Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem

Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank.     

Kinetics of peptide hydrolysis and amino acid decomposition at high temperature

Dipeptide hydrolysis and amino acid decomposition appear to follow a first-order rate law. The hydrolysis rate increases exponentially with increasing temperature in aqueous solution at both 265 atm and water steam pressures over the temperature range of 100 to 220 degrees C. Dipeptide hydrolysis has a lower apparent activation energy at 265 atm (44.1 KJ/mol) than at water steam pressure (98.9 KJ/mol). At lower temperatures (<200-220 degrees C), the rate of peptide bond hydrolysis is faster at 265 atm than at water steam pressure. At higher temperatures (>200-220 degrees C), however, peptide bond hydrolysis is slower at 265 atm than at water steam pressure. In aqueous solution, amino acid decomposition rates also increase exponentially with increasing temperature. Amino acid decomposition rates are much higher at 265 atm than at water steam pressure over the entire temperature range investigated.     

Calibration of Al/Si order variations in anorthite

New single crystal diffraction data for natural and heat-treated anorthite crystals (Angel et al. 1990) allow the determination of their states of Al/Si order in terms of a macroscopic order parameter,Q _OD , for the transition. Numerical values ofQ _OD obtained from estimates of site occupancies are shown to vary with the scalar spontaneous strain, _s , as _s Q _OD ² , and with the ratio of the sums of typeb (superlattice) reflections and typea (sublattice) reflections asI _b/I _a Q _OD ² . An empirical calibration for pure anorthite is obtained giving varies between 0.92 and 0.87 in samples equilibrated at T1300° C, but then falls off relatively rapidly with increasing temperature, reaching 0.7 near the melting point ( 1557° C). The observed temperature dependence does not conform to the predictions of the simplest single order parameter models; coupling ofQ _OD withQ of the transition is suspeeted.     

Origin of spongy textures in clinopyroxene and spinel from mantle xenoliths, Hessian Depression, Germany

Summary Spongy textures are observed in anhydrous Group 1 mantle xenoliths (harzburgite, lherzolite and wehrlite) hosted in Tertiary alkali basaltic lavas from the Hessian Depression, Germany. These textures are developed only on clinopyroxene and spinel, and occur as rims or cross-cutting veinlets and patches showing optical continuity with the host grain. They are often associated with pools of amorphous glassy material. There is no preferential development of spongy domains against the xenolith-lava contact suggesting that the host magma did not play any significant role in their formation. Spongy clinopyroxene and spinel occur in all rock types, but, are more pervasive in wehrlite. Chemically, spongy domains of clinopyroxene and spinel are more refractory than unaffected areas, which is consistent with their formation through a partial melting event. The associated glassy material shows chemical characteristics which suggest that the melt pools are genetically related to the development of the spongy textures. The partial melting event was probably triggered by the infiltration of a low-density fluid. The fluid may have evolved from a silicate melt responsible for the metasomatic Fe-enrichment recorded in wehrlite. In this context, the more pervasive development of spongy clinopyroxene in wehrlite may be explained by a higher concentration of the evolved fluid phase at proximity to its silicate melt source. Received March 15, 2000; revised version accepted September 6, 2001     

Structural properties of (Mn1-x Fe x )Nb2O6 columbites from X-ray diffraction and IR spectroscopy

A suite of (Mn_1-x Fe _x )Nb₂O₆ (x=0, 0.05, 0.25, 0.50, 0.75, 1) columbite samples has been prepared by solid-state reaction from oxides. X-ray diffraction and spectroscopic investigations have been carried out in order to gain different perspectives on how the solid solution adapts at different length scales to cation mixing. X-ray powder diffraction and powder absorption IR spectroscopy data are presented. The powder diffraction data show that there is no significant excess volume of mixing on the Fe–Mn columbite join. All the unit-cell parameters decrease linearly as a function of increasing Fe content. Substitution of Fe²⁺ for the larger Mn²⁺ cation causes a decrease in the volume of the A polyhedron, which also becomes more regular with respect to both bond-length and edge-length distortion parameters. No significant variation of the B site has been observed. Wavenumber shifts of the IR peaks nearly all vary linearly with composition, consistent with linear variations of the lattice parameters. Line broadening has been quantified by autocorrelation analysis of the IR spectra. This is interpreted as suggesting that there is some element of local strain or positional disorder at the length scale of second or third nearest neighbours around sites occupied by Fe.     

