Differences in the Feeding Ecology of Two Seagrass-Associated Snails

Grazing by small epifauna on live seagrass leaves was formerly viewed as unimportant in controlling plant biomass and growth, instead researchers focused on the indirect benefits of small invertebrates that crop algal competitors. Recent evidence shows that the emerald nerite Smaragdia viridis preferentially ingests seagrass leaf tissue. In contrast, the button snail Modulus modulus feeds on epiphytes and periphyton coating the leaves. We conducted laboratory microcosm and field experiments to investigate how the different feeding preferences of these seagrass-associated snails affect turtlegrass Thalassia testudinum primary production. Data revealed that after 24 h S. viridis reduced foliar biomass (25%) and chlorophyll (30%) and injured the equivalent of 50% of daily seagrass growth per shoot. Conversely, M. modulus did not affect these variables. Our results emphasize that in subtropical seagrass communities not all small epifauna browse off leaf surfaces and some can have important direct negative impacts on their seagrass host.     

Sediment Organic Carbon in Todos Santos Bay, Baja California, Mexico

Sediment grain size and organic carbon (OC) data collected over the past 50 years, together with δ¹³C values of OC in recently collected samples, were analyzed to improve understanding of sediment OC distribution and abundance in Todos Santos Bay. Sediments in the submarine canyon at the mouth of the bay and in quiet-water locations along the shore are fine grained, high in OC, and have generally low δ¹³C values; sediments in high-energy environments are low in OC and have high δ¹³C values. A bivariate isotopic mixing model indicates that none of the sediments contain >50% terrigenous OC (average ~30%), and that the terrigenous OC content of the sediments is a small proportion of the OC content of local soils. Sediment OC composition is apparently controlled by energy-related sorting and deposition, oxidation of much of the original terrigenous OC, and replacement of some terrigenous OC by marine OC.     

Paleoecology and radiocarbon dating of the Pleistocene megafauna of the Brazilian Intertropical Region

During the Pleistocene a fauna composed of large (biomass > 44 kg) and giant mammals (biomass > 1000 kg) that are usually associated with open environments lived in the Brazilian Intertropical Region. We present here new information concerning the paleoecology and chronology of some species of this megafauna. Carbon isotope analyses were performed for a better understanding of the paleoecology of the species Eremotherium laurillardi (Lund, 1842), Notiomastodon platensis (Ameghino, 1888) and Toxodon platensis (Owen, 1849). The δ¹³C data allow attributing a generalist diet to these species, which varied according to the kind of habitat in which they lived. In more open habitats all species were grazers; in mixed habitats E. laurillardi and T. platensis were mixed feeders, and N. platensis was grazer; and in more closed habitats all species were mixed feeders.     

Microfacies and diagenesis of older Pleistocene (pre‐last glacial maximum) reef deposits,Great Barrier Reef,Australia (IODP Expedition 325): A quantitative approach

During Integrated Ocean Drilling Program Expedition 325, 34 holes were drilled along five transects in front of the Great Barrier Reef of Australia, penetrating some 700 m of late Pleistocene reef deposits (post‐glacial; largely 20 to 10 kyr bp ) in water depths of 42 to 127 m. In seven holes, drilled in water depths of 42 to 92 m on three transects, older Pleistocene (older than last glacial maximum, >20 kyr bp ) reef deposits were recovered from lower core sections. In this study, facies, diagenetic features, mineralogy and stable isotope geochemistry of 100 samples from six of the latter holes were investigated and quantified. Lithologies are dominated by grain‐supported textures, and were to a large part deposited in high‐energy, reef or reef slope environments. Quantitative analyses allow 11 microfacies to be defined, including mixed skeletal packstone and grainstone, mudstone‐wackestone, coral packstone, coral grainstone, coralline algal grainstone, coral‐algal packstone, coralline algal packstone, Halimeda grainstone, microbialite and caliche. Microbialites, that are common in cavities of younger, post‐glacial deposits, are rare in pre‐last glacial maximum core sections, possibly due to a lack of open framework suitable for colonization by microbes. In pre‐last glacial maximum deposits of holes M0032A and M0033A (>20 kyr bp ), marine diagenetic features are dominant; samples consist largely of aragonite and high‐magnesium calcite. Holes M0042A and M0057A, which contain the oldest rocks (>169 kyr bp ), are characterized by meteoric diagenesis and samples mostly consist of low‐magnesium calcite. Holes M0042A, M0055A and M0056A (>30 kyr bp ), and a horizon in the upper part of hole M0057A, contain both marine and meteoric diagenetic features. However, only one change from marine to meteoric pore water is recorded in contrast with the changes in diagenetic environment that might be inferred from the sea‐level history. Values of stable isotopes of oxygen and carbon are consistent with these findings. Samples from holes M0032A and M0033A reflect largely positive values (δ¹⁸O: ?1 to +1‰ and δ¹³C: +1 to +4‰), whereas those from holes M0042A and M0057A are negative (δ¹⁸O: ?4 to +2‰ and δ¹³C: ?8 to +2‰). Holes M0055A and M0056A provide intermediate values, with slightly positive δ¹³C, and negative δ¹⁸O values. The type and intensity of meteroric diagenesis appears to have been controlled both by age and depth, i.e. the time available for diagenetic alteration, and reflects the relation between reef deposition and sea‐level change.     

