Northeast Atlantic Waters Research Articles

Microplastics in sea surface waters in the Southern Bight of the North Sea

Microplastic pollution in the marine environment is of concern, with evidence of harmful effects on marine biota and ecosystems. There is still a knowledge gap of the mass of plastics supplied to the ocean and plastics observed in the ocean, indicating a missing sink. Therefore, baseline and monitoring data are needed to inform policy and regulatory measures. The goal of this study was to collect harmonised data of microplastics from the surface of the ocean using the Neuston Microplastic Catamaran. This study shows that the surface water of the coastal ocean in the North Sea holds/sustains high concentrations of microplastic, which exceed previously recorded measurements from the North-East Atlantic and Scottish Waters, indicating that the total stock of plastics might be much higher than previously determined. Microplastics were detected in all samples with concentrations ranging from 857 to 25,462 items km−2. The majority of microplastics analysed were fragments of polyethylene, polypropylene, and polystyrene in the size range of 1,000–5,000 µm. Mesoplastics (>5,000 µm) mainly in the form of filaments were found with concentrations ranging from 0 to 2,139 items km−2, and macroplastics (>5,000 µm) in the form of fragments and filaments were also found with concentrations ranging from 0 to 1,078 items km−2. These fragments and filaments likely originate from the break-up of common macrolitter items in the environment, such as plastic bags, bottles, and fishing gears, which are commonly comprised of similar polymers to those found in the present study. Our findings demonstrate that litters of all size classes are abundant in surface water, highlighting that it is a key compartment for the transport of marine litter and should be monitored to better our understanding of the fate and danger of plastic contamination in our ocean.

Phytoplankton primary productivity: A dual‐incubation approach for direct comparison of photosystem II photosynthetic flux (JVPII) and 14C‐fixation experiments

AbstractSinge‐turnover active chlorophyll a fluorometry (STAF) can be used to assess phytoplankton photosynthetic rates in terms of the photosystem II photochemical flux (JVPII, μmol e− m−3 s−1) instantaneously, autonomously, and at high resolution. While JVPII provides an upper limit to rates of phytoplankton primary productivity in units of carbon fixation, the conversion between these two rates is variable, limiting our ability to utilize high‐resolution JVPII data to monitor phytoplankton primary productivity. Simultaneous measurements of JVPII and 14C‐fixation help in understanding the factors controlling the variable ratio between the two rates. However, to date, methodological inconsistencies, including differences in incubation lengths and light quality, have greatly inhibited practical assessment of such electron to carbon ratios (Φe,C, mol e− mol C−1). We here present data from a range of dual‐incubation experiments in northeast Atlantic waters during which JVPII and 14C‐fixation were measured simultaneously on the same sample. Time‐course experiments show how Φe,C increases with incubation length, likely reflecting the transition from gross to net 14C‐fixation. Dual‐incubation experiments conducted under different light levels show a tendency for increased Φe,C under (super‐)saturating light. Finally, data from a diurnal experiment demonstrate how Φe,C increases over the course of a day, due to downregulation of 14C‐fixation. We provide a detailed description of our methodological approach, including a critical discussion of improvements to the calculation of JVPII implemented in the LabSTAF instrument used for active fluorescence measurements and the limitations of the well‐established 14C‐fixation approach.

Microplastic pollution in the North-east Atlantic Ocean surface water: How the sampling approach influences the extent of the issue

