Evolution and decay of gravity wavefields in weak-rotating environments: a laboratory study

Gravity waves are prominent physical features that play a fundamental role in transport processes of stratified aquatic ecosystems. In a two-layer stratified basin, the equations of motion for the first vertical mode are equivalent to the linearised shallow water equations for a homogeneous fluid. We adopted this framework to examine the spatiotemporal structure of gravity wavefields weakly affected by the background rotation of a single-layer system of equivalent thickness \(h_{\ell }\), via laboratory experiments performed in a cylindrical basin mounted on a turntable. The wavefield was generated by the release of a diametral linear tilt of the air–water interface, \(\eta _{\ell }\), inducing a basin-scale perturbation that evolved in response to the horizontal pressure gradient and the rotation-induced acceleration. The basin-scale wave response was controlled by an initial perturbation parameter, \({\mathcal{A}}_{*} = \eta _{0}/h_{\ell }\), where \(\eta _{0}\) was the initial displacement of the air–water interface, and by the strength of the background rotation controlled by the Burger number, \({\mathcal{S}}\). We set the experiments to explore a transitional regime from moderate- to weak-rotational environments, \(0.65\le {\mathcal{S}} \le 2\), for a wide range of initial perturbations, \(0.05\le {\mathcal{A}}_{*}\le 1.0\). The evolution of \(\eta _{\ell }\) was registered over a diametral plane by recording a laser-induced optical fluorescence sheet and using a capacitive sensor located near the lateral boundary. The evolution of the gravity wavefields showed substantial variability as a function of the rotational regimes and the radial position. The results demonstrate that the strength of rotation and nonlinearities control the bulk decay rate of the basin-scale gravity waves. The ratio between the experimentally estimated damping timescale, \(T_{d}\), and the seiche period of the basin, \(T_{g}\), has a median value of \(T_{d}/T_{g}\approx 11\), a maximum value of \(T_{d}/T_{g}\approx 10^{3}\) and a minimum value of \(T_{d}/T_{g}\approx 5\). The results of this study are significant for the understanding the dynamics of gravity waves in waterbodies weakly affected by Coriolis acceleration, such as mid- to small-size lakes.     

Linking local to global properties in branching modular networks: gorgonian coral colonies

Branching growth is present both in plants and animals, either marine or terrestrial. Although cellular and other modular levels of organization in plants and animals have evolved through different molecular and physiological mechanisms, several aspects of their branching modular system and morphology are similar. We studied vessel organization and colony integration, in order to comprehend underlying relationships between different structural components in a gorgonian coral network. The theoretical formalism was validated in the gorgonian coral Eunicea mammosa (Plexauridae, Octocorallia) in Belize. As in vascular plants, these colonial animals create a complex network of connections among modular branches integrated in stem canals downstream toward the base. A new formalism is proposed for describing gorgonian branching. A global property of a colony is for instance the size of its base or its weight whereas a local property is the size of branch in a particular place of the colony. However, a global property is not the simple addition of local modular properties, as the case of stem canals in the colony base. Theoretically, the process of branching is tightly intertwined with the internal network organization. The colony network centralization is driven by a linear relationship between the total number of branches and the stem canals at the base of the colony. If stem canals play important roles in the transport of nutrients throughout the colony and the biomechanical support from the base up to the tips, we can assume that there is an underlying association between the number of stem canals at the base and the number of for example, terminal branches. These associations may provide new findings that extend our understanding of the functional organization of tree-like networks in octocorals and their vascular systems. The idea that the external components of a tree-like plant network are directly correlated and connected down to the main trunk seems to be analogous in an animal system.     

