Three‐dimensional post‐glacial expansion and diversification of an exploited oceanic fish

Vertical divergence in marine organisms is being increasingly documented, yet much remains to be carried out to understand the role of depth in the context of phylogeographic reconstruction and the identification of management units. An ideal study system to address this issue is the beaked redfish, Sebastes mentella – one of four species of ‘redfish’ occurring in the North Atlantic – which is known for a widely distributed ‘shallow‐pelagic’ oceanic type inhabiting waters between 250 and 550 m, and a more localized ‘deep‐pelagic’ population dwelling between 550 and 800 m, in the oceanic habitat of the Irminger Sea. Here, we investigate the extent of population structure in relation to both depth and geographic spread of oceanic beaked redfish throughout most of its distribution range. By sequencing the mitochondrial control region of 261 redfish collected over a decadal interval, and combining 160 rhodopsin coding nuclear sequences and previously genotyped microsatellite data, we map the existence of two strongly divergent evolutionary lineages with significantly different distribution patterns and historical demography, and whose genetic variance is mostly explained by depth. Combined genetic data, analysed via independent approaches, are consistent with a Late Pleistocene lineage split, where segregation by depth probably resulted from the interplay of climatic and oceanographic processes with life history and behavioural traits. The ongoing process of diversification in North Atlantic S. mentella may serve as an ‘hourglass’ to understand speciation and adaptive radiation in Sebastes and in other marine taxa distributed across a depth gradient.     

Structure of aggregations and principal populational characteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes: Scorpaenidae) in the pelagic zone of the Irminger Sea and adjacent waters

The spatial distribution of redfish Sebastes mentella in the pelagic zone of the northern part of the Atlantic Ocean (the Irminger Sea and the Labrador Sea) is investigated. Analysis of the data on size-age composition, sex ratio, ratio of mature and immature specimens, rate of maturation, composition of the parasite fauna, infestation level, infestation with the copepod Sphyrion lumpi, and occurrence of pigment formations on the body of redfish from the investigated areas indicate the absence of stable isolated aggregations of this species in the oceanic pelagial of the North Atlantic. Pelagic aggregations are formed of rapidly maturating specimens migrated from the slopes of Greenland. The spatial variation of the size-age composition of redfish depends on the life cycle and regional hydrological conditions.     

Recruitment of stock of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes,Scorpaenidae) in the pelagial of the Irminger Sea and adjacent waters

Results of comparative analysis of several ecologo-populational characteristics and fauna of parasites of deepwater redfish Sebastes mentella from the pelagial of the Irminger Sea and slopes of Greenland are provided. It was established that the nursery area of the species in this part of the northern Atlantic is located in the shelf and shallow-water sites of the Greenland slopes. Near the nursery area, at deepwater sites of the Greenland slope, aggregations of mainly immature specimens (68–86%) with an average length of 35–38 cm are located, and, in the oceanic pelagial, there are mainly mature specimens (91–95%) with a length of more than 30 cm. Considerable similarity and specific features of fauna of parasites of S. mentella from the southeastern slope of Greenland and the pelagial of the Irminger Sea indicate the belonging of fish aggregations in these areas to a single intraspecies group and the migration of maturing specimens from the slope to the pelagial. A conclusion is made that the aggregations of S. mentella in the pelagial of the Irminger and Labrador seas represent a pelagic ecological group formed by rapidly maturing specimens; a near-bottom ecological group at deepwater sites of the slope of Greenland is formed by slowly maturing specimens. No mass migration of the redfish from deepwater areas to shallow sites of the slope and to the oceanic pelagial of the northern Atlantic was recorded.     

Colonization of the deep sea by fishes

Analysis of maximum depth of occurrence of 11 952 marine fish species shows a global decrease in species number (N) with depth (x; m): log₁₀N = ?0·000422x + 3·610000 (r² = 0·948). The rate of decrease is close to global estimates for change in pelagic and benthic biomass with depth (?0·000430), indicating that species richness of fishes may be limited by food energy availability in the deep sea. The slopes for the Classes Myxini (?0·000488) and Actinopterygii (?0·000413) follow this trend but Chondrichthyes decrease more rapidly (?0·000731) implying deficiency in ability to colonize the deep sea. Maximum depths attained are 2743, 4156 and 8370 m for Myxini, Chondrichthyes and Actinopterygii, respectively. Endemic species occur in abundance at 7–7800 m depth in hadal trenches but appear to be absent from the deepest parts of the oceans, >9000 m deep. There have been six global oceanic anoxic events (OAE) since the origin of the major fish taxa in the Devonian c. 400 million years ago (mya ). Colonization of the deep sea has taken place largely since the most recent OAE in the Cretaceous 94 mya when the Atlantic Ocean opened up. Patterns of global oceanic circulation oxygenating the deep ocean basins became established coinciding with a period of teleost diversification and appearance of the Acanthopterygii. Within the Actinopterygii, there is a trend for greater invasion of the deep sea by the lower taxa in accordance with the Andriashev paradigm. Here, 31 deep‐sea families of Actinopterygii were identified with mean maximum depth >1000 m and with >10 species. Those with most of their constituent species living shallower than 1000 m are proposed as invasive, with extinctions in the deep being continuously balanced by export of species from shallow seas. Specialized families with most species deeper than 1000 m are termed deep‐sea endemics in this study; these appear to persist in the deep by virtue of global distribution enabling recovery from regional extinctions. Deep‐sea invasive families such as Ophidiidae and Liparidae make the greatest contribution to fish fauna at depths >6000 m.     

