Spatial distribution and features of biology of Pacific sleeper shark Somniosus pacificus in the North Pacific

The results of the investigations of spatial and vertical distribution of Pacific sleeper shark Somniosus pacificus in the North Pacific Ocean conducted for many years are presented. In addition, the size distribution and features of biology of the species are studied. The largest abundance of the species is registered in the Bering Sea, western Gulf of Alaska, eastern Aleutian Islands, and Pacific waters of northern Kuril Islands and southeastern Kamchatka. The species is the most abundant near the bottom at the depth from 200 to 700 m and in the pelagic waters at a depth of 100–200 m. The average depths of the catches of Pacific sleeper shark substantially change over the year reaching minimum values in June and maximum values in December. Vertical daily migrations (to the water column at night and to the bottom during the day) are registered. The catches are represented by fish 26–352 cm in length, and sharks 100–200 cm in length prevail. The males are noticeably smaller than the females. In general, condition of the fishes decreases and feeding intensity increases with growth. Food composition substantially changes with the increase of body length: consumption of squids decreases and consumption of crustaceans, fishes, and fishery wastes increases. The food composition is slightly different in the females and males.     

New insights into the trophic ecology of the scalloped hammerhead shark,Sphyrna lewini,in the eastern tropical Pacific Ocean

Scalloped hammerhead shark, Sphyrna lewini, is considered a generalist predator, showing individual specializations and different trophic levels. This species inhabits both oceanic islands and coastal nursery areas in the eastern tropical Pacific (ETP) Ocean. Existing trophic ecology studies on S. lewini have been focused on stomach contents. This study provides new insights into its foraging preferences, habitat use, and trophic position, using stable isotope analysis (SIA) of muscle tissue. Stable isotope signatures of δ¹³C and δ¹⁵N were determined in S. lewini muscles (n?=?29) from the Ecuadorian Pacific in 2013. Trophic position (TP), isotopic niches, and overlap of S. lewini were estimated by sex, age, and maturity stages to infer their dietary habits throughout life stages. SIA revealed complex movement patterns related to sex and age classes of S. lewini, highlighting high degrees of dietary plasticity and habitat use, with a stronger relation to coastal regions than previously reported. This study provides crucial information regarding essential areas and the related migration behavior of S. lewini, with important implications for their conservation and management in the ETP.

     

Correction to: New insights into the trophic ecology of the scalloped hammerhead shark,Sphyrna lewini,in the eastern tropical Pacific Ocean

Environmental Biology of Fishes -     

Environmental forcing of nitrogen fixation in the eastern tropical and sub-tropical North Atlantic Ocean

During the winter of 2006 we measured nifH gene abundances, dinitrogen (N(2)) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 10(6) L(-1)nifH gene copies, unicellular group A cyanobacteria with up to 10(5) L(-1)nifH gene copies and gamma A proteobacteria with up to 10(4) L(-1)nifH gene copies. N(2) fixation rates were low and ranged between 0.032-1.28 nmol N L(-1) d(-1) with a mean of 0.30 ± 0.29 nmol N L(-1) d(-1) (1σ, n = 65). CO(2)-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2 ± 3.2 in surface waters. Nevertheless, N(2) fixation rates contributed only 0.55 ± 0.87% (range 0.03-5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N(2) fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N(2) fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the consequences of climate warming for N(2) fixation in the North Atlantic.     

Ocular lesions associated with attachment of the copepod Ommatokoita elongata (Lernaeopodidae: Siphonostomatoida) to corneas of Pacific sleeper sharks Somniosus pacificus captured off Alaska in Prince William Sound