Modelling the effects of extreme events on the dynamics of the amphipod Corophium orientale

The brackish water amphipod Corophium orientale is the dominant macroinvertebrate species in the upper Mira estuary, a small mesotidal system located in the southwest coast of Portugal. As climate changes will increase the frequency and intensity of extreme events such as floods and droughts, these will have a negative effect on benthic estuarine invertebrates, namely C. orientale. In order to understand the effects of these events on C. orientale, a dynamic model, based on published information and calibrated with field data, was developed and different scenarios were tested.For model construction, the annual development of three cohorts of C. orientale, their growth rates, and the establishment of the timing of each cohort rise and extinction are introduced. This structure can be repeated indefinitely, for years, and few parameters are required. The model simulations highlight the need for refuge areas that enable a fast recovery of the amphipod population after an extreme event and the recolozination of the affected areas.     

Egg release and settlement patterns of dioecious and hermaphroditic fucoid algae during the tidal cycle

The timing of gamete release by fucoid algae, although known to be restricted to calm days is not clearly understood within a circadian time scale. The need for externally fertilizing species to avoid gamete dilution suggests that in wave-exposed areas spawning may occur during particular tidal phases. However, this may differ between mating systems, as selfing species may be less affected by gamete dilution. In this study, two different approaches were used to determine when egg release occurs during the tidal cycle in two sister species with different mating systems. First, egg settlement of Fucus vesiculosus (dioecious) and Fucus spiralis (selfing hermaphrodite) was quantified on removable substrates (egg settlement disks) every day for 2 months and settlement patterns were used to statistically estimate the radius of a circle that would encompass 99% of each patch of settled eggs (the egg dispersal radius). Also, egg release was quantified every 2 h during the tidal cycle. A significantly larger egg dispersal radius (P < 0.02) was found for F. spiralis than F. vesiculosus, and this difference was somewhat site dependent with a greater difference between species in exposed sites. The egg dispersal radius was negatively correlated with significant wave height and positively correlated with sea surface temperature for both the species (P < 0.05), with a greater effect of both the factors for F. spiralis than for F. vesiculosus. Egg release during the tidal cycle was variable between species and experiments, with F. vesiculosus releasing more eggs, later in the day, and at a lower tide, than F. spiralis, which released fewer eggs, throughout the day and at all tides. The dioecious species, F. vesiculosus, may have developed a specific adaptation for timing the egg release to periods when emersed in exposed habitats to avoid rapid dilution of gametes that require outcrossing for fertilization. On the other hand, egg release for F. spiralis, which can self-fertilize, occurred both when emersed and immersed, suggesting this species has developed less synchrony with specific environmental factors. Site dependence also suggests local wave conditions can modulate timing of release. The data are consistent with the relaxation of the selective constraints of water motion on fertilization success in a selfing hermaphrodite, relative to an obligate outcrossing species. Results support the idea that species with different mating systems evolve different sensitivities to environmental cues for gamete release with specific implications for inbreeding and successful external fertilization in the ocean.     

Habitat structure affects intraguild predation

Intraguild predation is thought to be ubiquitous in natural food webs. Yet, theory on intraguild predation predicts the intraguild prey to persist only under limited conditions. This gap between theory and empirical observations needs scrutiny. One reason might be that theory has focused on equilibrium dynamics and a limited set of species (usually three) that interact in well-mixed populations in unstructured habitats, and these assumptions will often not hold in natural systems. In this review, we focus on the effects of habitat structure on intraguild predation. Habitat structure could reduce encounter rates between predators and prey and could create refuges for prey. In both cases, habitat structure could reduce the strength of intraguild interactions, thereby facilitating species coexistence. A meta-analysis of studies on manipulation of habitat structure shows that intraguild prey indeed suffer less from intraguild predation in structured habitats. This was further confirmed by a meta-analysis in which studies on intraguild predation were classified according to habitat structure. Intraguild predation reduced densities of the intraguild prey significantly more in habitats with little structure than in habitats rich in structure. The effect of intraguild predation on the shared prey was negative, and not significantly affected by habitat structure. We conclude that habitat structure may increase persistence of the intraguild prey by decreasing the strength of the interaction between intraguild predator and intraguild prey.     