Ecologal and parasitological chracteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes: Sebastidae) from the Norwegian Sea and adjacent waters

Special traits of ecology, zoogeography, formation of fauna of parasites, and occurrence of external lesions are investigated in redfish Sebastes mentella from the Norwegian Sea and the adjacent area of the Barents Sea. A considerable weakening of connection with bottom biocenoses in redfish in the pelagial of the Norwegian Sea indicates that it lives here for most of its annual life cycle. In redfish from south of the open part of the Norwegian Sea, there are noticeable differences in the fauna of parasites and in occurrence of external lesions from those in the fish from the north and east of this sea while traits characteristic of redfish from the Irminger Sea are present.     

Structure and specific features of formation of aggregations of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) in the Norwegian Sea pelagial

Results of studies of the structure and specific features of formation of aggregations of deepwater redfish Sebastes mentella in the Norwegian Sea pelagial are provided. Data on the biological characteristics of S. mentella from different regions of the Norwegian Sea pelagial do not allow us to consider its aggregations as separate populations. On the basis of comparative analysis of the structure of aggregations in the Norwegian Sea and of population parameters and specific features of the life cycle of S. mentella in different parts of the Atlantic Ocean, its complex intraspecies organization at sites of overlapping of two largest populations—North Atlantic and Norwegian-Barents Sea-was established. The formation of pelagic aggregations in the water area of the Norwegian Sea occurs due to migration of maturing and mature individuals from the adjoining water areas. In the southern areas of the Norwegian Sea, dominant recruitment comes from the pelagial of the northeastern part of the Irminger Sea, which is promoted by the direction of streams of the North-Atlantic Current; it is not excluded either that fish can migrate to the southern part of the sea from the slopes of the Faeroes, Faeroes-Icelandic threshold, and the western coast of Norway. Migration to the northern areas of the sea is mainly performed by rapidly maturing fish from the rearing region from the western slopes of the Barents Sea and Spitsbergen Archipelago. The presence of seasonal migrations hinders the formation in the pelagial of perch isolated groups and promotes their migration.     

Population structure of beaked redfish (Sebastes mentella Travin, 1951) in the Irminger Sea and adjacent waters inferred from microsatellite data

Samples of beaked redfish from the Irminger Sea and adjacent waters were examined for polymorphism at ten microsatellite loci. The strategy of the material collection enabled investigation of geographic, bathymetric, and temporal variation of this species. The results did not support the evidence on spatial differentiation and temporal stability of the species distribution, favoring the idea that the water area examined was inhabited by a single pelagic population of beaked redfish.     

Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Elasmobranchii,Dasyatidae)

Hook selectivity, sex ratio of catches and relative abundance (Catch Per Unit Effort – CPUE) were assessed for the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1872), caught by longline gear in the southwestern Atlantic Ocean over the continental slope and adjacent oceanic area. The catches were carried out at depths of 200–4000 m by research cruises in 2002 and 2003, from Cabo Frio (22°52′S) to Laguna (28°28′S); and by hook selectivity experiments from 2004 to 2008, from Itajaí (26°54′S) to Tramandaí (29°59′S). Hook selectivity experiments indicated higher catches of stingrays with ‘J’ hooks (9/0, 10° offset) commonly used by the pelagic longline fleet than with ‘circle’ hooks (18/0, 10° offset). ‘circle’ hooks reduce the longline by‐catches of this species. Most of the stingrays caught were males (6 : 1). One female aborted mid‐term embryos at the time of capture. CPUE was highest between spring and autumn and lowest during winter.     

