Effects of ship‐induced waves on littoral benthic invertebrates

1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m^?2 was found for a structurally complex reed habitat, compared to 0.37 N m^?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h^?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance.     

Farms,pastures and woodlands: the fine‐scale distribution of Palearctic Culicoides spp. biting midges along an agro‐ecological gradient

The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.     

Age-specific Chaoborus predation on rotifer prey

SUMMARY. 1. This is the first study to examine predator-prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii. 2. In general, strike efficiencies (percentage of strikes resulting in inges- tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft- bodied S. obUmga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaohorus.     

The effect of suspended clay on ciliate population growth rates

• 1 Renewed batch cultures of three algivorous and one bacterivorous ciliate showed that ciliate reproductive rates increase with increasing food concentration up to an asymptote. Maximum r_m values for Strobilidium gyrans, Bursaridium difficile and Euplotes eurystomus feeding on the cryptomonad alga Rhodomonas minuta were 0.87, 0.86 and 0.45 day-¹, respectively, while Paramecium aurelia feeding on the bacterium Enterobactor aerogenes had an r_m of 0.40 day-¹. B. difficile had a food threshold (r_m= 0) of 0.38 μg Cml-¹ and P. aurelia had a threshold of 1.6μg Cml-¹.
• 2 The presence of suspended fine (particle size <1 μm) and coarse (particle size 1–2μm) clay suppressed the half maximum reproductive rate of the ciliate Strobilidium gyrans by up to 69% but had no effect on B. difficile, E. eurystomus or P. aurelia. Populations of ciliates unaffected by clay may be released in situations where suspended particles negatively affect their metazooplankton predators and competitors.

     

The production of hydrogen peroxide by high oxygen pressures

Hydrogen peroxide is formed in solutions of glutathione exposed to oxygen. This hydrogen peroxide or its precursors will decrease the viscosity of polymers like desoxyribonucleic acid and sodium alginate. Further knowledge of the mechanism of these chemical effects of oxygen might further the understanding of the biological effects of oxygen. This study deals with the rate of solution of oxygen and with the decomposition of hydrogen peroxide in chemical systems exposed to high oxygen pressures. At 6 atmospheres, the absorption coefficient for oxygen into water was about 1 cm./hour and at 143 atmospheres, it was about 2 cm./hour; the difference probably being due to the modus operandi. The addition of cobalt (II), manganese (II), nickel (II), or zinc ions in glutathione (GSH) solutions exposed to high oxygen pressure decreased the net formation of hydrogen peroxide and also the reduced glutathione remaining in the solution. Studies on hydrogen peroxide decomposition indicated that these ions act probably by accelerating the hydrogen perioxide oxidation of glutathione. The chelating agent, ethylenediaminetetraacetic acid disodium salt, inhibited the oxidation of GSH exposed to high oxygen pressure for 14 hours. However, indication that oxidation still occurred, though at a much slower rate, was found in experiments lasting 10 weeks. Thiourea decomposed hydrogen peroxide very rapidly. When GSH solutions were exposed to high oxygen pressure, there was oxidation of the GSH, which became relatively smaller with increasing concentrations of GSH.     

Photomorphogenesis and canopy dynamics. Phytochrome-mediated proximity perception accounts for the growth dynamics of canopies of Populus trichocarpa × deltoides'Beaupré'

The phytochrome family of signal-transducing photoreceptors provides plants with the capacity to perceive variations in the relative fluxes of red (R) and far-red (FR) radiation. This capacity has been proposed to be of ecological value in the perception of the proximity of neighbouring plants and the consequent induction of shade avoidance responses. The work reported here has evaluated this potential by determining quantitatively the effect of neighbour proximity on the growth of canopies of Populus trichocarpa×deltoides‘Beaupré’ trees, and relating the measured variables to the long-term vectoral radiation quality inside each canopy. The spectral distribution of radiation inside four canopies of Populus trichocarpa×deltoides‘Beaupre’ of different densities was monitored throughout the growing season. Spectral distributions inside the canopies were measured in 10° wedges at different heights and angles. The results are presented as PFD over 400–700 nm (PFD400–700) and PFD over 400–800 nm (PFD400–700). Results are also presented for the calculated phytochrome photoequilibrium (Pfr/P) and red:far-red ratio (R:FR). Data are presented as in-canopy angular and height profiles, and as diurnal and seasonal variations. PFD_400–700 and Pfr/P were found to be reduced inside each canopy, the reduction being greatest in the most dense canopy, and least in the most open canopy. At any height within each canopy, calculated Pfr/P decreased linearly with time throughout the growing season, until leaf senescence began. The reduction was greater in the denser canopies and was found to be similar for three consecutive field seasons. Linear relationships were found between plant stem growth rate, plant spacing and Pfr/P calculated from radiation propagated approximately horizontally within the canopies. The findings support the role of phytochrome in proximity perception in the natural environment and provide a quantitative basis for investigating the competitive interactions between plants growing in dense stands. The hypothesis is proposed that the dynamics of developing or regenerating canopies can be accounted for on the basis of phytochrome-mediated perception of the proximity of neighbouring plants.     

