Urea based osmoregulation and endocrine control in elasmobranch fish with special reference to euryhalinity

Since the landmark contributions of Homer Smith and co-workers in the 1930s there has been a considerable advance in our knowledge regarding the osmoregulatory strategy of elasmobranch fish. Smith recognised that urea was retained in the body fluids as part of the ‘osmoregulatory ballast’ of elasmobranch fish so that body fluid osmolality is raised to a level that is iso- or slightly hyper-osmotic to that of the surrounding medium. From studies at that time he also postulated that many marine dwelling elasmobranchs were not capable of adaptation to dilute environments. However, more recent investigations have demonstrated that, at least in some species, this may not be the case. Gradual acclimation of marine dwelling elasmobranchs to varying environmental salinities under laboratory conditions has demonstrated that these fish do have the capacity to acclimate to changes in salinity through independent regulation of Na⁺, Cl⁻ and urea levels. This suggests that many of the presumed stenohaline marine elasmobranchs could in fact be described as partially euryhaline. The contributions of Thomas Thorson in the 1970s demonstrated the osmoregulatory strategy of a fully euryhaline elasmobranch, the bull shark, Carcharhinus leucas, and more recent investigations have examined the mechanisms behind this strategy in the euryhaline elasmobranch, Dasyatis sabina. Both partially euryhaline and fully euryhaline species utilise the same physiological processes to control urea, Na⁺ and Cl⁻ levels within the body fluids. The role of the gills, kidney, liver, rectal gland and drinking process is discussed in relation to the endocrine control of urea, Na⁺ and Cl⁻ levels as elasmobranchs acclimate to different environmental salinities.     

Biomarkers of Whale Shark Health: A Metabolomic Approach

In a search for biomarkers of health in whale sharks and as exploration of metabolomics as a modern tool for understanding animal physiology, the metabolite composition of serum in six whale sharks (Rhincodon typus) from an aquarium collection was explored using ¹H nuclear magnetic resonance (NMR) spectroscopy and direct analysis in real time (DART) mass spectrometry (MS). Principal components analysis (PCA) of spectral data showed that individual animals could be resolved based on the metabolite composition of their serum and that two unhealthy individuals could be discriminated from the remaining healthy animals. The major difference between healthy and unhealthy individuals was the concentration of homarine, here reported for the first time in an elasmobranch, which was present at substantially lower concentrations in unhealthy whale sharks, suggesting that this metabolite may be a useful biomarker of health status in this species. The function(s) of homarine in sharks remain uncertain but it likely plays a significant role as an osmolyte. The presence of trimethylamine oxide (TMAO), another well-known protective osmolyte of elasmobranchs, at 0.1–0.3 mol L⁻¹ was also confirmed using both NMR and MS. Twenty-three additional potential biomarkers were identified based on significant differences in the frequency of their occurrence between samples from healthy and unhealthy animals, as detected by DART MS. Overall, NMR and MS provided complementary data that showed that metabolomics is a useful approach for biomarker prospecting in poorly studied species like elasmobranchs.     

Assessment of Caspian Seal By-Catch in an Illegal Fishery Using an Interview-Based Approach

The Caspian seal (Pusa caspica) has declined by more than 90% since 1900 and is listed as endangered by IUCN. We made the first quantitative assessment of Caspian seal by-catch mortality in fisheries in the north Caspian Sea by conducting semi-structured interviews in fishing communities along the coasts of Russia (Kalmykia, Dagestan), Kazakhstan and Turkmenistan. We recorded a documented minimum by-catch of 1,215 seals in the survey sample, for the 2008–2009 fishing season, 93% of which occurred in illegal sturgeon fisheries. Due to the illegal nature of the fishery, accurately quantifying total fishing effort is problematic and the survey sample could reflect less than 10% of poaching activity in the north Caspian Sea. Therefore total annual by-catch may be significantly greater than the minimum documented by the survey. The presence of high by-catch rates was supported independently by evidence of net entanglement from seal carcasses, during a mass stranding on the Kazakh coast in May 2009, where 30 of 312 carcasses were entangled in large mesh sturgeon net remnants. The documented minimum by-catch may account for 5 to 19% of annual pup production. Sturgeon poaching therefore not only represents a serious threat to Caspian sturgeon populations, but may also be having broader impacts on the Caspian Sea ecosystem by contributing to a decline in one of the ecosystem’s key predators. This study demonstrates the utility of interview-based approaches in providing rapid assessments of by-catch in illegal small-scale fisheries, which are not amenable to study by other methods.     

