Natural Beds Research Articles

Commercial raw materials from algaculture and natural stocks of Ulva spp.

Ulva species have potential uses in several industrial sectors as they are rich in proteins, vitamins, fibers, and minerals. They also produce the essential amino acid tryptophan, which can act as an anxiolytic. With the increasing use of bioactive compounds obtained from algal species for commercial purposes, it will be necessary to evaluate the best methods for obtaining them, whether harvesting from natural beds or seaweed cultivation. Aquaculture has been indicated as an alternative method of acquiring algal biomass that avoids the harvesting and depredation of natural beds. To assess the feasibility of harvesting natural stocks of Ulva spp. (U. lactuca and U. flexuosa), algal biomass and relative species abundances were quantified at three sites in southeastern Brazil during 14 sampling periods. The results of those field biomass analyses allowed us to estimate their annual productions and compare them with projected productions of Ulva spp. under algaculture conditions. Tryptophan production by cultivated U. lactuca (as a high value-added product) was compared with the tryptophan concentrations of Ulva spp. from natural beds. No consistent patterns of total biomass production or relative abundances of the Ulva spp. were obtained during the sampling periods, making it impossible to accurately estimate sustainable biomass production for commercial uses. We diagnosed greater production sustainability in algaculture than in algal beds. The concentration of tryptophan produced by U. lactuca in algaculture was 60% higher than that from natural stocks. Tryptophan was quantified for the first time here in U. flexuosa.

Flood risk mapping using uncertainty propagation analysis on a peak discharge: case study of the Mille Iles River in Quebec

This study uses uncertainty propagation in real flood events to derive a probabilistic flood map. The flood event of spring 2017 in Quebec was selected for this analysis, with the computational domain being a reach of the Mille Iles River. The main parameter deemed uncertain in this work is the upstream water discharge; a given value of this discharge is utilized to build a random sample of 500 scenarios using the Latin hypercube sampling method. Simulations were run using CuteFlow-Cuda, an in-house finite volume-based shallow water equations solver, to derive the statistical mean and the standard deviation of the free surface elevation and the water depth at each node. For this real flood case, the initial interface flux scheme had to be adapted, combining a developed version of the scheme introduced by Harten, Lax and van Leer at wet interfaces and the Lax–Friedrichs scheme with additional free surface corrections for wet and dry transitions. Comparisons with results obtained from TELEMAC and from in situ observations show generally close predictions, and overall good agreement with observations. Errors of the free surface prediction relative to observations are less than 2.75%. A map based on the standard deviation of the water depth is presented to enhance the areas most prone to flooding. Finally, a flood map is produced, showing the flooded inhabited areas near the municipalities of Saint-Eustache and Deux Montagnes around the reach of the Mille Iles River as it overflows its natural bed.

Evaluating the macroscopic system properties of kelp species planted on two artificial reefs: Implications for the restoration of perturbed subtidal areas

Macroscopic ecosystem properties based on an Ascendency theoretical framework were assessed for mass-balance trophic models representing ecological systems constructed by the kelp species Macrocystis pyrifera planted on artificial reefs installed on subtidal barren rocky and sandy bottoms (Antofagasta Peninsula, Chile). Information on biomass, production, diet and consumption was needed. The magnitudes of relative Ascendency, relative Overhead and Redundancy values indicated that kelp planted on artificial reefs allocated on soft bottoms would be more highly developed and less resistant to perturbations than ecological systems on artificial reefs disposed on barren and natural systems inhabiting soft bottoms and kelp habitats. The relative Ascendency corresponding to each component of the ecological systems constructed on artificial reefs on both habitats was represented principally by detritus (~37%), M. pyrifera (between 22 and 26%) and phytoplankton (between 10 and 13%). The compartments of Rhodophyta, Chlorophyta Mesophyllum sp. and the sea star Heliaster helianthus accounted for the system complexity in terms of flow, exhibiting the lowest Average Mutual Information. The Finn cycling index – considered as a ecosystem maturity index – showed contradictory outcomes compared to Ascendency. However, the values of System omnivory index and Average path length quantified for the ecological systems constructed on both artificial reefs showed similar network topologies compared to natural kelp beds. Based on our findings, artificial reefs seeded with M. pyrifera could be used to restore perturbed local marine benthic ecological systems along the Chilean coast. Likewise, this work shows that the trajectory of local ecological systems can be modified, enhancing their global-system health.

