Directed conservation of the world's reef sharks and rays

Many shark populations are in decline around the world, with severe ecological and economic consequences. Fisheries management and marine protected areas (MPAs) have both been heralded as solutions. However, the effectiveness of MPAs alone is questionable, particularly for globally threatened sharks and rays ('elasmobranchs'), with little known about how fisheries management and MPAs interact to conserve these species. Here we use a dedicated global survey of coral reef elasmobranchs to assess 66 fully protected areas embedded within a range of fisheries management regimes across 36 countries. We show that conservation benefits were primarily for reef-associated sharks, which were twice as abundant in fully protected areas compared with areas open to fishing. Conservation benefits were greatest in large protected areas that incorporate distinct reefs. However, the same benefits were not evident for rays or wide-ranging sharks that are both economically and ecologically important while also threatened with extinction. We show that conservation benefits from fully protected areas are close to doubled when embedded within areas of effective fisheries management, highlighting the importance of a mixed management approach of both effective fisheries management and well-designed fully protected areas to conserve tropical elasmobranch assemblages globally.

Widespread diversity deficits of coral reef sharks and rays

A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities.

Effects of human footprint and biophysical factors on the body-size structure of fished marine species

Marine fisheries in coastal ecosystems in many areas of the world have historically removed large-bodied individuals, potentially impairing ecosystem functioning and the long-term sustainability of fish populations. Reporting on size-based indicators that link to food-web structure can contribute to ecosystem-based management, but the application of these indicators over large (cross-ecosystem) geographical scales has been limited to either fisheries-dependent catch data or diver-based methods restricted to shallow waters (<20 m) that can misrepresent the abundance of large-bodied fished species. We obtained data on the body-size structure of 82 recreationally or commercially targeted marine demersal teleosts from 2904 deployments of baited remote underwater stereo-video (stereo-BRUV). Sampling was at up to 50 m depth and covered approximately 10,000 km of the continental shelf of Australia. Seascape relief, water depth, and human gravity (i.e., a proxy of human impacts) were the strongest predictors of the probability of occurrence of large fishes and the abundance of fishes above the minimum legal size of capture. No-take marine reserves had a positive effect on the abundance of fishes above legal size, although the effect varied across species groups. In contrast, sublegal fishes were best predicted by gradients in sea surface temperature (mean and variance). In areas of low human impact, large fishes were about three times more likely to be encountered and fishes of legal size were approximately five times more abundant. For conspicuous species groups with contrasting habitat, environmental, and biogeographic affinities, abundance of legal-size fishes typically declined as human impact increased. Our large-scale quantitative analyses highlight the combined importance of seascape complexity, regions with low human footprint, and no-take marine reserves in protecting large-bodied fishes across a broad range of species and ecosystem configurations.

Climate-assisted persistence of tropical fish vagrants in temperate marine ecosystems

Rising temperatures and extreme climate events are propelling tropical species into temperate marine ecosystems, but not all species can persist. Here, we used the heatwave-driven expatriation of tropical Black Rabbitfish (Siganus fuscescens) to the temperate environments of Western Australia to assess the ecological and evolutionary mechanisms that may entail their persistence. Population genomic assays for this rabbitfish indicated little genetic differentiation between tropical residents and vagrants to temperate environments due to high migration rates, which were likely enhanced by the marine heatwave. DNA metabarcoding revealed a diverse diet for this species based on phytoplankton and algae, as well as an ability to feed on regional resources, including kelp. Irrespective of future climate scenarios, these macroalgae-consuming vagrants may self-recruit in temperate environments and further expand their geographic range by the year 2100. This expansion may compromise the health of the kelp forests that form Australia's Great Southern Reef. Overall, our study demonstrates that projected favourable climate conditions, continued large-scale genetic connectivity between populations, and diet versatility are key for tropical range-shifting fish to establish in temperate ecosystems.

