Growth and Size of the Tropical Sea Cucumber Holothuria (Halodeima) atra Jager at Enewetak Atoll, Marshall Islands

In September 1975, 5031 sea cucumbers (Holothuria atra Jager) were tagged with tetracycline and returned to a gutter on the seaward reef bench of Ananij Island, Enewetak Atoll, Marshall Islands. A sample of 184 individuals was collected in September 1976. Animals were dissected and plates of the calcareous ring were examined with ultraviolet radiation for tetracycline lines. Based on 18 tagged individuals, the Brody-Bertalanffy growth constants are: K = 0.11 and P = 0.89 cm (for interradial plates). Length (L, cm) and weight (W, g) of individuals are related to plate size: L = 36.35P and W = 1950P3, giving maximum size as 32 cm and 1352 g. Length frequency distributions for the population did not change from 1975 to 1976. A preliminary estimate of annual loss is 50 to 70 percent of the total population based on the growth parameters and population size structure. Holothuria atra shows asexual reproduction by transverse fission, which appears to be the major source of recruitment at Ananij rather than from the plankton

Growth, Regeneration, and Damage Repair of Spines of the Slate-Pencil Sea Urchin Heterocentrotus mammillatus (L.) (Echinodermata: Echinoidea )

Spines of sea urchins are appendages that are associated with defense, locomotion, and food gathering. Spines are repaired when damaged, and the dynamics of repair was studied in the slate-pencil sea urchin Heterocentrotus mammillatus to provide insights not only into the processes of healing. but also into the normal growth of spines and the formation of growth lines. Regeneration of spines on tubercles following complete removal of a spine was slow and depended upon the size of the original spine. The maximum amount of regeneration occurred on tubercles with spines of intermediate size (1.6 g), which, on average, developed regenerated spines weighing 0.1, 0.3, and 0.7 g after 4, 8, and 12 months, respectively. Some large tubercles, which had original spines weighing over 3 g, failed to develop a new spine even after 8-12 months. Regeneration of a new tip on a cut stump was more rapid than production of a new spine on a tubercle. Regeneration to original size was more rapid for small spines than for large spines, but large stumps produced more calcite per unit time. In 4 months, a small spine with a removed tip weighing 0.15 g regenerated a new tip weighing 0.09 g, or 63% of its original weight. In the same time, a large spine with 2.35 g of tip removed regenerated 0.40 g of new tip, or 17% of the original weight. Holes were drilled in spines to serve as bench marks to document the production of new growth lines in response to damage. Blind holes drilled in spines caused 65% loss over 4 months, but holes drilled completely through spines caused only a 6% loss. Cutting a spine near its base did not initiate shedding of the stump. Repair of holes drilled in spines showed that major repair originated from the spine surface, and regeneration into the hole was over obtuse angles. For a slanting hole through a spine, filling of the hole carne from the distal edge for the distal opening and from the proximal edge for the proximal opening. Spines were tagged with tetracycline, but of 46 spines examined 4-12 months following treatment, only 1 displayed evidence that the spine surface had been marked. This suggests that spines usually are not growing. Abrasion of spines either by wiping with a cloth or sanding with emery paper failed to induce growth lines to form. Of 57 abraded spines and 64 unabraded spines, only 2 in each treatment category developed new growth lines. Results show that some growth lines in spines develop from trauma, but these tend to be local and do not extend from the base to the tip. Spines of Heterocentrotus mammillatus usually are not growing but occasionally undergo a growth episode that produces a growth line that extends from the milled ring to the spine tip. Such an episode is not related to damage repair from abrasion or breakage and appears to be endogenous. The SPINES OF A SEA URCHIN are morphological parts that serve as the animal's first defense against assaults from the environment (e.g., Fricke 1974, Strathmann 1981), appendages for gathering and manipulating food (e.g., Ebert 1968, Leighton 1968), and braces for wedging into crevices (e.g., Regis and Thomassin 1982). Spines form an important part of an urchin's maintenance mechanisms (Ebert 1982), and it is no surprise to find that they are repaired rapidly once damaged (Ebert 1967, Heat field 1971, Mischor 1975). Spine sizes vary greatly across taxa. For example, in St rongylocentrotus purpuratus (Stimpson 1857), calcite of a large primary spine weighs only about 0.03 g. In slate-pencil sea urchins of the genus Heterocentrotus, spines are substantially more massive. Calcite in a large H. mammillatus (Linneaus 1758) spine may weigh over 5 g, and calcite of a large primary spine of H. trigonarius (Lamarck 1816) may weigh over 11 g. Although spines from Strongylocentrotus purpuratus would be expected to be repaired rapidly (Ebert 1967, Heatfield 1971), it is less clear whether very large spines from Heterocentrotus species also would be repaired in just a few months or whether the benefits of large spines carry a potential burden of a long regeneration time. A second issue associated with damage repair focuses on growth lines in spines. In St rongylocentrotus purpuratus, lines form as a consequence of tip regeneration following breakage (Ebert 1967, Heatfield 1971 ), but growth lines in Heterocentrotus spp. have been interpreted as periodic (Dotan and Fishelson 1985, Weber 1969), an interpretation that has been disputed (Ebert 1985, 1987). The purpose of this paper is to present results of a 1-year study on Heterocentrotus mammillatus (family Echinometridae), a species with massive spines. The focus is on the responses of spines to damage, spine repair and regeneration in response to trauma, and the formation of growth lines. Data are presented on (a) regeneration following total removal of spines; (b) repair rates of calcite on cut spine stubs; (c) responses of spines to small holes drilled into or through them; (d) responses of spines to abrasion; and (e) results of tagging spines with tetracycline