Intertidal mussel reefs change the composition and size distribution of diatoms in the biofilm

Migrating diatoms are microscopic ecosystem engineering organisms that have functional consequences on the seascape scale by significantly contributing to the microphytobenthos biofilm. The microphytobenthos biofilm is a thin photosynthesising layer that covers the sediment on intertidal flats. It fuels the food web, increases sediment stability, and enhances the deposition of particles, providing ecosystem services to coastal communities. Here we tested the effect of another ecosystem engineering habitat, intertidal blue mussel reefs, on the composition and properties of migrating diatom communities. Small-scale reefs constructed in the intertidal mimicked and reinforced the natural pattern in diatom community composition and function that we documented in the field. The field experiment adding small reefs to the intertidal ran from 30 April to 10 June 2015 and the field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489°, E 6.230°). Both the constructed small-scale reefs and the natural reef changed the community composition of diatoms in the biofilm by promoting higher numbers of smaller-sized cells and species. Small diatoms have higher growth and gross photosynthesis rates, indicating that this explains the higher production and chlorophyll-a concentration of the biofilm measured on natural intertidal shellfish reefs. Our results showed that shellfish reefs have a large impact on biofilm functioning. However, biofilms are also fuel for the shellfish, indicating that the two very different ecosystem engineers may facilitate coexistence on tidal flats through a positive feedback loop.

Vertical distribution patterns of larval supply and spatfall of three species of Mytilidae in a Chilean fjord used for mussel farming: Insights for mussel spatfall efficiency

The spatfall of mussels on artificial collectors sustains the production of ~350,000 t of mussels per year in Chile, which is known as “capture based aquaculture” (CBA), although little is known about the processes that determine a successful or unsuccessful spatfall. We studied the vertical variability of the larval supply and spat of Mytilus chilensis, Choromytilus chorus and Aulacomya atra in a marine farm located in one of the most important fjords used for spatfall in Chile. Larval supply was sampled five times per day (between 8 am and 6 pm) on three dates, in four depth strata between 0 and 13 m. Environmental variables from the water column were also recorded during each sampling. The spatfall was sampled monthly from December 2014 to June 2015 in the same four depth strata by installing 13 m long collectors in the study area. Larval supply of the three Mytilidae species showed few clear patterns, although the water column showed wide variability in temperature, dissolved oxygen, salinity, and sigma-t. The spatfall of M. chilensis and A. atra showed almost homogeneous vertical distribution at first. However, after six months, a stratified distributional pattern of spat emerged, with M. chilensis dominating between 0 and 7 m depth, and A. atra dominating between 7 and 13 m depth. In both species there was ~90% spat loss in six months from their maximum abundance, which needs to be studied. Our results suggest low production efficiency of spatfall in the study area and we concluded that improving the efficiency of spat collection and monitoring mussel spatfall is a priority, including their potential relationship with natural beds in the vicinity.

Long-term Field Heave Studies on Various Foundation Techniques in Expansive Soils

Expansive soils being susceptible for moisture variations undergo cyclic seasonal movements that pose serious stability concerns for structures resting on them, especially when they are lightly loaded ones. The concerted efforts made by various researchers across the world enabled them to develop remedial solutions to mitigate these problems with varied degree of success. The present work is an effort to study the relative performance of the different remedial techniques in vogue and those proposed in the recent years. These techniques were adopted below the shallow footings at a site on NIT Warangal campus where natural expansive clay bed is present. This study revealed that the sand cushion and CNS cushion could reduce the heave by 56 to 64%; but in case of sand cushion, an increasing trend of heave with number of cycles of wetting and drying was observed. The chemical alteration by lime could reduce the heave by 59% and by CaCl2 and CaCl2–Na2SiO3 the heave could be reduced by 70 and 73%, respectively. The recently promulgated concrete and granular anchor piled footings have shown the heave reduction up to 63 and 78%, respectively. Further, it is found that the combined effect of CNS cushion along with chemical modification and/or tension/anchor piled footing systems were found to be synergistically more effective than individual techniques in controlling the seasonal movements of footings and flooring/lining panels. Interestingly, none of these remedial techniques could overcome the shrinkage movements though these movements are observed to be insignificant in case of piled footings.