Increased connectivity and depth improve the effectiveness of marine reserves

Marine reserves are a key tool for the conservation of marine biodiversity, yet only ~2.5% of the world's oceans are protected. The integration of marine reserves into connected networks representing all habitats has been encouraged by international agreements, yet the benefits of this design has not been tested empirically. Australia has one of the largest systems of marine reserves, providing a rare opportunity to assess how connectivity influences conservation success. An Australia-wide dataset was collected using baited remote underwater video systems deployed across a depth range from 0 to 100 m to assess the effectiveness of marine reserves for protecting teleosts subject to commercial and recreational fishing. A meta-analytical comparison of 73 fished species within 91 marine reserves found that, on average, marine reserves had 28% greater abundance and 53% greater biomass of fished species compared to adjacent areas open to fishing. However, benefits of protection were not observed across all reserves (heterogeneity), so full subsets generalized additive modelling was used to consider factors that influence marine reserve effectiveness, including distance-based and ecological metrics of connectivity among reserves. Our results suggest that increased connectivity and depth improve the aforementioned marine reserve benefits and that these factors should be considered to optimize such benefits over time. We provide important guidance on factors to consider when implementing marine reserves for the purpose of increasing the abundance and size of fished species, given the expected increase in coverage globally. We show that marine reserves that are highly protected (no-take) and designed to optimize connectivity, size and depth range can provide an effective conservation strategy for fished species in temperate and tropical waters within an overarching marine biodiversity conservation framework.

Global status and conservation potential of reef sharks

Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status^1,2. Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats³. Here we address this knowledge gap using data from more than 15,000 standardized baited remote underwater video stations that were deployed on 371 reefs in 58 nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

eDNA metabarcoding survey reveals fine-scale coral reef community variation across a remote, tropical island ecosystem

Environmental DNA (eDNA) metabarcoding, a technique for retrieving multispecies DNA from environmental samples, can detect a diverse array of marine species from filtered seawater samples. There is a growing potential to integrate eDNA alongside existing monitoring methods in order to establish or improve the assessment of species diversity. Remote island reefs are increasingly vulnerable to climate-related threats and as such there is a pressing need for cost-effective whole-ecosystem surveying to baseline biodiversity, study assemblage changes and ultimately develop sustainable management plans. We investigated the utility of eDNA metabarcoding as a high-resolution, multitrophic biomonitoring tool at the Cocos (Keeling) Islands, Australia (CKI)-a remote tropical coral reef atoll situated within the eastern Indian Ocean. Metabarcoding assays targeting the mitochondrial 16S rRNA and CO1 genes, as well as the 18S rRNA nuclear gene, were applied to 252 surface seawater samples collected from 42 sites within a 140 km² area. Our assays successfully detected a wide range of bony fish and elasmobranchs (244 taxa), crustaceans (88), molluscs (37) and echinoderms (7). Assemblage composition varied significantly between sites, reflecting habitat partitioning across the island ecosystem and demonstrating the localisation of eDNA signals, despite extensive tidal and oceanic movements. In addition, we document putative new occurrence records for 46 taxa and compare the efficiency of our eDNA approach to visual survey techniques at CKI. Our study demonstrates the utility of a multimarker metabarcoding approach in capturing multitrophic biodiversity across an entire coral reef atoll and sets an important baseline for ongoing monitoring and management.

An examination of introgression and incomplete lineage sorting among three closely related species of chocolate-dipped damselfish (genus: Chromis)

AIM

To determine the impact of ecological and environmental histories on the evolution of coral reef damselfishes at two adjacent marine biogeographic suture zones.

LOCATION

Indo-West Pacific, notably including two suture zones: Socotra and Christmas and Cocos/Keeling Islands.

TAXON

Chromis dimidiata, Chromis margaritifer, and Chromis fieldi.

METHODS

We utilized a combination of nuclear and mitochondrial genetic markers in addition to visual abundance survey data of these fishes.