Local variations of growth, feeding, regeneration and size structure in a natural population of the sea urchin, Strongylocentrotus purpuratus (Stimpson)

vi, 133 leaves : ill. ; 22 cm Photocopy of the 1966 edition Thesis--Oregon Bibliography: leaves 99-103 University of Oregon theses, Dept. of Biology, Ph.D., 196

The Origin of Primordial Dwarf Stars and Baryonic Dark Matter

I present a scenario for the production of low mass, degenerate dwarfs of mass $>0.1 M_{\odot}$ via the mechanism of Lenzuni, Chernoff & Salpeter (1992). Such objects meet the mass limit requirements for halo dark matter from microlensing surveys while circumventing the chemical evolution constraints on normal white dwarf stars. I describe methods to observationally constrain this scenario and suggest that such objects may originate in small clusters formed from the thermal instability of shocked, heated gas in dark matter haloes, such as suggested by Fall & Rees (1985) for globular clusters.Comment: TeX, 4 pages plus 2 postscript figures. To appear in Astrophysical Journal Letter

Atmospheric ice nuclei in the Eyjafjallajökull volcanic ash plume

We have sampled atmospheric ice nuclei (IN) and aerosol in Germany and in Israel during spring 2010. IN were analyzed by the static vapor diffusion chamber FRIDGE, as well as by electron microscopy. During the Eyjafjallajökull volcanic eruption of April 2010 we have measured the highest ice nucleus number concentrations (>600 l−1) in our record of 2 yr of daily IN measurements in central Germany. Even in Israel, located about 5000 km away from Iceland, IN were as high as otherwise only during desert dust storms. The fraction of aerosol activated as ice nuclei at −18 °C and 119% rhice and the corresponding area density of ice-active sites per aerosol surface were considerably higher than what we observed during an intense outbreak of Saharan dust over Europe in May 2008. Pure volcanic ash accounts for at least 53–68% of the 239 individual ice nucleating particles that we collected in aerosol samples from the event and analyzed by electron microscopy. Volcanic ash samples that had been collected close to the eruption site were aerosolized in the laboratory and measured by FRIDGE. Our analysis confirms the relatively poor ice nucleating efficiency (at −18 °C and 119% ice-saturation) of such "fresh" volcanic ash, as it had recently been found by other workers. We find that both the fraction of the aerosol that is active as ice nuclei as well as the density of ice-active sites on the aerosol surface are three orders of magnitude larger in the samples collected from ambient air during the volcanic peaks than in the aerosolized samples from the ash collected close to the eruption site. From this we conclude that the ice-nucleating properties of volcanic ash may be altered substantially by aging and processing during long-range transport in the atmosphere, and that global volcanism deserves further attention as a potential source of atmospheric ice nuclei

Comment on the new Ds(∗)+π0D_s^{(*)+} \pi^0 resonances

We propose an explanation of the new resonances observed in $D_s^{(*)+} \pi^0$ decays. We suggest that the data can be explained by the mixing of conventional p-wave excited $D_s^+$ mesons with 4-quark states. The narrow states observed in $D_s^+ \pi^0$ and $D_s^{*+}\pi^0$ are primarily p-wave $D_{sJ}^{*}$ states, while the predominantly 4-quark states are shifted above $D^{(*)} K$ threshold and should be broad. Ranges for the mixing parameter and mass of the 4-quark state in this scenario are given. Other experimental consequences are discussed.Comment: 4 pages, 2 figures. Updated references. To appear in Phys. Lett.

Messages of hope: Using positive stories of survival to assist recovery in Rwanda

For the past twenty years, the overriding story of Rwanda has been centred around the events and consequences of the genocide. In Rwanda, public expressions of that story have occurred in the gacaca courts, where survivors and perpetrators testified about their experiences and actions, during ongoing annual remembrance and mourning commemorations, and in memorial sites across the country that act as physical reminders of the genocide. While important as mechanisms for justice, testimony, and commemoration, on their own such events and installations also have the potential to re-traumatise. Accordingly, Rwandan agencies have encouraged a focus on the future as the overarching theme of recent national commemorations. Yet, opportunities for Rwandans to recount and disseminate positive, future-oriented stories of survival and healing remain sparse. Creation and awareness of positive stories have the potential to assist in recovery by increasing feelings of hope and efficacy; and recent research has demonstrated the value of hopefulness, well-being, and social support for vulnerable people. The Messages of Hope program seeks to leverage those ideas into a framework for generating positive messages by Rwandan survivors, providing an opportunity for everyday Rwandans to record and transmit their own positive stories of survival to demonstrate recovery and growth after the genocide, and to reinforce connectedness by sharing their challenges and aspirations. We describe the development and early implementation of this initiative and its potential longer-term application in other contexts of vulnerability

Radiation Driven Implosion and Triggered Star Formation

We present simulations of initially stable isothermal clouds exposed to ionizing radiation from a discrete external source, and identify the conditions that lead to radiatively driven implosion and star formation. We use the Smoothed Particle Hydrodynamics code SEREN (Hubber et al. 2010) and the HEALPix-based photoionization algorithm described in Bisbas et al. (2009). We find that the incident ionizing flux is the critical parameter determining the evolution: high fluxes simply disperse the cloud, whereas low fluxes trigger star formation. We find a clear connection between the intensity of the incident flux and the parameters of star formation.Comment: 4 pages, 2 figures, conference proceedings, IAU Symposium 270 (eds. Alves, Elmegreen, Girart, Trimble