Radioecological software package: an interactive computational system to simulate the behaviour of radionuclides in semi-natural environments

RSP (Radioecological Software Package) is an interactive support system that simulates the behaviour of radionuclides in semi-natural environments and the consequences on the population in terms of the external exposure. RSP consists of three modules: the first one, soil mobility, simulates the vertical transport of radionuclide in soil using the mathematical model RABES. The second module, soil -to-plant transfer, simulates the radionuclide soil-to-plant transfer factor reported in the literature. Soil properties, vegetation types and environmental conditions are taken into consideration in the simulation process. In the third module, dose assessment, the dose-rate factor in air at a height of 1 m above ground can be calculated for sources distributed in a slab of finite thickness dn sources which are exponentially distributed with depth. The calculations are performed using DAGES Model, a Monte Carlo algorithm developed to simulated the photon transport for the soil/air configuration. A free copy of RSP can be downloaded from the website: http://imasl-apat.unsl.edu.ar.     

Mechanical Property and Biodegradability of Cast Films Prepared from Blends of Oppositely Charged Biopolymers

Biodegradable cast films of about 50 m thickness were fabricated by blending oppositely charged biopolymers such as anionic starch–chitosan, and cationic starch–pectin. The tensile strength and elongation at break (%) of films were evaluated as well as their capacity to degrade in compost. Films recovered from soil every 48 h showed consistent degradation (weight loss), diminution of the polymers characteristic peak absorbance in the carbohydrate fingerprint region of the FTIR, and changes in the surface morphology via scanning electron microscopy (SEM). Anionic starch–chitosan films had much superior tensile strength and elongation compared to cationic starch–pectin, suggesting that the ionic bonds formed between anionic-starch and positively charged groups in chitosan polymer were much more stable and stronger. Initially, both films lost about 36% weight within 96 h, which also correlated well with the loss in the characteristic absorption peaks in the region of the infrared spectrum typical of biopolymers. The total mineralization of films by microorganisms in compost soil was also measured using respirometric techniques. Though the rate of mineralization differed for two formulations, total mineralization (extent) for both films were achieved within 45 days.     

Mussel transplantation and biomarkers as useful tools for assessing water quality in the NW Mediterranean

Mussels, coming from an aquaculture farm located in a clean open bay, were transplanted to several stations of the bays of Nice and Cannes (NW Mediterranean) including a reference site for one month at three periods. Several biomarkers: activities of glutathione S-transferase (GST; exposure to organics), of catalase (exposure to oxidative stress) and of acetylcholinesterase (inhibited by some pesticides) and the lipid peroxidation (thiobarbituric acid reactive substances: TBARS) were measured in transplanted mussels. Cd, Cu and Zn concentrations were also measured as well as their condition index. The results demonstrated some seasonal variations in GST and catalase activities with higher levels in June compared to October. The condition index was also higher in June than in October. Principal component analyses performed with the whole set of data allowed to separate stations or groups of stations according to their responses. The mussels from the harbour of Nice were characterized by high TBARS levels and catalase activity in October 1999 whereas in the harbour of Cannes, animals presented very high copper concentrations and GST activities in June 2000. At the reference site, mussels generally presented low enzymatic activities (except AChE activity) and peroxidation levels and low heavy metal concentrations.     

Rainfall and flooding in the Guayas river basin and its effects on the incidence of malaria 1982–1985

Inasmuch as health is at cross purposes with illness, suffering, disability and death, it is clear that all measures that are adopted with foresight to reduce the repercussions of natural disasters have consequences for health     

Investigation of Human and Animal Viruses in Water Matrices from a Rural Area in Southeastern Region of Brazil and Their Potential Use as Microbial Source-Tracking Markers

Food and Environmental Virology - This study assessed the sources of contamination of water matrices in a rural area using detection of a host-specific virus (human adenovirus [HAdV], porcine...