Twenty eyes from 10 Pacific sleeper sharks Somniosus pacificus, infected with the copepod Ommatokoita elongata, were collected in Prince William Sound, Alaska, and the eyes of an additional 18 S. pacificus captured in the same area were inspected for copepods. Prevalence of infection by adult female O. elongata was 97% (n = 28); mean intensity of infection was 1.89 (+/-1SD = 0.32) adult female copepods per infected shark and 1.0 (+/- 1SD = 0.0) adult female copepods per infected eye. Five of the 20 collected eyes were infected by O. elongata chalimi, and 9 of 20 eyes had 1 to several remnants of bullae embedded in the cornea. Bullae were each associated with a corneal opacity, and anchoring plugs of chalimi were associated with pinpoint lesions in the cornea or conjunctiva. All eyes exhibited marked edema and erosion of the bulbar conjunctiva, and this torus-shaped lesion corresponded to each O. elongata adult female's presumed feeding and abrasion radius. Histological examinations revealed lesions in the anterior segment of eyes to be generally similar, but graded, in severity, and in all eyes they involved the conjunctiva, cornea, filtration angle, and iris. Epithelial lesions were characterized by corneal ulceration, dysplasia, hyperplasia, and heterophilic keratitis, and by ulcerative conjunctivitis accompanied by epithelial hyperplasia with rete peg formation. Disorganization of fibers, necrosis, mineralization, minimal heterophilic influx, and perilimbic neovascularization were associated with bullae in the corneal stroma. Within the limbus there was diffuse histiocytic and lymphocytic inflammation and marked lymphofollicular hyperplasia. Heterophilic and mononuclear anterior uveitis affecting the filtration angle and anterior surface of the iris was also observed in most eyes. One eye had a partial transcorneal prolapse of a ruptured lens, with degenerative changes in the ruptured lens and severe keratitis associated with the anchoring devices of an adult copepod and several chalimi. Fourteen eyes exhibited 1 to several, randomly distributed, small, round to irregular, corneal opacities or pits that were not associated with copepods, and it is likely that these opacities represented lesions associated with adult female or larval anchoring devices from past infections. The avascular cornea represents a niche that is somewhat shielded from host immune reactions, and this, and the fact that the general body surface of sleeper sharks is covered by tall and sharp placoid scales, may partially explain the corneal attachment of O. elongata adult females. It was concluded that O. elongata infections can lead to severe vision impairment in Pacific sleeper sharks but that these infections do not significantly debilitate hosts because they probably do not need to rely on acute vision for their survival.     

Variation in trophic shift for stable isotope ratios of carbon, nitrogen, and sulfur

Use of stable isotope ratios to trace pathways of organic matter among consumers requires knowledge of the isotopic shift between diet and consumer. Variation in trophic shift among consumers can be substantial. For data from the published literature and supplementary original data (excluding fluid-feeding consumers), the mean isotopic shift for C was +0.5±0.13‰ rather than 0.0‰, as commonly assumed. The shift for C was higher for consumers analyzed as muscle (+1.3±0.30‰) than for consumers analyzed whole (+0.3±0.14‰). Among consumers analyzed whole, the trophic shift for C was lower for consumers acidified prior to analysis (−0.2±0.21‰) than for unacidified samples (+0.5±0.17‰). For N, trophic shift was lower for consumers raised on invertebrate diets (+1.4±0.21‰) than for consumers raised on other high-protein diets (+3.3±0.26‰) and was intermediate for consumers raised on plant and algal diets (+2.2±0.30‰). The trophic shift for S differed between high-protein (+2.0±0.65‰) and low-protein diets (-0.5±0.56‰). Thus, methods of analysis and dietary differences can affect trophic shift for consumers; the utility of stable isotope methods can be improved if this information is incorporated into studies of trophic relationships. Although few studies of stable isotope ratios have considered variation in the trophic shift, such variation is important because small errors in estimates of trophic shift can result in large errors in estimates of the contribution of sources to consumers or in estimates of trophic position.     

Planktonic foraminifera from the eastern Indian Ocean: distribution and ecology in relation to the Western Pacific Warm Pool (WPWP)

