Valéria da Silva Quaresma

Neotropical forest expansion during the last glacial period challenges refuge hypothesis

Significance The tropical forests of South America are among the most diverse and unique habitats in the world in terms of plant and animal species. One of the most popular explanations for this diversity and endemism is the idea that forests retracted and fragmented during glacial periods, forming ecological refuges, surrounded by dry lands or savannas. These historically stable forest refuges would have been responsible for maintaining the pattern of diversity and endemism observed today. Here, we show that the Atlantic Forest of eastern South America probably expanded, rather than contracted, during the last glacial period. In addition, the emerged Brazilian continental shelf played a major, yet neglected, role on the evolution of this biodiversity hotspot during the last glacial period. The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods.

THE INFLUENCES OF BIOLOGICAL ACTIVITY AND CONSOLIDATION TIME ON LABORATORY COHESIVE BEDS

ABSTRACT A small annular laboratory flume (Mini Flume) was used to investigate the changes in erosion threshold and erosion rate on natural mud taken from an intertidal mud flat surface in Southampton Water, U.K. Mud samples were wet sieved at 2 mm to remove shells and large macrofauna and macroflora and then mixed into a turbid slurry with local estuarine water. A mud bed was formed in the flume by letting the sediment deposit in still water at room temperature (20°C). The bed was subjected to steady flows of increasing magnitude in a series of steps. The flume was subjected to illumination on a dark-light cycle of 12 hours to simulate the solar cycle. Subsequent erosion experiments were carried out after periods of bed consolidation of 2, 6, 12, 24, 48, and 96 hours in order to examine changes in bed stability with time. This series of experiments was considered the baseline situation in which algal and bacterial binding were present. At the end of each experiment, the bed was fully resuspended, mixed for a period of 5 minutes, and then allowed to redeposit. A second series of experiments was undertaken using the same sediment, but in this case the bed was continuously held in darkness (no photosynthesis of microphytobenthos). A third series of experiments was carried out in darkness, but antibiotics were added to the flume to remove the effects of bacterial activity. A final series of experiments was carried out with the addition of 50 ml l-1 of sodium hypochlorite to remove all biological activity in order to examine the effects of electrochemical binding (the control). The results reveal that under the normal conditions of light (day-night) an increase in sediment stability (stabilization index, BI) of circa 3 was found over that of electrochemical bonding. The bed treated with antibiotics suffered an overall stabilization of 1.5 relative to the control.

Mid- to Late-Holocene estuarine infilling processes studied by radiocarbon dates, high resolution seismic and biofacies at Vitoria Bay, Espirito Santo, Southeastern Brazil

Vitoria Bay is a 20 km long estuary, morphologically narrow, with a microtidal regime and, as other modern estuaries, was formed during the last post-glacial transgression. The estuarine bed morphology is characterised by a main natural channel limited by tidal flats with developed mangroves. Original radiocarbon dates were obtained for the site. Five radiocarbon ages ranging from 1,010 to 7,240 years BP were obtained from two sedimentary cores, which represent a 5 m thick stratigraphic sequence. The results indicate that, until about 4,000 cal. yrs BP, environmental conditions in Vitoria Bay were still of an open bay, with a free and wide connection with marine waters. During the last 4,000 yrs, the bay has experienced a major regression phase, by becoming more restricted in terms of seawater circulation and probably increasing tidal energy. Three main stratigraphic surfaces were recognised, which limit trangressive, trangressive/highstand and regressive facies. The present channel morphology represents a tidal scouring surface or a tidal diastem, which erodes and truncates regressive facies bedding. Foraminiferal biofacies, which change from marine to brackish and mangrove tidal-flat environments, support the seismic stratigraphic interpretation. Absence of mangrove biofacies at one of the two cores is also an indication of modern tidal ravinement.

Morfologia e distribuição sedimentar em um sistema estuarino tropical: Baía de Vitória, ES

Vitoria Bay is an estuarine system along the eastern Brazilian coast that presents great economic importance and unique characteristics. The present study focused on describing the morphology, sedimentary distribution and sonographic patterns along the bay in order to recognize the prevailing sedimentary processes acting along the estuary. An integrated analysis allowed the recognition of four regions associated with distinct processes: the upper estuary is dominated by fluvial input and estuarine processes; a large portion of the central region of the system showed erosive characteristics and morphological adaptations related to the increase in currents caused by the man-induced narrowing of the bay, providing the formation of bedforms; the navigation channel, which shows high rates of sedimentation and is clearly modified by dredging and the estuarine mouth which is dominated by marine processes.