Distribution of skates and sharks in the North Sea: 112 years of change

How have North Sea skate and shark assemblages changed since the early 20th century when bottom trawling became widespread, whilst their environment became increasingly impacted by fishing, climate change, habitat degradation and other anthropogenic pressures? This article examines long‐term changes in the distribution and occurrence of the elasmobranch assemblage of the southern North Sea, based on extensive historical time series (1902–2013) of fishery‐independent survey data. In general, larger species (thornback ray, tope, spurdog) exhibited long‐term declines, and the largest (common skate complex) became locally extirpated (as did angelshark). Smaller species increased (spotted and starry ray, lesser‐spotted dogfish) as did smooth‐hound, likely benefiting from greater resilience to fishing and/or climate change. This indicates a fundamental shift from historical dominance of larger, commercially valuable species to current prevalence of smaller, more productive species often of low commercial value. In recent years, however, some trends have reversed, with the (cold‐water associated) starry ray now declining and thornback ray increasing. This shift may be attributed to (i) fishing, including mechanised beam trawling introduced in the 1960s–1970s, and historical target fisheries for elasmobranchs; (ii) climate change, currently favouring warm‐water above cold‐water species; and (iii) habitat loss, including potential degradation of coastal and outer estuarine nursery habitats. The same anthropogenic pressures, here documented to have impacted North Sea elasmobranchs over the past century, are likewise impacting shelf seas worldwide and may increase in the future; therefore, parallel changes in elasmobranch communities in other regions are to be expected.     

Coexistence of Low Coral Cover and High Fish Biomass at Farquhar Atoll,Seychelles

We report a reef ecosystem where corals may have lost their role as major reef engineering species but fish biomass and assemblage structure is comparable to unfished reefs elsewhere around the world. This scenario is based on an extensive assessment of the coral reefs of Farquhar Atoll, the most southern of the Seychelles Islands. Coral cover and overall benthic community condition at Farquhar was poor, likely due to a combination of limited habitat, localized upwelling, past coral bleaching, and cyclones. Farquhar Atoll harbors a relatively intact reef fish assemblage with very large biomass (3.2 t ha⁻¹) reflecting natural ecological processes that are not influenced by fishing or other local anthropogenic factors. The most striking feature of the reef fish assemblage is the dominance by large groupers, snappers, and jacks with large (>1 m) potato cod (Epinephelus tukula) and marbled grouper (E. polyphekadion), commonly observed at many locations. Napoleon wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are listed as endangered and vulnerable, respectively, but were frequently encountered at Farquhar. The high abundance and large sizes of parrotfishes at Farquhar also appears to regulate macroalgal abundance and enhance the dominance of crustose corallines, which are a necessary condition for maintenance of healthy reef communities. Overall fish biomass and biomass of large predators at Farquhar are substantially higher than other areas within the Seychelles, and are some of the highest recorded in the Indian Ocean. Remote islands like Farquhar Atoll with low human populations and limited fishing pressure offer ideal opportunities for understanding whether reefs can be resilient from global threats if local threats are minimized.     

A review of biology,fisheries and population structure of Dentex dentex (Sparidae)

The common dentex Dentex dentex (Linnaeus, 1758) is an iconic marine coastal fish in the Mediterranean Sea. It is a demersal sparid fish (0–200 m), that grows to a maximum length of 100 cm and a weight of 13 kg, with a relatively long life span (more than 20 years). As a high trophic level predator, it holds a key position in coastal marine food webs. The common dentex is of great economic importance for both artisanal (small-scale coastal fisheries) and recreational fishing. Despite its economic and ecological importance, scientific data on this species in its natural environment are still very scant. The global commercial catch of common dentex has fluctuated over the last 60 years on an interannual time scale, and has declined significantly since the 1990s. There are few data regarding fishing effort and total catch from recreational fishing for common dentex, but it appears that this species is particularly targeted by this activity. The common dentex is now classified as “vulnerable” in the Red List of Threatened Species in the Mediterranean Sea. This review summarizes the current literature on D. dentex in regard to biology, ecology, parasitology, population structure, commercial and recreational fishing, and management regulations. Future research directions to fill gaps in current knowledge are suggested.     