Effects of a trawling moratorium on the breeding success of the Yellow-legged Gull Larus cachinnans

The establishment of a two month commercial fishing moratorium, which overlapped each year with different stages of the breeding cycle of the Yellow-legged Gull Larus cachinnans at the Ebro Delta, Spain, provided the opportunity of testing the effects of food limitation on the breeding success of this species. The study was carried out in 1993, when the chick rearing stage occurred with normal commercial fishing activity and in 1994, when the chick rearing stage overlapped with the trawling moratorium. We recorded diet of the chicks, breeding phenology, clutch size, egg volume, hatching success and productivity of adult birds. There was a highly significant difference in the diet of the chicks between the two years and significantly lower productivity in 1994, whilst the other parameters examined did not change. These results show that a dependence on discards from commercial fishing activities may be a limiting factor in the breeding success of this seabird.     

Crepis novoana (Asteraceae), a new species restricted to coastal cliffs in northern Galicia (northwest Iberian Peninsula)

A new species of the section Lepidoseris (Rchb.) Benth. of the genus Crepis L. (Asteraceae) is described. The new species is restricted to a single known locality on near-vertical coastal cliffs of the Ria de Cedeira in northern Galicia (northwest Iberian Peninsula). Morphometric characters permitting discrimination from the most similar taxa are detailed, and possible phylogenetic relationships with other species of the section Lepidoseris (particularly those of the C. vesicaria complex) are discussed.     

Further observations on developmental polymorphism and its evolution in the rotifer Brachionus calyciflorus

SUMMARY. In laboratory experiments, long, Asplanchna-induced posterolateral spines of Brachionus calyciflorus were very effective in preventing their capture and subsequent ingestion by the predator Asplanchna sieboldi but provided no protection against predation by Mesocyclops edax. Young, short-spined B. calyciflorus were always captured after attack by adult A. sieboldi and were ingested in about 12 seconds. Adult, short-spined forms were captured on c. 35% of occasions when attacked by this predator and were ingested in about 50 s. Young and adult long-spined forms were captured by this predator on c. 60% of occasions when attacked, but they both almost invariably escaped or were rejected 20–35 s after capture. Short- and long-spined B. calyciflorus adults were always captured when attacked by adult, female M. edax and were completely ingested in about 20 s and 30 s, respectively. Life-table experiments conducted with B. calyciflorus at several levels of the food organism, Aerobacter aerogenes, showed that neither the possession of long posterolateral spines nor the production of offspring with long posterolateral spines interfered with survivorship, fecundity, or reproductive potential. In the laboratory, the volumes of the amictic parthenogenetic eggs of B. calyciflorus cultured on Euglena or Aerobacter were significantly greater in individuals from populations maintaining long posterolateral spines than in comparable-sized individuals from populations maintaining short spines. Egg volume was generally independent of adult body length, but it was significantly greater in Brachionus fed on Euglena compared with Aerobacter. Possible reasons why B. calyciflorus does not produce long posterolateral spines in the absence of Asplanchna are discussed. Few organisms other than B. calyciflorus are known to develop novel defensive phenotypes in direct response to the presence of a predator. It is suggested that such developmental responses evolve only when two conditions apply: (1) the defensive structure is primarily effective against a single type of predator, and (2) the prey organism exhibiting the response has a short generation time.     

Foraging ecology of hoverflies: morphology of the mouthparts in relation to feeding on nectar and pollen in some common urban species

Abstract. 1. Previous accounts of the feeding behaviour of hoverflies (Diptera: Syrphidae) are contradictory and in many cases do not correspond with field observations.
2. Patterns of feeding on nectar and pollen differ between species: these patterns are correlated with morphological differences.
3. The data indicate that there are two correlates of increasing tongue length: first, the proportion of pollen in the diet decreases; and second, the flies concentrate on visiting flowers with longer corollae, which contain more nectar sugar.
4. Reasons for these effects are discussed.