Urban Planning Principles and Methods of Returning Coastal Areas to Citizens

The extremely important issue of today is the return of coastal areas to city dwellers. The peculiarities of urban, landscape and integrated directions of organization of coastal territories are considered with the definition of their advantages and disadvantages. Bright examples of all three principles of coastal development are given. The basic town-planning methods of the organization of coastal territories are defined. The focus is on the urgency of reviving natural ecosystems in cities by revitalizing urban rivers with the return of rivers to their natural qualities - natural bed, flora, fauna, ecotones, which will improve the atmosphere of the urban environment, microclimate, create recreation areas for citizens. The most striking example of successful revitalization project is the revival of the Chongecheong River in Seoul (South Korea). The creation of Pochayna Park in the Obolonskyi district of Kyiv with the revival of the small Pochayna River by Kyiv designers and architects in partnership with Korean colleagues was presented. The creation of public spaces in coastal areas is a condition for improving the quality of life of urban residents. Concern for the human dimension in cities is at the heart of these projects.

Feeding and growth coupling during different development larvae phases of the Mediterranean mussel Mytilus galloprovincialis L. from Amsa Bay

Spat supply for mussel farming in Morocco is essentially based on seed capture and collection from natural beds. However, natural irregularity recruitment in exploited areas and encountered difficulties during spat collection operations have led to develop and improve reproduction techniques under controlled conditions in hatcheries. The present study focused on the larvae phase aiming at assessing growth rate varies between different development stages. Trocophore larva stage had a size of 63.25 μm and reached the pedivilegere stage with a size of 272.56 μm in 18 culture days. Length growth was more significant than width growth for both H-batch and T-batch. For instance, larvae grew in terms of length quickly in H-batch than T-batch (11.10± 1.30 and 9.67 ± 1.17 μm day-1), and the same pattern was observed for T-batch larvae. Inversely, the total biomass consumed was higher during T-batch larvae rearing than H-batch ones. In contrast, the effect of feeding on growth was observed more significantly for H-batch larvae (t=7.55, df=23, p<0.001) than T-batch ones (t=4.13, df=23, p<0.001). However, the specific feeding effect was revealed higher for I. galbana for both batches rather than C. calcitrans and T. suecica. However, the larvae growth reduction is linked to the beginning of tissue synthesis.

Reduced physiological performance in a free-living coralline alga induced by salmon faeces deposition

Maerl beds are formed by the accumulation of free-living coralline algae and have considerable ecological significance due to the high diversity of associated fauna and flora. The rapid expansion of the Atlantic salmon Salmo salar aquaculture industry in Norway may have major impacts on surrounding maerl beds through the release of effluents, including fish faeces. This study is the first to test the effects of salmon faeces and inorganic sediment deposition on the photosynthesis, respiration, calcification and pigment content of the coralline alga Lithothamnion soriferum. In a 6 wk laboratory experiment, inorganic sediment and salmon faeces deposition significantly reduced the amount of light reaching the surface of coralline algae. No impact of inorganic sediment deposition was detected on L. soriferum physiology, while salmon faeces deposition increased respiration rate and reduced net primary production and calcification. The accumulation of salmon faeces stimulates proliferation of bacteria, with adverse consequences on L. soriferum physiology due to the potential release of toxic compounds. Burial by salmon faeces deposition also affects the physiology of coralline algae due to the flocculation of sticky faeces particles, which may limit nutrient and gas exchanges in the vicinity of thalli. Carbon dioxide accumulation in the vicinity of L. soriferum may lead to a decline in pH and alter the calcification process in cell walls. In natural maerl beds, the negative effect of faeces deposition may be exacerbated by longer-term exposure and the presence of other chemicals released by fish farms.