Determination of Total Protein Content of Bacterial Cells by SYPRO Staining and Flow Cytometry

An assay has been developed for measuring protein biomass of marine planktonic bacteria by flow cytometry. The method was calibrated by using five species of Bacteria (an Arcobacter sp., a Cytophaga sp., an Oceanospirillum sp., a Pseudoalteromonas sp., and a Vibrio sp.) recently isolated from seawater samples and grown in culture at different temperatures. The intensity of SYPRO-protein fluorescence of these bacteria strongly correlated with their total protein content, measured by the bicinchoninic acid method to be in the range of 60 to 330 fg of protein cell⁻¹ (r² = 0.93, n = 34). According to the calibration, the mean biomass of planktonic bacteria from the North Sea in August 1998 was 24 fg of protein cell⁻¹.     

Influence of Climate Change and Trophic Coupling across Four Trophic Levels in the Celtic Sea

Climate change has had profound effects upon marine ecosystems, impacting across all trophic levels from plankton to apex predators. Determining the impacts of climate change on marine ecosystems requires understanding the direct effects on all trophic levels as well as indirect effects mediated by trophic coupling. The aim of this study was to investigate the effects of climate change on the pelagic food web in the Celtic Sea, a productive shelf region in the Northeast Atlantic. Using long-term data, we examined possible direct and indirect ‘bottom-up’ climate effects across four trophic levels: phytoplankton, zooplankton, mid-trophic level fish and seabirds. During the period 1986–2007, although there was no temporal trend in the North Atlantic Oscillation index (NAO), the decadal mean Sea Surface Temperature (SST) in the Celtic Sea increased by 0.66±0.02°C. Despite this, there was only a weak signal of climate change in the Celtic Sea food web. Changes in plankton community structure were found, however this was not related to SST or NAO. A negative relationship occurred between herring abundance (0- and 1-group) and spring SST (0-group: p = 0.02, slope = −0.305±0.125; 1-group: p = 0.04, slope = −0.410±0.193). Seabird demographics showed complex species–specific responses. There was evidence of direct effects of spring NAO (on black-legged kittiwake population growth rate: p = 0.03, slope = 0.0314±0.014) as well as indirect bottom-up effects of lagged spring SST (on razorbill breeding success: p = 0.01, slope = −0.144±0.05). Negative relationships between breeding success and population growth rate of razorbills and common guillemots may be explained by interactions between mid-trophic level fish. Our findings show that the impacts of climate change on the Celtic Sea ecosystem is not as marked as in nearby regions (e.g. the North Sea), emphasizing the need for more research at regional scales.     

Estimating the rate of increase for the finless porpoise with special attention to predictions for the Inland Sea population in Japan

The finless porpoise Neophocaena asiaeorientalis inhabits coastal waters and rivers in East Asia and is exposed to various human activities. This species is listed on the IUCN Red List of Threatened Species due to a reduction in abundance. Although human-induced mortality can be a threat to porpoise populations, future anthropogenic impacts have not been quantitatively evaluated due to lack of demographic information. Adequate future population projections are needed to form the basis for conservation measures before the population declines to critical levels. We conducted a population viability analysis for the population of finless porpoise in the Inland Sea, Japan using a Leslie matrix model composed of age-specific survival and fertility rates. We described the uncertainty in the annual rate of increase (λ) for the finless porpoise using randomly sampled estimates of survival rate for other cetaceans with similar life histories. Plausible median estimates of λ ranged from 1.041 (age at first reproduction [AFR] = 7) to 1.056 (AFR = 5). Future population changes and extinction probabilities were predicted after combining these estimates with a predicted human-induced mortality rate (M) and available abundance estimates. The extinction probability after 100 years was 0 %. However, the probability of the quasi-extinction (<100 individuals) was as high as 79.0 % after 100 years. The results also suggest that the persistence of the finless porpoise population could be achieved with a small effort to reduce anthropogenic mortality.     

