The predation of mysids by fish of the Rockall Trough,northeastern Atlantic Ocean

The stomach contents of representatives of approximately 100 species of pelagic and demersal fish caught in the Rockall Trough, northeastern Atlantic ocean, have been examined for the occurrence of mysids. More than 40 species of fish included mysids in their diets. The majority of the 21 species of mysids identified in the stomachs live in close association with the sediment and are rarely caught in pelagic nets. Mysids contributed significantly to the diets of many demersal fish but were not apparently important constituents of the food of pelagic fish.     

Incidence of parasitic worms in stomachs of pelagic and demersal fish of the Rockall Trough, northeastern Atlantic Ocean

The incidence of gyrocotyllid worms in chimaeroids and cestode larvae and nematodes in the stomachs of some 13 600 demersal and pelagic fish from the Rockall Trough, northeastern Atlantic is determined. The observations were made in conjunction with a detailed study of the diets of the fish which belonged to 117 species. No dietary sources of the infections could be identified with certainty. Pelagically caught fish, from between the surface and 2500 m depth, had no helminth infestation of their stomachs. Infestations of demersal fish were more pronounced between 1500 and 2900 m than between 500 and 1250 m depth.     

Morphology and sedimentology of (clustered) cold-water coral mounds at the south Rockall Trough margins,NE Atlantic Ocean

Cold-water coral mounds on both margins of the Rockall Trough (NE Atlantic Ocean) have a strongly different morphology. Single, isolated mounds occur on the SE margin and are mainly found on the upper slope between 900 and 650 m water depth, while large mound clusters are found on the SW margin in water depths between 600 and 1,000 m, in a narrow zone almost parallel to the slope. Sedimentation rates on the mounds are higher than on the surrounding seabed as a result of baffling of biogenic carbonate debris and siliciclastic particles by the coral framework covering the mounds. This is confirmed by ²¹⁰Pb measurements. The individual coral growth rate can be three times higher then the vertical growth rate of the coral cover (±10 mm year⁻¹) which in turn is more than an order of magnitude higher then the present-day overall mound growth rate (±0.25 mm year⁻¹). The presence of extensive hardgrounds and firmgrounds and the three-dimensional coral framework are considered to be responsible for the stability of the relatively steep slopes of the mounds. High current velocities in the intramound areas result in local non-sedimentation and erosion, as is shown by the presence of IRD (ice-rafted debris) lag deposits on the seabed and moats around some of the mounds. The morphology and sedimentology of cold-water coral-covered (mainly Lophelia pertusa and Madrepora oculata) mounds on the southern Rockall Trough margins (NE Atlantic Ocean) is discussed and a model describing the development of these mounds is presented.     

Benthic foraminifera associated with a hydrocarbon seep in the Rockall Trough (NE Atlantic)

Recent benthic foraminiferal assemblages in surface sediments of the Rockall Trough (NE Atlantic) have been qualitatively and quantitatively studied in order to investigate the effects of hydrocarbon seepage on benthic foraminiferal populations. Species diversity and abundance data have been examined in samples of similar lithology collected from hydrocarbon seep and non-seep (control) areas at a water depth of about 1000 m. Three species groups with different environmental preferences can be recognized. Group 1 dominates seep samples, and includes species tolerant to hydrocarbon emission, especially Angulogerina bradyana. In contrast, the less tolerant Group 2 species are weakly represented at seeps but dominate control samples. Group 3 species occur in low frequencies in both seep and non-seep samples. Furthermore, the measurement of species diversity (Shannon-Wiener and Simpson indices) demonstrates a difference in foraminiferal occurrence and frequencies between the seep and non-seep sites. Thus, the benthic foraminiferal distribution pattern is guided by different sensitivities of the species to hydrocarbons, reduced bottom-water oxygen usually associated with seepage and/or to a relatively elevated organic matter content in the sediment.     