A lack of standardization in monitoring protocols has hindered the accurate evaluation of microplastic (MP) pollution in the open sea and its potential impacts. As sampling techniques significantly influence the amounts of MPs contained in the sample, the aim of this study was to compare two sampling methods: Manta trawl (size selective approach) and grab sampling (volume selective approach). Both approaches were applied in the open sea surface waters of the North-east Atlantic Ocean. Onshore sample processing was carried out using the innovative tape lifting technique, which affords a series of advantages, including prevention of airborne contamination during analysis, without compromising integrity of the results. The results obtained indicated an MP concentration over four orders of magnitude higher using grab sampling compared to the Manta net approach (mean values equal to 0.24 and 4050 items/m3, respectively). Consequently, the sole quantification of MPs using results obtained with the Manta trawl resulted in a marked underestimation of abundance. Nevertheless, the grab sampling technique is intricately linked to a risk of collecting non-representative water volumes, consequently leading to an overestimation of MPs abundance and a significant inter-sample variability. Moreover, the latter method is unsuitable for use in sampling larger MPs or in areas with low concentrations of MP pollution. The optimal sampling method therefore is dependent on the specific objectives of the study, often resulting in a combination of size and volume selective methods. The results of this study have the potential to contribute to the standardization of monitoring protocols for microplastics, both during the sampling phase and sample processing.

Exploring Growth Patterns of Maurolicus muelleri across Three Northeast Atlantic Regions

Maurolicus muelleri is an important component of mesopelagic ecosystems; nevertheless, we possess only limited knowledge about its biological features. We collected samples of M. muelleri from six scientific surveys between 2019 and 2021 in three geographical areas in the Northeast Atlantic waters (from South to North): the Bay of Biscay, the Celtic Sea, and the Norwegian Sea. Geographical variations in otolith growth, fish age, length, weight, and condition, as well as length–weight relationships and von Bertalanffy growth models (VBGMs), were investigated. Length-weight relationships revealed differences associated with the fish’s origin, paralleling the annual and daily otolith growth. VBGM parameters increased progressively northwards, in accordance with Bergmann’s rules. Fish length was positively related to the otolith radio, and Lee’s phenomenon was undetected. The impact of environmental variables, such as temperature and food availability, is debated, with these considered potential drivers of this variability. Populations may belong to separated units, either genetically or morphologically, representing differences in biological parameters as a signal of geographical divergence.

Northeast Atlantic elasmobranch community on the move: Functional reorganization in response to climate change.

While spatial distribution shifts have been documented in many marine fishes under global change, the responses of elasmobranchs have rarely been studied, which may have led to an underestimation of their potential additional threats. Given their irreplaceable role in ecosystems and their high extinction risk, we used a 24-year time series (1997-2020) of scientific bottom trawl surveys to examine the effects of climate change on the spatial distribution of nine elasmobranch species within Northeast Atlantic waters. Using a hierarchical modeling of species communities, belonging to the joint species distribution models, we found that suitable habitats for four species increased on average by a factor of 1.6 and, for six species, shifted north-eastwards and/or to deeper waters over the past two decades. By integrating species traits, we showed changes in habitat suitability led to changes in the elasmobranchs trait composition. Moreover, communities shifted to deeper waters and their mean trophic level decreased. We also note an increase in the mean community size at maturity concurrent with a decrease in fecundity. Because skates and sharks are functionally unique and dangerously vulnerable to both climate change and fishing, we advocate for urgent considerations of species traits in management measures. Their use would make it better to identify species whose loss could have irreversible impacts in face of the myriad of anthropogenic threats.

A first ecological coherent assessment of eutrophication across the North-East Atlantic waters (2015–2020)

