548 research outputs found
Diversity of Zoanthids (Anthozoa: Hexacorallia) on Hawaiian Seamounts: Description of the Hawaiian Gold Coral and Additional Zoanthids
The Hawaiian gold coral has a history of exploitation from the deep slopes and seamounts of the Hawaiian Islands as one of the precious corals commercialised in the jewellery industry. Due to its peculiar characteristic of building a scleroproteic skeleton, this zoanthid has been referred as Gerardia sp. (a junior synonym of Savalia Nardo, 1844) but never formally described or examined by taxonomists despite its commercial interest. While collection of Hawaiian gold coral is now regulated, globally seamounts habitats are increasingly threatened by a variety of anthropogenic impacts. However, impact assessment studies and conservation measures cannot be taken without consistent knowledge of the biodiversity of such environments. Recently, multiple samples of octocoral-associated zoanthids were collected from the deep slopes of the islands and seamounts of the Hawaiian Archipelago. The molecular and morphological examination of these zoanthids revealed the presence of at least five different species including the gold coral. Among these only the gold coral appeared to create its own skeleton, two other species are simply using the octocoral as substrate, and the situation is not clear for the final two species. Phylogenetically, all these species appear related to zoanthids of the genus Savalia as well as to the octocoral-associated zoanthid Corallizoanthus tsukaharai, suggesting a common ancestor to all octocoral-associated zoanthids. The diversity of zoanthids described or observed during this study is comparable to levels of diversity found in shallow water tropical coral reefs. Such unexpected species diversity is symptomatic of the lack of biological exploration and taxonomic studies of the diversity of seamount hexacorals
Molecular diversity of coral reef-associated zoanthids off Qeshm Island, northern Persian Gulf
The role of herbivores in shaping subtropical coral communities in warming oceans
Tropicalization is rapidly restructuring subtropical marine communities. A key driver for tropicalization is changes in herbivory pressure that are linked with degrading ecosystem stability. Consequently, subtropical algal beds are being displaced by climate-mediated colonisation of coral communities. This process is thought to be aided by the elevated herbivory resulting from tropicalization, but the relative contribution to herbivory by different taxa is not fully understood. Evaluating herbivory pressure and its effect on coral cover and rugosity across a subtropical latitudinal gradient will help predict how these processes may change with further tropicalization and ocean warming. Herbivory pressure exerted by fishes and urchins across this subtropical latitudinal gradient remains unquantified. Using in-situ feeding observations, we quantify fish and urchin herbivory pressure at seven sites across non-accreting coral communities, and warmer accreting coral reefs in southern Japan. We then relate herbivory pressure to respective fish and urchin community structure and coral cover and rugosity. Urchin herbivory is greater on non-accreting coral communities than on true coral accreting reefs; a result which is reversed for fish herbivory. Overall, herbivory pressure is greater on accreting coral reefs than on coral non-accreting communities, but is dependent on reef characteristics as community structures differ more strongly among reefs than between regions. These factors are linked to coral cover and rugosity that differ between reefs, but not between climatic regions, further emphasising the influence of local factors on the benthic cover and the associated fish and urchin community, and thus herbivory pressure. Our findings provide a foundation for understanding how non-accreting coral communities may respond to ongoing tropicalization, given the fish and invertebrate herbivores they host
Temperate functional niche availability not resident-invader competition shapes tropicalisation in reef fishes
Temperate reefs are at the forefront of warming-induced community alterations resulting from poleward range shifts. This tropicalisation is exemplified and amplified by tropical species’ invasions of temperate herbivory functions. However, whether other temperate ecosystem functions are similarly invaded by tropical species, and by what drivers, remains unclear. We examine tropicalisation footprints in nine reef fish functional groups using trait-based analyses and biomass of 550 fish species across tropical to temperate gradients in Japan and Australia. We discover that functional niches in transitional communities are asynchronously invaded by tropical species, but with congruent invasion schedules for functional groups across the two hemispheres. These differences in functional group tropicalisation point to habitat availability as a key determinant of multi-species range shifts, as in the majority of functional groups tropical and temperate species share functional niche space in suitable habitat. Competition among species from different thermal guilds played little part in limiting tropicalisation, rather available functional space occupied by temperate species indicates that tropical species can invade. Characterising these drivers of reef tropicalisation is pivotal to understanding, predicting, and managing marine community transformation
A community and functional comparison of coral and reef fish assemblages between four decades of coastal urbanisation and thermal stress
1. Urbanized coral reefs experience anthropogenic disturbances caused by coastal development, pollution, and nutrient runoff, resulting in turbid, marginal conditions in which only certain species can persist. Mortality effects are exacerbated by increasingly regular thermal stress events, leading to shifts towards novel communities dominated by habitat generalists and species with low structural complexity.
