Exploited species impacts on trophic linkages along reef-seagrass interfaces in the Florida Keys

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.     

A 700-year paleoecological record of boreal ecosystem responses to climatic variation from Alaska

Recent observations and model simulations have highlighted the sensitivity of the forest-tundra ecotone to climatic forcing. In contrast, paleoecological studies have not provided evidence of tree-line fluctuations in response to Holocene climatic changes in Alaska, suggesting that the forest-tundra boundary in certain areas may be relatively stable at multicentennial to millennial time scales. We conducted a multiproxy study of sediment cores from an Alaskan lake near the altitudinal limits of key boreal-forest species. Paleoecological data were compared with independent climatic reconstructions to assess ecosystem responses of the forest tundra boundary to Little Ice Age (LIA) climatic fluctuations. Pollen, diatom, charcoal, macrofossil, and magnetic analyses provide the first continuous record of vegetation fire-climate interactions at decadal to centennial time scales during the past 700 years from southern Alaska. Boreal-forest diebacks characterized by declines of Picea mariana, P. glauca, and tree Betula occurred during the LIA (AD 1500-1800), whereas shrubs (Alnus viridis, Betula glandulosa/nana) and herbaceous taxa (Epilobium, Aconitum) expanded. Marked increases in charcoal abundance and changes in magnetic properties suggest increases in fire importance and soil erosion during the same period. In addition, the conspicuous reduction or disappearance of certain aquatic (e.g., Isoetes, Nuphar, Pediastrum) and wetland (Sphagnum) plants and major shifts in diatom assemblages suggest pronounced lake-level fluctuations and rapid ecosystem reorganization in response to LIA climatic deterioration. Our results imply that temperature shifts of 1-2 degrees C, when accompanied by major changes in moisture balance, can greatly alter high-altitudinal terrestrial, wetland, and aquatic ecosystems, including conversion between boreal-forest tree line and tundra. The climatic and ecosystem variations in our study area appear to be coherent with changes in solar irradiance, suggesting that changes in solar activity contributed to the environmental instability of the past 700 years.     

Partitioning the factors of spatial variation in regeneration density of shade-tolerant tree species

Understanding coexistence of highly shade-tolerant tree species is a longstanding challenge for forest ecologists. A conceptual model for the coexistence of sugar maple (Acer saccharum) and American beech (Fagus grandibfolia) has been proposed, based on a low-light survival/high-light growth trade-off, which interacts with soil fertility and small-scale spatiotemporal variation in the environment. In this study, we first tested whether the spatial distribution of seedlings and saplings can be predicted by the spatiotemporal variability of light availability and soil fertility, and second, the manner in which the process of environmental filtering changes with regeneration size. We evaluate the support for this hypothesis relative to the one for a neutral model, i.e., for seed rain density predicted from the distribution of adult trees. To do so, we performed intensive sampling over 86 quadrats (5 x 5 m) in a 0.24-ha plot in a mature maple-beech community in Quebec, Canada. Maple and beech abundance, soil characteristics, light availability, and growth history (used as a proxy for spatiotemporal variation in light availability) were finely measured to model variation in sapling composition across different size classes. Results indicate that the variables selected to model species distribution do effectively change with size, but not as predicted by the conceptual model. Our results show that variability in the environment is not sufficient to differentiate these species' distributions in space. Although species differ in their spatial distribution in the small size classes, they tend to correlate at the larger size class in which recruitment occurs. Overall, the results are not supportive of a model of coexistence based on small-scale variations in the environment. We propose that, at the scale of a local stand, the lack of fit of the model could result from the high similarity of species in the range of environmental conditions encountered, and we suggest that coexistence would be stable only at larger spatial scales at which variability in the environment is greater.     