The deep-water pycnogonids (Arthropoda: Pycnogonida) of the northeastern Atlantic Ocean

Over 2000 specimens of pycnogonid from deep-sea collections made in the northeastern Atlantic Ocean by IOS and SMBA between 1971 and 1994 have been analysed. Thirty-five species were identified, two being new to science, viz Nymphon akanthochoeros and an unnamed Anoplodactylus species. The deep-sea Pycnogonida of the northeastern Atlantic are reviewed using these data and records from the literature. Keys are presented for the six families represented by more than one species. The pycnogonid fauna of this area is characterized particularly by Paranymphon spinosum and Colossendeis clavata , with other dominant species including Colossendeis species, notably C. macenima , and Nymphon laterospinum, Anoplodactylus typhlops and A. arnaudae. Of the 54 species recorded below 200 m in the northeastern Atlantic, available evidence suggests that nine are 'endemic'. Relative distributions of the other species are discussed. A distinct change in the pycnogonid fauna with depth was found at around 1400 m. There is latitudinal separation of species groupings, shown most conspicuously by the shallower water species.     

Maturity, oocyte dynamics and fecundity of the roundnose grenadier from the Rockall Trough

The reproductive biology of roundnose grenadier Coryphaenoides rupestris was investigated against a background of increasing commercial exploitation. Samples were taken from surveys carried out in Rockall Trough between 1993 and 1995. An eight-point maturity scale was developed based on both visual inspection of the ovaries and histological screening. The various stages of development of roundnose grenadier oocytes were described and the relative proportion of oocyte types and their respective size range in each maturity stage were investigated. The dynamic organization of the ovary indicated a determinate maturation cycle in this species. Population spawning appears to be prolonged, extending from July to at least November. However, data were insufficient to clarify individual spawning duration. The potential fecundity of 29 mature fish ranged from 11 083-55 175 (63-95 cm total length). The results were very similar to previous values from the North Atlantic. The reproductive strategy of the roundnose grenadier is discussed in the light of the current commercial exploitation of the Species.     

A comparison of the deep-water demersal fish assemblages of the Rockall Trough and Porcupine Seabight, eastern North Atlantic: continental slope to rise

Fishery surveys of the continental slope to the west of the British Isles have shown quite marked differences between areas in both the proportion and abundance of marketable or potentially marketable species. In general, the northern slopes lying to the west of Scotland were considered to have a greater potential for exploitation than the southern slopes off Ireland. Subsequent detailed studies of a northern (Rockall Trough) and a southern slope area (Porcupine Seabight) sampled the demersal fish fauna using a Granton trawl fished on paired warps to depths of 1200 m, and a semi-balloon trawl fished on a single warp to depths of about 3000 m. The Granton trawl catches differed significantly between the two areas, especially at the greatest depths fished. The semi-balloon trawl catches did not differ between the areas. This slower trawl was poor at catching large, mobile species and efficient in the capture of the deep-waler eel Synaphobranchus kaupi. This eel was numerically dominant over the mid to lower slope and probably accounts for much of the similarity between areas at these depths.     

Pelagic-benthic coupling of nucleic acids in an abyssal location of the northeastern Atlantic Ocean.

Spatial and temporal changes in sedimentary nucleic acid concentrations in an abyssal locality of the northeastern Atlantic Ocean were investigated in relation to fluxes of nucleic acids produced in the photic layer. Sediment trap material, collected between 1996 and 1998 at depths of 1,000, 3,000, and 4,700 m, and sediment samples were analyzed for DNA and RNA content. Nucleic acid concentrations in the sediments were very high and displayed significant temporal changes, whereas mesoscale variability was low. DNA and RNA concentrations generally displayed opposite temporal patterns, which are likely to be dependent on the nature and characteristics of DNA and RNA molecules. Nucleic acid fluxes were high and displayed clear seasonal changes apparently coupled with seasonal pulses of primary production. However, while median values of DNA fluxes were relatively similar in all sediment traps, median values of RNA fluxes almost doubled from the 1,000- to the 4,700-m depth, suggesting differences in the metabolic activity of microbes associated with sinking particles. Significant relationships between DNA concentrations in the sediments and DNA fluxes and between RNA concentrations and RNA fluxes, indicating the presence of a clear pelagic-benthic coupling of particulate nucleic acids, were observed. The benthic system investigated was not steady state since we estimated that, from September 1996 to October 1998, nucleic acid concentration in the sediments decreased by about 165 mg of DNA m(-2). Vertical profiles revealed a significant decrease in DNA concentration with depth in the sediments, reaching an asymptotic value of about 5 microg g(-1). This DNA fraction constitutes a pool of potentially refractory DNA (accounting for 16 to 40% of the total DNA pool) that might be buried in the sediments.     