This paper presents the outcomes of the fourth application of the Common Procedure for the Identification of the Eutrophication Status of the OSPAR Maritime Area (the “Common Procedure”), conducted for the period 2015–2020 for the North East Atlantic. Previously, OSPAR has assessed eutrophication based on national assessment areas and disparate approaches lacking a transparent and comparable basis. A more harmonized approach has now been achieved through development of ecologically relevant assessment areas defined by oceanographic criteria rather than international boundaries, allowing for consistent assessments across exclusive economic zones and acknowledging that eutrophication is a transboundary problem. Thresholds that were specific for those harmonized assessment areas and eutrophication parameters have been derived primarily from an ensemble modeling approach to determine pre-eutrophic conditions. Common assessment areas and harmonized thresholds have enabled, for the first time, an objective and comparable assessment of the eutrophication status of the whole OSPAR Maritime Area. This establishes a level playing field for managing eutrophication and a solid basis for deriving OSPAR nutrient reduction targets as a prerequisite for targeted and successful regional eutrophication management. This assessment shows that eutrophication problem areas persist, in particular along the continental coasts from France to Denmark/Sweden and in the Greater North Sea and the Bay of Biscay and Iberian coast. The main areas affected by eutrophication are the plumes and adjacent coastal areas in the Greater North Sea and Bay of Biscay/Iberian Coast, with riverine nutrient inputs remaining the major source of nutrient pollution. Approximately 6% (152,904 km2) of the OSPAR Maritime Area is eutrophic, with the impacted area supporting many important ecosystem services. Fifty-eight percent of river plume areas (eight assessment areas out of 14), 22% (five of 27) of the coastal areas and 10% (three of 17) of the shelf areas were classified as problem areas. Application of the current assessment process to historical data from the previous three OSPAR assessment periods shows a gradual improvement since 2000. However, the OSPAR 2010 objective “to combat eutrophication, with the ultimate aim of achieving and maintaining a healthy marine environment where anthropogenic eutrophication does not occur” has not yet been fully achieved. Further measures to reduce nutrient loads are needed to ensure long-term sustainability of our coastal waters.

Circles in the sea: annual courtship "torus" behaviour of basking sharks Cetorhinus maximus identified in the eastern North Atlantic Ocean.

Groups of basking sharks engaged in circling behaviour are rarely observed, and their function remains enigmatic in the absence of detailed observations. Here, underwater and aerial video recordings of multiple circling groups of basking sharks during late summer (August and September 2016-2021) in the eastern North Atlantic Ocean showed groups numbering between 6 and 23 non-feeding individuals of both sexes. Sharks swam slowly in a rotating "torus" (diameter range: 17-39 m), with individuals layered vertically from the surface to a maximum depth of 16 m. Within a torus, sharks engaged in close-following, echelon, close-flank approach or parallel-swimming behaviours. Measured shark total body lengths were 5.4-9.5m (mean LT : 7.3m ± 0.9s.d.; median: 7.2m, n= 27), overlapping known lengths of sexually mature males and females. Males possessed large claspers with abrasions that were also observed on female pectoral fins. Female body colouration was paler than that of males, similar to colour changes observed during courtship and mating in other shark species. Individuals associated with most other members rapidly (within minutes), indicating toroidal behaviours facilitate multiple interactions. Sharks interacted through fin-fin and fin-body contacts, rolling to expose the ventral surfaces to following sharks, and breaching behaviour. Toruses formed in late summer when feeding aggregations in zooplankton-rich thermal fronts switched to non-feeding following and circling behaviours. Collectively, the observations explain a courtship function for toruses. This study highlights northeast Atlantic coastal waters as a critical habitat supporting courtship reproductive behaviour of endangered basking sharks, the first such habitat identified for this species globally.

Marine Debris Floating in Arctic and Temperate Northeast Atlantic Waters

Floating marine debris is ubiquitous in marine environments but knowledge about quantities in remote regions is still limited. Here, we present the results of an extensive survey of floating marine debris by experts, trained scientists from fields other than pollution or non-professional citizen scientists. A total of 276 visual ship-based surveys were conducted between 2015 and 2020 in the Northeast (NE) Atlantic from waters off the Iberian Peninsula to the Central Arctic, however, with a focus on Arctic waters. Spatiotemporal variations among regional seas (Central Arctic, Barents Sea, Greenland Sea, Norwegian Sea, North Sea) and oceanic regions (Arctic waters and the temperate NE Atlantic) were explored. The overall median debris concentration was 11 items km-2, with considerable variability. The median concentration was highest in the North Sea with 19 items km-2. The Nordic seas, except the Central Arctic showed median concentrations ranging from 9 to 13 items km-2. Plastic accounted for 91% of all floating items. Miscellaneous fragments, films, ropes and nets, packaging materials, expanded polystyrene and straps were the most frequently observed plastic types. Although the median debris concentration in the Central Arctic was zero, this region was not entirely free of floating debris. The variations between regional seas and oceanic regions were statistically not significant indicating a continuous supply by a northward transportation of floating debris. The data show a slight annual decrease and clear seasonal differences in debris concentrations with higher levels observed during summer. A correlation between debris concentrations and environmental and spatial variables was found, explaining partly the variability in the observations. Pollution levels were 500 times lower than those recorded on the seafloor indicating the seafloor as a sink for marine debris. The Arctic was characterised by similar pollution levels as regions in temperate latitudes highlighting that Arctic ecosystems face threats from plastic pollution, which add to the effects of rapid climate change.