Photosynthetic performance of giant clams, Tridacna maxima and T. squamosa, Red Sea

Two species of giant clams, Tridacna maxima and T. squamosa, coexist in the Red Sea, but exhibit distinctly different depth distributions: T. maxima mostly occurs in shallow waters (reef flat and edge), while T. squamosa may occur down to the lower fore-reef slope. Giant clams have been described as mixotrophic, capable of both filter-feeding and photosynthesis due to algal symbionts (zooxanthellae), therefore, observed depth preferences were investigated in relation to possible differences in autotrophy vs. heterotrophy. This study was conducted from April to June 2004, at the reef near the Marine Science Station, Aqaba, Gulf of Aqaba, Red Sea, and in May 2007, at a reef near Dahab, Sinai Peninsula, Egypt. In situ measurements using a submersible pulse amplitude modulated fluorometer (Diving PAM), revealed no significant differences in effective PSII quantum yield (ΔF/Fm′) and relative electron transport rates (ETR) between the two species; but rapid light curves (ETR vs. light, photosynthetically active irradiance, PAR) showed significant differences in maximum photosynthetic rates (ETR_max), with 20% higher values in T. maxima. Chamber incubations displayed higher net and gross oxygen production by T. maxima (88.0 and 120.3 μmol O₂ cm⁻² mantle area day⁻¹) than T. squamosa (56.7 and 84.8 μmol O₂ cm⁻² mantle area day⁻¹); even under shading conditions (simulated depth of 20 m) T. maxima still achieved 93% of the surface gross O₂ production, whereas T. squamosa reached only 44%. A correlation was found between ETR and net photosynthesis measured as oxygen production (T. maxima: R ² = 0.53; T. squamosa: R ² = 0.61). Calculated compensation depth (CD) (gross photosynthesis equals respiration) in T. maxima (16 m) matches the maximum depth of occurrence in this study (17 m). By contrast, the CD of T. squamosa (9 m) was much shallower than the maximum vertical range (42 m). Findings suggest T. maxima is a strict functional photoautotroph limited by light, whereas T. squamosa is a mixotroph whose photoautotrophic range is extended by heterotrophy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relationship between heavy metal concentrations of herbaceous plants and soils at four Pb-Zn mining sites in Yunnan, China

This paper studied the relationship between heavy metal concentrations of herbaceous plants and soils at four Pb-Zn mining sites in Yunnan, China. 50 herbaceous plant samples of 9 plant species from 4 families and 50 soil samples were collected and then ana1yzed for the tota1 concentrations of Pb, Cd, and Zn. The results showed that the average concentrations of Pb, Cd, and Zn in soil samples were 3772.83, 168.81, and 5385.65 mg/kg, respectively. The average concentrations of Pb, Cd, and Zn were 395.68, 28.14, and 1664.20 mg/kg in the shoots, and 924.12, 57.25, and 1778.75 mg/kg in the roots, respectively. Heterospecific plants at the same site and conspecific plants at various sites had different average levels of Pb, Cd, and Zn, both in the shoots and the roots. Enrichment coefficients of Pb, Cd, and Zn were greater than 1 in 2, 3, and 9 herbaceous plant samples, respectively. Translocation factors of Pb, Cd, and Zn were greater than 1 in 10, 17, and 25 herbaceous plant samples, respectively. In all 50 samples, the concentrations of Pb, Cd, and Zn between the shoots and the roots, the shoots, and the soils, and the roots and the soils had significant positive relationships.     

安捷伦液相/离子阱(XCT)质谱检测虾仁及家禽中的硝基呋喃代谢物

在液相/离子阱质谱上,利用液相/质谱/质谱方法对鸡肉及虾仁中硝基呋喃代谢物残留进行了定性定量分析.对于四种硝基呋喃代谢物,其定量限在0125到05μg·kg-1的范围内,分析结果完全满足欧盟的1μg·kg-1的最低检测限量的要求.     

Archetypical patterns and trajectories of land systems in Europe

Regional Environmental Change - Assessments of land-system change have dominantly focused on conversions among broad land-use categories, whereas intensity changes within these categories have...     

An empirical perspective for understanding climate change impacts in Switzerland

Regional Environmental Change - Planning for the future requires a detailed understanding of how climate change affects a wide range of systems at spatial scales that are relevant to humans....