Analysis of sedimentation and resuspension processes of aquaculture biosolids using an oscillating grid

Sedimentation and resuspension processes of aquaculture biosolids (non-ingested feed and faeces) are analysed using vertically oscillating grids as a source of turbulence in fluid tanks. An oscillating grid system consists of a container in which a grid is stirred vertically generating a well-known turbulent field that is function of amplitude and frequency of oscillation, distance between grid and measurement point, and mesh spacing of the grid. The grid used in this study had a mesh spacing of 1.2 cm, and was calibrated using different amplitudes (1, 1.5 and 2 cm), frequencies (from 1 to 6 Hz) and distances (2.4, 2.7 and 3 cm). After calibration, the turbulence needed to resuspend biosolids and to maintain them in the water column following different times of consolidation, and with biosolids of different origin, was analysed. It was observed that the turbulence needed to resuspend aquaculture biosolids increased with the time of consolidation. When the turbulence was decreased after a resuspension process, the next sedimentation of biosolids showed a hysteretic behaviour: turbulence needed to resuspend a fixed percent of biosolids from the tank bottom is substantially higher than that needed to maintain the same percentage suspended in the water column. Differences in resuspension behaviour of biosolids originated in different tanks were also observed.

The method provides useful information that can be compared with turbulence generated by fish swimming activity, in order to determine the culture conditions, which can promote self-cleaning conditions in a particular tank.     

Geostatistical methods to study spatial variability of soil cations after a prescribed fire and rainfall

Prescribed fire is a technique sometimes used in forest management but the effects on soil are not fully understood. Soil is a complex system and the spatial variability of properties and processes may increase after a disturbance like fire. We modelled three soil cations Ca²⁺, Mg²⁺ and K⁺ with probabilistic methods and geostatistics in order to assess the spatial effects of a prescribed fire within a plot (108 m²). Soil samples were collected during 6 different sampling campaigns (pre fire, post fire, 2 months, 5 months, 1 year, and 3 years after the prescribed fire). The sampling interval was designed to detect the effect of rainfall (1315 mm for the 3 years with 72 mm/h peak intensity) on the spatial soil changes as consequence of processes such as: leaching, soil erosion, etc. We developed an index of response to compare each cation after the prescribed fire with its pre-fire levels. Results showed that calcium and magnesium recover with time to their original concentrations. Potassium increase slightly in half of the plot just after fire; however, three years after fire the concentration was two orders of magnitude lower than the pre-fire state. The divalent cations (Ca²⁺ and Mg²⁺) were more homogeneous but the monovalent cation (K⁺) was more heterogeneous after the fire. Furthermore the maximum rainfall period triggered different spatial processes and the type of process was a function of the valence of the cation.     

A rapid spectral-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events

Purpose  

This paper reports on the development of a rapid and simple spectra-reflectance-based fingerprinting approach for documenting suspended sediment sources during storm runoff events. The methodology was applied in the rural Wollefsbach catchment (4.4 km², NW Luxembourg).     

Interference competition in a threatened seabird community: A paradox for a successful conservation

It is often assumed that conservation actions targeting a threatened community (e.g. habitat protection) will result in similar benefits for all species. However, complex interactions between species, such as interference competition, may result in displacement of subordinate, vulnerable species. We analysed here the spatio-temporal population dynamics of a threatened seabird community since the protection in the 1980s of several breeding sites at the Ebro Delta, western Mediterranean, Spain during 1980-2007. Competition for the most suitable patches was governed by body size, with smaller species avoiding associations with larger, dominant species. We tested whether the density increase of the larger species (yellow-legged gull Larus michahellis and Audouin’s gull Larus audouinii) at La Banya (the highest quality patch within the Delta) affected species diversity at the local level. As expected, such diversity decreased, resulting also from the colonisation of other sites by smaller species, some abandoning the former area. The conservation paradox appeared because the interference competition was dominated not only by the largest species of the community, the yellow-legged gull, which is sometimes considered a pest species, but also by the vulnerable Audouin’s gull, a flagship species which has ca. 65% of the total world population at La Banya. Nevertheless, the availability of alternative patches within the Ebro Delta ensured a high biodiversity at regional scale. Results highlight the role of turnover of competing species within a community in ecosystem function and stability, and the importance of alternative sites and dispersal abilities for the conservation of vulnerable communities.     

Inter-individual consistency in habitat selection patterns and spatial range constraints of female little bustards during the non-breeding season

Background

Identifying the factors that affect ranging behavior of animals is a central issue to ecology and an essential tool for designing effective conservation policies. This knowledge provides the information needed to predict the consequences of land-use change on species habitat use, especially in areas subject to major habitat transformations, such as agricultural landscapes. We evaluate inter-individual variation relative to environmental predictors and spatial constraints in limiting ranging behavior of female little bustards (Tetrax tetrax) in the non-breeding season. Our analyses were based on 11 females tracked with GPS during 5 years in northeastern Spain. We conducted deviance partitioning analyses based on different sets of generalized linear mixed models constructed with environmental variables and spatial filters obtained by eigenvector mapping, while controlling for temporal and inter-individual variation.

Results

The occurrence probability of female little bustards in response to environmental variables and spatial filters within the non-breeding range exhibited inter-individual consistency. Pure spatial factors and joint spatial-habitat factors explained most of the variance in the models. Spatial predictors representing aggregation patterns at?~?18 km and 3–5 km respectively had a high importance in female occurrence. However, pure habitat effects were also identified. Terrain slope, alfalfa, corn stubble and irrigated cereal stubble availability were the variables that most contributed to environmental models. Overall, models revealed a non-linear negative effect of slope and positive effects of intermediate values of alfalfa and corn stubble availability. High levels of cereal stubble in irrigated land and roads had also a positive effect on occurrence at the population level.

