine species of which four were already known from off Mauritania. Four new species are proposed herein: Granulina reginae sp. nov., G. ronaldi sp. nov., G. sandrae sp. nov. and G. sigridae sp. nov. These four sympatric new species lack labial denticles and they probably form a phyletic clade with a common ancestor. Most hitherto known species in Granulina from the NE Atlantic Ocean and the Mediterranean possess labial denticles. One additional new species with denticles was left in open nomenclature because the material available was considered inadequate. Species in Granulina from Mauritania and Western Sahara have not been found off NW Morocco or the Canary Islands, and the species known from NW Morocco and the Canary Islands have not been found off Mauritania and Western Sahara. The southern extents of the distributions of the Mauritanian species are currently uncertain as additional sampling would be required off Senegal or further South. A key to Mauritanian species in Granulina is given.

Spatial and temporal variability of the two main caught species of an artisanal trap fishery in an oceanic island

Abstract This study analysed the catches of trap fishing in the Canary Archipelago, NE Atlantic Ocean. This study was conducted from October 2016 to September 2017, April to November 2018 and September 2020, in five ports (San Cristóbal, Taliarte, Castillo del Romeral, Arguineguín and Mogán). The primary gear were traps with small mesh size (31.6 mm) and large mesh size (50.8 mm). A total of 2587 small mesh size traps and 141 large mesh size traps were analysed from 20‐ to 130‐m depth. The main target species were Dentex gibbosus and Stephanolepis hispidus. Catches of traps with large mesh size showed D. gibbosus above first maturity and S. hispidus in small mesh size traps. Both species exhibit larger specimens during reproductive periods. The most effective traps for D. gibbosus (large mesh) were located on the western coast (&gt;30‐m depth), with the highest catch per unit of effort (CPUE) in Mogán (857.7 g trap−1 day−1). The most effective traps for S. hispidus (small mesh) were located in southern areas, especially in sandy habitats (124.9 g trap−1 day−1 in Castillo del Romeral, 102.9 g trap−1 day−1 in Arguineguín). The highest catchability of D. gibbosus was observed in April (CPUE of 962.8 g trap−1 day−1), and the highest catchability of S. hispidus was found in June (CPUE of 165.9 g trap−1 day−1). The traps with small mesh size showed a great selectivity of sizes for S. hispidus; though high catch rates of immature specimens of D. gibbosus pose a threat to species conservation. The management recommendations' proposed measures include revising minimum catch sizes for both species. Additionally, we suggested depth limitations for mesh sizes of traps. The study highlights the need for new management strategies to ensure the conservation of targeted demersal species, with special emphasis on addressing the threat posed by small mesh sizes to immature D. gibbosus. The findings provide valuable insights for adapting fishery management practices to sustainably conserve the targeted species in the Canary Archipelago.

Mollusks (Gastropoda, Bivalvia) from Miocene cold-seep deposits in northern Italy: revisions and additions

Here, we report on 33 molluscan species from Miocene ’Calcari a Lucina’ hydrocarbon-seep deposits in northern Italy. Three new species are described: the chilodontaid gastropod Putzeysia diversii sp. nov., the lucinid bivalve Miltha (sensu lato) romaniae sp. nov., and Sisonia ultimoi sp. nov., a heterodont bivalve of uncertain taxonomic affinity. Fourteen species are described in open nomenclature. The common but enigmatic gastropod species Phasianema taurocrassa is here suggested to belong to the seguenzioid genus Cataegis. Most gastropod species are inhabitants of the deep-sea floor in general, and are not restricted (obligate) to sites of hydrocarbon-seepage. The gastropod Putzeysia diversii sp. nov. and the bivalve Sisonia ultimoi sp. nov. are the geologically oldest members of their genera known to date. While the genus Putzeysia is geographically restricted to the NE Atlantic Ocean and the Mediterranean Sea, Sisonia ultimoi sp. nov. represents another link of the Miocene Mediterranean seep fauna to that of the central Indo-West Pacific Ocean.

