5 research outputs found
LITHOTHAMNION SPECIES (HAPALIDIALES, RHODOPHYTA) IN THE ARCTIC AND SUBARCTIC: PROVIDING A SYSTEMATICS FOUNDATION IN A TIME OF RAPID CLIMATE CHANGE
International audienceCoralline red algae in the genera Clathromorphum, Phymatolithon and Lithothamnion are important benthic ecosystem engineers in the photic zone of the Arctic and Subarctic. In these regions, the systematics and biogeography of Clathromorphum and Phymatolithon species have mostly been resolved whereas Lithothamnion species have not. Seventy-three specific and infraspecific names have been given to Arctic and Subarctic Lithothamnion specimens, the vast majority by Mikael H. Foslie in the late 19th and early 20th century. From the type specimens of 38 of these names, partial rbcL sequences were obtained that enabled us to correctly apply the earliest available names and to correctly place the remainder in synonymy. Three of the four Arctic and Subarctic Lithothamnion species, L. lemoineae, L. soriferum and L. tophiforme were distinct based on all three sequenced genes, two plastid encoded, rbcL and psbA, and the mitochondrial encoded COI-5P; rbcL and COI-5P also segregated L. glaciale from L. tophiforme but psbA did not. Based on DNA sequences, morpho-anatomy and biogeography, we recognize all four species. It is difficult to identify these species based on morpho-anatomy and they can all occur as encrusting corallines, as rhodoliths or as maerl. We demonstrate the importance of sequencing these historical type specimens by showing that the recently proposed northeast Atlantic L. erinaceum is a synonym of one of the earliest published Arctic species of Lithothamnion, L. soriferum, itself incorrectly placed in synonymy under L. tophiforme based on morpho-anatomy. Based on sequenced specimens, we update the distributions and ecology of these species.
Lithothamnion (Hapalidiales, Rhodophyta) in the changing Arctic and Subarctic: DNA sequencing of type and recent specimens provides a systematics foundation*
Coralline red algae in the non-geniculate genera Clathromorphum, Phymatolithon and Lithothamnion are important benthic ecosystem engineers in the photic zone of the Arctic and Subarctic. In these regions, the systematics and biogeography of Clathromorphum and Phymatolithon have mostly been resolved whereas Lithothamnion has not, until now. Seventy-three specific and infraspecific names were given to Arctic and Subarctic Lithothamnion specimens in the late 19th and early 20th century by Frans R. Kjellman and Mikael H. Foslie. DNA sequences from 36 type specimens, five historical specimens, and an extensive sampling of recent collections resulted in the recognition of four Arctic and Subarctic Lithothamnion species, L. glaciale, L. lemoineae, L. soriferum and L. tophiforme. Three genes were sequenced, two plastid-encoded, rbcL and psbA, and the mitochondrial encoded COI-5P; rbcL and COI-5P segregated L. glaciale from L. tophiforme but psbA did not. Partial rbcL sequences obtained from type collections enabled us to correctly apply the earliest available names and to correctly place the remainder in synonymy. We were unable to sequence another 22 type specimens, but all of these are more recent names than those that are now applied. It is difficult to identify these species solely on morpho-anatomy as they can all occur as encrusting corallines or as maerl (rhodoliths). We demonstrate the importance of sequencing historical type specimens by showing that the recently proposed North-east Atlantic L. erinaceum is a synonym of one of the earliest published Arctic species of Lithothamnion, L. soriferum, itself incorrectly placed in synonymy under L. tophiforme based on morpho-anatomy. Based on sequenced specimens, we update the distributions and ecology of these species
Potential predation rates by the sea stars Asterias rubens and Marthasterias glacialis, on juvenile scallops, Pecten maximus, ready for sea ranching
What’s Hiding Behind Ontogenetic δ13C Variations in Mollusk Shells? New Insights from the Great Scallop (Pecten maximus)
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Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum
Abstract
Inelastic beam-gas collisions at the Large Hadron Collider
(LHC), within a few hundred metres of the ATLAS experiment, are
known to give the dominant contribution to beam backgrounds. These
are monitored by ATLAS with a dedicated Beam Conditions Monitor
(BCM) and with the rate of fake jets in the calorimeters. These two
methods are complementary since the BCM probes backgrounds just
around the beam pipe while fake jets are observed at radii of up to
several metres. In order to quantify the correlation between the
residual gas density in the LHC beam vacuum and the experimental
backgrounds recorded by ATLAS, several dedicated tests were
performed during LHC Run 2. Local pressure bumps, with a gas
density several orders of magnitude higher than during normal
operation, were introduced at different locations. The changes of
beam-related backgrounds, seen in ATLAS, are correlated with the
local pressure variation. In addition the rates of beam-gas events
are estimated from the pressure measurements and pressure bump
profiles obtained from calculations. Using these rates, the
efficiency of the ATLAS beam background monitors to detect beam-gas
events is derived as a function of distance from the interaction
point. These efficiencies and characteristic distributions of fake
jets from the beam backgrounds are found to be in good agreement
with results of beam-gas simulations performed with the
Fluka Monte Carlo programme.</jats:p