Occurrence of stones, sediment and fish scales in stomach contents of demersal fish of the Rockall Trough

The occurrence of stones, sediment and fish scales was determined among the stomach contents of some 5000 fish. These fish comprised representatives of more than 70 different demersal species, sampled at 250 m bathymetric intervals, from the Rockall Trough, northeastern Atlantic Ocean, at depths ranging from 500 to 2900 m. Stones only occurred in stomachs of fish caught at 500–1000 m depth, their incidence in stomachs with food present being 4.6% at 500m, 1.1% at 750 m and 1.3% at 1000m depth. Sediment occurred in 9%, fish scales in 7%, of stomachs with contents. Sediment and scales co-occurred in the stomachs of primarily benthopelagic feeding fish. The sediment, however, was associated with the less dominant epibenthic components of the diets while the scales occurred with the more common benthopelagic components. The co-occurrence of sediment, scales and benthopelagic prey may arise through the former items having longer residence times in the stomachs than, for example, epibenthic prey. There is no evidence of increased occurrence of sediment (and its associated meiofauna) in the diets of fish on the lower slope at depths of 1500–2900 m in the Rockall Trough.     

A long-finned specimen of Beryx decadactylus caught in the North-eastern Atlantic of Rockall

A long-finned specimen of Beryx decadactylus from of Rockall is reported and the Northeastern Atlantic persistence of juvenile characters in subadult and adult fish is discussed.     

Catch and discards from experimental trawl and longline fishing in the deep water of the Rockall Trough

Comparative bottom trawl and longline surveys were carried out on two chartered commercial fishing vessels in the deep waters (350-1300 m) of the Rockall Trough, an area subjected to heavy commercial exploitation. The species composition, catch rates and length distributions from each survey were very different and reflected the fundamental difference in the two types of fishing operations. Bottom-trawled catches produced greater species diversity and higher discard rates. Longline catches produced larger specimens of teleost fish and were dominated by squalid shark. Trawl discards, expressed as kgs of discards per tonne of roundnose grenadier Coryphaenoides rupestris landed, were calculated for a broad range of the most abundant species taken in the catch. First estimates of total international discarding from deep-water trawling operations in the Rockall Trough area (7530 tonnes; 26.5 million individuals) were made by raising the discard rates using international grenadier landings for 1995. The outlook for the continued exploitation of the deep-water fish resource in the Rockall Trough and possible management options are discussed.     

Six captures of a dark-rumped, fork-tailed storm-petrel in the northeastern Atlantic

We report here the occurrence of at least six records since 1983 of dark-rumped and fork-tailed Storm-petrels. The first one was attributed to the Swinhoe's Storm-petrel Oceanodroma monorhis , a subspecies or a close relative of Leach's Storm-petrel O. leucorhoa , breeding in Japan. As it seemed unlikely that six birds from Japan would appear in the northeastern Atlantic nearly simultaneously, a closer examination of measurements and calls was performed. However, after a careful study of systematics within the Leach's Storm-petrel complex, it is concluded that the European birds are inseparable from monorhis , and it is suggested that a yet undiscovered colony may exist in the North Atlantic.     

The reproductive biology of two deep-water,reef-building scleractinians from the NE Atlantic Ocean

The reproductive ecology of colonies of Lophelia pertusa (Linné 1758) and Madrepora oculata Linné (1758) from the Porcupine Seabight (Thérèse Mound and South Porcupine Seabight site) and the Darwin Mounds (NE Rockall Trough—L. pertusa only) was investigated using histological techniques. Samples of L. pertusa exhibited seasonal reproduction, whereas the evidence for M. oculata is equivocal but suggests multiple cohorts of gamete production. L. pertusa produces a single cohort of around 3,000 oocytes, whereas M. oculata produces two cohorts, with a total fecundity of around 60 oocytes. The maximum observed oocyte size in L. pertusa was 140 μm and in M. oculata was 405 μm. From these oocyte sizes and the timing of reproduction, a lecithotrophic larva is expected, though not observed. This seasonality of reproduction fits with the phytodetrital food fall occurring around July in the Seabight area. L. pertusa was found to be non-reproductive at the Darwin Mound site. Though unable to be specifically tested, this may suggest that the increased trawling activity in this area might be keeping colonies below sexually viable sizes, as seen in numerous shallow water situations. All areas in the NE Atlantic are coming under threat from increased fishing and commercial exploration practices. This study shows that these highly seasonal reproducers could be sensitive to these fishing operations and care must be taken so as not to repeat the destruction that has occurred on shallower reefs.     

