Hypoxic environments as refuge against predatory fish in the Amazonian floodplains

Several groups of Amazonian fishes exhibit behavioral, morphological and physiological characteristics that allow occupying hypoxic environments, despite the energetic costs of living in such harsh conditions. One of the supposed advantages of occupying hypoxic habitats would be a lower predation pressure resulting from a lower number of piscivorous fishes in those environments. We tested this hypothesis in an area of the Amazon River floodplain through gill net fishing in normoxic and hypoxic habitats. From the 103 species caught, 38 were classified as piscivores. We found no difference in the number of piscivorous species captured in hypoxic and normoxic habitats (χ2 = 0.23; p = 0.63; df = 1) but piscivorous individuals were more numerous in normoxic than in hypoxic sampling stations (χ2 = 104.4; p < 0.001; df = 1). This indicates that environments submitted to low oxygen conditions may in fact function as refuges against piscivorous fishes in the Amazonian floodplains

Spectral hole burning: examples from photosynthesis

The optical spectra of photosynthetic pigment–protein complexes usually show broad absorption bands, often consisting of a number of overlapping, ‘hidden’ bands belonging to different species. Spectral hole burning is an ideal technique to unravel the optical and dynamic properties of such hidden species. Here, the principles of spectral hole burning (HB) and the experimental set-up used in its continuous wave (CW) and time-resolved versions are described. Examples from photosynthesis studied with hole burning, obtained in our laboratory, are then presented. These examples have been classified into three groups according to the parameters that were measured: (1) hole widths as a function of temperature, (2) hole widths as a function of delay time and (3) hole depths as a function of wavelength. Two examples from light-harvesting (LH) 2 complexes of purple bacteria are given within the first group: (a) the determination of energy-transfer times from the chromophores in the B800 ring to the B850 ring, and (b) optical dephasing in the B850 absorption band. One example from photosystem II (PSII) sub-core complexes of higher plants is given within the second group: it shows that the size of the complex determines the amount of spectral diffusion measured. Within the third group, two examples from (green) plants and purple bacteria have been chosen for: (a) the identification of ‘traps’ for energy transfer in PSII sub-core complexes of green plants, and (b) the uncovering of the lowest k = 0 exciton-state distribution within the B850 band of LH2 complexes of purple bacteria. The results prove the potential of spectral hole burning measurements for getting quantitative insight into dynamic processes in photosynthetic systems at low temperature, in particular, when individual bands are hidden within broad absorption bands. Because of its high-resolution wavelength selectivity, HB is a technique that is complementary to ultrafast pump–probe methods. In this review, we have provided an extensive bibliography for the benefit of scientists who plan to make use of this valuable technique in their future research

Raman spectra in vanadate nanotubes revisited

In this letter we report the Raman spectra of vanadate nanotubes (VONTs). The spectra present a clear signature that can be used for probing the tubular structure. The temperature effects on the structure of dodecylamine- and Cu-intercalated VONTs were studied by changing the laser power density during the Raman measurements. We have found that low laser power densities promote the decomposition of VONTs, leading to the collapse of the tubular structure and converting the nanotubes into V2O5 oxide. The decomposition occurs through an intermediate compound that is isostructural to V2O5 xerogel. The Raman experiments in VONT-based systems should be performed at extremely low laser power densities.4112099210

The intertidal zone of the North-East Atlantic region: pattern and process.