Sediment Suspension and Deposition Across Restored Oyster Reefs of Varying Orientation to Flow: Implications for Restoration

The eastern oyster, Crassostrea virginica, is a prominent ecosystem engineer, whose reefs exhibit strikingly consistent morphologies at multiple spatial scales throughout its North American range. These distinct morphologies are thought to form by interactions of nascent reef structures with hydrodynamics. We carried out two field studies to determine if historical reef configurations applied in a restoration context would improve reef persistence and restoration outcomes. We collected seabed and water column observations across constructed reefs of three orientations representative of those found historically throughout the oyster’s range: parallel or perpendicular to tidal currents or circular. Areas adjacent to reefs were sites of fine sediment trapping, with lower flow velocities, evidence of particle settling, and more fine sediments on the seabed relative to off-reef reference sites. The water column above the reef crest exhibited higher acoustic backscatter, higher flow velocities, and larger particles in suspension, consistent with local erosion of flocculated fine sediment from the reef crest. Perpendicular reefs produced conditions that were more conducive to reef persistence and improved oyster performance, including high flow velocities and enhanced resuspension of sediments from the reef, compared to parallel or circular reefs. Particle trapping in areas between reefs has the potential to inhibit reef growth between existing reef structures, providing support for hypotheses of landscape-scale reef pattern formation. Oyster reef restoration efforts can benefit from this improved understanding of biophysical interactions arising from reef orientation that contribute to sediment dynamics on constructed oyster reefs.     

Spinel assemblages in lunar meteorites Graves Nunataks 06157 and Dhofar 1528: Implications for impact melting and equilibration in the Moon's upper mantle

Magnesium‐rich spinel assemblages occur in the two lunar vitric breccia meteorites—Dhofar (Dho) 1528 and Graves Nunataks (GRA) 06157. Dho 1528 contains up to ~0.7 mm cumulate Mg‐rich spinel crystals associated with Mg‐rich olivine, Mg‐ and Al‐rich pyroxene, plagioclase, and rare cordierite. Using thermodynamic calculations of these mineral assemblages, we constrain equilibration depths and discuss an origin of these lithologies in the upper mantle of the Moon. In contrast, small, 10 to 20 μm spinel phenocryst assemblages in glassy melt rock clasts in Dho 1528 and GRA 06157 formed from the impact melting of Mg‐rich rocks. Some of these spinel phenocrysts match compositional constraints for spinel associated with “pink spinel anorthosites” inferred from remote sensing data. However, such spinel phenocrysts in meteorites and Apollo samples are typically associated with significant amounts of olivine ± pyroxene that exceed the compositional constraints for pink spinel anorthosites. We conclude that the remotely sensed “pink spinel anorthosites” have not been observed in the collections of lunar rocks. Moreover, we discuss impact‐excavation scenarios for the spinel‐bearing assemblages in Dhofar 1528 and compare the bulk rock composition of Dho 1528 to strikingly similar compositions of Luna 20 samples that contain ejecta from the Crisium impact basin.     

