Body volumes and internal space constraints in articulate brachiopods

first_imgBrachiopods were once dominant in all the oceans of the world. but their distributions are non more restricted. There are few species which are found in shallow warm habitats and these are predominantly small. They have exceptionally low metabolic rates and exhibit low energy lifestyles. The majority of living articulate brachiopods are punctate (possessing mantle extensions. or caeca. which traverse the shell). Evidence produced hei-e suggests that the evolution of these phenomena may have been strongly affected by architectural constraints placed on articulate brachiopods by the use of the lophophore for feeding and respiration. They are essentially space limited because of the large volume needed for this organ. In some punctate brachiopods over 75% of their total body volume may be occupied by the lophophore and mantle cavity. This figure is only 60% in an impunctate (no caeca) species and may be only 20% in bivalve molluses. The implications are that caeca evolved to reduce pressure on space requirements, that maximum sizes may be set by the scaling patterns of space allocation and metabolic efficiency is a consequence of space constraints. Current distribution patterns may be strongly affected by the low metabolism and low energy lifestyles. The relative success of small brachiopods in warm shallow seas may have been facilitated by the scaling patterns of space allocations which show small specimens to have similar mantle cavity volumes to bivalve molluscs.last_img read more

A simplified method for determining the gross chemical composition of pinniped milk samples

first_imgRecent studies of lactation in wild mammals have emphasised the need for accurate information on milk composition, requiring the analysis of large numbers of samples. A simplified method for determining milk composition in pinnipeds was assessed using samples collected from Antarctic fur seals (Arctocephalus gazella). The stoichiometric relationships between elemental C, H, and N in the ash-free dry mass were used to determine the organic composition and energy content of samples. The results were compared with those obtained by conventional biochemical analyses. Stoichiometric estimates of lipid content were positively correlated with those obtained by methanol–chloroform extraction (r2 = 0.62, P < 0.0001) but consistently lower (P < 0.0005). The mean difference between the results of the two methods was 3.56 ± 0.89% of total milk volume (range −16.98 to +7.47%). Variation between replicates was significantly lower when the stoichiometric method was used (P < 0.05). Gross energy content, calculated from stoichiometric estimates of milk composition, was closely correlated with, though consistently higher than (P < 0.0005), that determined by bomb calorimetry (r2 = 0.96, P < 0.0001). The difference between the two methods, however, was negligible (1.8 ± 0.08%, range −5.0 to +5.6%). The sum of the milk components measured by the stoichiometric method accounted, on average, for 96.5% of the wet mass and varied inversely with lipid content (r2 = 0.29, P < 0.001). This small error is most likely due to retained water in the oven-dried milk. The stoichiometric method for determining organic composition allows the processing of samples at a much faster rate, requiring much smaller volumes, than conventional techniques and should prove useful in ecological studies of lactation.last_img read more

Foraging location and range of white-chinned petrels Procellaria aequinoctialis breeding in the South Atlantic

first_imgThe foraging range and principal feeding areas of White-chinned Petrels breeding at South Georgia were determined using satellite telemetry. Foraging trips during incubation lasted 12–15 days and covered 3000–8000 km and 2–11 days and 1100–5900 km during chick-rearing. Adults covered less distance per day during chick-rearing (71 km) than during incubation (91 km) but the proportion covered at night (47%) was the same. Mean (31–34 km/h) and maximum (80 km/h) flight velocities were similar during both periods of the breeding season and during day and night. Between incubation shifts, White-chinned Petrels travelled to the Patagonian shelf; during chick-rearing they foraged more extensively. Most locations were between 30° to 55°W and 52° to 60°W around South Georgia/Shag Rocks and south to the South Orkney Islands. Diet samples from known foraging locations suggested birds fed mainly on krill and squid. They caught the squid Brachioteuthis? picta and Galiteuthis glacialis around Shag Rocks/South Georgia and also at sites close to the South Orkney Islands; Illex argentinus on the Patagonian shelf. Dispersal of adults after breeding failure was south to the South Orkney Islands then west to the Falkland Islands. This study confirms that breeding White-chinned Petrels are amongst the widest-ranging of seabirds; they may minimise competition with other Procellariiformes in the South Atlantic by their more extensive foraging range. The nature and extent of their range also brings substantial risk of high mortality rate in South Atlantic long-line fisheries.last_img read more