Plastitar records in marine coastal environments worldwide from 1973 to 2023

Plastics embedded in tar residues encrusting rocky coastlines were discovered on the Canary Islands (NE Atlantic Ocean) and termed “plastitar” in 2022. As plastic and tar pollution is widespread in marine pelagic and benthic habitats, it was predicted that this novel plastic form could occur on other coasts as well. To test this prediction, we reviewed the literature on plastic embedded in tar and examined rocky coastlines in our regions for plastitar. We found eight studies which reported plastic embedded in tar under several descriptions and terms (including “tar-bonded beach-conglomerate tarcrete”, “plasto-tar crust”, “plasto-tarball” and “plastitar”) in India (Arabian Sea), Bermuda (Saragossa Sea), the Bahamas (NW Atlantic Ocean), the United Arabic Emirates (Arabian Gulf and Gulf of Oman), Malta (central Mediterranean Sea), Croatia (Adriatic Sea), Italy (Adriatic and Ligurian Sea), Cabrera island, Menorca island and Sardinia island (western Mediterranean Sea) and Indonesia (Java Sea) from 1973 to 2023. We also detected plastitar during our field surveys in Japan (Sea of Japan) and Mallorca island (western Mediterranean Sea) in 2022 and 2023, respectively. Using Fourier-transform infrared spectroscopy (FTIR), we verified the contained plastics as polyethylene (PE). Pyrolysis-gas chromatography-mass spectrometry (PY-GC/MS) indicated that the tar residues derived from crude oil. Furthermore, plotting all these plastitar records in a global map revealed that almost all plastitar findings were made along the major oil transportation routes across the northern hemisphere suggesting that plastitar resulted from tanker-released crude oils. Overall, our study shows, for the first time, that plastitar has been a widespread and long overlooked plastic form in coastal systems worldwide.

Interspecific variability in internal anatomy in Terebellides Sars, 1835 (Annelida, Trichobranchidae) revealed with micro-CT

The number of new species described of the genus Terebellides Sars, 1835 (Annelida, Trichobranchidae) in the eastern Atlantic Ocean has greatly increased in the last years. Eleven of these species, all originally described in NE Atlantic Ocean, from the Barents Sea to the Gulf of Guinea, have been studied using micro-computed tomography (micro-CT) thus revealing interspecific differences in several elements of the internal anatomy such as the proportion between stomach regions and size of nephridia, and in the number of lamellae in the digestive gland. Two stomach morphotypes have been distinguished regarding differences in relative length between regions, as well as two morphotypes of nephridia according to their size and wall thickness, and four types of the digestive gland regarding their number of lamellae. Differences in nephridia sizes is the only character apparently related to the geographic distribution of species (i.e. NE Atlantic vs. Gulf of Guinea) but examination of more taxa is needed. A third distinct region was distinguished in the stomach, named here as mid stomach, that differs from the fore and hind stomach in epithelia thickness and by lacking connective muscular sheath. The potential of the micro-CT technique in the search for internal anatomical characters with taxonomic value is discussed.

Fecundity, an overlooked life-history trait for coastal management of commercial molluscs?

Gonadal development in limpets is well-known. However, the integration of fecundity data on coastal management actions remains overlooked. Here, we use fecundity of two exploited limpets (Patella ordinaria and P. aspera) to demonstrate its potential as a conservation tool to preserve the harvested populations of both species. From October 2021 to June 2022, 158 females of P. ordinaria and 70 of P. aspera were collected from the coastal rocky shores of the archipelago of Madeira (NE Atlantic Ocean). The fecundity in both species appears to be determinate, and estimated batch fecundity 365,638 ± 204,462 oocytes for P. ordinaria and 73,029 ± 43,496 oocytes for P. aspera. The presence of spawning individuals of both species until May is of significant relevance to their management and conservation. A harvest-ban (November-March) is currently implemented in the coastal governance actions of P. ordinaria and P. aspera. Based on the fecundity results, small adjustments can be made to further improve the conservation of adult individuals, which are important for the continuity of future generations. So far, fecundity data constitute an overlooked life trait of key importance to preserve populations of exploited species, primarily those with limited mobility such as semi-sessile littoral limpets.