Environment outweighs the effects of fishing in regulating demersal community structure in an exploited marine ecosystem

Global climate change has already caused bottom temperatures of coastal marine ecosystems to increase worldwide. These ecosystems face many pressures, of which fishing is one of the most important. While consequences of global warming on commercial species are studied extensively, the importance of the increase in bottom temperature and of variation in fishing effort is more rarely considered together in these exploited ecosystems. Using a 17 year time series from an international bottom trawl survey, we investigated covariations of an entire demersal ecosystem (101 taxa) with the environment in the Celtic Sea. Our results showed that over the past two decades, biotic communities in the Celtic Sea were likely controlled more by environmental variables than fisheries, probably due to its long history of exploitation. At the scale of the entire zone, relations between taxa and the environment remained stable over the years, but at a local scale, in the center of the Celtic Sea, dynamics were probably driven by interannual variation in temperature. Fishing was an important factor structuring species assemblages at the beginning of the time series (2000) but decreased in importance after 2009. This was most likely caused by a change in spatial distribution of fishing effort, following a change in targeted taxa from nephrops to deeper water anglerfish that did not covary with fishing effort. Increasing bottom temperatures could induce additional changes in the coming years, notably in the cold‐water commercial species cod, hake, nephrops, and American plaice. We showed that analyzing covariation is an effective way to screen a large number of taxa and highlight those that may be most susceptible to future simultaneous increases in temperature and changes in exploitation pattern by fisheries. This information can be particularly relevant for ecosystem assessments.     

The likelihood of extinction of iconic and dominant herbivores and detritivores of coral reefs: the parrotfishes and surgeonfishes

Parrotfishes and surgeonfishes perform important functional roles in the dynamics of coral reef systems. This is a consequence of their varied feeding behaviors ranging from targeted consumption of living plant material (primarily surgeonfishes) to feeding on detrital aggregates that are either scraped from the reef surface or excavated from the deeper reef substratum (primarily parrotfishes). Increased fishing pressure and widespread habitat destruction have led to population declines for several species of these two groups. Species-specific data on global distribution, population status, life history characteristics, and major threats were compiled for each of the 179 known species of parrotfishes and surgeonfishes to determine the likelihood of extinction of each species under the Categories and Criteria of the IUCN Red List of Threatened Species. Due in part to the extensive distributions of most species and the life history traits exhibited in these two families, only three (1.7%) of the species are listed at an elevated risk of global extinction. The majority of the parrotfishes and surgeonfishes (86%) are listed as Least Concern, 10% are listed as Data Deficient and 1% are listed as Near Threatened. The risk of localized extinction, however, is higher in some areas, particularly in the Coral Triangle region. The relatively low proportion of species globally listed in threatened Categories is highly encouraging, and some conservation successes are attributed to concentrated conservation efforts. However, with the growing realization of man's profound impact on the planet, conservation actions such as improved marine reserve networks, more stringent fishing regulations, and continued monitoring of the population status at the species and community levels are imperative for the prevention of species loss in these groups of important and iconic coral reef fishes.     

Physiology and Phylogeny of Green Sulfur Bacteria Forming a Monospecific Phototrophic Assemblage at a Depth of 100 Meters in the Black Sea

The biomass, phylogenetic composition, and photoautotrophic metabolism of green sulfur bacteria in the Black Sea was assessed in situ and in laboratory enrichments. In the center of the western basin, bacteriochlorophyll e (BChl e) was detected between depths of 90 and 120 m and reached maxima of 54 and 68 ng liter⁻¹. High-pressure liquid chromatography analysis revealed a dominance of farnesyl esters and the presence of four unusual geranyl ester homologs of BChl e. Only traces of BChl e (8 ng liter⁻¹) were found at the northwestern slope of the Black Sea basin, where the chemocline was positioned at a significantly greater depth of 140 m. Stable carbon isotope fractionation values of farnesol indicated an autotrophic growth mode of the green sulfur bacteria. For the first time, light intensities in the Black Sea chemocline were determined employing an integrating quantum meter, which yielded maximum values between 0.0022 and 0.00075 μmol quanta m⁻² s⁻¹ at the top of the green sulfur bacterial layer around solar noon in December. These values represent by far the lowest values reported for any habitat of photosynthetic organisms. Only one 16S rRNA gene sequence type was detected in the chemocline using PCR primers specific for green sulfur bacteria. This previously unknown phylotype groups with the marine cluster of the Chlorobiaceae and was successfully enriched in a mineral medium containing sulfide, dithionite, and freshly prepared yeast extract. Under precisely controlled laboratory conditions, the enriched green sulfur bacterium proved to be capable of exploiting light intensities as low as 0.015 μmol quanta m⁻² s⁻¹ for photosynthetic ¹⁴CO₂ fixation. Calculated in situ doubling times of the green sulfur bacterium range between 3.1 and 26 years depending on the season, and anoxygenic photosynthesis contributes only 0.002 to 0.01% to total sulfide oxidation in the chemocline. The stable population of green sulfur bacteria in the Black Sea chemocline thus represents the most extremely low-light-adapted and slowest-growing type of phototroph known to date.     