The Influence of Articulated and Disarticulated Cockle Shells on the Erosion of a Cohesive Bed

Abstract An annular flume (Lab Carousel) was used to investigate the influence of shells on the erosion rates of an artificial laboratory cohesive bed (potters clay) under unidirectional flow. Specimens of articulated and disarticulated cockle shells (Cerastoderma edule), separated into six size classes (of maximum diameter from 13 to 26 mm), were used. The fluid-transmitted shear stresses and shell-induced bed erosion for the six classes were measured in triplicate, as well as shell settling velocity, sedimentation diameter, and shell drag coefficient. Bed erosion began after the shells started to move: erosion rates were influenced by shell size and the mode of transport. Two different modes of shell transport were observed: (i) rolling and saltation of articulated shells, and (ii) sliding and saltation of disarticulated shells. Peak bed erosion rates were associated with rolling and sliding modes of transport. Higher values of the solid-transmitted shear stress were calculated for saltating shells (in some cases two times higher), but contact with the bed was less frequent than rolling or sliding. The presence of cockle shells in an environment with hydrodynamic conditions strong enough to induce shell transport could significantly increase the loss of mass (erosion) of the surface bed or cliff. At Hythe intertidal area, where the shell specimens were collected, the presence of miniature furrows containing shells deposits in the troughs is widespread, and the troughs and walls show tool marks indicating shell abrasion.

Sonar de varredura lateral e sísmica de alta resolução aplicados no estudo de ecofácies na baía de Vitória-ES

High resolution geophysical surveys and sediment sampling were undertaken along Vitoria Bay in order to acoustically map the seabed. Integrated analysis of sidescan sonar and seismic records allowed the recognition of 4 distinct echo facies. Echo facies Type 1 is associated with no penetration of the acoustic signal and high backscatter sonograms with bedforms. This echo facies is related to sandy beds. Echo facies Type 2 is mainly associated with sandy mud bottoms, showing a high penetration of the acoustic signal and low backscatter sonograms. Echo facies Type 3 is related to reflection free deposits, commonly associated with muddy beds or fluid muds. Echo facies Type 4 represents rocky beds. These facies are related to different types of seabed and can be used to interpret the main sedimentary processes acting along the bay.

Modern sedimentary processes along the Doce river adjacent continental shelf

In areas of the continental shelf where sediment supply is greater than the sediment dispersion capacity, an extensive terrigenous deposits and consequently submerged deltas can be formed. The Eastern Brazilian shelf is characterized by the occurrence of river feed deltas in between starving coasts. Herein, modern sedimentary processes acting along the Doce river adjacent continental shelf are investigated. The main objective was to understand the shelf sediment distribution, recognizing distinct sedimentary patterns and the major influence of river sediment discharge in the formation of shelf deposits. The study used 98 surficial samples that were analyzed for grain size, composition and bulk density. Results revealed 3 distinct sectors: south - dominated by mud fraction with a recent deposition from riverine input until 30 m deep and from this depth bioclastic sands dominate; central north - sand mud dominated, been recognized as a bypass zone of resuspended sediment during high energy events; and north - relict sands with high carbonate content. The modern sedimentation processes along the Doce river continental shelf is dominated by distinct sedimentary regimes, showing a strong fluvial influence associated with wave/wind induced sediment dispersion and a carbonate regime along the outer shelf. These regimes seem to be controlled by the distance from the river mouth and bathymetric gradients.

