The role of schizogenesis in population dynamics of Timarete filigera (Polychaeta: Cirratulidae): 2-years observations in the Port of Bari (South Adriatic Sea)

Different aspects of reproductive biology of the polychaete Timarete filigera (Delle Chiaje) were studied during a period of 2 years (from September 2002 to August 2003 and from September 2004 to August 2005). Timarete filigera specimens were collected monthly in the port of Bari (South Adriatic Sea, Mediterranean Sea). For population analysis, regenerating and entire specimens were separately analyzed, the regenerating individuals were assigned to different categories related to the region of the body from which they derived. Regenerating individuals were present throughout the year. There were three to four times more individuals deriving from the middle part than the anterior and posterior regenerating portions. From the high percentage of regenerating individuals observed in the T. filigera population, it can be supposed that this species reproduces mainly asexually by schizogenesis. However, histological analysis revealed the presence of female gametes in a few individuals. In contrast, males were never collected, probably due to the limited number of reproductive individuals collected. The abundance has shown wide fluctuations during the year, with a decrease from Winter to Spring. The analysis of the size‐frequency histograms has shown a growing phase of whole specimens from Spring to Winter. The life cycle of the investigated species is discussed with the hypothesis that strategies could be linked to the colonized environments, agamic reproduction coupled with sexual reproduction assures the presence and expansion of the population after the colonization by a limited number of larvae.     

Regional variation in springtime ichthyoplankton assemblages in the northeast Pacific Ocean

The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log₁₀ (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast.     

Phytoliths as indicators of pedogenesis and paleoenvironmental changes in the Brazilian cerrado

This paper presents the preliminary results of phytolith analyses of a peat located in the cerrado of the Uberaba municipality, State of Minas Gerais, Brazil. The phytolith soil sequence is discussed by comparison with phytolith assemblages extracted from dominant plants (Cyperaceae and Poaceae). Increasing mean age of phytolith assemblages with depth is assumed. Poaceae Cuneiform bulliform cell, Parallelepiped bulliform cell and Elongate smooth long cell types dominate up to 80 cm, rapidly drop to 42% at 80 cm and regularly decrease from 42% to 2% upwards. Cyperaceae Rondel concave type shows the inverse trend, being dominant in the upper part of the profile. This pattern can be assigned to increasing selective dissolution of the Cyperaceae phytolith type with depth, or/and to a decrease of water stress suffered by the grasses, leading to a decrease of bulliform cell silicification. Soil processes and paleo-environmental changes hypotheses are discussed.     

Regional record of a global oceanic anoxic event: OAE1a on the Apulia Platform margin, Gargano Promontory, southern Italy

The Gargano Promontory of southern Italy, located on the eastern margin of the Apulia Platform, represents a peculiar Tethyan area where the transition between carbonate platform and adjacent basins is exposed on land. The Aptian stratigraphic record, represented in shallow-water, slope and deep-water deposits, provides a good opportunity to investigate the regional response to the worldwide documented climatic, biotic and palaeoceanographic changes related to Oceanic Anoxic Event 1a (OAE1a). A synthesis of data previously published (Ischitella and Coppitella sections), together with original data (Val Carbonara and Coppa della Guardia sections), from four stratigraphic sections from different depositional settings (proximal to distal) is provided, using an integrated, high-resolution micropalaeontological (planktonic foraminifera and calcareous nannofossils) and, for one section, geochemical (stable carbon and oxygen isotopes) approach. Organic matter preservation is confined to the more distal areas and consists of two thin intervals of black shales in the Aptian portion of the Marne a Fucoidi Formation. Biostratigraphic data assign the older black shale (5 cm thick) to the Selli Level equivalent (OAE1a, Lower Aptian); this carbon-rich interval is immediately followed by another black shale (7–10 cm thick) of early Late Aptian age.OAE1a is generally interpreted as a high-productivity event during a warming interval, followed by a cooling trend. In the Gargano Promontory, although the oxygen isotope curve indicates the above-mentioned climatic evolution, the micropalaeontological data do not support high fertility of the surface water, whereas micropalaeontological and geochemical data for the younger black shale do record high productivity (radiolarian increase in overall abundance, low nannofossil and foraminiferal species richness, increase in abudance of nannofossil fertility indices) associated with a cooling trend. The carbon and oxygen isotope record is in line with evidence from the curves documented elsewhere, whereas, among the biotic events, only the “nannoconid crisis” preceding OAE1a is revealed to be globally correlable.Environmental models for the two episodes of organic matter preservation are proposed, taking into account both global and local controlling factors.     

Early Holocene water budget of the Nakuru-Elmenteita basin, Central Kenya Rift

The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange.     