Morphometric and molecular characterization of Kudoa encrasicoli n. sp. (Myxozoa: Myxosporea) from the European anchovy, Engraulis encrasicolus (L.) (Clupeiformes: Engraulidae)

The European anchovy represents the main fisheries for countries in the Mediterranean and Black Sea basins. The skeletal muscle of 13 of 48 (27.1%) Engraulis encrasicolus (L.) specimens from North East Atlantic waters (FAO 27.8.c) was found infected with interfibrillar elongated plasmodia (130-980 µm in length) containing mature myxospores belonging to the genus Kudoa Meglitsch, 1947. No flesh softening was found associated with infection. Fresh myxospores were 10.8 ± 0.7 (9.1-12.3) µm in width 1, 11.3 ± 0.9 (9.5-13.4) µm in width 2, 6.7 ± 0.4 (5.8-7.4) µm in thickness, and 6.9 ± 0.5 (5.8-7.5) µm in length. They were almost stellate in apical view having three pointed-edged shell valves bearing three small polar capsules equal in size 5.0 ± 0.3 (4.4-5.4) μm long and 2.4 ± 0.2 (2.0-3.0) μm wide, and one rounded- to rarely bluntly pointed-edged shell valve bearing a large and particularly wide polar capsule 6.8 ± 0.4 (5.9-7.6) μm long and 4.1 ± 0.2 (3.6-4.4) μm wide. Morphological and morphometrical comparisons between these myxospores and those of Kudoa thyrsites (Gilchrist, 1923) from the clupeid Sardina pilchardus (Walbaum) (North East Atlantic waters, FAO 27.9.a), with which exhibited a similarity of 98.9% and 96.2% using SSU and LSU rDNA sequences, respectively, support the creation of Kudoa encrasicolin. sp. Morphometrical analysis of the polar capsules of flattened myxospores is suggested as a useful approach to differentiate phylogenetically related kudoids with stellate or almost stellate myxospores bearing four polar capsules.

A Novel Detection Refinement Technique for Accurate Identification of Nephrops norvegicus Burrows in Underwater Imagery.

With the evolution of the convolutional neural network (CNN), object detection in the underwater environment has gained a lot of attention. However, due to the complex nature of the underwater environment, generic CNN-based object detectors still face challenges in underwater object detection. These challenges include image blurring, texture distortion, color shift, and scale variation, which result in low precision and recall rates. To tackle this challenge, we propose a detection refinement algorithm based on spatial–temporal analysis to improve the performance of generic detectors by suppressing the false positives and recovering the missed detections in underwater videos. In the proposed work, we use state-of-the-art deep neural networks such as Inception, ResNet50, and ResNet101 to automatically classify and detect the Norway lobster Nephrops norvegicus burrows from underwater videos. Nephrops is one of the most important commercial species in Northeast Atlantic waters, and it lives in burrow systems that it builds itself on muddy bottoms. To evaluate the performance of proposed framework, we collected the data from the Gulf of Cadiz. From experiment results, we demonstrate that the proposed framework effectively suppresses false positives and recovers missed detections obtained from generic detectors. The mean average precision (mAP) gained a 10% increase with the proposed refinement technique.

