Desiccation tolerance ofEurypanopeus depressus (smith) (Decapoda: Xanthidae) and the exploitation of microhabitat

Investigations into zonation of estuarine invertebrates often indicate that animals living higher in the intertidal region have greater tolerance to effects of aerial exposure. Desiccation tolerances ofEurypanopeus depressus, a xanthid mud crab, were measured in the laboratory for both intertidal and subtidal populations to determine whether intertidal distribution is the result of either increased physiological resistance to drying or other factors. Initially, both populations had a similar percentage of body weight due to water, and at time of death both had lost a similar percentage of water. Desiccation tolerance increased exponentially with size. In laboratory experiments,E. depressus appears very susceptible to desiccation stress with loss of tactile response occurring at 30% depletion of body water. This crab may be able to avoid desiccation and survive in the intertidal zone by remaining in the shelter and moisture of oyster shells and mud at low tide. However,E. depressus may not be limited strictly by physical factors of its environment. Biotic factors such as behavior leading to predator avoidance are possibly more important components in limiting distribution.     

Ecotopic and ontogenetic trophic variation in mojarras (Pisces: Gerreidae)

Seven species of mojarras (Gerreidae) were collected from three stations in the Indian River lagoon near the Sebastian Inlet, Florida over an eighteen month period to study spatial and temporal variations in occurrence and feeding habits. Two major habitats common to this area were represented in the study; a sandy beach and a seagrass flat. Of the 2,899 gerreids collected,Eucinostomus gula represented 67% and was found primarily in theHalodule seagrass site. The next most abundant species,E. argenteus (11%),E. jonesi andE. lefroyi (each 10%), were found most frequently at the inlet site.Diapterus auratus, E. melanopterus, andGerres cinereus were captured infrequently and were considered incidental. Prey items found included amphipods, bivalves, copepods, fish eggs, foraminifera, isopods, nematodes, ostracods, polychaetes and crustacean parts. Significant amounts of sand and unidentifiable amorphous debris were also included in the gut content analysis. Little interspecific variation in diet was found among the four major species examined. The general shift seen from a diet composed primarily of copepods and other crustaceans to one of polychaetes suggests an intraspecific ontogenetic progression. Spatial variations in diet composition were also indicated between the two major habitats. Feeding analyses showed gerreids to be diurnal feeders with the greatest consumption (total gut content weight) occurring at dusk.     

Chemistry of submarine hydrothermal solutions at 21 °N,East Pacific Rise

The three hydrothermal fields at 21°N latitude, East Pacific Rise, were resampled and an additional one was discovered. Maximum fluid temperatures observed were within a few degrees of 350°C and these waters had concentrations of Mg and sulfate indistinguishable from zero. One field, NGS, which had active 350°C springs in 1979, was inactive when first located in 1981. However, when a chimney was broken open during sampling, water issued at 273°C and continued to flow for at least five days. The chemical composition strongly suggests that these waters cooled conductively from 350°C in the sealed conduit.The major ion data are consistent with the estimates based on extrapolation of the original measurements made on the hot springs from the Galapagos Spreading Center (Edmondet al., 1979a). The fluids have a pH of 3.5 and the sulfide-forming element concentrations show significant inter-field variations. Fe levels range from 0.8 to 2.4 mmoles/kg; the ratio Fe:Mn varies from 0.9 to 2.9 similar to metalliferous sediments on the ridge flanks, but much higher than observed at Galapagos (where sub-surface precipitation of iron sulfides occurs) indicating that the overwhelming proportion of the mass flux from hydrothermal systems occurs at high temperatures. Zn ranges from 40 to 106 μmoles/kg with Cu being substantially lower. Since the ratio of these elements in tholeiites is about unity, there is strong net preferential mobilization of Zn. Lead ranges from 183 to 359 nmoles/kg. Nickel and Be are highly immobile relative to the other trace elements. The abundance of H₂S is about three times that of the total sulfide-forming cations. These data demonstrate that acid solutions at elevated temperatures can transport substantial amounts of ore-forming elements in the presence of large excesses of sulfide.     

Sodium trisilicate: A new high-pressure silicate structure (Na2Si[Si2O7])

Crystals of sodium trisilicate (Na₂Si₃O₇) have been grown in the presence of melt at 9 GPa, 1200 °C using the MA6/8 superpress at Edmonton, and the X-ray structure determined at room pressure (R=2.0%). Na₂Si₃O₇ is monoclinic with a=8.922(2) Å, b= 4.8490(5) Å, c=11.567(1) Å, β=102.64(1)° (C2/c), D _x = 3.295 g·cm^-3. Silicon occurs in both tetrahedral and octahedral coordination (^[6]Si∶^[4]Si = l∶2). The SiO₄ tetrahedra form a diorthosilicate [Si₂O₇] group and are linked by the isolated SiO₆ octahedra via shared corners into a framework of 6-membered (^[4]Si-^[4]Si-^[6]Si^[4]Si-^[4] Si-^[6]Si) and 4-membered (^[4]Si-^[6]Si-^[4]Sr-^[6]Si) rings: 〈^[6]Si-O〉=1.789 Å, 〈^[4]Si-O〉= 1.625 Å, ^[4]Si-O-^[4]Si=132.9° and the bridging oxygen is overbonded (s = 2.22). Channels parallel to b-axis and [110] accommodate Na in irregular 6-fold coordination: 〈Na-O〉 = 2.511 Å.     

The translation of turbulent wind energy to individual corn plant motion during senescense

Wind flow within inflexible plant canopies is turbulent and leads to an oscillatory motion of individual plants. A study was conducted to describe the motion of corn (Zea mays L.) stalks in the wind using a transfer function in the frequency domain to gain insight into the transfer of energy between the turbulent wind and the corn plant. Plant motion was measured and the wind moment was estimated on 23 plants during six windy days in October 1988, at West Lafayette, IN. Plant motion was theoretically described by a rigid rod. The results showed that lower stalk motion was generally well described by a second-order response model defined by a damping coefficient, natural frequency, and rotary stiffness.Published as Paper Number 12,541 of the Purdue University Agricultural Experiment Station.     

Mineralogical and isotopic evidence for phenocryst-matrix disequilibrium in the Garner Mountain andesite

Petrographic, trace element and isotopic evidence demonstrates that magma mixing preceded the eruption of the Garner Mountain andesite. The flow contains reversely zoned plagioclase phenocrysts and amphibole pseudomorphs composed of plagioclase, clinopyroxene, orthopyroxene and opaque oxides. Partially resorbed quartz grains are also present. In contrast to the isotopically uniform matrix, plagioclase phenocrysts have ⁸⁷Sr/⁸⁶Sr ratios that correlate negatively with matrix Sr and positively with matrix Rb abundances. These observations demonstrate increasing isotopic disequilibrium between the plagioclase and matrix in the more evolved varieties of the flow.Plagioclase phenocrysts and matrix are assumed to record fractionation-assimilation events in different parts of the magma chamber. Early formed plagioclase phenocrysts crystallized under AFC conditions close to the roof of the chamber and were subsequently entrained in a liquid mixture composed of evolved interstitial liquid held in the partly crystallized roof zone and newly injected parental magma.