RESULTS

Despite genetic patterns consistent with incomplete lineage sorting and relatively low genetic differentiation among the three studied Chromis species, there is evidence of hybridization between C. margaritifer and C. fieldi at Christmas Island based on molecular and visual identification. Introgression appears to be spreading westwards to other C. fieldi populations based on COI haplotype comparison. Moreover, the genetic distance between C. margaritifer and C. fieldi suggests that Pleistocene sea-level fluctuations may have contributed to allopatric divergence and secondary contact between these two closely related species.

MAIN CONCLUSIONS

Our study highlights that evolutionary processes in coral reef fishes operate differently between suture zones, possibly due to different ecological and environmental predispositions regulating secondary contact of sister species. While secondary contact likely led to hybridization and introgression at Christmas and Cocos/Keeling Islands, none of those processes seem present at Socotra for the chocolate-dipped damselfish. This difference is likely due to an environmental barrier caused by hydrodynamic regimes in the Gulf of Aden.

Cryptic lineages in the Wolf Cardinalfish living in sympatry on remote coral atolls

Coral reef health and biodiversity is under threat worldwide due to rapid climate change. However, much of the inter- and intra-specific diversity of coral reefs are undescribed even in well studied taxa such as fish. Delimiting previously unrecognised diversity is important for understanding the processes that generate and sustain biodiversity in coral reef ecosystems and informing strategies for their conservation and management. Many taxa that inhabit geographically isolated coral reefs rely on self-recruitment for population persistence, providing the opportunity for the evolution of unique genetic lineages through divergent selection and reproductive isolation. Many such lineages in corals and fish are morphologically similar or indistinguishable. Here, we report the discovery and characterisation of cryptic lineages of the Wolf Cardinalfish, Cheilodipterus artus, from the coral atolls of northwest Australia using multiple molecular markers from mitochondrial (CO1 and D-loop) and nuclear (microsatellites) DNA. Concordant results from all markers identified two highly divergent lineages that are morphologically cryptic and reproductively isolated. These lineages co-occurred at daytime resting sites, but the relative abundance of each lineage was strongly correlated with wave exposure. It appears, therefore, that fish from each lineage are better adapted to different microhabitats. Such cryptic and ecologically based diversity appears to be common in these atolls and may well aid resilience of these systems. Our results also highlight that underwater surveys based on visual identification clearly underestimate biodiversity, and that a taxonomic revision of the Cheilodipterus genus is necessary.

The Microbiome of the Gastrointestinal Tract of a Range-Shifting Marine Herbivorous Fish

Globally, marine species’ distributions are being modified due to rising ocean temperatures. Increasing evidence suggests a circum-global pattern of poleward extensions in the distributions of many tropical herbivorous species, including the ecologically important rabbitfish Siganus fuscescens. Adaptability of a species to such new environments may be heavily influenced by the composition of their gastrointestinal microbe fauna, which is fundamentally important to animal health. Siganus fuscescens thus provides an opportunity to assess the stability of gastrointestinal microbes under varying environmental conditions. The gastrointestinal microbial communities of S. fuscescens were characterized over 2,000 km of Australia’s western coast, from tropical to temperate waters, including near its current southern distributional limit. Sequencing of the 16S rRNA gene demonstrated that each population had a distinct hindgut microbial community, and yet, 20 OTUs occurred consistently in all samples. These OTUs were considered the ‘core microbiome’ and were highly abundant, composing between 31 and 54% of each population. Furthermore, levels of short chain fatty acids, an indicator of microbial fermentation activity, were similar among tropical and temperate locations. These data suggest that flexibility in the hindgut microbiome may play a role in enabling such herbivores to colonize new environments beyond their existing range.

Visually induced analgesia in a deep tissue experimental pain model: A randomised crossover experiment

BACKGROUND

Visualizing one's own painful body part appears to have an effect on reported pain intensity. Furthermore, it seems that manipulating the size of the viewed image can determine the direction and extent of this phenomenon. When visual distortion has been applied to clinical populations, the analgesic effects have been in opposition to those observed in some experimental pain models. To help resolve this problem, we explored the effect of visualisation and magnification of the visual image on reported pain using a delayed onset muscle soreness (DOMS) pain model.

