Deep-water stands of Cystoseira zosteroides C. Agardh (Fucales,Ochrophyta) in the Northwestern Mediterranean: Insights into assemblage structure and population dynamics

Populations dominated by Cystoseira zosteroides, an endemic and threatened Mediterranean seaweed, colonize deep-water rocky habitats down to more than 50 m depth. Assemblages dominated by this species display high algal and invertebrate species richness. Algal biomass averages 1134 g dw m⁻². Erect and turf algae account for only 25% of total algal dry weight, while encrusting corallines are responsible for the remaining 75%. Sponges, bryozoans and ascidians constitute the dominant sessile macrofauna. Cystoseira zosteroides is the dominant erect algae, with a mean biomass of 60.6 g dw m⁻², and densities ranging from 4 to 7 plants m⁻². The alien turf alga Womersleyella setacea has a biomass of 104.2 g dw m⁻² and covers most of the understory substrate. The size-frequency distribution of C. zosteroides populations shows differences over time. Mean annual growth of the main axis is around 0.5 cm and mean annual mortality rate is lower than 2%. Recruitment was almost nil during the studied period of time (10 years). Processes structuring these deep-water Cystoseira stands must be driven by episodic disturbances, after-disturbance recruitment pulses, and long periods of steady growth that last at least 10 years. However, it is also possible that recruitment is irreversibly inhibited by the alien alga W. setacea in which case these old-growth stands are faced with extinction. The highly diversified assemblages and the low growth and low mortality rates of C. zosteroides indicate high vulnerability to natural and anthropogenic disturbances, and call for effective measures to ensure their conservation.     

Trophic relations of capelin Mallotus villosus and polar cod Boreogadus saida in the Barents Sea as a factor of impact on the ecosystem

The purpose of the study is to assess the role of trophic relations of the dominant pelagic fishes capelin and polar cod in the Barents Sea with regard to distribution and accessibility as prey for the Atlantic cod in warm years (2004–2005). Unlike in the previous period, during these warm years a dramatic increase of the polar cod population resulted in a northwards expansion of the feeding grounds where overlapping of polar cod and capelin concentrations was observed. This caused an increased competition for copepods, which are the main food item for young fish. In the areas dominated by polar cod the shortage of copepods forced immature capelin to switch to the chaetognath Sagitta, which affected their fatness negatively.During the warm years the feeding grounds of Atlantic cod also expanded, to a large degree caused by the shortage of their main food, the capelin. In 2004–2005 the cod formed feeding concentrations in the north and northeast Barents Sea where they fed on the capelin. In this area the consumption of polar cod by cod increased, and in some local areas the polar cod practically replaced the capelin in the diet of cod. In general polar cod in the diet of Atlantic cod were more important in the northern than in the southern part of the Barents Sea. The fatness of cod was extremely low during the whole spring–summer period (until August), and after the feeding period the fatness index of the Atlantic cod became lower than the average long-term autumn value.     

The use of macroalgal species richness and composition on intertidal rocky seashores in the assessment of ecological quality under the European Water Framework Directive

The EC Water Framework Directive (WFD) suggests using abundance and species composition of intertidal seaweed communities for ecological quality classification of rocky seashores. There are two difficulties with this. According to WFD all sensitive species should be present on a shore. There is no accepted list of sensitive seaweed species and those which may be sensitive in one location may not be so in another. Second, natural successions can result in very large abundance changes of common species, e.g. from almost completely fucoid-dominated shores to almost totally barnacle-dominated shores, without any change in ecological quality. Studies have shown that numerical species richness, not the list of actual species present, is broadly constant in the absence of disturbance. The ephemeral species, possibly the sensitive members of the community, change regularly in such a way as to conserve species richness. It is proposed that species richness on a defined length of shore be used as a criterion of ecological quality. A database of species found on over 300 shores in the British Isles, under strictly controlled sampling conditions, has given ranges of values of species richness to be expected and has allowed for variations in these values due to sub-habitat variability, wave exposure and turbidity to be factored in. A major problem in applying such a tool is the lack of expertise of many workers in critical identification of seaweed species. A reduced species list has been extracted from the database using species commonly present and identifiable with reasonable certainty. A numerical index of ecological quality is proposed based on scores for various aspects of the physical nature of the habitat combined with a score for species richness which may be based on the reduced species list. The scoring system also uses further aspects of community structure, such as ecological status groups and the proportions of rhodophyta, chlorophyta and opportunist species. For this system to be effective there has to be close control of the way in which sampling is carried out to ensure a uniform level of thoroughness.     