Paleohydrology of arid southeastern maui, hawaiian islands, and its implications for prehistoric human settlement

Arid slopes on the southeastern side of Maui are densely covered with archaeological remains of Hawaiian settlement from the late prehistoric to early postcontact period (ca. A.D. 1500-1860). Permanent habitation sites, agricultural features, and religious structures indicate perennial occupation and farming in a subregion called Kahikinui, yet there is presently no year-round water source. We explore the possibility that postcontact deforestation led to the loss of either (1) perennial channel flow or (2) perennial springs or seeps. To investigate the first possibility, we estimated ancient peak flows on 11 ephemeral channels in Kahikinui using field measurements and paleohydrology. Peak-flow estimates (3-230 m³/s) for a given drainage area are smaller than those for current perennial Maui streams, but are equivalent to gauged peak flows from ephemeral and intermittent streams in the driest regions of Hawai’i and Maui islands. This is consistent with the long-term absence of perennial channel flow in Kahikinui. On the other hand, others have shown that canopy fog-drip in Hawai’i can be greater than rainfall and thus a large part of groundwater recharge. Using isolated live remnants and snags, we estimate the former extent of the forest upstream from archaeological sites. We use rough estimates of the loss of fog-drip recharge caused by deforestation and apply a simple, steady-state hydrologic model to calculate potential groundwater table fall. These order-of-magnitude estimates indicate that groundwater could have fallen by a minimum of several meters, abandoning perennial seeps. This is consistent with archaeological evidence for former perennial seeps, such as stonewalls enclosing potential seeps to protect them. Although longer-term reductions in rainfall cannot be ruled out as a factor, deforestation and loss of fog-drip recharge are obvious and more immediate reasons for a recent loss of perennial water in Kahikinui, Maui.     

Variability of the Intertropical Convergence Zone recorded in coral isotopic records from the central Indian Ocean (Chagos Archipelago)

We have analyzed the stable oxygen isotopic composition of two Porites corals from the Chagos Archipelago, which is situated in the geographical center of the Indian Ocean. Coral δ¹⁸O at this site reliably records temporal variations in precipitation associated with the Intertropical Convergence Zone (ITCZ). Precipitation maxima occur in boreal winter, when the ITCZ forms a narrow band across the Indian Ocean. The Chagos then lies within the center of the ITCZ, and rainfall is strongly depleted in δ¹⁸O. A 120-yr coral isotopic record indicates an alternation of wet and dry intervals lasting 15 to 20 yr. The most recent 2 decades are dominated by interannual variability, which is tightly coupled to the El Niño-Southern Oscillation (ENSO). This is unprecedented in the 120 yr of coral record. As the ITCZ is governed by atmospheric dynamics, this provides evidence of a major change in the coupled ENSO-monsoon system.     

Advances in lunar science from the Clementine mission: A decadal perspective

The Clementine spacecraft orbited the Moon and acquired science data for 10 weeks in the Spring of 1994. During this time it collected global 11-band multispectral images and near global altimetry. Select areas of the Moon were imaged at 25 m/pixel in visible light and 60 m/pixel in thermal wavelengths. From these datasets a new paradigm for the evolution of the lunar crust emerged. The Moon is no longer viewed as a two-terrane planet, the Apollo samples were found not to represent the lunar crust as a whole, and the complexity of lunar crustal stratigraphy was further revealed. More than ten years later the Clementine datasets continue to significantly advance lunar science and will continue to do so as new measurements are returned from planned missions such as Chandrayaan, SELENE, and Lunar Reconnaissance Orbiter. This paper highlights the scientific research conducted over the last decade using Clementine data and summarizes the influence of Clementine on our understanding of the Moon.     

Potential Salinity and Temperature Futures for the Chesapeake Bay Using a Statistical Downscaling Spatial Disaggregation Framework

Estuaries are productive and ecologically important ecosystems, incorporating environmental drivers from watersheds, rivers, and the coastal ocean. Climate change has potential to modify the physical properties of estuaries, with impacts on resident organisms. However, projections from general circulation models (GCMs) are generally too coarse to resolve important estuarine processes. Here, we statistically downscaled near-surface air temperature and precipitation projections to the scale of the Chesapeake Bay watershed and estuary. These variables were linked to Susquehanna River streamflow using a water balance model and finally to spatially resolved Chesapeake Bay surface temperature and salinity using statistical model trees. The low computational cost of this approach allowed rapid assessment of projected changes from four GCMs spanning a range of potential futures under a high CO₂ emission scenario, for four different downscaling methods. Choice of GCM contributed strongly to the spread in projections, but choice of downscaling method was also influential in the warmest models. Models projected a ~2–5.5 °C increase in surface water temperatures in the Chesapeake Bay by the end of the century. Projections of salinity were more uncertain and spatially complex. Models showing increases in winter-spring streamflow generated freshening in the Upper Bay and tributaries, while models with decreased streamflow produced salinity increases. Changes to the Chesapeake Bay environment have implications for fish and invertebrate habitats, as well as migration, spawning phenology, recruitment, and occurrence of pathogens. Our results underline a potentially expanded role of statistical downscaling to complement dynamical approaches in assessing climate change impacts in dynamically challenging estuaries.