Population structure of beaked redfish (<Emphasis Type="Italic">Sebastes mentella</Emphasis> Travin, 1951) in the Irminger Sea and adjacent waters inferred from microsatellite data

Samples of beaked redfish from the Irminger Sea and adjacent waters were examined for polymorphism at ten microsatellite loci. The strategy of the material collection enabled investigation of geographic, bathymetric, and temporal variation of this species. The results did not support the evidence on spatial differentiation and temporal stability of the species distribution, favoring the idea that the water area examined was inhabited by a single pelagic population of beaked redfish.     

The distribution and specific features of the biology of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) during mating in the pelagial of the northern Atlantic

Data on the spatial-bathymetric distribution, size and age composition, sex ratio, and feeding of deepwater redfish Sebastes mentella in the pelagial of the northern Atlantic (Irminger and Labrador seas) during mating are provided. From 1982 to 1999, the mating of S. mentella took place in the central and southern parts of the Irminger Sea (56°–62° N, 30°–43° W); since 2000 it took place in two geographically isolated areas: in the water area of the open part of the Labrador Sea, at sites of the south of the Irminger Sea adjacent to it (54°–58° N, 38°–50° W), and above the western slopes of the Reykjanes Ridge (62°–65° N, 25°–34° W). It is assumed that during mating in the northern area mixed aggregations of two ecological groups of S. mentella—an oceanic group that distributes in the pelagial and a bottom group that inhabits the slopes of Iceland—are formed. The formation of isolated areas of mating of the species is determined by the orientation of feeding migrations that are simultaneously migrations to spawning grounds. Fish of medium sizes migrate to spawning grounds in the southwestern direction, while large fish migrate in the northern direction; the fertilization of females in these areas occurs at the end of summer. In S. mentella, the seasonal and age differences in food composition are clearly pronounced. With the onset of mating, the males’ intensity of feeding in both regions decreases by a factor of 1.5–2.0, while females continue to feed actively.     

Role of deep sponge grounds in the Mediterranean Sea: a case study in southern Italy

The Mediterranean spongofauna is relatively well-known for habitats shallower than 100 m, but, differently from oceanic basins, information upon diversity and functional role of sponge grounds inhabiting deep environments is much more fragmentary. Aims of this article are to characterize through ROV image analysis the population structure of the sponge assemblages found in two deep habitats of the Mediterranean Sea and to test their structuring role, mainly focusing on the demosponges Pachastrella monilifera Schmidt, 1868 and Poecillastra compressa (Bowerbank, 1866). In both study sites, the two target sponge species constitute a mixed assemblage. In the Amendolara Bank (Ionian Sea), where P. compressa is the most abundant species, sponges extend on a peculiar tabular bedrock between 120 and 180 m depth with an average total abundance of 7.3 ± 1.1 specimens m⁻² (approximately 230 gWW m⁻² of biomass). In contrast, the deeper assemblage of Bari Canyon (average total abundance 10.0 ± 0.7 specimens m⁻², approximately 315 gWW m⁻² of biomass), located in the southwestern Adriatic Sea between 380 and 500 m depth, is dominated by P. monilifera mixed with living colonies of the scleractinian Madrepora oculata Linnaeus, 1758, the latter showing a total biomass comparable to that of sponges (386 gWW m⁻²). Due to their erect growth habit, these sponges contribute to create complex three-dimensional habitats in otherwise homogenous environments exposed to high sedimentation rates and attract numerous species of mobile invertebrates (mainly echinoderms) and fish. Sponges themselves may represent a secondary substrate for a specialized associated fauna, such zoanthids. As demonstrated in oceanic environments sponge beds support also in the Mediterranean Sea locally rich biodiversity levels. Sponges emerge also as important elements of benthic–pelagic coupling in these deep habitats. In fact, while exploiting the suspended organic matter, about 20% of the Bari sponge assemblage is also severely affected by cidarid sea urchin grazing, responsible to cause visible damages to the sponge tissues (an average of 12.1 ± 1.8 gWW of individual biomass removed by grazing). Hence, in deep-sea ecosystems, not only the coral habitats, but also the grounds of massive sponges represent important biodiversity reservoirs and contribute to the trophic recycling of organic matter.     

Additional records and notes for Wheeler's (1992) List of the Common and Scientific Names of Fishes of the British Isles

This paper compiles information new to an earlier list published in 1992. Most changes are (1) additions largely resulting from importation of freshwater species, (2) range extensions of neritic and oceanic epipelagic species, together with (3) the incidental capture of species from within the 200 m bathymetric limit of resident deep pelagic and demersal deep‐sea representatives. A list of such species with the potential to stray from residence in the deeper strata of the oceanic region to shelf waters (<200 m) is presented in appendices.     

