Benthic-planktonic coupling, regime shifts, and whole-lake primary production in shallow lakes

Alternative stable states in shallow lakes are typically characterized by submerged macrophyte (clear-water state) or phytoplankton (turbid state) dominance. However, a clear-water state may occur in eutrophic lakes even when macrophytes are absent. To test whether sediment algae could cause a regime shift in the absence of macrophytes, we developed a model of benthic (periphyton) and planktonic (phytoplankton) primary production using parameters derived from a shallow macrophyte-free lake that shifted from a turbid to a clear-water state following fish removal (biomanipulation). The model includes a negative feedback effect of periphyton on phosphorus (P) release from sediments. This in turn induces a positive feedback between phytoplankton production and P release. Scenarios incorporating a gradient of external P loading rates revealed that (1) periphyton and phytoplankton both contributed substantially to whole-lake production over a broad range of external P loading in a clear-water state; (2) during the clear-water state, the loss of benthic production was gradually replaced by phytoplankton production, leaving whole-lake production largely unchanged; (3) the responses of lakes to biomanipulation and increased external P loading were both dependent on lake morphometry; and (4) the capacity of periphyton to buffer the effects of increased external P loading and maintain a clear-water state was highly sensitive to relationships between light availability at the sediment surface and the of P release. Our model suggests a mechanism for the persistence of alternative states in shallow macrophyte-free lakes and demonstrates that regime shifts may trigger profound changes in ecosystem structure and function.     

Benthic algal production across lake size gradients: interactions among morphometry, nutrients, and light

Attached algae play a minor role in conceptual and empirical models of lake ecosystem function but paradoxically form the energetic base of food webs that support a wide variety of fishes. To explore the apparent mismatch between perceived limits on contributions of periphyton to whole-lake primary production and its importance to consumers, we modeled the contribution of periphyton to whole-ecosystem primary production across lake size, shape, and nutrient gradients. The distribution of available benthic habitat for periphyton is influenced by the ratio of mean depth to maximum depth (DR = z/ z(max)). We modeled total phytoplankton production from water-column nutrient availability, z, and light. Periphyton production was a function of light-saturated photosynthesis (BPmax) and light availability at depth. The model demonstrated that depth ratio (DR) and light attenuation strongly determined the maximum possible contribution of benthic algae to lake production, and the benthic proportion of whole-lake primary production (BPf) declined with increasing nutrients. Shallow lakes (z < or =5 m) were insensitive to DR and were dominated by either benthic or pelagic primary productivity depending on trophic status. Moderately deep oligotrophic lakes had substantial contributions by benthic primary productivity at low depth ratios and when maximum benthic photosynthesis was moderate or high. Extremely large, deep lakes always had low fractional contributions of benthic primary production. An analysis of the world's largest lakes showed that the shapes of natural lakes shift increasingly toward lower depth ratios with increasing depth, maximizing the potential importance of littoral primary production in large-lake food webs. The repeatedly demonstrated importance of periphyton to lake food webs may reflect the combination of low depth ratios and high light penetration characteristic of large, oligotrophic lakes that in turn lead to substantial contributions of periphyton to autochthonous production.     

Interindividual variability in metal status in the shore crab<Emphasis Type="Italic"> Carcinus maenas</Emphasis>: the role of physiological condition and genetic variation

The relations between genetic variation, physiological condition, size and metal status in the shore crab Carcinus maenas (L.) were investigated. Shore crabs were collected at three sites around the island of Funen, Denmark, and carapace width, colour, moulting stage and major ions and protein in the haemolymph were determined. Concentrations of water, cadmium, copper and zinc in midgut glands, muscles and gills were measured, and allozyme variation at 15 loci was studied. Generally, tissue water content and copper, zinc and cadmium concentrations decreased from the moulting stages C₃ over C₄ to D crabs, whereas the opposite was true for copper and zinc concentrations in gills and muscle. However, the water content of the tissues increased with the size of the crabs. Since tissue water contents changed consistently over moulting stages, conclusions on changes in metal concentrations sometimes diverged when expressed on a dry versus wet weight basis. Regarding allozymes, esterase, malate dehydrogenase and phosphoglucomutase were polymorphic. The crabs showed a low level of genetic variability for both polymorphism (0.14) and for heterozygosity (0.07) at the three sites. Allelic frequencies showed very low levels of differentiation among the samples, no evidence of inbreeding and no population subdivision. Multilocus heterozygosity was positively correlated with size. Concentrations of copper and zinc in midgut gland, muscle tissue and gill were not correlated with genotype, whereas a weak correlation between phosphoglucomutase genotypes and concentrations of cadmium in the midgut gland was found.Communicated by M. Kühl, Helsingør     

印度洋-太平洋海洋生态系统的占有:活礁鱼食品贸易的实例研究

我们对珊瑚礁渔业,特别是活礁鱼食品贸易(FT)的生态足迹的分析表明,许多国家目前的消费量超过了估计的可持续的人均全球、地区及地方珊瑚礁生产水平.香港通过其FT需求占有了东南亚年礁鱼生产量135 260～286 560t的25%,超过地区生物生产力8.3倍;礁鱼渔业需求超过印度洋-太平洋和东南亚地区可持续产量2.5～6倍.相比之下,大多数太平洋岛屿靠本身的礁渔业手段维持生计,当地的需求小于大洋洲整个能力的20%.FT每年需要多达40%东南亚的估计礁鱼产量以及几乎所有其估计的(鱼旨)科鱼产量.我们的研究分析结果强调了FT的不可持续性以及对印度洋-太平洋珊瑚礁渔业加以区域管理和保护的迫切必要性.     

Development of the German version of the Hospital Survey on Patient Safety Culture: Dimensionality and psychometric properties

Despite the importance of safety climate assessment in healthcare, the psychometric properties of existing safety climate surveys have seldom been tested. We developed a German version of the HSOPSC and investigated its dimensionality and predictive validity. In adapting the survey we differentiated between the two management levels (hospital, unit) by duplicating dimensions of the HSOPSC. Based on a sample of n = 568, confirmatory and exploratory factor analyses (CFA, EFA) were applied. Relationships between safety climate and outcome variables were investigated by regression analyses. CFA did not replicate the proposed factor structure, supporting evidence from other European countries. EFAs revealed eight factors (instead of twelve proposed for the original instrument) and allowed for differentiating between management levels (hospital, unit). For physicians and nurses, different predictors were identified for overall safety climate perception. Further cross-cultural investigations of dimensionality are necessary for international comparisons of safety climate in healthcare. Our results highlight the importance of capturing the impact of different management levels, especially in large hospitals, and differences between professional groups in order to design interventions accordingly.     

Cladistic analysis of Bantu languages: a new tree based on combined lexical and grammatical data

The phylogeny of the Bantu languages is reconstructed by application of the cladistic methodology to the combined lexical and grammatical data (87 languages, 144 characters). A maximum parsimony tree and Bayesian analysis supported some previously recognized clades, e.g., that of eastern and southern Bantu languages. Moreover, the results revealed that Bantu languages south and east of the equatorial forest are probably monophyletic. It suggests an unorthodox scenario of Bantu expansion including (after initial radiation in their homelands and neighboring territories) just a single passage through rainforest areas followed by a subsequent divergence into major clades. The likely localization of this divergence is in the area west of the Great Lakes. It conforms to the view that demographic expansion and dispersal throughout the dry-forests and savanna regions of subequatorial Africa was associated with the acquisition of new technologies (iron metallurgy and grain cultivation).Electronic supplementary material  Supplementary material is available for this article at