A matter of size: the population structure of the smallest known living shark,Etmopterus perryi (Springer & Burgess, 1985), from deep waters off the Colombian Caribbean coast

The dwarf lanternshark (Etmopterus perryi) is the smallest known described shark, and practically no information has been available on this species since first described in the mid-1980s. Therefore, the aim of this work is to describe, for the first time, the population structure regarding dwarf lanternshark in the Colombian Caribbean Sea. During deep-water research surveys conducted along the Colombian Caribbean coast, 87 stations were sampled using the swept area method. A total of 153 dwarf lanternshark individuals were caught in depths ranging from 230 to 530 m. This information was used to describe the size structures, morphological measurements including length-at-weight relationship, length at maturity in females and the spatial distribution of mean length and biomass of the species. The lengths of individuals ranged from 78.02 to 289.00 mm total length (TL), which is a new record of maximum length for this species. The spatial distribution of mean lengths and biomass distributions show high abundances and high relative mean lengths in the northeast area off Santa Marta and the area northwest of Riohacha. The mean biomass density in the whole prospected area was 5.52 kg km⁻². Length at 50% maturity in females was estimated in 203 mm TL (95% C.I. : 190–214 mm). Deep-water elasmobranch species, such as the dwarf lantern shark, are expected to show extremely low resilience to fishing exploitation, even when they are not targeted by commercial fishing. Therefore, the information reported in this study can serve as a baseline upon which management measurements can be proposed for the conservation of this shark species.     

Microfungi and Microbial Activity Along a Heavy Metal Gradient

Soil fungal biomass, microfungal species composition, and soil respiration rate of conifer mor soil were studied along a steep copper and zinc gradient (up to 20,000 μg of Cu and 20,000 μg of Zn g⁻¹ dry soil) around a brass mill near the town of Gusum in South Sweden. Fungal biomass and soil respiration rate decreased by about 75% along the metal gradient. Above 1,000 μg of Cu g⁻¹, the decrease was clearly evident; below 1,000 μg of Cu g⁻¹, no obvious effects were observed, but there was a tendency for a decrease in total mycelial length. No decrease in CFU was found along the gradient, but fungal species composition was drastically changed. The frequency of the genera Penicillium and Oidiodendron decreased from about 30 and 20%, respectively, at the control sites to only a few percent close to the mill. Mortierella was most frequently isolated in moderately polluted sites, but at the highest pollution levels, a decrease in isolation frequency was evident. Some fungal taxa increased in abundance towards the mill, e.g., Geomyces (from 1 to 10%), Paecilomyces (0 to 10%), and sterile forms (from 10 to 20%). Analyses with a multivariate statistical method (partial least squares) showed that organic matter content and soil moisture had little influence on the fungal community compared with the heavy metal pollution.     

Life history and seasonal occurrence of the spotted eagle ray,Aetobatus narinari,in the eastern Gulf of Mexico