2. There is limited data on the turnover processes that occur due to this convergence of anthropogenic stressors, and how novel urban ecosystems are structured both at the community and functional levels. As such, it is unclear how they will respond to future disturbance events.
3. Here, we examine the patterns of coral reef community change and determine whether ecosystem functions provided by specialist species are lost post-disturbance. We present a comparison of community and functional trait-based changes for scleractinian coral genera and reef fish species assemblages subject to coastal development, coastal modification, and mass bleaching between two time periods, 1975–1976 and 2018, in Nakagusuku Bay, Okinawa, Japan.
4. We observed an increase in fish habitat generalists, a dominance shift from branching to massive/sub-massive corals and increasing site-based coral genera richness between years. Fish and coral communities significantly reassembled, but functional trait-based multivariate space remained constant, indicating a turnover of species with similar traits. A compression of coral habitat occurred, with shallow (8 m) coral genera shifting towards the mid-depths (5–8 m).
5. We show that although reef species assemblages altered post disturbance, new communities retained similar ecosystem functions. This result could be linked to the stressors experienced by urban reefs, which reflect those that will occur at an increasing frequency globally in the near future. Yet, even after shifts to disturbed communities, these fully functioning reef systems may maintain high conservation value
Detection of Gamma-Ray Emission from the Starburst Galaxies M82 and NGC 253 with the Large Area Telescope on Fermi
We report the detection of high-energy gamma-ray emission from two starburst
galaxies using data obtained with the Large Area Telescope on board the Fermi
Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been
detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from
sources positionally coincident with locations of the starburst galaxies M82
and NGC 253. The total fluxes of the sources are consistent with gamma-ray
emission originating from the interaction of cosmic rays with local
interstellar gas and radiation fields and constitute evidence for a link
between massive star formation and gamma-ray emission in star-forming galaxies.Comment: Submitted to ApJ Letter
Fermi Gamma-ray Imaging of a Radio Galaxy
The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating
from the giant radio lobes of the radio galaxy Centaurus A. The resolved
gamma-ray image shows the lobes clearly separated from the central active
source. In contrast to all other active galaxies detected so far in high-energy
gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the
total source emission. The gamma-ray emission from the lobes is interpreted as
inverse Compton scattered relic radiation from the cosmic microwave background
(CMB), with additional contribution at higher energies from the
infrared-to-optical extragalactic background light (EBL). These measurements
provide gamma-ray constraints on the magnetic field and particle energy content
in radio galaxy lobes, and a promising method to probe the cosmic relic photon
fields.Comment: 27 pages, includes Supplementary Online Material; corresponding
authors: C.C. Cheung, Y. Fukazawa, J. Knodlseder, L. Stawar
Coral assemblages at higher latitudes favour short-term potential over long-term performance
The persistent exposure of coral assemblages to more variable abiotic regimes is assumed to augment their resilience to future climatic variability. Yet, while the determinants of coral population resilience across species remain unknown, we are unable to predict the winners and losers across reef ecosystems exposed to increasingly variable conditions. Using annual surveys of 3171 coral individuals across Australia and Japan (2016-2019), we explore spatial variation across the short- and long-term dynamics of competitive, stress-tolerant, and weedy assemblages to evaluate how abiotic variability mediates the structural composition of coral assemblages. We illustrate how, by promoting short-term potential over long-term performance, coral assemblages can reduce their vulnerability to stochastic environments. However, compared to stress-tolerant, and weedy assemblages, competitive coral taxa display a reduced capacity for elevating their short-term potential. Accordingly, future climatic shifts threaten the structural complexity of coral assemblages in variable environments, emulating the degradation expected across global tropical reef
Fermi Large Area Telescope observations of PSR J1836+5925
The discovery of the gamma-ray pulsar PSR J1836+5925, powering the formerly
unidentified EGRET source 3EG J1835+5918, was one of the early accomplishments
of the Fermi Large Area Telescope (LAT). Sitting 25 degrees off the Galactic
plane, PSR J1836+5925 is a 173 ms pulsar with a characteristic age of 1.8
million years, a spindown luminosity of 1.1 erg s, and a
large off-peak emission component, making it quite unusual among the known
gamma-ray pulsar population. We present an analysis of one year of LAT data,
including an updated timing solution, detailed spectral results and a long-term
light curve showing no indication of variability. No evidence for a surrounding
pulsar wind nebula is seen and the spectral characteristics of the off-peak
emission indicate it is likely magnetospheric. Analysis of recent XMM
observations of the X-ray counterpart yields a detailed characterization of its
spectrum, which, like Geminga, is consistent with that of a neutron star
showing evidence for both magnetospheric and thermal emission.Comment: Accepted to Astrophysical Journa
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