Deep genetic divergences and geographic distribution of the red algal genus Caulacanthus (Gigartinales)

An increasing number of studies have demonstrated that genetic differentiation and cryptic diversity in the sea occur over considerably smaller spatial scales than previously comprehended, considering the wide distribution range of many morphologically defined macroalgal species. However, knowledge of the turf-forming red alga Caulacanthus is incomplete regarding its species diversity, as well as genetic differentiation within the genus. We analyzed Caulacanthus specimens from the NW Pacific, NE Pacific, Central Pacific, SW Pacific, SE Indian, NE Atlantic, and SE Atlantic Ocean using mitochondrial cytochrome oxidase subunit I (COI-5P), plastid ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL), and Rubisco spacer (rbcL-S). The objectives of this study were to 1) determine the number of species that exhibit the morphology of C. ustulatus, 2) investigate the present distribution pattern of Caulacanthus species, and 3) estimate the degree of genetic connectivity between the populations of Caulacanthus species from different regions. Our results revealed molecular evidence that the genus Caulacanthus comprises of at least seven species with deep genetic divergence, which is indicative of not only a strong geographical subdivision but also a relatively long temporal discontinuity. Most species exhibited limited geographic distribution, showing considerable genetic divergence in the populations isolated by distance. Our study provides evidence of a greater evolutionary independence of Caulacanthus populations, which have undergone a series of allopatric diversification events.

Characteristics of supersaturation in midlatitude cirrus clouds and their adjacent cloud-free air

Abstract. Water vapor measurements of midlatitude cirrus clouds, obtained by the WAter vapour Lidar Experiment in Space (WALES) lidar system during the Mid-Latitude Cirrus (ML-CIRRUS) airborne campaign, which took place in the spring of 2014 over central Europe and the NE Atlantic Ocean, are combined with model temperatures from the European Centre for Medium-Range Weather Forecasts (ECMWF) and analyzed. Our main focus is to derive the distribution and temporal evolution of humidity with respect to ice within cirrus clouds and in their adjacent cloud-free air. We find that 34.1 % of in-cloud data points are supersaturated with respect to ice. Supersaturation is also detected in 6.8 % of the cloud-free data points. When the probability density of the relative humidity over ice (RHi) is calculated with respect to temperature for the in-cloud data points from the ML-CIRRUS dataset, there are two peaks: one around 225 K and close to saturation, RHi = 100 %, and a second one at colder temperatures around 218 K in subsaturation, RHi = 79 %. These two regions seem to represent two cirrus cloud categories: in situ formed and liquid origin. Regarding their vertical structure, most clouds have higher supersaturations close to the cloud top and become subsaturated near the cloud bottom. Finally, we find that the vertical structure of RHi within the clouds is also indicative of their life stage. RHi skewness tends to go from positive to negative values as the cloud ages. RHi modes are close to saturation in young clouds, supersaturated in mature clouds and subsaturated in dissipating clouds.