Fading bioluminescence of the tropical Atlantic Ocean

Bioluminescence intensity acts as the indicator of the functional state of a plankton community. Data on bioluminescence intensity, zooplankton biomass, and chlorophyll a from the expeditions to the tropical and subtropical Atlantic Ocean were analyzed. The regression models implied a ~10-fold decline of bioluminescence intensity [bioluminescence potential (BP)] and zooplankton biomass for the 46 year time range from 1970 to 2016. The correlation was low between chlorophyll a (the indicator of phytoplankton biomass) and BP, but it was significant for the zooplankton biomass BP annual time series. The decline of BP was associated with the decreasing abundance of bioluminescent zooplankton, and increasing global warming-driven temperature.     

Population genetic studies of the Atlantic halibut in the North Atlantic Ocean

Significant variation in frequency distribution of electrophoretically detectable protein variants between samples of Atlantic halibut Hippoglossus hippoglossus showed that the halibut from northern Norway and from the Faroes–Iceland–Greenland region may not belong to one panmictic population.     

Age estimation of the exploited deepwater shark Centrophorus squamosus from the continental slopes of the Rockall Trough and Porcupine Bank

Dorsal spine sections of the deepwater squalid shark Centrophorus squamosus provided age estimates of 21–70 years. Small specimens were not recorded in the study area. It was not possible to obtain estimates from vertebral centra. The estimates are discussed in the context of other studies using dorsal spines of squalid sharks. Sexual maturity was achieved at large size, >75% of maximum length. Total length at 50% maturity was calculated as 101 cm (males) and 128 cm (females).     

Large-scale species-richness gradients in the Atlantic Ocean

The increase in species richness from the poles to the Equator has been observed in numerous terrestrial and aquatic taxa. A number of different hypotheses have been put forward as explanations for this trend, e.g. area and energy availability. However, whether these hypotheses apply to large spatial scales in marine environments remains unclear. The present study shows a clear latitudinal gradient from high to low latitude (from 80 degrees N to 70 degrees S) in marine species richness for 6643 species (fishes and invertebrates) in 10 different taxa dwelling in benthic and pelagic habitats on both sides of the Atlantic. The patterns in benthic taxa are strongly influenced by coastal hydrographic processes, with marked peaks and troughs, and consequently the gradients are not symmetric along both Atlantic sides. Pelagic taxa show a plateau-shaped distribution and the influence from coastal events on gradients could not be demonstrated. The relationships between species richness and different environmental factors indicate that area size does not explain the latitudinal pattern in benthic species richness on a large spatial scale. Sea-surface temperature (positive relationship) is the best predictor of this pattern for benthic species, and nitrate concentration (negative relationship) is the best predictor for pelagic species. The results call into question the existence of a single primary cause that would explain the pattern in marine species richness on a large spatial scale.     

Primary organic production in the Atlantic Ocean

Summary The determination of 24-h primary organic production of phytoplankton photosynthesis under 1 m² in the vast areas of open parts of the Atlantic ocean was made by using isopic technique. It was stated that the production is maximal in coastal waters of Europe (0,8–1,3 g C/m²) and especially of the west coast of Africa (to 3,4 g C/m²). Middle rate of production was observed in the North Atlantic Current, and the Equatorial Current (0,2–0,6 g C/m²). Relatively low organic production was found in the tropical waters of the Equatorial Current (about 0,1 g C/m²). Production in the transparent waters of the Sargasso sea was very low (0,03–0,05 g C/m²). Upper data corresponds well with that which had been collected by the Galathea expedition in the same regions of the Ocean. Definite correlation between the rate of primary production and standing crop of crustacean zooplankton was observed in tropical waters.