A century of change: Reconstructing the biogeochemical history of Hubbard Brook

Ecosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate, and previous physical disturbances. Such disturbances create overlapping ‘biogeochemical legacies’ affecting modern nutrient mass balances. To understand how ‘legacies’ affected watershed-ecosystem (WEC) biogeochemistry during five decades of studies within the Hubbard Brook Experimental Forest (HBEF), we extended biogeochemical trends and hydrologic fluxes back to 1900 to provide an historical framework for our long-term studies. This reconstruction showed acid rain peaking at HBEF in the late 1960s-early 1970s near the beginning of the Hubbard Brook Ecosystem Study (HBES). The long-term, parabolic arc in acid inputs to HBEF generated a corresponding arc in the ionic strength of stream water, with acid inputs generating increased losses of H⁺ and soil base cations between 1963 and 1969 and then decreased losses after 1970. Nitrate release after disturbance is coupled with previous N-deposition and storage, biological uptake, and hydrology. Sulfur was stored in soils from decades of acid deposition but is now nearly depleted. Total exports of base cations from the soil exchange pool represent one of the largest disturbances to forest and associated aquatic ecosystems at the HBEF since the Pleistocene glaciation. Because precipitation inputs of base cations currently are extremely small, such losses can only be replaced through the slow process of mineral weathering. Thus, the chemistry of stream water is extremely dilute and likely to become even more dilute than pre-Industrial Revolution estimates. The importance of calculating chemical fluxes is clearly demonstrated in reconstruction of acid rain impacts during the pre-measurement period. The aggregate impact of acid rain on WEC exports is far larger than historical forest harvest effects, and even larger than the most severe deforestation experiment (Watershed 2) at HBEF. A century of acid rain had a calcium stripping impact equivalent to two W2 experiments involving complete deforestation and herbicide applications.     

Watershed studies at the Hubbard Brook Experimental Forest: Building on a long legacy of research with new approaches and sources of data

The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting experiments. The Hubbard Brook Ecosystem Study (HBES) originated in 1963, with the idea of using the small watershed approach to study element fluxes and cycling and the response of forest ecosystems to disturbances, such as forest management practices and air pollution. Early evidence of acid rain was documented at the HBEF and research by scientists at the site helped shape acid rain mitigation policies. New lines of investigation at the HBEF have built on the long legacy of watershed research resulting in a shift from comparing inputs and outputs and quantifying pools and fluxes to a more mechanistic understanding of ecosystem processes within watersheds. For example, hydropedological studies have shed light on linkages between hydrologic flow paths and soil development that provide valuable perspective for managing forests and understanding stream water quality. New high frequency in situ stream chemistry sensors are providing insights about extreme events and diurnal patterns that were indiscernible with traditional weekly sampling. Additionally, tools are being developed for visual and auditory data exploration and discovery by a broad audience. Given the unprecedented environmental change that is occurring, data from the small watersheds at the HBEF are more relevant now than ever and will continue to serve as a basis for sound environmental decision-making.     

Origin,evolution and anatomy of silt‐prone submarine external levées

Submarine external levées are constructional features that develop outside slope channel systems, and are a volumetrically significant component of continental margins. However, detailed observations of their process sedimentology and depositional architecture are rare. Extensive exposures of external levées at multiple stratigraphic intervals and well‐constrained palaeogeographic positions in the Fort Brown Formation, Karoo Basin, South Africa, have been calibrated with research boreholes. This integrated data set permits their origin, evolution and anatomy to be considered, including high‐resolution analysis of sedimentary facies distribution and characterization of depositional sub‐environments. An idealized model of the stratigraphic evolution and depositional architecture of external levées is presented, and variations can be attributed to allogenic (for example, sediment supply) and autogenic (for example, channel migration) factors. Initiation of external levée construction is commonly marked by deposition of a basal sand‐rich facies with sedimentary structures indicating rapid deposition from unconfined flows. These deposits are interpreted as frontal lobes. Propagation of the parent channel, and resultant flow confinement, lead to partial erosion of the frontal lobe and development of constructional relief (levées) by flow overspill and flow stripping. Overall fining‐upwards and thinning‐upwards profiles reflect increased flow confinement and/or waning flow magnitude through time. Identification of a hierarchy of levée elements is not possible due to the absence of internal bounding surfaces or sharp facies changes. The down‐slope taper in levée height and increasing channel sinuosity results in increasing numbers of crevasse lobe deposits, and is reflected by the increased occurrences of channel avulsion events down‐dip. External levées from the Fort Brown Formation are silt‐rich; however their stratigraphic evolution and the distribution of many components (such as sediment waves and crevasse lobe) share commonalities with mud‐rich external levées. This unique integrated data set has permitted the first high‐resolution characterization of external submarine levée systems.     

Distinction between the Youngest Toba Tuff and Oldest Toba Tuff from northern Sumatra based on the area density of spontaneous fission tracks in their glass shards

Determination of the area density of spontaneous fission tracks (ρ_s) in glass shards of Toba tephra is a reliable way to distinguish between the Youngest Toba Tuff (YTT) and the Oldest Toba Tuff (OTT). The ρ_s values for YTT, uncorrected for partial track fading, range from 70 to 181 tracks/cm² with a weighted mean of 108 ± 5 tracks/cm², based on 15 samples. Corrected ρ_s values for YTT are in the range of 77–140 tracks/cm² with a weighted mean of 113 ± 8 tracks/cm², within the range of uncorrected ρ_s values. No significant difference in ρ_s exists between YTT samples collected from marine and continental depositional settings. The uncorrected ρ_s for OTT is 1567 ± 114 tracks/cm² so that confusion with YTT is unlikely.     

Infrasound produced by debris flow: propagation and frequency content evolution

Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.     

Spatiotemporal Variability in Dissolved Organic Matter Composition is More Strongly Related to Bacterioplankton Community Composition than to Metabolic Capability in a Blackwater Estuarine System

The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.