Anisakid Nematodes and Potential Risk of Human Anisakiasis through the Consumption of Hake, Merluccius spp., Sold Fresh in Spanish Supermarkets

Nematode parasite species belonging to the Anisakis simplex complex are the most important cause of human anisakiasis through the consumption of (mainly) undercooked, previously not frozen, or conveniently treated fish. In Spain, the consumption of hake has been recognized as an important source of this parasitosis. With the aim of shedding light on the risk factors that can influence the potential risk of human anisakiasis in Spain through the consumption of fresh hake sold by nationwide supermarket chains, a total of 536 small hake specimens belonging to the species Merluccius bilinearis caught off the Northeast American coasts and Merluccius merluccius caught in the Northeast Atlantic and Mediterranean waters was analysed. Anisakids morphologically identified as Anisakis type I were found as the most prevalent and the most abundant species and were considered the main potential cause of human anisakiasis. Intrinsic and extrinsic factors concerning the hake, such as its origin and season of capture, its size, as well as the days passed between its capture and consumption, should be taken into account to avoid this human parasitosis. It is essential that consumers have access to fish label information which should include, as regulated by the European Commission, traceability data.

Effects of season, bottom substrate and population dynamics on fish communities in shallow subarctic northeast Atlantic waters

Fish communities in the shallow waters (9–20 m depth) of outer Malangen (69o N), Northern Norway was studied to investigate effects of season, bottom substrate associations and population dynamic parameters on the fish assemblages. In four fieldtrips during one year at four locations, fish were sampled by trammel nets and bottom substrate composition was monitored by underwater video. A total of 16 species of fish were caught, including four species from Pleuronectidae and six from the Gadidae family. Cod (Gadus morhua Linnaeus, 1758) was the most numerous species followed by plaice (Pleuronectes platessa Linnaeus, 1758), lemon sole (Microstomus kitt Walbaum, 1792) and halibut (Hippoglossus hippoglossus Linnaeus, 1758). Cod dominated the catches in all months except March, in which plaice and other flatfishes were most dominant. On a community scale, fish species richness was highest in October and lowest in March. Furthermore, the species richness and diversity were generally higher at locations with greater bottom substrate evenness. Cod showed a positive association with large macroalgae coverage and were less numerous at locations dominated by sand and pebble. Plaice and common dab (Limanda limanda Linnaeus, 1758) showed positive associations with sand and pebble coverage, while lemon sole was more associated with maerl beds, cobble and low algae coverage. Only halibut younger than 8 years of age were observed, and the sampling areas are suggested to be nursery area for this species. Von Bertalanffy growth functions were estimated for cod, plaice and lemon sole, and the growth coefficient K of cod and plaice were higher than for populations from adjacent fjords or the North Sea populations. Total mortality rates of cod and plaice were lower than for areas further south, and this may contribute to high and relative stable biomasses in the shallow Malangen area.

Distribution of Cetaceans in the Canary Islands (Northeast Atlantic Ocean): Implications for the Natura 2000 Network and Future Conservation Measures