METHODS

We induced DOMS in the quadriceps of 20 healthy volunteers. Forty-eight hours later, participants performed a series of painful contractions of the DOMS-affected muscle under four randomised conditions: (1) Viewing the injured thigh; (2) Viewing the contralateral thigh; (3) Viewing a neutral object; and (4) Viewing the injured thigh through magnifying glasses. For each condition, participants rated their pain intensity during a series of painful contractions.

RESULTS

We observed that direct visualisation of the injured thigh had no effect on pain intensity when compared to viewing the contralateral thigh or neutral object. However, magnification of the DOMS-affected leg during the performance of painful contractions caused participants to report more pain than when viewing the injured thigh normally.

CONCLUSIONS

These results further demonstrate that the effect of visualisation varies between different pain conditions. These results may have implications for the integration of visual feedback into clinical practice.

SIGNIFICANCE

We present delayed onset muscle soreness as a model for exploring visually induced analgesia. Our findings suggest that this phenomenon is expressed differently in exogenous and endogenous experimental pain models. Further exploration may offer a potential pathway for the integration of visual analgesia into the management of clinical pain.

Strong population structure deduced from genetics, otolith chemistry and parasite abundances explains vulnerability to localized fishery collapse in a large Sciaenid fish, Protonibea diacanthus

As pressure on coastal marine resources is increasing globally, the need to quantitatively assess vulnerable fish stocks is crucial in order to avoid the ecological consequences of stock depletions. Species of Sciaenidae (croakers, drums) are important components of tropical and temperate fisheries and are especially vulnerable to exploitation. The black‐spotted croaker, Protonibea diacanthus, is the only large sciaenid in coastal waters of northern Australia where it is targeted by commercial, recreational and indigenous fishers due to its food value and predictable aggregating behaviour. Localized declines in the abundance of this species have been observed, highlighting the urgent requirement by managers for information on fine‐ and broad‐scale population connectivity. This study examined the population structure of P. diacanthus across north‐western Australia using three complementary methods: genetic variation in microsatellite markers, otolith elemental composition and parasite assemblage composition. The genetic analyses demonstrated that there were at least five genetically distinct populations across the study region, with gene flow most likely restricted by inshore biogeographic barriers such as the Dampier Peninsula. The otolith chemistry and parasite analyses also revealed strong spatial variation among locations within broad‐scale regions, suggesting fine‐scale location fidelity within the lifetimes of individual fish. The complementarity of the three techniques elucidated patterns of connectivity over a range of spatial and temporal scales. We conclude that fisheries stock assessments and management are required at fine scales (100 s of km) to account for the restricted exchange among populations (stocks) and to prevent localized extirpations of this species. Realistic management arrangements may involve the successive closure and opening of fishing areas to reduce fishing pressure.

The radio spectra of planar aromatic heterocycles: how to quantify and predict the negative inertial defects

The simplest tricyclic aromatic nitrogen heterocyclic molecules 5,6-benzoquinoline and 7,8-benzoquinoline are possible candidates for detection of aromatic systems in the interstellar medium.

Characterization, development and multiplexing of microsatellite markers in three commercially exploited reef fish and their application for stock identification

Thirty-four microsatellite loci were isolated from three reef fish species; golden snapper Lutjanus johnii, blackspotted croaker Protonibea diacanthus and grass emperor Lethrinus laticaudis using a next generation sequencing approach. Both IonTorrent single reads and Illumina MiSeq paired-end reads were used, with the latter demonstrating a higher quality of reads than the IonTorrent. From the 1–1.5 million raw reads per species, we successfully obtained 10–13 polymorphic loci for each species, which satisfied stringent design criteria. We developed multiplex panels for the amplification of the golden snapper and the blackspotted croaker loci, as well as post-amplification pooling panels for the grass emperor loci. The microsatellites characterized in this work were tested across three locations of northern Australia. The microsatellites we developed can detect population differentiation across northern Australia and may be used for genetic structure studies and stock identification.