Deglacial history of the West Antarctic Ice Sheet in the western Amundsen Sea Embayment

first_imgThe Amundsen Sea Embayment (ASE) drains approximately 35% of the West Antarctic Ice Sheet (WAIS) and is one of the most rapidly changing parts of the cryosphere. In order to predict future ice sheet behaviour, modellers require long-term records of ice-sheet melting to constrain and build confidence in their simulations. Here, we present detailed marine geological and radiocarbon data along three palaeo-ice stream tributary troughs in the western ASE to establish vital information on the timing of deglaciation of the WAIS since the Last Glacial Maximum (LGM). We have undertaken multi-proxy analyses of the cores (core description, shear strength, x-radiographs, magnetic susceptibility, wet bulk density, total organic carbon/nitrogen, carbonate content and clay mineral analyses) in order to: (1) characterise the sedimentological facies and depositional environments; and (2) identify the horizon(s) in each core that would yield the most reliable age for deglaciation. In accordance with previous studies we identify three key facies, which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments. These facies are: i) subglacial, ii) proximal grounding line, and iii) seasonal open marine. In addition, we incorporate ages from other facies (e.g., glaciomarine diamictons deposited at some distance from the grounding line, such as glaciogenic debris flows and iceberg-rafted diamictons and turbates) into our deglacial model. In total, we have dated 78 samples (mainly the acid insoluble organic (AIO) fraction, but also calcareous foraminifers), which include 63 downcore and 15 surface samples. Through careful sample selection prior to dating, we have established a robust deglacial chronology for this sector of the WAIS. Our data show that deglaciation of the western ASE was probably underway as early as 22,351 calibrated years before present (cal yr BP), reaching the mid-shelf by 13,837 cal yr BP and the inner shelf to within c.10-12 km of the present ice shelf front between 12,618 and 10,072 cal yr BR The deglacial steps in the western ASE broadly coincide with the rapid rises in sea-level associated with global meltwater pulses 1 a and 1b, although given the potential dating uncertainty, additional, more precise ages are required before these findings can be fully substantiated. Finally, we show that the rate of ice-sheet retreat increased across the deep (up to 1600 m) basins of the inner shelf, highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation.last_img read more

Geothermal environments in Antarctica

first_imgGeothermal environments in Antarctica have profound ecological and scientific value. They are single points of heat and moisture in an icy and dry landscape, and provide habitats for diverse living organisms, some of which are found nowhere else on Earth. They may have provided refuges through repeated glacial cycles for diverse moss and invertebrate communities, crucially stabilizing populations in non-geothermal sites over long time periods. The unique features of these sites render them easily impacted, with physical damage and foreign biological contamination being the principal concerns. To address the need to manage activities that impact terrestrial geothermal environments in Antarctica, a Code of Conduct has been developed by SCAR and endorsed by Antarctic Treaty Parties.last_img read more

Statistical properties of plasmaspheric hiss from Van Allen Probes observations

first_imgVan Allen Probes observations are used to statistically investigate plasmaspheric hiss wave properties. This analysis shows that the wave normal direction of plasmaspheric hiss is predominantly field aligned at larger L shells, with a bimodal distribution, consisting of a near‐field aligned and a highly oblique component, becoming apparent at lower L shells. Investigation of this oblique population reveals that it is most prevalent at L 0.01 (or f > 700 Hz), low geomagnetic activity levels, and between 1900 and 0900 magnetic local time. This structure is similar to that reported for oblique chorus waves in the equatorial region, perhaps suggesting a causal link between the two wave modes. Ray tracing results from HOTRAY confirm that it is feasible for these oblique chorus waves to be a source of the observed oblique plasmaspheric hiss population. The decrease in oblique plasmaspheric hiss occurrence rates during more elevated geomagnetic activity levels may be attributed to the increase in Landau resonant electrons causing oblique chorus waves to be more substantially damped outside of the plasmasphere. In turn, this restricts the amount of wave power that can access the plasmasphere and evolve into oblique plasmaspheric hiss. These results confirm that, despite the difference in location of this bimodal distribution compared to previous studies, a direct link between oblique equatorial chorus outside of the plasmasphere and oblique hiss at low L shells is plausible. As such, these results are in keeping with the existing theory of chorus as the source of plasmaspheric hiss.last_img read more

A “shallow bathtub ring” of local sedimentary iron input maintains the Palmer Deep biological hotspot on the West Antarctic Peninsula shelf

first_imgPalmer Deep (PD) is one of several regional hotspots of biological productivity along the inner shelf of the West Antarctic Peninsula. The proximity of hotspots to shelf-crossing deep troughs has led to the ‘canyon hypothesis’, which proposes that circumpolar deep water flowing shoreward along the canyons is upwelled on the inner shelf, carrying nutrients including iron (Fe) to surface waters, maintaining phytoplankton blooms. We present here full-depth profiles of dissolved and particulate Fe and manganese (Mn) from eight stations around PD, sampled in January and early February of 2015 and 2016, allowing the first detailed evaluation of Fe sources to the area’s euphotic zone. We show that upwelling of deep water does not control Fe flux to the surface; instead, shallow sediment-sourced Fe inputs are transported horizontally from surrounding coastlines, creating strong vertical gradients of dissolved Fe within the upper 100 m that supply this limiting nutrient to the local ecosystem. The supply of bioavailable Fe is, therefore, not significantly related to the canyon transport of deep water. Near shore time-series samples reveal that local glacial meltwater appears to be an important Mn source but, surprisingly, is not a large direct Fe input to this biological hotspot.last_img read more