Augmentation of the insufficient tissue bed for surgical repair of hypospadias using acellular matrix grafts: A proof of concept study

Acellular matrices produced by tissue decellularisation are reported to have tissue integrative properties. We examined the potential for incorporating acellular matrix grafts during procedures where there is an inadequate natural tissue bed to support an enduring surgical repair. Hypospadias is a common congenital defect requiring surgery, but associated with long-term complications due to deficiencies in the quality and quantity of the host tissue bed at the repair site. Biomaterials were implanted as single on-lay grafts in a peri-urethral position in male pigs. Two acellular tissue matrices were compared: full-thickness porcine acellular bladder matrix (PABM) and commercially-sourced cross-linked acellular matrix from porcine dermis (Permacol™). Anatomical and immunohistological outcomes were assessed 3 months post-surgery. There were no complications and surgical sites underwent full cosmetic repair. PABM grafts were fully incorporated, whilst Permacol™ grafts remained palpable. Immunohistochemical analysis indicated a non-inflammatory, remodelling-type response to both biomaterials. PABM implants showed extensive stromal cell infiltration and neovascularisation, with a significantly higher density of cells (p < 0.001) than Permacol™, which showed poor cellularisation and partial encapsulation. This study supports the anti-inflammatory and tissue-integrative nature of non-crosslinked acellular matrices and provides proof-of-principle for incorporating acellular matrices during surgical procedures, such as in primary complex hypospadias repair.

Growth and survival of oyster Crassostrea iredalei (Faustino, 1932): A comparison of wild and hatchery-bred spat in grow-out culture

Oyster farming is an important industry both in developed and developing countries. The high demand for oysters has caused overexploitation of natural stocks. This led to dwindling spat fall and unstable production. This study was conducted to compare growth and survival of wild and hatchery-bred spat of the oyster Crassostrea iredalei in grow-out culture. Results of the experiment revealed that both wild (n = 1450) and hatchery-bred spat (n = 1450) had comparable growth rates in grow-out culture. Growth rates of wild and hatchery-bred oysters did not differ significantly at 5.69 ± 0.88 mm shell length (SL) and 8.85 ± 1.07 g body weight (BW) mo−1 and 6.88 ± 1.33 mm SL and 8.26 ± 1.15 g BW mo−1, respectively. Growth rates, in terms of shell length, both for wild (p < 0.05, r = 0.74) and hatchery-bred oysters (p < 0.05, r = 0.76), showed strong positive correlation with salinity. Meat yield was almost the same at 16.41 ± 0.57% for wild oysters and 15.59 ± 0.37% for the hatchery-bred ones. Proximate composition of dried whole flesh oyster samples also showed the same amounts of crude protein, crude fat, crude fiber, nitrogen free extract, and ash in both wild and hatchery-bred oysters. The length-weight relationships of wild [W = 0.000492 L2.6512 (R2 = 86.8%, p < 0.001)] and hatchery-bred [W = 0.000052 L3.1779 (R2 = 92.6%, p < 0.001)] C. iredalei were also calculated from the length and weight data obtained during the duration of culture and revealed higher b for the smaller hatchery-bred oysters. Moreover, mean survival at harvest did not significantly differ at 85.03 ± 1.09% for wild oysters and 85.31 ± 1.40% for the hatchery-bred ones (Two-sample t-test, p > 0.05). The results of this study showed the potential of hatchery-bred oyster spat as seeds for grow-out culture to address the declining number of spat fall in natural oyster beds. Producing the same quality of oysters, it can be inferred that the hatchery-bred spat are just as competent as their wild conspecifics.

An Investigation on the Impact of Physical Environment on the Formation and Continuity of Ancient settlements, Case Study the Merek River Catchment, Central Zagros, Iran

The geographical environment, especially its natural bed, is the area of all actions and reactions resulting from phenomena located on the surface of the earth. The natural environment is the most important factor in the formation of human settlements, especially in different periods. Factors such as altitude, slope, geological structure, faults, water resources, soil, vegetation and land use are natural substrates affecting the distribution of human settlements. The present study aims to investigate the relationship between the formation and continuity of ancient settlements and their environmental bed in the Merek River catchment. To achieve the objectives of the research, 6 natural criteria were considered environmental factors or independent variables, and the area of ancient sites was regarded as a dependent variable. To investigate these factors, Arc Gis and SPSS software programs and inferential statistics quantitative analysis with the Pearson correlation method were used. Additionally, multiple linear Regression was used to investigate the effect of several independent variables on the dependent variable. The results indicate that the areas of the Merek River catchment are directly related to natural factors such as altitude, distance from rivers, and distance from communication routes and type of land use, and a number of other environmental factors are slightly associated with ancient sites. They have caused the people of the past in this region to choose two types of livelihood for their lives.