Real-time PCR validation of visually identified snapper Chrysophrys auratus (Sparidae) eggs

In this study, a total of 212 eggs were visually identified as snapper Chrysophrys auratus. Real-time PCR confirmed visual identification in 69% of cases but corroboration varied widely among plankton samples. The use of molecular tools to support visual identification prior to adopting daily egg production stock assessment methods should be considered.

Subtle genetic structure reveals restricted connectivity among populations of a coral reef fish inhabiting remote atolls

We utilized a spatial and temporal analyses of genetic structure, supplemented with ecological and oceanographic analysis, to assess patterns of population connectivity in a coral reef fish Chromis margaritifer among the unique and remote atolls in the eastern Indian Ocean. A subtle, but significant genetic discontinuity at 10 microsatellite DNA loci was detected between atoll systems corresponding with a low (≤ 1%) probability of advection across the hundreds of kilometers of open ocean that separates them. Thus, although genetic connections between systems are likely maintained by occasional long-distance dispersal of C. margaritifer larvae, ecological population connectivity at this spatial scale appears to be restricted. Further, within one of these atoll systems, significant spatial differentiation among samples was accompanied by a lack of temporal pairwise differentiation between recruit and adult samples, indicating that restrictions to connectivity also occur at a local scale (tens of kilometers). In contrast, a signal of panmixia was detected at the other atoll system studied. Lastly, greater relatedness and reduced genetic diversity within recruit samples was associated with relatively large differences among them, indicating the presence of sweepstakes reproduction whereby a small proportion of adults contributes to recruitment in the next generation. These results are congruent with earlier work on hard corals, suggesting that local production of larvae drives population replenishment in these atoll systems for a range of coral reef species.

A cross-sectional study on levels of second-hand smoke in restaurants and bars in five cities in China

OBJECTIVES

To assess indoor second-hand smoke (SHS) exposure in restaurants and bars via PM(2.5) (fine particles 2.5 μm in diameter and smaller) level measurements in five cities in China.

METHODS

The study was conducted from July to September in 2007 in Beijing, Xi'an, Wuhan, Kunming and Guiyang. Portable aerosol monitors were used to measure PM(2.5) concentrations in 404 restaurants and bars. The occupant density and the active smoker density were calculated for each venue sampled.

RESULTS

Among the 404 surveyed venues, 23 had complete smoking bans, 9 had partial smoking bans and 313 (77.5%) were observed to have allowed smoking during sampling. The geometric mean of indoor PM(2.5) levels in venues with smoking observed was 208 μg/m(3) and 99 μg/m(3) in venues without observed smoking. When outdoor PM(2.5) levels were adjusted, indoor PM(2.5) levels in venues with smoking observed were consistently significantly higher than in venues without smoking observed (F=80.49, p<0.001). Indoor PM(2.5) levels were positively correlated with outdoor PM(2.5) levels (partial rho=0.37 p<0.001) and active smoker density (partial rho=0.34, p<0.001).

CONCLUSIONS

Consistent with findings in other countries, PM(2.5) levels in smoking places are significantly higher than those in smoke-free places and are strongly related to the number and density of active smokers. These findings document the high levels of SHS in hospitality venues in China and point to the urgent need for comprehensive smoke-free laws in China to protect the public from SHS hazards, as called for in Article 8 of the Framework Convention on Tobacco Control, which was ratified by China in 2005.

A cross-sectional study on levels of secondhand smoke in restaurants and bars in five cities in China

OBJECTIVES

To assess indoor secondhand smoke (SHS) exposure in restaurants and bars via PM(2.5) level measurements in five cities in China.

METHODS

The study was conducted from July to September in 2007 in Beijing, Xi'an, Wuhan, Kunming and Guiyang. PM(2.5) concentrations were measured in 404 restaurants and bars using portable aerosol monitors. The occupant density and the active smoker density were calculated for each venue sampled.