Internal tidal sloshing and a non-linear wave source away from topography

The ocean-interior shows omnipresent internal wave motions whose importance becomes more and more acknowledged for deep mixing across the stable vertical density stratification for heat and suspended matter redistribution. To observationally study vertical propagation variations of internal tides away from a steep topographic slope, a >1-km long mooring with 760 high-resolution temperature sensors was deployed at 2380 m depth halfway Mount Josephine NE-Atlantic Ocean for 4 months. In the lower 150 m above the seafloor, internal waves slosh, become highly non-linear and break vigorously, every tidal cycle. After signal separation using semidiurnal band-pass and harmonic filters, the vertical phase propagation shows: 1. Phase differences of 90° are observed in isotherms and cross-slope currents over typically 600 m in the vertical, 2. Non-linearity is already found in harmonic records that describe 300-m large-scale internal tides, 3. Non-uniform thin-layer stratification causes about 50% of the semidiurnal variance in small-scales, 4. Upward internal tide propagation starts at the top of non-linear wave breaking, 5. Downward propagation from above leading to energy-focusing at 700 m above the ocean-floor and about 700 m below the nearest seamount-ridge generates interior hydraulic jumps during spring tide.

Commercial sharks under scrutiny: Baseline genetic distinctiveness supports structured populations of small-spotted catsharks in the Mediterranean Sea

The present study, based on microsatellite markers, describes a population genetic analysis of the small-spotted catshark Scyliorhinus canicula (Linnaeus, 1758), representing one of the most abundant and commonly caught cartilaginous fishes in the Mediterranean Sea and adjacent areas. The analyses were performed to unravel the genetic features (variability, connectivity, sex-biased dispersal) of their relative geographic populations, both at the small (around the coast of Sardinia, Western Mediterranean Sea) and at a larger spatial scale (pan-Mediterranean level and between the Atlantic Ocean and the Mediterranean Sea). Individual clustering, multivariate and variance analyses rejected the hypothesis of genetic homogeneity, with significant genetic differences mainly within the Mediterranean between the Western and Eastern basins, as well as between the Mediterranean and the NE Atlantic Ocean. In detail, our results seem to confirm that the Strait of Gibraltar could not represent a complete barrier to the exchange of individuals of small-spotted catshark between the Atlantic Ocean and the Mediterranean Sea. In the latter area, a complex genetic structuring for S. canicula was found. Apart from differences among the Western, Eastern and Adriatic sites, within the Western basin the small-spotted catsharks around Sardinian waters are strongly differentiated from all others (both from the eastern Tyrrhenian Sea and southernmost part of the Algerian basin) and are demographically stable. Several possible mechanisms, both biological and abiotic (e.g., migratory behavior, waterfronts, and oceanographic discontinuities), are discussed here to explain their peculiar characteristics. Overall, the genetic data presented, both at the local and regional level, could represent a baseline information, useful for the temporal monitoring of populations, and to assess the effects of present or future fishing/management/conservation measures.

Fecundity strategy of the highly exploited limpet Patella ordinaria from an oceanic archipelago

Limpet harvesting dates to the 15th century in Madeira archipelago (NE Atlantic Ocean). This activity is size-selective, removing older and larger individuals with greater commercial value. It can lead to a lower reproductive output as individual fecundity is size-dependent. The decrease of limpet populations has led to the implementation of a series of management measures including a closed season during the reproductive season (November–March). So far, sizes and the reproductive parameters, size and age at first maturity, have been previously used to determine the exploitation status of Patella ordinaria in Madeira archipelago, with no study performed on the reproductive strategy of this limpet. This is pivotal to comprehend the population dynamics of any species, being fecundity one of the reproduction parameters that should be analysed. This work aims to provide for the first time data on the fecundity of P. ordinaria. An average of 17 females per month were randomly collected over the spawning 2021/2022 season from the subtidal rocky shores of the Madeira archipelago. Four criteria were analysed over the spawning season: (i) the presence of a hiatus between pre- and vitellogenic oocytes; (ii) the number and (iii) mean size of advanced vitellogenic oocytes; and (iv) the incidence of atresia. A hiatus between pre- and vitellogenic oocytes across the spawning season was observed. An increasing trend in the number of vitellogenic oocytes was observed over the spawning season. The size of vitellogenic oocytes showed significant differences among months and the relative intensity of atresia varied from 7.86 to 20.79%. The information on the fecundity strategy leads to a better understanding of the reproductive capacity of this species. It also identifies the best approach for future estimations of relative annual fecundity estimations, with direct implications on the sustainable exploitation of this commercial species.