Biogeographical patterns in soil bacterial communities across the Arctic region

first_imgThe considerable microbial diversity of soils and key role in biogeochemical cycling have led to growing interest in their global distribution and the impact that environmental change might have at the regional level. In the broadest study of Arctic soil bacterial communities to date, we used high-throughput DNA sequencing to investigate the bacterial diversity from 200 independent Arctic soil samples from 43 sites. We quantified the impact of spatial and environmental factors on bacterial community structure using variation partitioning analysis, illustrating a nonrandom distribution across the region. pH was confirmed as the key environmental driver structuring Arctic soil bacterial communities, while total organic carbon (TOC), moisture and conductivity were shown to have little effect. Specialist taxa were more abundant in acidic and alkaline soils while generalist taxa were more abundant in acidoneutral soils. Of the 48 147 bacterial taxa, a core microbiome composed of only 13 taxa that were ubiquitously distributed and present within 95% of samples was identified, illustrating the high potential for endemism in the region. Overall, our results demonstrate the importance of spatial and edaphic factors on the structure of Arctic soil bacterial communities.last_img read more

Non-contact measurement system for hot water drilled ice boreholes

first_imgA programmable borehole measurement system was deployed in hot water drilled ice holes during the ‘Bed Access and Monitoring of Ice Sheet History’ (BEAMISH) project to drill to the bed of the Rutford Ice Stream in West Antarctica. This system operates autonomously (no live data) after deployment, and records borehole diameter (non-contact measurement), water column pressure, heading and inclination. Three cameras, two sideways looking and one vertical, are also included for visual inspection of hole integrity and sediments. The system is small, lightweight (~35.5 kg) and low power using only 6 ‘D’ cell sized lithium batteries, making it ideal for transport and use in remote field sites. The system is 2.81 m long and 165 mm in diameter, and can be deployed attached to the drill hose for measurements during drilling or on its own deployment line afterwards. The full system is discussed in detail, highlighting design strengths and weaknesses. Data from the BEAMISH project are also presented in the form of camera images showing hole integrity, and sensor data used to calculate borehole diameter through the full length of the hole. These data are used to show confidence in hole verticality and subsurface cavity development and connection.last_img read more

Late Home Run Clinches WCC Title for Cougars

first_imgGame Summary Player Highlights Abraham Valdez: 2-3, HR, 2 R, BB, 2 RBIJustin Sterner: 7.0 IP, 1 ER, 0 BB, 6 KReid McLaughlin: W (7-1), 2.0 IP, 0 ER, 0 BB, 2 K At 36-15 and 19-8 in conference play, the Cougars claim their third WCC regular season title to go with championships in 2016 and 2017. BYU now awaits the results of the Gonzaga and LMU series – should Gonzaga lose Saturday night or Sunday at LMU, BYU will win the WCC title outright and claim the No. 1 seed in the conference tournament next week. If the Bulldogs win both games, Gonzaga and BYU will tie in the standings and the Cougars will be the No. 2 seed. May 18, 2019 /Sports News – Local Late Home Run Clinches WCC Title for Cougars Robert Lovell BYU will next play at the WCC Tournament held at Banner Island Ballpark in Stockton, California. The double elimination tournament begins Thursday, May 23, and will be aired live on TheW.tv, BYU Radio and ESPN960. Cougar starter Justin Sterner carried BYU through the first seven innings of the game, allowing just two hits with no walks and six strikeouts on the day. BYU and Santa Clara exchanged runs in the second inning before bats on both sides fell mostly silent over the next six. But in the top of the ninth, BYU freshman first baseman Austin Deming led off the inning with a single for the Cougars. Two batters later, Valdez launched a 1-0 pitch over the left field wall to put BYU ahead, 3-1. After closing out the Broncos and earning the save in game two Friday night, freshman Reid McLaughlin came on in relief in the eighth Saturday, striking out two to earn the win. Now at 7-1 with four saves on the year, McLaughlin is the first pitcher in BYU history to win at least seven games and have at least four saves in a single season. FacebookTwitterLinkedInEmailSANTA CLARA, Calif. – A two-run homer by Abraham Valdez in the ninth inning gave No. 24 BYU baseball the 3-1 win over Santa Clara and clinched at least a share of the West Coast Conference regular season title on Saturday. “The guys really stepped up today and got it done,” BYU head coach Mike Littlewood said. “We got a great start from Justin (Sterner) and Abe came up huge. This was an incredibly tough series.” Abraham Valdez had the game-winning hit on the first home run of his career to break a 1-1 tie in the top of the ninthJustin Sterner and Reid McLaughlin combined to hold the Broncos to one run while allowing zero walks and collecting eight strikeoutsThe Cougars have now won six of seven series against Santa Clara since beginning WCC play in 2013 Written by Tags: BYU Cougars Baseball/WCC/WCC Championslast_img read more