Using sclerochronology to estimate the growth rate in Pinna nobilis: a case study of Les Alfaques Bay population (Ebro Delta, Spain).

Pinna nobilis is the biggest Mediterranean bivalve, endemic and semi-infaunal. Provide hard substrates to colonize, increasing the spatial heterogeneity of the softbottom communities. P. nobilis suffer a drastic decline due to the anthropogenic pressures. It’s included in the Habitats Directive, in the Barcelona Convention, and in the red lists of many Mediterranean countries. Estimates the growth rate allows to understand the population dynamics of species and yield knowledge to improve protection efforts. In this study a new methodology based on sclerochronology was used to estimate the age and the growth rate of a P. nobilis population located in Les Alfaques bay. The shells of 35 specimens were cataloged. A subsample of 20 individuals was selected, and one valve of each specimens was cut into radial sections along PAMS (Posterior Adductor Muscle Scar) to study the inner register. Thus, the positions of PAMS obscured by nacre were identified, and the number of missing records was estimated by the width of the calcitic layer in the anterior part of the shell. The first growth curve for the Les Alfaques bay population was calculated from the length/age data. To simulate the growth rate of this population, the growth model based on the modified Von Bertalanffy equation was used. Shallow water usually hosts small sized populations of P. nobilis, while in deeper waters specimens reaches larger size. In Les Alfaques bay the population is composed by large size individuals though it’s located in shallows waters. This unusual size pattern is probably due to a sand bar that offers protection from hydrodynamic stress, allowing individuals to elongate more. This study contributes to the knowledge on P. nobilis biology and, with the aim to monitor this species, the growth curve could be used as baseline for future studies on habitat characteristics that may affect the population structure and dynamics in Les Alfaques Bay.

Influence of microstructure variability on short crack growth behavior

Fatigue life in metals is predicted utilizing regression analysis of large sets of experimental data, thus representing the material’s macroscopic response. Furthermore, a high variability in the short crack growth (SCG) rate has been observed in polycrystalline materials, in which the evolution and distributionof local plasticity is strongly influenced by the microstructure features. The present work serves to (a) identify the relationship between the crack driving force based on the local microstructure in the proximity of the crack-tip and (b) defines the correlation between scatter observed in the SCG rates to variability in the microstructure. A crystal plasticity model based on the fast Fourier transform formulation of the elasto-viscoplastic problem (CP-EVP-FFT) is used, since the ability to account for the both elastic and plastic regime is critical in fatigue. Fatigue is governed by slip irreversibility, resulting in crack growth, which starts to occur during local elasto-plastic transition. To investigate the effects of microstructure variability on the SCG rate, sets of different microstructure realizations are constructed, in which cracks of different length are introduced to mimic quasi-static SCG in engineering alloys. From these results, the behavior of the characteristic variables of different length scale are analyzed: (i) Von Mises stress fields (ii) resolved shear stress/strain in the pertinent slip systems, and (iii) slip accumulation/irreversibilities. Through fatigue indicator parameters (FIP), scatter within the SCG rates is related to variability in the microstructural features; the results demonstrate that this relationship between microstructure variability and uncertainty in fatigue behavior is critical for accurate fatigue life prediction.

Evaluation of green algae deployment for organic pollutant removal in urban wastewater through ERE-CALUX potency assessment

The interest of the scientific community towards organic pollutants in freshwater streams is fairly recent. During the past 50 years, thousands of chemicals have been synthesized and released into the general environment. Nowadays their occurrence and effects on several organism, invertebrates, fish, birds, reptiles and also humans are well documented. Because of their action, some of these chemicals have been defined as Endocrine Disrupters Compounds (EDCs) and the public health implications of these EDCs have been the subject of scientific debate. Most interestingly, among those that were noticed to have some influence and effects on the endocrine system were the estrone, the 17β-estradiol, the 17α-estradiol, the estriol, the 17α-ethinylestradiol, the testosterone and the progesterone. This project focused its attention on the 17β-estradiol. Estradiol, or more precisely, 17β-estradiol (also commonly referred to as E2) is a human sex hormone. It belongs to the class of steroid hormones. In spite of the effort to remove these substances from the effluents, the actual wastewater treatment plants are not able to degrade or inactivate these organic compounds that are continually poured in the ecosystem. Through this work a new system for the wastewater treatment was tested, to assess the decrease of the estradiol in the water. It involved the action of Chlorella vulgaris, a fresh water green microalga belonging to the family of the Chlorellaceae. This microorganism was selected for its adaptability and for its photosynthetic efficiency. To detect the decrease of the target compound in the water a CALUX bioassay analysis was chosen. Three different experiments were carried on to pursue the aim of the project. By analysing their results several aspects emerged. It was assessed the presence of EDCs inside the water used to prepare the culture media. C. vulgaris, under controlled conditions, could be efficient for this purpose, although further researches are essential to deepen the knowledge of this complex phenomenon. Ultimately by assessing the toxicity of the effluent against C. vulgaris, it was clear that at determined concentrations, it could affect the normal growth rate of this microorganism.