Faunal assemblages, principal component (PCA), canonical correspondence (CCA), and factor analysis are applied to planktonic foraminifera from 57 core-top samples from the eastern Indian Ocean. The foraminiferal lysocline occurs at 2400 m north of 15°S where carbonate dissolution is induced by the Java upwelling system, and occurs deeper south of 15°S where carbonate dissolution is characteristic of the oligotrophic regions in the Indian Ocean. Dissolution effects, the February standing stock at the time of collection of the plankton-tow material, and different production rates explain the different foraminiferal assemblages found between plankton-tow and core-top samples. Core-top samples are differentiated by PCA into four groups — Upwelling, Western Pacific Warm Pool (WPWP), Transitional, and Southern — that are related to environmental variables (temperature, salinity and nutrients); all environmental variables follow a strong latitudinal component as indicated by the CCA analysis. Similarly, three assemblages are recognized by factor analysis: Factor 1 (dominated by Globigerinoides sacculifer, G. ruber, Globigerinita glutinata and Globorotalia cultrata), factor 2 (dominated by Globigerina bulloides and Globorotalia inflata) and factor 3 (dominated by Neogloboquadrina dutertrei) explain more than 92% of the variance, and are related to sea-surface temperature, thermocline depth and nutrient levels. The seasonal influence of the Java upwelling system supplies nutrients, phyto- and zooplankton to the oligotrophic eastern Indian Ocean (factor 1). South of 24°S, a deep chlorophyll maximum, a deep euphotic zone, a deep thermocline, SSTs below 22°C, and brief upwelling pulses seem to explain factors 2 and 3. The ratio of G. sacculifer and N. dutertrei, two mutually excluding species, appears to indicate the southern boundary of the WPWP. This ratio is applied to core Fr10/95-11 to demonstrate past shifts of the southern boundary of the WPWP.     

Nitrite oxidation in the upper water column and oxygen minimum zone of the eastern tropical North Pacific Ocean

Nitrogen (N) is an essential nutrient in the sea and its distribution is controlled by microorganisms. Within the N cycle, nitrite (NO₂⁻) has a central role because its intermediate redox state allows both oxidation and reduction, and so it may be used by several coupled and/or competing microbial processes. In the upper water column and oxygen minimum zone (OMZ) of the eastern tropical North Pacific Ocean (ETNP), we investigated aerobic NO₂⁻ oxidation, and its relationship to ammonia (NH₃) oxidation, using rate measurements, quantification of NO₂⁻-oxidizing bacteria via quantitative PCR (QPCR), and pyrosequencing. ¹⁵NO₂⁻ oxidation rates typically exhibited two subsurface maxima at six stations sampled: one located below the euphotic zone and beneath NH₃ oxidation rate maxima, and another within the OMZ. ¹⁵NO₂⁻ oxidation rates were highest where dissolved oxygen concentrations were <5 μM, where NO₂⁻ accumulated, and when nitrate (NO₃⁻) reductase genes were expressed; they are likely sustained by NO₃⁻ reduction at these depths. QPCR and pyrosequencing data were strongly correlated (r²=0.79), and indicated that Nitrospina bacteria numbered up to 9.25% of bacterial communities. Different Nitrospina groups were distributed across different depth ranges, suggesting significant ecological diversity within Nitrospina as a whole. Across the data set, ¹⁵NO₂⁻ oxidation rates were decoupled from ¹⁵NH₄⁺ oxidation rates, but correlated with Nitrospina (r²=0.246, P<0.05) and NO₂⁻ concentrations (r²=0.276, P<0.05). Our findings suggest that Nitrospina have a quantitatively important role in NO₂⁻ oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean.     

A new genus and species of rattail fish (Macrouridae) from the eastern North Atlantic and eastern Indian Ocean, with notes on its ecology

A new genus, Macrosmia , and species ( M. phalacra ) of benthopelagic macrourid fish is described from single male specimens caught in 1650–1699 m soundings in the northeastern Atlantic and south-eastern Indian Oceans. This elongate macrourine rattail, with 7 branchiostegal and 11–12 pelvic rays, is unique in its massive olfactory organ, the cavity of which almost equals the diameter of the orbit. This cavity is a reverse D-shape, with the posterior margin deforming the orbital rim into a D-shape. Macrosmia has a short deep snout, lacks prominent ridges on the head, has anteriorly placed plevic fins and a weakly serrated second spinuous ray in the first dorsal fin. The anus is contiguous with the anal fin. These characters, among others, show affinity with the Cetonurus group of genera. The distribution and diet of the species is briefly discussed and M. phalacra is shown to be at least partly dependent on benthic food which, from one example, is of crustacean origin.     