Additional records and notes for Wheeler's (1992) List of the Common and Scientific Names of Fishes of the British Isles

This paper compiles information new to an earlier list published in 1992. Most changes are (1) additions largely resulting from importation of freshwater species, (2) range extensions of neritic and oceanic epipelagic species, together with (3) the incidental capture of species from within the 200 m bathymetric limit of resident deep pelagic and demersal deep‐sea representatives. A list of such species with the potential to stray from residence in the deeper strata of the oceanic region to shelf waters (<200 m) is presented in appendices.     

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.     

Reef fish community structure of the Fernando de Noronha Archipelago (Equatorial Western Atlantic): the influence of exposure and benthic composition

We studied the reef fish assemblage of eight reefs within the oceanic archipelago of Fernando de Noronha, off northeastern Brazil. In a total of 91 belt transects (20 × 2 m) we recorded 60 species from 28 families. The 25 most abundant species accounted for about 98% of all fish recorded in this study and most of these species are widely distributed in the Western Atlantic. The majority of fish counted were planktivores (37.0%), followed by mobile invertebrate feeders (28.5%), territorial herbivores (11.3%), roving herbivores (10.5%), omnivores (7.1%), macrocarnivores (6.5%) and sessile invertebrate feeders (0.03%). In terms of biomass, roving herbivores were the most representative (41.8%), followed by mobile invertebrate feeders (19.9%), macrocarnivores (14.3%), omnivores (14.0%), piscivores (8.3%), planktivores (1.4%), territorial herbivores (0.3%), and sessile invertebrate feeders (0.03%). Overall, density and biomass of fishes were positively correlated with coral cover and depth, and negatively correlated with wave exposure. These relationships are probably a response to the habitat complexity provided by the higher coral cover in deeper reefs (>10 m) of the archipelago or to the lower water turbulence below 10 m deep. Carnivores and mobile invertebrate feeders were mainly influenced by depth and non-consolidated substratum, planktivores and omnivores by wave exposure and herbivores by algal cover. Although our results suggest that habitat characteristics may play a role in determining the distribution of some fish species, we also found several habitat generalists, suggesting that the community is dominated by versatile species.     

Community structure of pelagic cnidarians off Adélie Land, East Antarctica, during austral summer 2008

Some studies have suggested that pelagic cnidarians are important components of the Southern Ocean ecosystem due to their high abundance and diversity and their high predatory effects, although little information on these animals is available. Thus, we examined the spatial distribution of pelagic cnidarians from the oceanic to neritic zone off Adélie Land, East Antarctica. Discrete depth sampling was conducted from the surface to 2,000 m depth from late January to early February 2008. In total, 3347 individuals representing 45 species/taxa from eight orders were collected. Cluster analysis revealed three major clusters: (1) an epipelagic group in the oceanic zone composed mainly of Pegantha martagon, the abundance and species diversity of which were very low; (2) a meso- and bathy-pelagic group characterised by high abundance and species diversity with dominance of Dimophyes arctica, Vogtia serrata, and Halicreas minimum; and (3) a neritic group represented by a high abundance of Diphyes antarctica. Cnidarian communities in the epipelagic zone were divided by hydrographic structures such as the Southern Boundary of the Antarctic Circumpolar Current and Antarctic Slope Front, whereas those in the meso- and bathy-pelagic layers dominated by circumpolar deep water were relatively stable with higher diversity throughout the oceanic zone.     

Biological and ecological characteristics of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) at different depths in the pelagial of the Irminger Sea

Results of comparative analysis of several ecological and biological indices of Sebastes mentella from the northern Atlantic (the Irminger Sea, Reykjanes Ridge) inhabiting different depths, 0–500 and 501–1000 m, are provided. A considerable similarity in the rates of linear and weight growth, sexual maturation, composition of parasitofauna, the degree of invasion by parasites of most species, specific features of invasion by copepod Sphyrion lumpi, as well as the pattern of pigment formations on the skin of S. mentella from two studied layers, testify to the absence of isolated groups of this species in the pelagial of the Irminger Sea. It was established that the formation of perch aggregations at a depth larger than 500 m takes place due to a partial redistribution from the upper layer of individuals aged 5 to 18 years and a complete departure to large depths of perch individuals older than 18 years. A conclusion was made that it is incorrect to use as a criterion for the intraspecies differentiation of the perch the insignificant differences in the occurrence of pigment formations on the skin that are the result of age changes in fish and an obvious pathology of this phenomenon. A decrease in the occurrence of melanin inclusions in the muscular tissue of fish at a depth larger than 500 m is also related to age changes and the change in the diet of the perch. Vertical variation, in particular biological parameters in pelagic aggregations, was determined by specific features of biology, ecology, and the life cycle of the species. In establishing measures of control of the international fishery in the pelagial of the Irminger Sea, it is necessary to proceed from the unity of aggregations of S. mentella throughout the vertical of their distribution.     