Sea bottom culture ofChondracanthus chamissoi(Rhodophyta: Gigartinales) by vegetative propagation at Puerto Aldea, Tongoy Bay (Northern Chile)

Seaweed exploitation in Chile has increased over the last decades, resulting in a reduction of seaweeds landings and the overharvesting of natural beds. In response, ecological baselines for their sustainable exploitation and the development of seaweed aquaculture have been implemented. In recent years, the culture of commercial red seaweed Chondracanthus chamissoi has been developed experimentally by spore and vegetative reproduction. These methods are facilitated by the formation of secondary attachment discs (SADs), generated to fasten the inoculated algae to substrates. In this study, the vegetative propagation was carried over an artificial substrate installed in a sea bottom culture system. The biomass yields, total amount of epiphytes, length of new thalli and number of SADs, per season and culture times (1, 2, 3 and 4 months) are reviewed in this work. Chondracanthus chamissoi showed growth under all treatments, with a maximum accumulated biomass of 60 g m−1, recorded in summer, and with no significant differences in biomass yield reported in autumn and spring seasons. A similar pattern was observed for epiphyte biomass, while the greatest SAD number and thalli lengths were recorded in winter.

Enhancing yield on Macrocystis pyrifera (Ochrophyta): The effect of gametophytic developmental strategy

Macrocystis pyrifera gametophytes growing under controlled conditions produce juveniles with different numbers of fronds, i.e. few (≤ 2) or multiple fronds (≥ 3). We describe these morphotypes and test whether the number of fronds may impact juvenile growth by performing laboratory and field experiments. Kelp reproductive material was collected in southern Chile and 133 female gametophytes were individually monitored for 90 days until they become fertilized and formed sporophytes. Samples of each individual frond were taken for genetic analysis to determine genetic homogeneity. A factorial experiment combining temperature (12 and 18 °C) and N-NO3 (N-NO3 limited and N + NO3 non-limited concentrations) was conducted using juvenile sporophytes. Growth was assessed by measuring individual surface area and wet weight, and the physiological status by quantifying photosynthetic pigments, nitrate reductase activity and photosynthetic parameters. Field experiments with both morphotypes were carried out to measure growth, on the seabed within a natural kelp bed, and a farm using sporophytes. Following the development of female gametophytes with different numbers of oogonia, we found that those with a higher number of oogonia produced a sporophytic unit united by a single holdfast (i.e. multiple fronds morphotype). These sporophytic units were genetically diverse suggesting that oogonia were fertilized by antherozoids from different male gametophytes. The laboratory experiment indicated that these sporophytic units can withstand better nitrogen limiting conditions at 12 °C as shown by a significantly higher growth rate. This trend was also found for chlorophyll and partially supported by the photosynthetic parameters (higher light compensation point). Nitrate reductase activity revealed that under N limitation its activity increased only in the multiple frond morphotype, independent of temperature. M. pyrifera multiple frond morphotype out-planted to on-growing sites showed a significant higher biomass. These results indicate that morphotype is as important as genetic management when pursuing kelp growth.

Estimation of Basic Geometric and Hydraulic Characteristics of Natural Torrent Beds