Seasonal occurrence and risk assessment of endocrine-disrupting compounds in Tagus estuary biota (NE Atlantic Ocean coast).

Estuaries are continually threatened by anthropogenic pressures, consequently, a large group of contaminants harmful to human health affects the aquatic biota; therefore, it is necessary to monitor their quality. This study deals with the determination of a large group of compounds representing different endocrine-disrupting compounds (EDCs) classes [21 pesticides, 4 polycyclic musk fragrances, 4 UV-filters, 7 bisphenols, 6 polybrominated diphenyl ethers (PBDEs) and 8 of their methoxylated (MeO-BDEs)] in several estuarine species (fish, bivalves, crustaceans, earthworm, and macroalgae) collected seasonally along one year in two distinct areas of Tagus River estuary ("contaminated" vs. "clean" areas). The most abundant compounds found were galaxolide (HHCB) (81% positive samples; 0.04-74ng/g ww), isoamyl 4-methoxycinnamate (IMC) (64%; 1.13-251ng/g ww), alachlor (44%; 0.08-16ng/g ww), and BDE-47 (36%; 0.06-2.26ng/g ww). Polycyclic musks were the most frequent contaminants in fish (seabass, barbus, mullet, and sole) and macroalgae samples, while UV-filters were predominant in bivalves and crustaceans, and bisphenols in earthworms. Seasonal variation was verified for Σpesticides and Σmusks, with significantly higher levels in summer and autumn, whereas ΣUV-filters highest levels were found in spring and summer, and for ΣPBDEs statistically higher levels were registered in cold seasons (autumn and winter). Σbisphenols were significantly lower in spring than in the other seasons. In general, considering all species analysed in both areas, no statistically significant differences (p>0.05) were verified between the two collection areas. Based on the estimated daily intake data, consumption of fish from this estuary is unlikely to be a human health concern, since the levels of contamination were below the toxicological threshold values. Overall, the data obtained in this study will allow regulatory authorities to identify and prioritize contaminants monitoring programs in estuaries, such as the case of bisphenol A, which was found, for the first time, in earthworm and clam species.

Molecular-level evidence of early lipid transformations throughout oceanic depths

Our understanding of lipid biogeochemistry of the ocean’s interior is still in its infancy. Here we focus on early lipid transformation and the formation of lipid degradation products in the NE Atlantic Ocean (49.0°N, 16.5°W). We employed high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), a method that allows observation and elemental composition assignment of thousands of lipids in a single sample. Using these data, we infer molecular-level changes that occur during lipid transformation in the oceanic water column to shed new light on early lipid transformation processes and the formation of lipid decomposition intermediates, here termed CHO compounds (i.e., lipid-derived species that contain carbon, hydrogen and oxygen in their molecular formula). We considered the distribution of molecular rings and/or double bonds (DBE), H/C and O/C ratios, molecular diversity based on the number of mass spectral signals for monoisotopic species, and carbon number in CHO molecules. Data are elaborated for the four ocean zones, the epipelagic, mesopelagic, bathypelagic and abyssal. The highest molecular diversity characterizes CHO compounds associated with the epipelagic zone, which is explained by numerous and diverse planktonic communities inhabiting the epipelagic and by the effects of both biotic and abiotic processes on lipid transformation. Lipid transformations include crosslinking (condensation), partial degradation or fragmentation, double bond reduction, oxidation, hydrogenation, dehydrogenation and cyclization. Crosslinking likely results in a unimodal distribution of carbon number of CHO compounds, in contrast to cell lipids (referred to as Reported lipids based on the Lipid Maps Database), which have a bimodal distribution of carbon number. CHO compounds that appear to be formed by fragmentation (decrease of the number of C atoms) and ring/double bond reduction were more stable to further transformation and remained longer in the water column, i.e., these compounds were transferred deeper into the water column. Low unsaturation and fast transport to depth promotes CHO compound preservation in the water column. Dehydrogenation leads to increased unsaturation (average DBE up to 21.3), condensation, and cyclization, resulting in high molecular weight compounds with a high degree of unsaturation. Our data demonstrate that lipids with cyclic structures are more refractory than those with acyclic structures. The formation of aromatic structures is not a significant process during early lipid transformation in the oceanic water column.