Sperm whale population structure in the eastern and central North Pacific inferred by the use of single-nucleotide polymorphisms, microsatellites and mitochondrial DNA

We use mitochondrial DNA (mtDNA) (400 bp), six microsatellites and 36 single-nucleotide polymorphisms (SNPs), 20 of which were linked, to investigate population structure of sperm whales (Physeter macrocephalus) in the eastern and central North Pacific. SNP markers, reproducible across technologies and laboratories, are ideal for long-term studies of globally distributed species such as sperm whales, a species of conservation concern because of both historical and contemporary impacts. We estimate genetic differentiation among three strata in the temperate to tropical waters where females are found: California Current, Hawai`i and the eastern tropical Pacific. We then consider how males on sub-Arctic foraging grounds assign to these strata. The California Current stratum was differentiated from both the other strata (P < 0.05) for mtDNA, microsatellites and SNPs, suggesting that the region supports a demographically independent population and providing the first indication that males may exhibit reproductive philopatry. Comparisons between the Hawai`i stratum and the eastern tropical Pacific stratum are not conclusive at this time. Comparisons with Alaska males were statistically significant, or nearly so, from all three strata and individuals showed mixed assignment to, and few exclusions from, the three potential source strata, suggesting widespread origin of males on sub-Arctic feeding grounds. We show that SNPs have sufficient power to detect population structure even when genetic differentiation is low. There is a need for better analytical methods for SNPs, especially when linked SNPs are used, but SNPs appear to be a valuable marker for long-term studies of globally dispersed and highly mobile species.     

Anaerobic respiration on tellurate and other metalloids in bacteria from hydrothermal vent fields in the eastern Pacific Ocean

This paper reports the discovery of anaerobic respiration on tellurate by bacteria isolated from deep ocean (1,543 to 1,791 m) hydrothermal vent worms. The first evidence for selenite- and vanadate-respiring bacteria from deep ocean hydrothermal vents is also presented. Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. Isolates from Axial Volcano and Explorer Ridge were tested for their ability to reduce tellurate, selenite, metavanadate, or orthovanadate in the absence of alternate electron acceptors. In the presence of metal(loid)s, strains showed an ability to grow and produce ATP, whereas in the absence of metal(loid)s, no growth or ATP production was observed. The protonophore carbonyl cyanide m-chlorophenylhydrazone depressed metal(loid) reduction. Anaerobic tellurate respiration will be a significant component in describing biogeochemical cycling of Te at hydrothermal vents.     

Late Holocene sea level indicators from twelve atolls in the central and eastern Tuamotus (Pacific Ocean)

New sea-level data for the late Holocene period are reported from twelve atolls of the Tuamotu archipelago: Faaite, Hikueru, Marokau, Hao, Amanu, Tatakoto, Pukarua, Nukutavake, Vairaatea, Tureia, Nukutipipi, and Hereheretue. The data come from coral conglomerate outcrops, coral colonies in growth position, in situ reef framework and marine notches; they give consistent results, and their ages are controlled by 29 radiocarbon datings. The Holocene MSL remained 0.8±0.2 m higher than at present, from before 4000 years BP until at least 1500 years BP, then dropped gradually to the present level. This pattern is very similar to that reported from the northwest Tuamotus, suggesting the absence of measurable differential vertical movements over a distance greater than 1300 km during the late Holocene. Effects of the 1983 cyclones on reef morphology are reported from some atolls and radiocarbon dates of some storm-generated reef blocks are given.     

Feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, inferred from stable isotopes and stomach contents analysis

The feeding ecology and trophic level of the banded guitarfish, Zapteryx exasperata, from the Gulf of California, were assessed using stable isotope analysis (SIA) of carbon and nitrogen in muscle samples, and stomach contents analysis (SCA). Males and females showed similar diet preferences with a high diet overlap (C???=?0.99) and similar values of ??¹³C and ??¹⁵N (ANOVA, F?=?0.0 p?=?0.94 for ??¹³C; F?=?0.1 p?=?0.78 for ??¹⁵N). The main prey groups found were demersal fishes dominated by the daisy midshipman, Porichthys margaritatus, (>90%IRI), however, pelagic fishes were also found (Engraulis mordax 2%IRI). An ontogenetic diet shift was found, indicated by the importance of crustaceans in the juvenile diet and the significant isotopic differences between juveniles and adults (??¹³C, ANOVA, F?=?13.3 p?=?0.0004 and ??¹⁵N, ANOVA, F?=?4.7 p?=?0.03). An overall trend of increase in ??¹⁵N values with increasing body length (F?=?8.15 p?=?0.005) was observed. The mean trophic level estimated in this work by the two methods was ~4.1, indicating that this species is a top predator in the Gulf of California. Zapteryx exasperata is a specialist feeder (Bi?=?0.11, H???=?2.32), consuming mainly benthic fishes in coastal areas of the Gulf of California. The importance of this species in the benthic ecosystem equilibrium as a top predator is an important point to keep in mind when developing future management plans of the batoid fishery in the Gulf of California.     