Many mountainous regions and their watersheds lack the mathematical description of their hydraulic geometry such as the High Tatras region in Slovakia. Therefore, the aim of the paper is to determine the geometric and hydraulic characteristics of natural torrent beds and to propose a regional equations of mountain watersheds for the High Tatras region. In the paper is also proposed a new equation to determine the relationships between the watershed area and the geometric characteristics of flow profiles. Derived regional equations can help in nature-friendly and ecological shaping and dimensioning of channel cross sections in torrent control designing. The research was conducted in 26 natural torrents and their watersheds on the reference sections and profiles under the sediment source zones. Two different regression equations to determine the regional relationships (hitherto used without asymptote and newly proposed with asymptote) were compared. The analyses showed a strong correlation relationship between watershed area Aw (km2) and bankfull geometric characteristics of natural cross-sections: width of the channel inside the banks Bbf (m), mean channel depth Hbf (m), channel cross-section area Abf (m2) and hydraulic characteristic – bankfull discharge Qbf (m3.s-1). These relations were tested by t-test and Shapiro-Wilk test. The determination coefficient (R12) for the relationships without asymptote ranged between R12 = 0.919 and R12 = 0.972; p1 – values from Shapiro-Wilk test ranged between p1 = 0.0359 and p1 = 0.8027. The determination coefficient (R22) for the relationships with asymptote ranged between R22 = 0.952 and R22 = 0.974; p2 – values from Shapiro-Wilk test ranged between p2 = 0.0221 and p2 = 0.8617. At the same time, we tested and confirned the hypothesis that the correlation coefficients R1 from equation without the asymptote are only randomly different from the correlation coefficients R2 from equation with the asymptote and the difference between these coefficients is also random. Derived regional equations make it possible to the gradual creation of hydrologic landscape regions in the SR. They can be also used as a valuable input to the ecological cross sections designing in torrent control and revitalization for the regions with a similar natural conditions.

Turbulence anisotropy and intermittency in open-channel flows on rough beds

An experimental campaign, based on Particle Image Velocimetry measurements in a laboratory flume with different median sediment sizes in the no-motion condition, has been carried out aiming at investigating the effects of bed roughness on turbulence anisotropy in two different vertical zones of the turbulent open-channel flow. An analysis of turbulence anisotropy, which relies on second-order structure functions and anisotropy angle, has been performed. The scale-dependent anisotropy level has been quantified, verifying the tendency of the system to span from large-scale anisotropy, due to the main shear of the boundary layer, to small-scale isotropy. Isotropy is well-established for the largest sediment sizes. High-order structure function analysis reveals that intermittency is more pronounced in the near-bed layers, where the flow is more populated by coherent vortices. Spectral anisotropy and intermittency strongly characterize the transport properties of turbulence and are, therefore, important phenomena for natural bed rivers.

Genetic variability in Ruditapes decussatus clam combined with Perkinsus infection level to support founder population selection for a breeding program.

Clam farmers worldwide face several challenges, including irregular seed supply and high mortalities due to pathogenic organisms such as Perkinsus olseni. In Europe, there is a high unmet consumer demand for native clam species such as Ruditapes decussatus. The high market value of R. decussatus makes the culture of this species potentially more attractive than that culture of the alien species Ruditapes philippinarum. Thus, there is a market opportunity in breeding and producing R. decussatus at an industrial scale. A selective breeding program to improve R. decussatus performance will be carried out in Portugal; and the first critical step to develop such a breeding program is the establishment of a founder population. In this study, intra- and interpopulation genetic diversity was assessed using 13 microsatellite markers in eight natural beds located in Portugal, Spain and Italy. Also, allele and genotypic frequencies of each microsatellite locus were assessed discriminating between clams infected and non-infected by P. olseni. All locations showed similar values for several genetic diversity parameters. Analyses of population differentiation (FST, Bayesian clustering and AMOVAs) revealed five genetically differentiated regions: Rías Altas and Rías Baixas (NW Spain), North/Central Coast of Portugal, Gulf of Cadiz and Adriatic Sea. Significant differences in the allelic and genotypic frequency distribution between infected clams and non-infected ones at four microsatellite loci are reported suggesting that resistance to the disease could have a genetic basis. Moreover, a positive or negative relationship between the frequency of certain alleles and the parasite infection was inferred. Further studies should confirm the potential use of those alleles as genetic markers for P. olseni infection. Integrating results of genetic diversity within and between populations and Perkinsus infection levels, a founder population for a R. decussatus breeding program is proposed, composed by individuals from Barallobre (Rías Altas), Pontevedra or Cangas (Rías Baixas), Óbidos (North/Central Coast of Portugal), Algarve (Gulf of Cadiz) and Venice (Adriatic Sea).