The waters of the Canary Islands are considered a hotspot for marine biodiversity, especially regarding cetacean species. Based on this fact, this study pays attention to the spatial distribution pattern of cetacean species and the conservation role of the Natura 2000 Network, a set of Special Areas of Conservation (SACs), which were defined mainly based on data compiled in 1996, under the framework of the European Habitats Directive. In recent years, the declaration of conservation areas for cetaceans between the Tenerife—La Gomera Islands by two global conservation programs, Mission Blue (“Hope Spots”) and Whale Heritage Site (“Whale Sanctuary”) sent clear signals of scientific and social interest to promote better protection of the cetacean species in the Canary Islands. The main aim of the designated SACs is the conservation of its biological and ecological diversity, ensuring the long-term survival of the target species in the waters around islands. In this case, the enactment of the SACs was based only on the sparse data available for the common bottlenose dolphin,Tursiops truncatus. This study shows that the spatial distribution of cetaceans in the Canary archipelago generated from a large database of cetacean sightings, from 2007 to 2018. The results obtained show the main marine areas where the different cetacean species are distributed around the different islands of the archipelago. The spatial distribution maps of the cetacean species, when compared with the existing SACs of the Natura 2000, show the need to extend these SACs into the open sea to include more cetacean species and a larger number of individuals for better conservation of the endangered marine mammals. As a consequence, some suggestions were proposed to improve and update the role of SACs in European Northeast Atlantic waters as a key environmental tool for cetacean conservation. The data supporting the recent declarations of these two new milestones the “Hope Spot” and the “Whale Sanctuary” enhance more keystone information to promote a large marine protected area in the Eastern Atlantic Ocean, such as the “Macaronesian Biodiversity and Ecological Migration Corridor for Cetaceans,” a conservation figure that has been already proposed in the scientific literature as a deserving candidate of governmental regulations and policies by Portugal and Spain; it would also require joint cross-border cooperation efforts for marine spatial planning.

Living on the edge: Overlap between a marine predator’s habitat use and fisheries in the Northeast Atlantic waters (NW Spain)

The impact of commercial fisheries on marine top predators is currently the focus of considerable international concern. In spite of the recognition of the competition between fisheries and marine predators for the same resources, few comprehensive assessments of the level of overlap between marine predators and fisheries have been conducted. Data from 273 daily boat surveys over a period of 4 years along the northwestern coast of Spain were used to assess the environmental, topographic, and anthropogenic correlates of habitat use and relative density of short-beaked common dolphins. Moreover, the degree of vulnerability of this marine top predator to coastal fisheries was assessed by identifying the type of fisheries associated with the presence of common dolphins. Our results reported that common dolphin presents a fine-scale pattern of habitat use, with an unequal use of available habitat and varying relative abundance, which was mostly related to the variation in environmental, topographic, and anthropogenic variables. The high occurrence of common dolphins in zones characterized by a high bottom trawl fishing pressure was indirectly linked to the susceptibility of these marine predators to fishing activities. These findings can be used as a relevant indicator of the degree of vulnerability of common dolphins to human pressure providing comprehensive information on which to base conservation and management strategies.

The resilience and sensitivity of Northeast Atlantic deep water εNd to overprinting by detrital fluxes over the past 30,000 years

The neodymium isotope proxy has become a valuable tool for the reconstruction of past ocean water mass provenance and mixing. For its accurate application, knowledge about the origin and preservation of Nd in sedimentary archives is crucial. Recently, concerns have emerged regarding the applicability of neodymium isotopes as a conservative palaeo water mass tracer, given potential Nd fluxes from sediments into bottom waters (Abbott et al., 2015a) and inferred relabelling of ocean waters by settling detrital material (Roberts and Piotrowski, 2015). Consequently, a decoupling of water mass provenance and proxy variations may arise. We investigate the mobility of Nd around extreme detrital sedimentation events such as glacial ice rafting pulses and turbidite deposition in the Northeast Atlantic. The constructed records from sediment leachates span extreme Nd isotope variations including volcanic (εNd ∼ 0) and Laurentian (εNd ∼ −27) sources. We find that Nd was released into pore waters from reactive detritus inside some detrital layers during early diagenesis, thereby overprinting any archived bottom water Nd signature and precluding the reconstruction of past water mass provenance during the affected time intervals. However, we do not observe any definite indication of diffusive vertical migration of Nd into adjacent layers. Furthermore, bottom water Nd isotope signatures were not modified to a measurable degree by any potential benthic flux of Nd during the deposition of these detrital sediment layers. Consequently, the Nd isotope composition of the pelagic glacial Northeast Atlantic water masses were resilient to such episodic large detrital fluxes.Apart from extreme local sedimentation events, we confirm the presence of detritally overprinted deep waters north of 47°N during the peak glacial from comparison of Northeast Atlantic depth transects. We furthermore suggest that the sensitivity of deep waters to this overprinting effect increased during periods of reduced Atlantic Meridional Overturning Circulation and elevated ice rafting.Overall, our study demonstrates that a thorough evaluation of the proportion of Nd originating from physical water mass advection versus in situ chemical inputs is crucial for the reliable application of Nd isotopes as a water mass tracer.