Phylogenetic relationships among North Atlantic redfish (genus Sebastes) as revealed by mitochondrial DNA sequence analyses

Species structure and phylogenetic relationships among the four currently recognised North Atlantic redfish species, Sebastes mentella (‘deep‐sea’ and ‘oceanic’ phenotype), S. marinus (including ‘giant’ phenotype), S. fasciatus and S. viviparus, were investigated by sequencing the complete mitochondrial NADH dehydrogenase subunit 3 (ND3) gene for 313 individuals (333 including outliers). Low levels of sequence divergence of 0.3–2.3% between the North Atlantic Sebastes haplotypes, low resolution in phylogenetic trees and a star‐like statistical parsimony network indicate a population bottleneck and/or founder event with a subsequent population expansion and a rapid speciation in North Atlantic Sebastes. Diagnostic mutations within the ND3 gene were recognised for some of the species. The results lead to the hypothesis that the ancestral haplotype lineage is now very rare or has suffered extinction and that the most basal lineage is found in S. viviparus. The results further indicate direct descendants in the S. fasciatus and S. marinus lineages from the S. mentella lineage, whereas the S. viviparus lineage originates from an earlier division. The observation of two haplotype lineages in S. marinus with a relatively high level of intraspecific genetic divergence, points towards a possible cryptic speciation.     

Numerical Simulation of Environmental Modulation of Chemical Signal Structure and Odor Dispersal in the Open Ocean

Hydrodynamic models were used to simulate the dispersal of amodel fish pheromone at three characteristic depth regimes (mixedlayer, and 300 and 1000 m) of broad extent in the open oceanat the scale of individual organisms. The models were calibratedto experimental studies of dye dispersal at these depths andthe goldfish pheromone system was used as the model odorant.There are profound differences in the time course and geometryof dispersing odor fields with depth. Below the thermoclineodor fields spread primarily as horizontal patches with dispersalrates about five times slower at 1000 m as compared to 300 m.In the mixed layer, odors disperse rapidly in all directionsand the maximum radial distance of spread of a physiologicallyactive odor patch is less than half of the deep water value.Increases in the threshold sensitivity of olfactory receptorscan greatly increase effective odor field size. Chemical signalsimpact the encounter dynamics among oceanic organisms by affectingthe distance at which the target (emitting) individual is perceived.Perception distances due to olfactory cues can be significantlygreater than for other senses in pelagic oceanic environments.Environment specific modulation of odor fields then affectsthe signal properties and therefore utility of chemoreceptionthat, in turn, bear on encounter probabilities and transferfunctions in oceanic ecosystems. Chem. Senses 21: 121–134,1996.     

Phylogenetic measures reveal eco-evolutionary drivers of biodiversity along a depth gradient

Energy and environmental stability are positively correlated with species richness along broad-scale spatial gradients in terrestrial ecosystems, so their relative importance in generating and preserving diversity cannot be readily disentangled. This study seeks to exploit the negative correlation between energy and stability along the oceanic depth gradient to better understand their relative contribution in shaping broadscale biodiversity patterns. We develop a conceptual framework by simulating speciation and extinction along energy and stability gradients to generate expected patterns of biodiversity for a suite of complementary phylogenetic diversity metrics. Using a time-calibrated molecular phylogeny for New Zealand marine ray-finned fishes and a replicated community ecological sampling design, we then modelled these metrics along large-scale depth and latitude gradients. Our results indicate that energy-rich shallow waters may be an engine of diversity for percomorphs, but also suggest that recent speciation occurs in ancient fish lineages in the deep sea, hence questioning the role of energy as a key driver of speciation. Despite potentially facing high extinction early in their evolution, ancient phylogenetic lineages specialized for the deep-sea were likely preserved by environmental stability during the Cenozoic. Furthermore, intermediate depths might be a ‘museum’ (or zone of overlap) for distinct lineages that occur predominantly in either shallow or deep-sea waters. These intermediate depths (500–900 m) may form a ‘phylogenetic diversity bank’, perhaps providing a refuge during ancient (Mesozoic) extreme anoxic events affecting the deep sea and more recent (Pliocene–Pleistocene) climatic events occurring in shallow ecosystems. Finally, the phylogenetic structures observed in fish communities at intermediate depths suggest other processes might restrict the co-occurrence of closely related species. Overall, by combining a conceptual framework with models of empirical phylogenetic diversity patterns, our study paves the way for understanding the determinants of biodiversity across the largest habitat on earth.