Shock deformation confirms the impact origin for the Cerro do Jarau,Rio Grande do Sul,Brazil, structure

Cerro do Jarau is a conspicuous, circular morpho‐structural feature in Rio Grande do Sul State (Brazil), with a central elevated core in the otherwise flat “Pampas” terrain typical for the border regions between Brazil and Uruguay. The structure has a diameter of approximately 13.5 km. It is centered at 30^o12′S and 56^o32′W and was formed on basaltic flows of the Cretaceous Serra Geral Formation, which is part of the Paraná‐Etendeka Large Igneous Province (LIP), and in sandstones of the Botucatu and Guará formations. The structure was first spotted on aerial photographs in the 1960s. Ever since, its origin has been debated, sometimes in terms of an endogenous (igneous) origin, sometimes as the result of an exogenous (meteorite impact) event. In recent years, a number of studies have been conducted in order to investigate its nature and origin. Although the results have indicated a possible impact origin, no conclusive evidence could be produced. The interpretation of an impact origin was mostly based on the morphological characteristics of the structure; geophysical data; as well as the occurrence of different breccia types; extensive deformation/silicification of the rocks within the structure, in particular the sandstones; and also on the widespread occurrence of low‐pressure deformation features, including some planar fractures (PFs). A detailed optical microscopic analysis of samples collected during a number of field campaigns since 2007 resulted in the disclosure of a large number of quartz grains from sandstone and monomict arenite breccia from the central part of the structure with PFs and feather features (FFs), as well as a number of quartz grains exhibiting planar deformation features (PDFs). While most of these latter grains only carry a single set of PDFs, we have observed several with two sets, and one grain with three sets of PDFs. Consequently, we here propose Cerro do Jarau as the seventh confirmed impact structure in Brazil. Cerro do Jarau, together with Vargeão Dome (Santa Catalina state) and Vista Alegre (Paraná State), is one of very few impact structures on Earth formed in basaltic rocks.     

An index of biotic integrity based on the summer polyhaline zooplankton community of the Chesapeake Bay

A zooplankton index of biotic integrity was developed for the polyhaline waters of the Chesapeake Bay using data from a long-term environmental assessment program in which both zooplankton and water quality were regularly monitored. Summer (July to September) sampling events were classified as either coming from impaired or reference (least-impaired) conditions based on water quality conditions. Seventeen zooplankton community metrics were evaluated under these criteria and nine were chosen for a composite index. These were the Simpson diversity index, and abundance of barnacle larvae, rotifers, cladocerans, copepods, total mesozooplankton, and predators. The composite index of biotic integrity correctly classified about 94% of the impaired samples and about 82% of the reference samples. Average classification efficiency was 88%. This index appears to be an effective measure of eutrophication for the summer polyhaline waters of the Chesapeake Bay ecosystem.     

Combining pixel and object based image analysis of ultra-high resolution multibeam bathymetry and backscatter for habitat mapping in shallow marine waters

Habitat mapping data are increasingly being recognised for their importance in underpinning marine spatial planning. The ability to collect ultra-high resolution (cm) multibeam echosounder (MBES) data in shallow waters has facilitated understanding of the fine-scale distribution of benthic habitats in these areas that are often prone to human disturbance. Developing quantitative and objective approaches to integrate MBES data with ground observations for predictive modelling is essential for ensuring repeatability and providing confidence measures for habitat mapping products. Whilst supervised classification approaches are becoming more common, users are often faced with a decision whether to implement a pixel based (PB) or an object based (OB) image analysis approach, with often limited understanding of the potential influence of that decision on final map products and relative importance of data inputs to patterns observed. In this study, we apply an ensemble learning approach capable of integrating PB and OB Image Analysis from ultra-high resolution MBES bathymetry and backscatter data for mapping benthic habitats in Refuge Cove, a temperate coastal embayment in south-east Australia. We demonstrate the relative importance of PB and OB seafloor derivatives for the five broad benthic habitats that dominate the site. We found that OB and PB approaches performed well with differences in classification accuracy but not discernible statistically. However, a model incorporating elements of both approaches proved to be significantly more accurate than OB or PB methods alone and demonstrate the benefits of using MBES bathymetry and backscatter combined for class discrimination.