PAHs and trace metals in marine surficial sediments from the Porcupine Bank (NE Atlantic): A contribution to establishing background concentrations

Little is known about pollutant concentrations in marine remote areas such as the Porcupine Bank in the NE Atlantic Ocean. Remote locations are much less studied than the more readily accessible coastal areas, nevertheless, are of great importance both to unveil how far human influence has reached and, are more challenging, to infer background concentrations (BCs) of naturally occurring and/or anthropogenic pollutants. Knowledge of contaminant background levels are critical for establishing remediation and management strategies; in addition, background assessment is heavily emphasised in legislative monitoring requirements. Obtaining suitable sampling locations to assess background concentrations can be challenging, as samples should match characteristics to the target area and not be impacted by historical or current inputs of the chemical substances of study. Anthropogenic impacts generally deem local-based sampling to be unsuitable to infer background pollution values. Sampling in remote areas such as the Porcupine Bank better fulfils low impact and pressure requirements making them more suitable for the derivation of background concentration estimates for organic compounds and metals.The total concentrations of polycyclic aromatic hydrocarbons (PAHs) and metal(loid)s in deep sea sediments were evaluated and both an environmental status and a set of concentration data were adequate to derive BCs concentrations is presented. Concentration data indicated, in comparison with previous published data, trace level presence of PAHs and metal(loids) in sediments from the Porcupine Bank. These values will provide a valuable tool to identify the natural presence of organic and inorganic compounds and be the basis to perform a sound environmental assessment.

Interaction of marine heatwaves and grazing on two canopy-forming algae

Brown canopy-forming macroalgae species form complex assemblages known as marine forests, which are highly productive systems and provide multiple ecosystem services. In many regions worldwide, these key foundation species are being replaced by generalist species due to numerous underlying impacts acting at local, regional and global scales (i.e. overgrazing, marine heatwaves (MHWs), rising temperatures, among others). In Madeira Island (Macaronesia, NE Atlantic Ocean), rocky bottoms on the south coast are dominated by bare rocks, sediments and high densities of sea urchins and turfs. One of the most common macroalgae in these degraded systems is the cryptogenic red algae Asparagopsis taxiformis, naturally competing with other canopy-forming algae such as Cystoseira foeniculacea. In this study, we analysed 37-year high-resolution sea surface temperature data on the occurrence of MHWs in Macaronesia, finding a significant increase in the frequency of moderate and extreme events in the last 20 years. We performed a mesocosm experiment to understand how these two foundation species respond to heat stress and grazing activity by the sea urchin Paracentrotus lividus under different scenarios simulating moderate and extreme MHWs. Biomass and productivity of C. foeniculacea showed a significant reduction under the interaction of MHWs and grazing, with higher loss of biomass at the moderate event. The biomass of A. taxiformis decreased significantly by the increase in temperatures, independetly of the grazing pressure. The productivity of A. taxiformis was significantly reduced at extreme MHWs, where respiration rate was higher than C. foeniculacea, which outperformed in the dark phase. Results suggest that under control conditions and moderate MHWs, A. taxiformis is not impacted by grazing and is possibly more efficient in resource utilisation than C. foeniculacea, but losing this potential advantage under extreme MHWs. Under the context of future climate change, marine forests in Madeira are, thus, expected to be threatened by the combined effects of more common extreme climatic events (e.g. MHWs) and local changes in the biotic interactions (e.g. grazing and competition).