The spotted eagle ray, Aetobatus narinari, is listed on the IUCN Red List of Threatened Species as Near Threatened with a decreasing population trend, but many aspects of this ray’s biology and population status are unknown. Aerial and on-water surveys were conducted in the eastern Gulf of Mexico off southwest Florida 2008–2013, to document seasonal occurrence and life history characteristics of this species. Aerial surveys documented spotted eagle rays mostly in spring, summer, and autumn months with larger aggregations observed near inlet passes. Boat-based surveys documented rays on 152 out of 176 survey days, mostly as solitary individuals but sometimes in aggregations of up to 60. More rays were observed when water temperatures were 23-31?ºC. A total of 393 rays (231 males, 161 females, 1 unrecorded sex) were captured, measured, sampled, tagged, and released. Sizes ranged 41.4–203.0 cm disc width (DW) and weight 1.1–105.5 kg. Male size at 50 % maturity was 127 cm DW. Five percent (19) of tagged rays were recaptured after 5–1,293 days at liberty and recaptured rays exhibited faster growth than previously estimated from vertebral readings. Based on observations of rays relative to survey effort, numbers of observed rays declined after 2009 for reasons not yet understood. This observation, together with concerns about sustainability of fisheries targeting these rays in nearby Mexico and Cuba, underscore the need for investigations into stock structure, population trends, growth, and critical habitat of spotted eagle rays throughout the Gulf of Mexico, Caribbean Sea, and elsewhere in their range.     

Species, sex, size and male maturity composition of previously unreported elasmobranch landings in Kuwait, Qatar and Abu Dhabi Emirate

This paper presents data from the first major survey of the diversity, biology and fisheries of elasmobranchs in the Persian (Arabian) Gulf. Substantial landings of elasmobranchs, usually as gillnet by-catch, were recorded in Kuwait, Qatar and the Emirate of Abu Dhabi (part of the United Arab Emirates), although larger elasmobranchs from targeted line fisheries were landed in Abu Dhabi. The elasmobranch fauna recorded was distinctive and included species that are undescribed, rare and have a highly restricted known distribution. Numerical abundance was dominated by sharks (c. 80%), of which carcharhinids were by far the most important. The milk shark Rhizoprionodon acutus and whitecheek shark Carcharhinus dussumieri together comprised just under half of all recorded individuals. Around 90% of recorded sharks were small (50-90 cm total length, L(T) ) individuals, most of which were mature individuals of species with a small maximum size (<100 cm L(T) ), although immature individuals of larger species (e.g. Carcharhinus sorrah and other Carcharhinus spp.) were also important. The most frequently recorded batoid taxa were cownose rays Rhinoptera spp., an undescribed whipray, and the granulated guitarfish Rhinobatos granulatus. The first size, sex and maturity data for a wide range of Gulf elasmobranch species are presented (including L(T) at 50% maturity for males of four shark species) and include some notable differences from other locations in the Indo-West Pacific Ocean. A number of concerns regarding the sustainability of the fishery were highlighted by this study, notably that most of the batoid species recorded are classed by the IUCN Red List as vulnerable, endangered, data deficient or not evaluated. Despite their considerable elasmobranch landings, none of the three countries sampled have developed a 'Shark Plan' as encouraged to do so under the FAO International Plan of Action: Sharks. Furthermore, Kuwait and Qatar currently report zero or no elasmobranch landings to the FAO.     

Embryonic diapause in the elasmobranchs

Embryonic diapause is a temporary suspension of development at any stage of embryogenesis, which prolongs the gestation period, allowing parturition to occur in conditions that are more suitable for newborns. This reproductive trait is widespread among all vertebrates, including elasmobranchs. Although it has only been confirmed in two elasmobranchs (Rhizoprionodon taylori and Dasyatis say), evidence indicates that at least 14 species of rays and two sharks undergo diapause, suggesting that this form of reproduction exists within a wide range of elasmobranch reproductive modes, including lecithotrophs and matrotrophs. Where it has been studied, embryogenesis is arrested at the blastodisc stage and preserved in the uterus for periods from four to 10?months. There are still many questions that remain unanswered concerning the knowledge on the biology of most diapausing species but it is clear that species benefit differently from this reproductive trait. As in other vertebrates, it is likely that environmental cues and hormones (especially progesterone and prolactin) are involved in the control of diapause in elasmobranchs, however rigorous testing of current hypothesis remains to be carried out.     

