Invasions in Marine Communities: Contrasting Species Richness and Community Composition Across Habitats and Salinity

While many studies of non-native species have examined either soft-bottom or hard-bottom marine communities, including artificial structures at docks and marinas, formal comparisons across these habitat types are rare. The number of non-indigenous species (NIS) may differ among habitats, due to differences in species delivery (trade history) and susceptibility to invasions. In this study, we quantitatively compared NIS to native species richness and distribution and examined community similarity across hard-bottom and soft-sediment habitats in San Francisco Bay, California (USA). Benthic invertebrates were sampled using settlement panels (hard-bottom habitats) and sediment grabs (soft-bottom habitats) in 13 paired sites, including eight in higher salinity areas and five in lower salinity areas during 2 years. Mean NIS richness was greatest in hard-bottom habitat at high salinity, being significantly higher than each (a) native species at high salinity and (b) NIS richness at low salinity. In contrast, mean NIS richness in soft-bottom communities was not significantly different from native species richness in either high- or low-salinity waters, nor was there a difference in NIS richness between salinities. For hard-bottom communities, NIS represented an average of 79% of total species richness per sample at high salinity and 78% at low salinity, whereas the comparable values for soft bottom were 46 and 60%, respectively. On average, NIS occurred at a significantly higher frequency (percent of samples) than native species for hard-bottom habitats at both salinities, but this was not the case for soft-bottom habitats. Finally, NIS contributed significantly to the existing community structure (dissimilarity) across habitat types and salinities. Our results show that NIS richness and occurrence frequency is highest in hard-bottom and high-salinity habitat for this Bay but also that NIS contribute strongly to species richness and community structure across each habitat evaluated.     

Dust production from the hypervelocity impact disruption of the Murchison hydrous CM2 meteorite: Implications for the disruption of hydrous asteroids and the production of interplanetary dust

More than half of the C-type asteroids, the dominant type of asteroid in the outer half of the main-belt, show evidence of hydration in their reflectance spectra. In order to understand the collisional evolution of asteroids and the production of interplanetary dust and to model the infrared signature of small particles in the Solar System it is important to characterize the dust production from primary impact disruption events, and compare the disruption of hydrous and anhydrous targets. We performed a hypervelocity impact disruption experiment on an ∼30 g target of the Murchison CM2 hydrated carbonaceous chondrite meteorite, and compared the results with our previous disruption experiments on anhydrous meteorites including Allende, a CV3 carbonaceous chondrite, and nine ordinary chondrites. Murchison is significantly more friable than the ordinary chondrites or Allende. Nonetheless, on a plot of mass of the largest fragment versus specific impact energy, the Murchison disruption plots within the field of the anhydrous meteorites points, suggesting that Murchison is at least as resistant to impact disruption as the anhydrous meteorites, which require about twice the energy for disruption as terrestrial anhydrous basalt targets. We determined the mass-frequency distribution of the debris from the Murchison disruption over a nine order-of-magnitude mass range, from ∼10⁻⁹ g to the mass of the largest fragment produced in the disruption. The cumulative mass-frequency distribution from the Murchison disruption is fit by three power-law segments. For masses >10⁻² g the slope is only slightly steeper than that of the corresponding segment from the disruption of most anhydrous meteorites. Over the range from ∼10⁻⁶ to 10⁻² g the slope is significantly steeper than that for the anhydrous meteorites. For masses <10⁻⁶ g the slopes of both the Murchison and the anhydrous meteorites are almost flat. Thus the Murchison disruption significantly over-produced small fragments (10⁻⁶-10⁻³ g) compared to anhydrous meteorite targets. If the Murchison results are representative of hydrous asteroids, the hydrous asteroids may dominate over anhydrous asteroids in the production of interplanetary dust >100 μm in size, the size of micrometeorites recovered from the polar ices, while both types of asteroids might produce comparable amounts of ∼10 μm interplanetary dust. This would explain the puzzle that polar micrometeorites (>100 μm in size) are similar to hydrous meteorites, while the majority of the ∼10 μm interplanetary dust particles are anhydrous.     