The north-east Atlantic region is an area where clades originating in the north Pacific (fucoids, balanoids, littorinids, thaids, laminarians) collide with clades from further south in the Atlantic (e.g., patellids, trochids, chthamalids). At high latitudes in the north, seaweeds dominate the midshore zone of all but the most exposed shores. Further south, midshore space-occupying invertebrates (mussels and barnacles) win, facilitated by grazing by patellid limpets that controls algal recruitment; propagule pressure is much less as fucoids become rarer, and juvenile growth is slower due to environmental stress, thereby reducing the probability of escapes from grazing (Figure 2.4) (Ferreira et al., 2014, 2015a, 2015b). Low on the shore seaweeds dominate space by forming algal turfs or kelp or fucoid canopies. These algae outpace the ability of grazing limpets to control them in the low-intertidal zone. L. digitata canopies can lead to rock covered by encrusting algae and sponges, facilitating limpets. If canopy is removed, then colonising ephemeral algae and turf-forming algae swamp the limpets. There is usually too much water movement immediately either side of low water for effective foraging by sea urchins. Psammechinus miliaris and Echinus esculentus only appear in the subtidal, and Paracentrotus lividus is confined to refuges in burrows relying mainly on the drift of food (Benedetti-Cecchi and Cinelli, 1995;Boudouresque and Verlaque, 2007; Jacinto and Cruz, 2012). High on the shore, physical factors dominate. At high latitudes in the north of the Atlantic, ephemeral algae are present all year round. Further south they are only present in the winter, dying-off in the summer. Grazing has limited effects, only occurring around refuges that littorinids maintain (Stafford and Davies, 2005; Skov et al., 2010, 2011). Patterns are also strongly modified by mesoscale processes driven by upwelling that influences nutrient and larval supply (North Africa, Iberia) and coastal configuration, where embayed versus headlands also strongly influence larval supply (France northwards). In high-recruitment areas, interactions can be intense between spaceoccupying species, also driving predator abundance (e.g., dog whelks). Connell’s (1961a) classic paper on competition was possible on the Isle of Cumbrae because space was almost saturated; elsewhere lower larval supply would have created less intense interactions, as shown by Gordon and Knights (2017) in Plymouth. The north-east Atlantic has faster rates of warming than any other ocean, although the region south of Greenland and Iceland is undergoing cooling due to a climate-driven slowdown in the Atlantic meridional overturning circulation, causing a weakening in the Gulf Stream (Rahmstorf et al., 2015). Species are responding to rapid alterations in the marine climate by adapting or exhibiting range shifts, or by becoming locally extinct. There is a high degree of spatial and temporal heterogeneity in the resultant impacts on marine communities due to the idiosyncratic responses of individual species. Warming seas have resulted in biogeographic range shifts of intertidal and subtidal species in coastal waters of the northeast Atlantic. The leading range edges of Lusitanian species are expanding, while the trailing edges of boreal species are retracting to higher latitudes, but with some cold-water species showing surprising resilience (Southward et al., 1995; Mieszkowska et al., 2006, 2014b; Lima et al., 2007; Hawkins et al., 2008, 2009; Wethey and Woodin, 2008; Mieszkowska and Sugden, 2016). In addition to changes in the distribution ofspecies, community structure is also altering as species dominance and interactions change (Poloczanska et al., 2008; Hawkins et al., 2008, 2009; Mieszkowska et al., 2014b). In a warming world the midshore of France and the British Isles are likely to show much less cover by large canopy-forming fucoids as harsher warmer, drier and stormier conditions coupled with increased grazing pressure from more grazing species reduces the probability of fucoids recruiting to form adult populations. Lowshore kelp forests will likely change with less L. digitata and A. esculenta and more S. polyschides. The late autumn to early spring window of dense ephemeral algal growth high on the shore (Hawkins and Hartnoll, 1983a) will also constrict, except in the north and in extreme exposure. These changes will have consequences for biodiversity (Thompson et al., 1996; Smale et al., 2013; Teagle et al., 2017) and productivity (Hawkins et al., 1992) – particularly the decrease in export of algal detritus (Notman et al., 2016). More shores will become dominated by suspension-feeding barnacles and mussels. Thus, there will be switches on many mid-latitude shores as many become net importers rather than exporters of energy (Hawkins et al., 2008, 2009)

Reproductive cycle of Macrobrachium amazonicum females (Crustacea, Palaemonidae)

Macrobrachium amazonicum is considered a favorite Brazilian species of freshwater prawn for cultivation as a result of its quick development and because it is easy to maintain in captivity. The aim of this work is to describe the sexual cycle stages and determine maturation age of the female M. amazonicum, which was collected monthly from June, 2002 to May, 2003 in the Jaguaribe River, Itaiçaba, Ceará. A monthly sample of water was also collected to determine the following parameters: temperature, dissolved oxygen, pH and salinity. A monthly sample of females was selected among the individuals caught, to determine the total weight (W T), carapace length (L C) and abdomen+telson length (L A+T) and to register the number of non-ovigerous females (NOF) and ovigerous females (OF). Determining ovarian maturation stages of M. amazonicum was done in a laboratory by observing macroscopic characters such as coloring, size, location and appearance of ovarians examined by transparent carapace. The first maturation age was determined from the relative frequency of the total length (L T) of young and adult females. The environmental parameters of the Jaguaribe River did not hold any influence in the number of individuals collected. A total of 1,337 prawns were sampled, 513 males (38.4%) and 824 females (61.6%). The proportion between males and females in the studied population was of 1:1.6. Among the collected females, 492 (50.7%) did not carry eggs in their abdomens (NOF) and 332 (40.3%) carried eggs in their abdomens (OF). There was no record of intact females. Non-ovigerous females with mature ovaries were recorded throughout all the months of collection. The female ovaries were classified as immature (IM), rudimentary (RU), intermediary (IN) and mature (M). M. amazonicum females reach their first sexual maturity between 4.5 and 5.5 cm of total length