Concise review of the genus Meristotheca (Rhodophyta: Solieriaceae)

The genus Meristotheca (Solieriaceae) includes fifteen currently accepted species. They are widely distributed throughout the tropics and subtropics of both hemispheres, inhabiting the intertidal and subtidal regions of rocky shores. Molecular phylogenetic studies allowed a precise understanding of the species diversity and biogeography of the genus. The commercial value of certain species of Meristotheca lies in its use primarily as food for direct human consumption and to some extent as raw materials for extraction of carrageenan and other bioactive compounds. Intensified harvesting of the seaweeds resulted in the depletion of their natural beds; hence, several attempts have been made for mariculture. The management effort for the farming of Meristotheca on a commercial scale is still at its early stage. Studies on the phenology, sporulation, callus induction and thallus regeneration, photosynthesis, and growth of these potentially useful species contributed to the advancement of cultivation technologies. Further research on the biochemistry and utilization of Meristotheca species is necessary for the commercial competitiveness of these promising seaweed resources.

Рhysical simulation of erosion of bottom pits

The present paper is devoted to research of the erosion of large-scale sand pits in the water flow. The investigations were performed in the hydrodynamic flume with sandy bottom. To provide suitable conditions for sediment transport in the flume, the analysis of the factors leading to the motion of sediments was carried out in accordance with the Shields diagram. It was shown that the flow regime created in the laboratory channel promotes the development of natural bed forms such as ripples. Estimations of the velocity of movement of the ripples were obtained. The experiments with large sand pits on the flume bottom demonstrated that those disturb the balance of sediments and cause the reformatting of the water flow. To assess the influence of the pit configuration on the erosion process, two-dimensional triangular and trapezoidal pits were considered. It was found that the longitudinal profile of the triangular pit changes due to sediment deposition on its upper slope and erosion of the lower slope. The pit upper slope levels out and shifts forward due to the continuous flow of sediment in this region. The depth of the unevenness also decreases owing to deposition of the sediment directly on its bottom. Due to the blow of water jet to the pit lower slope, the zone of maximum erosion of the bottom surface is observed here. The bottom reformatting leads to the displacement of the pit downstream. Studies of the erosion of the trapezoidal pit have shown that its upper slope is first shifted toward the lower slope until the trapezoidal profile turns into a triangular one. The pit erosion causes also the deformation of natural forms of the channel bed and destabilization of sediment discharge. The analysis of the obtained data demonstrated that the reformation of channel bed is a durable process depending of the ratio of pit scales to the volume of sediment. The present study is useful for development of engineering solutions directed to reduction of risks caused by the interaction of sand quarries with hydraulic structures in rivers.

Levels of PAHs, PCBs, and toxic metals in Ruditapes philippinarum and Donax trunculus in Marmara Sea, Turkey.

The manila clam Ruditapes philippinarum and the wedge clam Donax trunculus are economic bivalve species which constitute an important part of the natural bivalve beds in the Marmara Sea, Turkey. Toxic chemicals such as, dioxins, dioxin-like polychlorinated biphenyls (PCBs), polycyclic hydrocarbons (PAHs), and toxic metals are recognized as important health risk factors that threaten public health via food or directly in the environment. In the present study, we aimed to determine and monitor levels of these toxic chemicals in both clam species, R. philippinarum and D. trunculus, between 2013 and 2017. According to the results, maximum levels of dioxins, PAHs, and toxic metals (lead, cadmium, mercury) during the period were determined as 0.18 pg g-1 , 2.43 mg kg-1 , and 0.44-0.53-0.1 mg kg-1 , respectively. The level of contaminants in both clam species were determined to be below the threshold or tolerable daily intake values established by the European Commission, European Food Safety Authority (EFSA), and Food and Agriculture Organization/World Health Organization (FAO/WHO). Seasonal fluctuations were observed to be similar in both species and also in seasons, but elevated levels of PCBs and PAHs were detected in warmer months during the period. As a consequence, toxic chemicals in both clam species were found at low concentrations in this study from the point of view of public health concerns; however, the contaminants should be closely monitored in the future due to their elevated levels in samples. © 2020 Society of Chemical Industry.