14C-Photosynthesis of Phytoplankton in an Oligotrophic Alpine Lake (Traunsee,Austria) and its Response to Turbidity Caused by Industrial Tailings

The influence of industrial tailings on the biological integrity of the phytoplankton was assessed from annual measurements of photosynthetic rates in the alpine lake Traunsee. The mean annual integral production of 21 mmol C m^-2 d^-1 corresponded to the oligotrophic nature of the lake. Effects of effluents were tested by comparing photosynthesis at a station close to the industrial outlet (EB) and at a reference site with a maximum depth of 190 m (VI). Between-site optical properties (vertical attenuation coefficient, euphotic depth) were statistically significant different. The euphotic zone at the impacted station was on average 2 m shallower than at the reference site, owing to turbidity emanating from the industrial plant. The adaptation to low light intensities by the algal community at this station was evident from a high maximum light utilisation coefficient (^* at low light saturation (E _K). Algae at the deep reference site were photosynthetically less efficient but adapted to high light intensities. Photosynthetic adaptation to different light climates in the euphotic zone without significant quantitative biomass alterations at the impacted site gave a clear signature of biological integrity of the phytoplankton in the oligotrophic Traunsee.     

Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States

Bankfull hydraulic geometry relationships are used to estimate channel dimensions for streamflow simulation models, which require channel geometry data as input parameters. Often, one nationwide curve is used across the entire United States (U.S.) (e.g., in Soil and Water Assessment Tool), even though studies have shown that the use of regional curves can improve the reliability of predictions considerably. In this study, regional regression equations predicting bankfull width, depth, and cross‐sectional area as a function of drainage area are developed for the Physiographic Divisions and Provinces of the U.S. and compared to a nationwide equation. Results show that the regional curves at division level are more reliable than the nationwide curve. Reliability of the curves depends largely on the number of observations per region and how well the sample represents the population. Regional regression equations at province level yield even better results than the division‐level models, but because of small sample sizes, the development of meaningful regression models is not possible in some provinces. Results also show that drainage area is a less reliable predictor of bankfull channel dimensions than bankfull discharge. It is likely that the regional curves can be improved using multiple regression models to incorporate additional explanatory variables.     

A novel marine silk

The discovery of a novel silk production system in a marine amphipod provides insights into the wider potential of natural silks. The tube-building corophioid amphipod Crassicorophium bonellii produces from its legs fibrous, adhesive underwater threads that combine barnacle cement biology with aspects of spider silk thread extrusion spinning. We characterised the filamentous silk as a mixture of mucopolysaccharides and protein deriving from glands representing two distinct types. The carbohydrate and protein silk secretion is dominated by complex β-sheet structures and a high content of charged amino acid residues. The filamentous secretion product exits the gland through a pore near the tip of the secretory leg after having moved through a duct, which subdivides into several small ductules all terminating in a spindle-shaped chamber. This chamber communicates with the exterior and may be considered the silk reservoir and processing/mixing space, in which the silk is mechanically and potentially chemically altered and becomes fibrous. We assert that further study of this probably independently evolved, marine arthropod silk processing and secretion system can provide not only important insights into the more complex arachnid and insect silks but also into crustacean adhesion cements.     

Navigational strategies of homing pigeons at familiar sites: do landmarks reduce the deflections induced by clock-shifting?

To analyze the navigational strategy of homing pigeons at familiar sites in view of a possible role of local landmarks, two groups of pigeons—one familiar to the release site, the other unfamiliar—were released with their internal clock shifted 6 h fast, with untreated birds of both groups serving as controls. The two groups showed median deflections of 67% and 57%, respectively, of the expected size, with no consistent difference in the size of the deflection between familiar and unfamiliar birds. This clearly shows that familiarity with the release site and with the local landscape features does not affect the size of the deflections induced by clock-shifting. Obviously, pigeons familiar with the release site do not change their navigational strategy, but still continue to determine their home course solely as a compass course. General problems with orientation by landmarks are discussed; however, landmarks may help birds to recognize a site and recall the respective course.

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The sea-finding behavior of hatchling olive ridley sea turtles, Lepidochelys olivacea, at the beach of San Miguel (Costa Rica)

Newly hatched olive ridley sea turtles (Lepidochelys olivacea) were tested for their directional preferences in a sand-filled circular arena in total darkness. Hatchlings that had crawled about 5 m on the beach, toward the sea preferred the southwesterly direction that would have brought them to the water line, whereas hatchlings that had been denied this experience headed eastward, a direction of unclear origin. These data suggest that a short crawl across the natural beach can set the direction in which the young turtles subsequently move. The crawling experience was sufficient to acquire the compass course that they later follow, probably with the help of a magnetic compass, not only in the water, but already while still on land.     

Are Declines in North American Insectivorous Songbirds Due to Causes on the Breeding Range?

Previous studies have reported a recent decline in breeding populations of migratory songbirds in eastern and central North America. Several explanations have been suggested: deforestation on the wintering grounds in the tropics and habitat loss, increased predation pressure, and increased cowbirds parasitism on the breeding range. We used these factors to assign 47 species of insectivorous passerines to groups with contrasting vulnerability, and then used the North America Breeding Bird Survey to analyze population trends in these groups on a large continental scale. Variables indexing susceptibility to predation on the breeding ground were most strongly correlated with population trends form 1968 to 1987. During the period from 1978 to 1987, migratory status was also significantly associated with population trends long-distance migrants to the neotropics exhibited a small, nonsignificant decreasing trend, whereas residents and short-distance migrants increased strongly. During the same time period, the group of species with low nest location, open nest, and high cowbird parasitism declined significantly. Although it is difficult to separate the effects of multiple factors, our analyses suggest that predation on the breeding ground in North America has played a larger role in the decline of migratory songbirds than deforestation on the wintering grounds in the tropics.     

Preliminary screening of perfluorooctane sulfonate (PFOS) and other fluorochemicals in fish, birds and marine mammals from Greenland and the Faroe Islands

Extensive screening analyses of perfluorooctane sulfonate (PFOS) and related perfluorinated compounds in biota samples from all over the world have identified PFOS as a global pollutant and have shown its bioaccumulation into higher trophic levels in the food chain. Perfluorinated compounds have been found in remote areas as the Arctic. In this study a preliminary screening of PFOS and related compounds has been performed in liver samples of fish, birds and marine mammals from Greenland and the Faroe Islands. PFOS was the predominant fluorochemical in the biota analyzed, followed by perfluorooctane sulfonamide (PFOSA). PFOS was found at concentrations above LOQ (10 ng/g wet weight) in 13 out of 16 samples from Greenland and in all samples from the Faroe Islands. The results from Greenland showed a biomagnification of PFOS along the marine food chain (shorthorn sculpin < ringed seal < polar bear). The greatest concentration of PFOS was found in liver of polar bear from east Greenland (mean: 1285 ng/g wet weight, n = 2). The geographical distribution of perfluorinated compounds in Greenland was similar to that of persistent organohalogenated compounds (OHCs), with the highest concentrations in east Greenland, indicating a similar geographical distribution to that of OHCs, with higher concentrations in east Greenland than in west Greenland.     

Detecting general plant functional type responses in fragmented landscapes using spatially-explicit simulations

Habitat loss and increasing landscape fragmentation are known to be key forces driving the ongoing loss of plant species diversity. While the combined effects of increasing isolation and decreasing population size have been studied intensively; it is less understood how plant population performance in heterogeneous landscapes is affected by changes in fragmentation alone.