RESULTS

Among the 404 surveyed venues, 23 had complete smoking bans, nine had partial smoking bans and 313 (77.5%) had smoking observed during sampling. The geometric mean of indoor PM(2.5) levels in venues with smoking observed was 208 μg/m(3) and 99 μg/m(3) in venues without smoking observed. When outdoor PM(2.5) levels were adjusted, indoor PM(2.5) levels in venues with smoking observed were consistently significantly higher than those in venues without smoking observed (F=80.49, p<0.001). Indoor PM(2.5) levels were positively correlated with outdoor PM(2.5) levels (partial ρ=0.37 p<0.001) and active smoker density (partial ρ=0.34, p<0.001).

CONCLUSIONS

Consistent with findings in other countries, PM(2.5) levels in smoking places are significantly higher than those in smoke-free places and are strongly related to the number and density of active smokers. These findings document the high levels of SHS in hospitality venues in China and point to the urgent need for comprehensive smoke-free laws in China to protect the public from SHS hazards, as called for in Article 8 of the Framework Convention on Tobacco Control, which was ratified by China in 2005.

A 32-country comparison of tobacco smoke derived particle levels in indoor public places

OBJECTIVE

To compare tobacco smoke-derived particulate levels in transportation and hospitality venues with and without smoking in 32 countries using a standardised measurement protocol.

METHODS

The TSI SidePak AM510 Personal Aerosol Monitor was used to measure the concentration of particulate matter less than 2.5 microns in diameter (PM(2.5)) in 1822 bars, restaurants, retail outlets, airports and other workplaces in 32 geographically dispersed countries between 2003 and 2007.

RESULTS

Geometric mean PM(2.5) levels were highest in Syria (372 microg/m(3)), Romania (366 microg/m(3)) and Lebanon (346 microg/m(3)), while they were lowest in the three countries that have nationwide laws prohibiting smoking in indoor public places (Ireland at 22 microg/m(3), Uruguay at 18 microg/m(3) and New Zealand at 8 microg/m(3)). On average, the PM(2.5) levels in places where smoking was observed was 8.9 times greater (95% CI 8.0 to 10) than levels in places where smoking was not observed.

CONCLUSIONS

Levels of indoor fine particle air pollution in places where smoking is observed are typically greater than levels that the World Health Organization and US Environmental Protection Agency have concluded are harmful to human health.

Exposure to secondhand smoke at home and in public places in Syria: a developing country's perspective

This study employs sensitive methods to address the issue of exposure to secondhand smoke among children and women in an understudied developing country setting (Syria). The study combines data collected by the Syrian Center for Tobacco Studies as part of two international studies conducted in 2006: the Secondhand Smoke Exposure among Women and Children study (Johns Hopkins) and the Global Air Monitoring Study (Roswell Park Cancer Institute). We employed objective measures (hair nicotine, and ambient household nicotine assessed by passive monitors) to assess children's and mothers' exposure to secondhand smoke at home, and used the TSI SidePak personal aerosol monitor to sample respirable suspended particles less than 2.5 microm diameter (PM(2.5)) in the air in public places (40 restaurants/cafés in Aleppo). In homes, the mean ambient nicotine level (+/- standard deviation, SD) was 2.24 +/- 2.77 microg/m(3). Mean level of hair nicotine was 11.8 ng/mg among children (n = 54), and was higher if the mother was a smoker (19.4 +/- 23.6 ng/mg) than nonsmoker (5.2 +/- 6.9 ng/mg) (p < .05). Mean hair nicotine among nonsmoking mothers (n = 23) was 1.17 +/- 1.56 ng/mg. Children's hair nicotine level was strongly correlated with ambient household nicotine and number of cigarettes smoked daily in the house (r = .54 and r = .50, respectively, p < .001), and also was related to having a father who smoked in the children's presence. In public places, average PM(2.5) in the monitored 40 hospitality venues was 464 microg/m(3) and correlated with smoker density measured as cigarettes-waterpipes/100 m(3) (r = .31, p = 0.049). Thus, children in Syria are exposed to high levels of secondhand smoke at home, in which mothers' smoking plays a major role. Also, levels of respirable hazardous particles are high in public hospitality venues, putting customers and workers at serious health risks. Efforts to limit exposure of children and women at home and to adopt clean air policies should become a public health priority in Syria and the Arab region.