Feeding habits and trophic niche of rainbow runner Elagatis bipinnulata in the western and central Pacific Ocean

Environmental Biology of Fishes - Possible changes in the feeding habits and trophic niche width of rainbow runner, Elagatis bipinnulata, were investigated using stomach content analysis (SCA) and...     

Modelling the vertical distribution of Prochlorococcus and Synechococcus in the North Pacific Subtropical Ocean

A simple model was developed to examine the vertical distribution of Prochlorococcus and Synechococcus ecotypes in the water column, based on their adaptation to light intensity. Model simulations were compared with a 14-year time series of Prochlorococcus and Synechococcus cell abundances at Station ALOHA in the North Pacific Subtropical Gyre. Data were analysed to examine spatial and temporal patterns in abundances and their ranges of variability in the euphotic zone, the surface mixed layer and the layer in the euphotic zone but below the base of the mixed layer. Model simulations show that the apparent occupation of the whole euphotic zone by a genus can be the result of a co-occurrence of different ecotypes that segregate vertically. The segregation of ecotypes can result simply from differences in light response. A sensitivity analysis of the model, performed on the parameter alpha (initial slope of the light-response curve) and the DIN concentration in the upper water column, demonstrates that the model successfully reproduces the observed range of vertical distributions. Results support the idea that intermittent mixing events may have important ecological and geochemical impacts on the phytoplankton community at Station ALOHA.     

Pre-whaling genetic diversity and population ecology in eastern Pacific gray whales: insights from ancient DNA and stable isotopes

Commercial whaling decimated many whale populations, including the eastern Pacific gray whale, but little is known about how population dynamics or ecology differed prior to these removals. Of particular interest is the possibility of a large population decline prior to whaling, as such a decline could explain the ~5-fold difference between genetic estimates of prior abundance and estimates based on historical records. We analyzed genetic (mitochondrial control region) and isotopic information from modern and prehistoric gray whales using serial coalescent simulations and Bayesian skyline analyses to test for a pre-whaling decline and to examine prehistoric genetic diversity, population dynamics and ecology. Simulations demonstrate that significant genetic differences observed between ancient and modern samples could be caused by a large, recent population bottleneck, roughly concurrent with commercial whaling. Stable isotopes show minimal differences between modern and ancient gray whale foraging ecology. Using rejection-based Approximate Bayesian Computation, we estimate the size of the population bottleneck at its minimum abundance and the pre-bottleneck abundance. Our results agree with previous genetic studies suggesting the historical size of the eastern gray whale population was roughly three to five times its current size.     

Vertical distribution and phylogenetic composition of bacteria in the Eastern Tropical North Pacific Ocean

The vertical community structure of bacteria along a depth profile in the Eastern Tropical North Pacific Ocean (13 degrees N, 104 degrees W) was studied by flow cytometry measurement and 16S rRNA gene clone libraries analysis. Picoeukaryotes and Synechococcus peaked at 30 m and decreased sharply below 50 m, while Prochlorococcus peaked at both 30 and 100 m layers and disappeared below 200 m. Heterotrophic bacteria peaked above shallow thermocline and decreased along the depth profile. Sequences of total 322 clones from four clone libraries (10, 100, 1000, and 3000 m) clustered into nine major lineages. gamma-Proteobacteria dominated all the depths and occupied almost the whole bacterial community at the 3000 m. alpha-Proteobacteria was abundant throughout the water column except near the sea bottom, and delta-Proteobacteria peaked at the 1000 m depth. Cyanobacteria were primarily limited to the photic zone, and the genetic diversity of Prochlorococcus showed a good correlation with niche adaptation. The appearance of the Cytophaga-Flexibacter-Bacteroides (CFB) group did not show a clear relationship with depth. Actinobacteria were found both in the photic zone and in deep water. Planctomyetes, Acidobacteria, and Verrucomicrobia were present as minor groups and more dominant in the deeper layers of water.