Low phase angle effects in photometry of trans-neptunian objects: 20000 Varuna and 19308 (1996 TO66)

We present the results of photometric observations of trans-neptunian object 20000 Varuna, which were obtained during 7 nights in November 2004-February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude-phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 TO₆₆) in 1997-1999.     

Biosorption of Rare-Earth Elements and Yttrium by Heterotrophic Bacteria in an Aqueous Environment

This paper reports the results of the experimental determination of the coefficient of sorption of rare-earth elements and yttrium (REY) under conditions of acidic pH using several strains of heterotrophic bacteria (Microbacterium sp., Curtobacterium sp., Bacillus subtilis, Pseudomonas putida, and Bacillus pumilis) that are widespread in natural and technogenic waters of the Far East (Russia). Insignificant fractionation between heavy and light rare-earth elements, negative cerium and dysprosium anomalies, and a positive europium anomaly were revealed. The selectivity of REY biosorption by gram-positive and gram-negative bacteria, as well as inertia of the biosorption process under more acidic conditions of the medium, were shown.     

Fine structure in the sunspot spectrum-2 to 70 years

Application of a new data adaptive approach to power spectrum estimation has yielded evidence for a double solar cycle line in the Zurich sunspot time history. There is significant power from 8 to 15 yr in the spectrum with the primary line at 11.1 yr and three attendant multiplets that may be significant. The first four harmonics of the solar cycle are detected too. Quite marginal evidence for a peak at 65 yr in the spectrum is presented. These results closely correspond to those recently found in the geomagnetic spectrum.     

Grains accretion processes in a proto-planetary nebula

Some mechanisms which are expected to produce the growth of dust grains in the protosolar nebula are studied during the isothermal and the adiabatic phase of the gravitational collapse. Owing to the low sticking efficiency in the grain-grain collisions and also to the impossibility of gas capture by solid particles in the physical environment considered, the main result is the production in about 10⁶ yr of a set of particles similar in mass. The obtained mass limit (10⁻⁸–10⁻⁹ g) depends on the physical properties of the grains, and seems to be independent of the turbulence model used for the gas motion.     

Comparing Solar Minimum 23/24 with Historical Solar Wind Records at 1 AU

Based on the variations of sunspot numbers, we choose a 1-year interval at each solar minimum from the beginning of the acquisition of solar wind measurements in the ecliptic plane and at 1 AU. We take the period of July 2008??C?June 2009 to represent the solar minimum between Solar Cycles 23 and 24. In comparison with the previous three minima, this solar minimum has the slowest, least dense, and coolest solar wind, and the weakest magnetic field. As a result, the solar wind dynamic pressure, dawn?Cdusk electric field, and geomagnetic activity during this minimum are the weakest among the four minima. The weakening trend had already appeared during solar minimum 22/23, and it may continue into the next solar minimum. During this minimum, the galactic cosmic ray intensity reached the highest level in the space age, while the number of solar energetic proton events and the ground level enhancement events were the least. Using solar wind measurements near the Earth over 1995??C?2009, we have surveyed and characterized the large-scale solar wind structures, including fast-slow stream interaction regions (SIRs), interplanetary coronal mass ejections (ICMEs), and interplanetary shocks. Their solar cycle variations over the 15 years are studied comprehensively. In contrast with the previous minimum, we find that there are more SIRs and they recur more often during this minimum, probably because more low- and mid-latitude coronal holes and active regions emerged due to the weaker solar polar field than during the previous minimum. There are more shocks during this solar minimum, probably caused by the slower fast magnetosonic speed of the solar wind. The SIRs, ICMEs, and shocks during this minimum are generally weaker than during the previous minimum, but did not change as much as did the properties of the undisturbed solar wind.