Conclusions

Our results provide evidence that female little bustard ranging behavior was spatially constrained beyond environmental variables during the non-breeding season. This pattern may result from different not mutually exclusive processes, such as cost–benefit balances of animal movement, configurational heterogeneity of environment or from high site fidelity and conspecific attraction. Measures aimed at keeping alfalfa availability and habitat heterogeneity in open landscapes and flat terrains, in safe places close to breeding grounds, could contribute to protect little bustard populations during the non-breeding season.

     

A Survey of Trunk Disease Pathogens within Rootstocks of Grapevines in Spain

Grapevine trunk disease pathogens, and specifically Petri disease pathogens, can be spread by planting infected plants. Due to the increasing incidence of Petri disease and other young grapevine declines reported lately in Spain, a sampling of plants used before for new vineyards were carried out in 2002 and 2004. A total number of 208 plants (grafted and non grafted) were collected, of which 94 plants (45.2%) were infected with at least one of the following pathogens: Phaeomoniella chlamydospora, and species of Phaeoacremonium, Botryosphaeria, Cylindrocarpon, and Phomopsis. Species of the genera Phaeoacremonium and Botryosphaeria isolated in 2004 were identified using morphological and molecular characters. Species of Phaeoacremonium identified were P. aleophilum and P. parasiticum; and those of Botryosphaeria were B. obtusa, B. dothidea and B. parva. This is the first report of P. parasiticum and B. parva occurring on grapevines in Spain. Distribution of pathogens within the plants was studied in 2004. Phaeomoniella chlamydospora was not detected in the graft union of any plant; however, species of Botryosphaeria and Phomopsis were detected along the plant, but mainly in the graft union; Phaeoacremonium aleophilum was detected along the grafted plants, but not in rooted rootstocks. The results suggest that infected plants used for new plantings in Spain are an important source of primary inoculum of the pathogens associated with grapevine trunk diseases in the field.     

Rebuilding Mediterranean fisheries: a new paradigm for ecological sustainability

In Mediterranean European countries, 85% of the assessed stocks are currently overfished compared to a maximum sustainable yield reference value (MSY) while populations of many commercial species are characterized by truncated size‐ and age‐structures. Rebuilding the size‐ and age‐structure of exploited populations is a management objective that combines single species targets such as MSY with specific goals of the ecosystem approach to fisheries management (EAF), preserving community size‐structure and the ecological role of different species. Here, we show that under the current fishing regime, stock productivity and fleet profitability are generally impaired by a combination of high fishing mortality and inadequate selectivity patterns. For most of the stocks analysed, a simple reduction in the current fishing mortality (F_cur) towards an MSY reference value (F_MSY), without any change in the fishing selectivity, will allow neither stock biomass nor fisheries yield and revenue to be maximized. On the contrary, management targets can be achieved only through a radical change in fisheries selectivity. Shifting the size of first capture towards the size at which fish cohorts achieve their maximum biomass, the so‐called optimal length, would produce on average between two and three times higher economic yields and much higher biomass at sea for the exploited stocks. Moreover, it would contribute to restore marine ecosystem structure and resilience to enhance ecosystem services such as reservoirs of biodiversity and functioning food webs.     

Cyclic fluctuations of blue whiting (Micromesistius poutassou) linked to open‐sea convection processes in the northwestern Mediterranean

In the Mediterranean, blue whiting, Micromesistius poutassou, constitutes a traditional fisheries resource. Over several decades, blue whiting landings in the Catalan coast (northwestern Mediterranean) have displayed cyclical variations, of c. 6 yrs, slightly decreased to five in the last two decades, as shown through wavelet analysis. These fluctuations have persisted under very different levels of fishing effort. This study evaluates the hypothesis that deep‐water formation in the adjacent Gulf of Lions, and the enhanced primary productivity related to it, determines recruitment strength in blue whiting that results ultimately in the observed periodicity of the blue whiting landings. The link between landings and environmental drivers was explored using lagged cross‐correlations, with 0‐ and 1‐yr lag. The variables considered included large‐scale indices [North Atlantic Oscillation (NAO) and the Atlantic Multi‐decadal Oscillation (AMO)], Mediterranean climate indices [MO and Western Mediterranean Oscillation (WeMO)], and variables defining the local environmental conditions in the northwestern Mediterranean (sea‐air heat flux, winter air temperature anomaly and Rhône river runoff). Significant correlations were only found between landings (1961–2011) and sea‐air heat flux, which is generally taken as an indicator of processes of deep water convection, at 0 and 1‐yr lag. These results suggest that the observed fluctuations in blue whiting landings respond to oceanographic processes taking place in the Gulf of Lions.     

Co‐viability of a Mediterranean demersal fishery affected by the discard ban under alternative management scenarios

The joint viability, or co‐viability, of a Mediterranean Sea mixed demersal fishery was examined by applying a bioeconomic fisheries model to the main seven target stocks of the fishery under biological, social and economic constraints. The stocks of interest were hake, black‐bellied angler, deep‐water rose shrimp, red mullet, blue and red shrimp, Norway lobster and blue whiting, all of which were assessed as overexploited. Their combined production corresponds to 34% by volume and 52% by value of the landings of the demersal fishery studied. Simulation scenarios based on effort reduction, changes in the selectivity pattern and implementing a fisheries restricted area were compared over the simulation horizon of 2015–2030. The latter two scenarios were also examined in terms of full or partial compliance. The effect of a discard ban on the economy of the fleet was also analysed. The results show that the fishery is not co‐viable because some stocks are not viable in the projection period, but social and economic viability was ensured in all cases. As is often the case for mixed fisheries, a unique management measure is unlikely to improve the situation of all stocks simultaneously, but all the management measures tested are better than the status quo.