Anisakis species composition and infection characteristics in Atlantic mackerel, Scomber scombrus, from major European fishing grounds — reflecting changing fish host distribution and migration pattern

Atlantic mackerel (Scomber scombrus) ranks among the most valuable fish species in Europe. The NE Atlantic mackerel population is considered to comprise three main stocks (southern, western and North Sea), with variable proportions of these three intermixing at the northerly feeding grounds. The southern and western mackerel stocks have moved over the past 4–5 years further north- and westward. Consequently, large-scale mackerel fishing and processing have become thriving industries in Iceland and the Faroe Islands in just a few years. The mackerel population structure in the Mediterranean Sea is less well known but seems to comprise at least one, more or less isolated, spawning component. Although mackerel is an important food resource, systematic and concerted epidemiological surveys of Anisakis species in Atlantic mackerel from European fishing grounds have been lacking. As part of the EU FP7 PARASITE project (GA no. 312068), occurrence and specific identity of Anisakis spp. from 1801 mackerel from Northeast Atlantic and Mediterranean waters was investigated. In general, mackerel caught at the Atlantic fishing grounds exhibited markedly higher Anisakis spp. infection levels than fish from the Mediterranean localities. Mackerel caught off NW Spain and Portugal (ICES VIIIc, IXa) showed highest overall and muscular prevalence, reaching 87% and 52%, respectively, which differed significantly from all other Atlantic samples. Lowest overall Anisakis spp. prevalence and abundance was recorded in mackerel from Faroe Isles waters, while lowest muscular infection levels were found in the samples from the North Sea. Genetic nematode species identification showed that A. simplex (sensu stricto) is the dominating species in mackerel from the Atlantic areas, while A. pegreffii dominated in the samples from the Mediterranean Sea. The latter species showed generally low prevalence and intensity in the flesh, not exceeding 6% and one larva, respectively. While A. simplex (s. s.) and A. pegreffii seem to co-occur in mackerel from off NW Spain and Portugal, several A. pegreffii were also recorded in mackerel from the North- and Norwegian Seas. These findings imply that the actual mackerel started their feeding migration in waters south to the British Isles, which include parts of the sympatric area of the two sibling species. Thus, A. pegreffii could prove a useful supplementary marker to track migration routes of the different mackerel stock components in NE Atlantic waters.

Metazoan parasite communities in Alosa alosa (Linnaeus, 1758) and Alosa fallax (Lacépède, 1803) (Clupeidae) from North-East Atlantic coastal waters and connected rivers

Metazoan parasites were studied in 96 Alosa alosa and 78 Alosa fallax from North-East Atlantic coastal waters and connected rivers (among them three sympatric sites) in order to increase knowledge on these anadromous endangered fish and measure the parasitic impact on host condition. All shads were infected by one to six metazoan parasite taxa among the 12 identified in the whole sampling, with a mean abundance of parasites higher for A. alosa (167±10) than for A. fallax (112±11). Helminths, mostly trophically transmitted, were the best represented (eight taxa, prevalence up to 99%) in contrast with crustaceans and Petromyzontidae that rarely occurred (four taxa, prevalence <6%). Despite some quantitative differences, metazoan parasite communities of A. alosa and A. fallax remained stable in composition whatever the host developmental stage, sex, sample site, and salinity. Among the nine parasite taxa harbored by each Alosa species, six were shared with some differences in distribution patterns including in sympatric conditions, suggesting increasing dissimilarities between A. alosa and A. fallax with the age. Information on feeding ecology provided by trophically transmitted helminths confirmed euryphagous opportunistic diet of immatures and adults of both shad species, and assessed feeding of adults during spawning migrations. Our study also revealed the significant negative impact of Hemiurus appendiculatus on A. alosa and Pronoprymna ventricosa on A. fallax. Because helminth parasites are omnipresent in the shads and decrease their fitness, parasitological data must be included in further investigations and management programs on A. alosa and A. fallax.