Molecular phylogeny of elasmobranchs inferred from mitochondrial and nuclear markers

The elasmobranchs (sharks, rays and skates) being the extant survivors of one of the earliest offshoots of the vertebrate evolutionary tree are good model organisms to study the primitive vertebrate conditions. They play a significant role in maintaining the ecological balance and have high economic value. Due to over-exploitation and illegal fishing worldwide, the elasmobranch stocks are being decimated at an alarming rate. Appropriate management measures are necessary for restoring depleted elasmobranch stocks. One approach for restoring stocks is implementation of conservation measures and these measures can be formulated effectively by knowing the evolutionary relationship among the elasmobranchs. In this study, a total of 30 species were chosen for molecular phylogeny studies using mitochondrial cytochrome c oxidase subunit I, 12S ribosomal RNA gene and nuclear Internal Transcribed Spacer 2. Among different genes, the combined dataset of COI and 12S rRNA resulted in a well resolved tree topology with significant bootstrap/posterior probabilities values. The results supported the reciprocal monophyly of sharks and batoids. Within Galeomorphii, Heterodontiformes (bullhead sharks) formed as a sister group to Lamniformes (mackerel sharks): Orectolobiformes (carpet sharks) and to Carcharhiniformes (ground sharks). Within batoids, the Myliobatiformes formed a monophyly group while Pristiformes (sawfishes) and Rhinobatiformes (guitar fishes) formed a sister group to all other batoids.     

Energetics of Syntrophic Propionate Oxidation in Defined Batch and Chemostat Cocultures

Propionate consumption was studied in syntrophic batch and chemostat cocultures of Syntrophobacter fumaroxidans and Methanospirillum hungatei. The Gibbs free energy available for the H₂-consuming methanogens was <−20 kJ mol of CH₄⁻¹ and thus allowed the synthesis of 1/3 mol of ATP per reaction. The Gibbs free energy available for the propionate oxidizer, on the other hand, was usually >−10 kJ mol of propionate⁻¹. Nevertheless, the syntrophic coculture grew in the chemostat at steady-state rates of 0.04 to 0.07 day⁻¹ and produced maximum biomass yields of 2.6 g mol of propionate⁻¹ and 7.6 g mol of CH₄⁻¹ for S. fumaroxidans and M. hungatei, respectively. The energy efficiency for syntrophic growth of S. fumaroxidans, i.e., the biomass produced per unit of available Gibbs free energy was comparable to a theoretical growth yield of 5 to 12 g mol of ATP⁻¹. However, a lower growth efficiency was observed when sulfate served as an additional electron acceptor, suggesting inefficient energy conservation in the presence of sulfate. The maintenance Gibbs free energy determined from the maintenance coefficient of syntrophically grown S. fumaroxidans was surprisingly low (0.14 kJ h⁻¹ mol of biomass C⁻¹) compared to the theoretical value. On the other hand, the Gibbs free-energy dissipation per mole of biomass C produced was much higher than expected. We conclude that the small Gibbs free energy available in many methanogenic environments is sufficient for syntrophic propionate oxidizers to survive on a Gibbs free energy that is much lower than that theoretically predicted.     

Sphingomonas alaskensis Strain AFO1, an Abundant Oligotrophic Ultramicrobacterium from the North Pacific

Numerous studies have established the importance of picoplankton (microorganisms of ≤2 μm in length) in energy flow and nutrient cycling in marine oligotrophic environments, and significant effort has been directed at identifying and isolating heterotrophic picoplankton from the world's oceans. Using a method of diluting natural seawater to extinction followed by monthly subculturing for 12 months, a bacterium was isolated that was able to form colonies on solid medium. The strain was isolated from a 10⁵ dilution of seawater where the standing bacterial count was 3.1 × 10⁵ cells ml⁻¹. This indicated that the isolate was representative of the most abundant bacteria at the sampling site, 1.5 km from Cape Muroto, Japan. The bacterium was characterized and found to be ultramicrosized (less than 0.1 μm³), and the size varied to only a small degree when the cells were starved or grown in rich media. A detailed molecular (16S rRNA sequence, DNA-DNA hybridization, G+C mol%, genome size), chemotaxonomic (lipid analysis, morphology), and physiological (resistance to hydrogen peroxide, heat, and ethanol) characterization of the bacterium revealed that it was a strain of Sphingomonas alaskensis. The type strain, RB2256, was previously isolated from Resurrection Bay, Alaska, and similar isolates have been obtained from the North Sea. The isolation of this species over an extended period, its high abundance at the time of sampling, and its geographical distribution indicate that it has the capacity to proliferate in ocean waters and is therefore likely to be an important contributor in terms of biomass and nutrient cycling in marine environments.