Depositional processes on oceanic island shelves – Evidence from storm‐generated Neogene deposits from the mid‐North Atlantic

Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands.     

Gravimetric and magnetic fabric study of the Sintra Igneous complex: laccolith-plug emplacement in the Western Iberian passive margin

International Journal of Earth Sciences - The geometry and emplacement of the ~ 96 km2, Late Cretaceous Sintra Igneous complex (SIC, ca. 80 Ma) into the West Iberian passive...     

Estimates of groundwater discharge to a coastal wetland using multiple techniques: Taylor Slough, Everglades National Park, USA

Quantifying water exchange between a coastal wetland and the underlying groundwater is important for closing water, energy and chemical budgets. The coastal wetlands of the Florida Everglades (USA) are at the forefront of a large hydrologic restoration project, and understanding of groundwater/surface-water interactions is needed to comprehend the effects of the project. Four independent techniques were used to identify water exchange at varying spatial and temporal scales in Taylor Slough, Everglades National Park. The techniques included a water-budget study and measurements of hydraulic head gradients, geochemical tracers, and temperature. During the 18-month study, the four methods converged as to the timing of groundwater discharge, typically between June and September, contemporaneous with the wet season and increasing surface-water levels. These results were unexpected, as groundwater discharge was predicted to be greatest when surface-water levels were low, typically during the dry season. Either a time lag of 1?C5?months in the response of groundwater discharge to low surface-water levels or precipitation-induced groundwater discharge may explain the results. Groundwater discharge was a significant contributor (27?%) to the surface water in Taylor Slough with greater rates of discharge observed towards the coastline in response to seawater intrusion.     

The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

An arcuate structure, comparable in size with the Ibero-Armorican arc, is delineated by Variscan folds and magnetic anomalies in the Central Iberian Zone of the Iberian Massif. Called the Central Iberian arc, its sense of curvature is opposite to that of the Ibero-Armorican arc, and its core is occupied by the Galicia-Trás-os-Montes Zone of NW Iberia, which includes the Rheic suture. Other zones of the Iberian Massif are bent by the arc, but the Ossa-Morena and South Portuguese zones are not involved. The arc formed during the Late Carboniferous, at final stages of thermal relaxation and collapse, and an origin related with right-lateral ductile transpression at the scale of the Variscan belt is proposed. The Central Iberian arc explains the width of the Central Iberian Zone, clarifies the position of the allochthonous terranes of NW Iberia, and opens new perspectives for correlations with the rest of the Variscan belt, in particular, with the Armorican Massif, whose central zone represents the continuation of the southwest branch of the arc detached by strike-slip tectonics.     

Spatial and temporal variation of the nekton and hyperbenthos from a temperate European estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.     

Volcanic ash forecast during the June 2011 Cordón Caulle eruption

We modelled the transport and deposition of ash from the June 2011 eruption from Cordón Caulle volcanic complex, Chile. The modelling strategy, currently under development at the Argentinean Naval Hydrographic Service and National Meteorological Service, couples the weather research and forecasting (WRF/ARW) meteorological model with the FALL3D ash dispersal model. The strategy uses volcanological inputs inferred from satellite imagery, eruption reports and preliminary grain-size data obtained during the first days of the eruption from an Argentinean ash sample collection network. In this sense, the results shown here can be regarded as a quasi-syn-eruptive forecast for the first 16 days of the eruption. Although this article describes the modelling process in the aftermath of the crisis, the strategy was implemented from the beginning of the eruption, and results were made available to the Buenos Aires Volcanic Ash Advisory Centers and other end users. The model predicts ash cloud trajectories, concentration of ash at relevant flight levels, expected deposit thickness and ash accumulation rates at relevant localities. Here, we validate the modelling strategy by comparing results with satellite retrievals and syn-eruptive ground deposit measurements. Results highlight the goodness of the combined WRF/ARW-FALL3D forecasting system and point out the usefulness of coupling both models for short-term forecast of volcanic ash clouds.