The structural heterogeneity of an urbanised mangrove forest area in southeastern Brazil: Influence of environmental factors and anthropogenic stressors

The objective of this study is to evaluate the characteristics of the forest in an urbanised mangrove using vegetation structure and abiotic conditions to distinguish habitat heterogeneity/quality. A total of 16 points in Vitoria Bay were selected in the fringe and basin forests. The variables evaluated were height and diameter of the individual trees, basal area, density, dominance, interstitial water, litter mass, grain size, organic matter and anthropogenic influences. The results indicated that the mangrove area, due to suffering intensely from various anthropogenic effects, forests with varying degrees of maturity. Areas more distant from direct human effects had a higher degree of development and environmental quality relative to points closer to urban pressures. Intermediate development levels were also observed, which indicated pulses of environmental change. Human interventions caused alterations in the development of the forest which increased the mortality rate and reduced the diameter and height of the trees. The environmental variables of salinity, organic matter, litter mass, grain size and anthropogenic stressors contributed to the structural patterns. Our data suggest that an analysis of the vegetation structure and the abiotic factors are useful indicators to evaluate habitat quality, thus providing a basis for future management.

Modern sedimentation processes in a wave-dominated coastal embayment: Espírito Santo Bay, southeast Brazil

Sediment dynamics in wave-dominated coastal embayments are generally controlled by seasonal meteorological conditions, storms having a particularly strong influence. In the present study, such hydrodynamic processes and associated deposits have been investigated in a coastal embayment located along the southeast coast of Brazil, i.e. Espírito Santo Bay, in the winter (June/July) of 2008. The bay has undergone a series of human interventions that have altered the local hydrodynamic processes and, consequently, the sediment transport patterns. Facies distribution and sediment dynamics were examined by acoustic seabed mapping, sediment and core sampling, hydrodynamic measurements and sand transport modelling. The results show that sediment distribution can be described in terms of nearshore and offshore zones. The offshore bay sector is predominantly composed of “palimpsest” lithoclastic medium–coarse sands deposited in the course of the early Holocene transgression that peaked about 5,000 years ago. In the inner bay or nearshore zone (up to depths of 4–8 m), these older transgressive deposits are today overlain by a thin (up to 30-cm-thick) and partly patchy blanket of younger regressive fine sand/muddy fine sands. Both coarse- and fine-grained facies are being reworked during high-energy events (Hs>1.5 m) when fine sediment is resuspended, weak tide-induced drift currents causing the sand patches to be displaced. The coarser sediment, by contrast, is mobilized as bedload to produce wave ripples with spacings of up to 1.2 m. These processes lead to a sharp spatial delimitation between a fine sand/mud facies and a rippled coarse sand facies. The fine sand patches have a relief of about 20–30 cm and reveal a typical internal tempestite depositional sequence. Fair-weather wave-induced sediment transport (Hs<1 m), supported by weak tidal currents, seems to only affect the fine sediment facies. Sediment dynamics in Espírito Santo Bay is thus essentially controlled by wave action during storms, tidal currents playing a very subordinate role. Anthropogenic changes due to the construction of a port at the entrance of the bay have not only produced erosion along the beach, but could also explain the occurrence of sand patches concentrated in the north-eastern part of the bay. Because storm-induced deposits of the type observed in this study have an inherently patchy distribution, this feature needs to be taken into consideration when interpreting the rock record in terms of modern analogues.

Hydrodynamic Aspects at Vitória Bay Mouth, ES

Understading the hydrodynamic behavior and suspended particulated matter (SPM) transport are of great importance in port regions such as Vitória Harbor, which is located at Vitória Bay, Vitória - ES, Brazil. Vitória Bay is an estuary that has not been systematically assessed through a temporal analysis in order to identify its hydrodynamics characteristics and SPM exchange. This study aims to investigate salt and suspended particulate matter flux at the estuarine mouth of Vitória Bay by understanding the temporal variation of salinity, temperature and tidal currents within the water column and at the channel crosssection. Results showed that the estuarine mouth tended to present partial stratification periods during neap tides and little stratification in spring tides. The circulation pattern was mainly influenced by the tide, with little influence from river discharge. With regard to the SPM, the mouth of the estuary tended to show low concentrations, with the highest values occurring during the dry season. A close relationship between momentary discharge, SPM and salt fluxes was observed. Despite all the data was collected at the mouth of the estuary, the system showed an importation trend of salt in all cycles and SPM importation for three of the four studied tidal cycles. Thus, Vitoria Bay is not exporting SPM to the adjacent inner shelf.