The trophic structure of Spongosorites coralliophaga-coral rubble communities at two northeast Atlantic cold water coral reefs

ABSTRACTWe examined the isotopic signatures (δ13C, δ15N) of fauna living in association with the sponge Spongosorites coralliophaga colonizing coral rubble on cold-water coral reefs in the northeast Atlantic – the shallow inshore (122–131 m collection depth) Mingulay 01 area and the deep offshore (683–800 m) Logachev 02 mound. The δ15N signatures of suspended particulate organic matter and three primary consumers, i.e. Spongosorites coralliophaga, Reteporella beaniana and Parazoanthus anguicomus were used as trophic baselines and the resulting trophic structure was compared. In both regions four trophic levels were distinguished. However, the use of S. coralliophaga or R. beaniana as baselines resulted in a skewed trophic structure due to the enriched δ15Ν signatures of these two species on the Logachev 02 mound. Using suspended particulate organic matter and P. anguicomus as baselines, the Mingulay 01 area communities were characterized by elevated relative biomass of lower trophic levels compared to the Logachev 02 mound. Relative biomass of suspension/filter feeders was also higher at the Mingulay 01 area. The two regions differed significantly with regard to the prevailing environmental conditions: apart from the difference in depth and distance from shore, the Mingulay 01 area was characterized by higher primary production in surface waters, tight pelagic–benthic coupling and higher velocity of bottom currents, and it is hypothesized that these characteristics were the main drivers of the observed differences. This study highlighted that multiple trophic baselines can provide a better interpretation of food-web structure and that the use of sponges or bryozoans as baselines across bathymetric gradients should be avoided.

Chaetozone corona (Polychaeta, Cirratulidae) in the Bay of Biscay: a new alien species for the North-east Atlantic waters?

The cirratulid species Chaetozone corona is reported for the first time from the North-east Atlantic waters. Several specimens were collected during oceanographic surveys between 1996 and 2015 from soft bottom habitats along the coasts of Brittany (Western France). This species, originally described from the coast of California, was recently recorded for the first time from the Mediterranean Sea. We hypothesize that this species could have been recently introduced to the Atlantic coasts of Europe and colonized the northern coast of Bay of Biscay from the Loire estuary to the Iroise Sea. We discuss the potential vectors of introduction and the main environmental factors that could explain its current distribution. An identification key to all the known North-east Atlantic species of Chaetozone is given.

Spatial distribution and impact of the gill-parasitic Mazocraes alosae (Monogenea Polyopisthocotylea) on Alosa alosa and A. fallax (Actinopterygii, Clupeidae)

Are the distribution of Mazocraes alosae and its impact on the host similar between Alosa alosa and A. fallax according to their resemblances? Parasites were numbered on each gill of shads sampled in North-East Atlantic coastal waters and connected rivers. Their impact on host condition was measured using girth, gonado-somatic ratio, C/N ratio, and Fulton’s K. Prevalence and mean intensity of M. alosae were significantly higher for A. alosa than for A. fallax, including in sympatric conditions. The mean intensity varied among sites whatever fish species; it was higher in coastal–estuarine versus fresh waters only for A. fallax. The distribution of M. alosae was aggregated in the host population whatever species. At the host individual level, some gills (second and third for A. alosa, second for A. fallax) were significantly more inhabited than others, probably in relation with larger water volumes flowing on these gills and mazocraeid sedentary lifestyle. Despite high prevalence and intensity, no negative impact of M. alosae was demonstrated on the host condition whatever the index considered. Our study underlines the major occurrence of M. alosae on shads and the potential use of such benign parasite as biological tag to discriminate closely related host species.