Microwave Spectra of the Methylpolyynes CH3(C identical withC)4H and CH3(C identical withC)5H

Following the laboratory detection by Fourier transform microwave spectroscopy of the four new methylcyanopolyynes described in the accompanying paper by W. Chen et al. (J. Mol. Spectrosc. 1998), we detected two new methylpolyynes, CH3(C identical withC)4H and CH3(C identical withC)5H. The strongest lines of both molecules, obtained in a discharge with a dilute mixture of methylacetylene and diacetylene in neon, were quite intense: after 4 min of integration, a signal to noise of about 300 for the strongest lines of CH3(C identical withC)4H and 30 for those of CH3(C identical withC)5H. Enough rotational transitions from the K = 0 and 1 ladders were detected in either molecule to be confident of the identification and to determine the rotational and leading centrifugal distortion constants to high accuracy. Like other carbon chains, the two here may be important in combustion processes and may be detectable in the interstellar gas, where the two shortest methylpolyynes have already been observed. Copyright 1998 Academic Press.

Microwave Spectra of the Methylcyanopolyynes CH3(C&tbond;C)nCN, n = 2, 3, 4, 5

The ground state rotational spectra of four methylcyanopolyynes CH3(C&tbond;C)2CN, CH3(C&tbond;C)3CN, CH3(C&tbond;C)4CN, and CH3(C&tbond;C)5CN were measured between 6 and 22 GHz by Fourier transform microwave spectroscopy. For CH3(C&tbond;C)2CN, previously observed by Alexander et al. [J. Mol. Spectrosc. 70, 84-94 (1978)] eight transitions were observed, each with sufficient resolution to determine the nitrogen quadrupole hyperfine constant for the first time: eqQ = -4.25(3) MHz. The longer three methylcyanopolyynes are new; for these, from 10 to 21 rotational transitions were detected and precise values for the rotational and the leading centrifugal distortion constants, and eqQ for CH3(C&tbond;C)3CN, were determined. Copyright 1998 Academic Press.

First astronomical detection of the cumulene carbon chain molecule H2C6 in TMC-1

The cumulene carbenes are important components of hydrocarbon chemistry in low-mass star-forming cores. Here we report the first astronomical detection of the long-chain cumulene carbene H2C6 in the interstellar cloud TMC-1, from observations of two of its rotational transitions: J(K,K') = 7(1,7) --> 6(1,6) at 18.8 GHz and 8(1,8) --> 7(1,7) at 21.5 GHz, using NASA's Deep Space Network 70 m antenna at Goldstone, California. In addition we also observed the shorter cumulene carbene H2C4 at the same position. The fractional abundance of H2C6 relative to H2 is about 4.7 x 10(-11) and that of H2C4 is about 4.1 x 10(-9). The abundance of H2C6 is in fairly good agreement with gas-phase chemical models for young molecular cloud cores, but the abundance of H2C4 is significantly larger than predicted.

Detection and Characterization of the Cumulene Carbenes H2C5 and H2C6

Two cumulene carbenes, H2C5 and H2C6, were detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Their rotational and leading centrifugal distortion constants were determined with high accuracy, such that the entire radio spectrum can now be calculated. Like the known carbenes H2C3 and H2C4, both molecules have singlet electronic ground states and linear carbon-chain backbones. They can be produced in sufficiently high concentrations in the laboratory that their electronic spectra, expected to lie in the visible, should be readily detectable by laser spectroscopy. The microwave spectra of other, more exotic isomers may be detectable as well.