Modifying Surber sampling technique increases capture of freshwater crabs in African upland streams

We compared 2 methods for sampling the freshwater crab Potamonautes odhneri (Colosi) in Kenyan streams: standard Surber sampling, in which a sample is taken over a period of several minutes; and rapid Surber sampling, in which the process is reduced to around 10 seconds. Rapid Surber sampling caught more crabs than standard Surber sampling, This suggests that the crab species investigated is normally able to evade capture if sampling is carried out at an unhurried pace, but that if precision is sacrificed for speed, then capture efficiency increases. The size of crabs caught using the 2 techniques was similar, and use of baited traps set in the same locations showed that Surber sampling methods were not capturing larger individuals. Like all methods available to sample large benthic crustaceans, rapid Surber sampling has its limitations, but this study demonstrates that it can be used as a method for rapid assessment of crab presence and for comparative determination of population density, to significantly greater effect than the standard method of Surber sampling

Riparian plant litter quality increases with latitude

Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107 degrees) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce 'syndromes' resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen: phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.We thank the many assistants who helped with field work (Ana Chara-Serna, Francisco Correa-Araneda, Juliana Franca, Lina Giraldo, Stephanie Harper, Samuel Kariuki, Sylvain Lamothe, Lily Ng, Marcus Schindler, etc.), Cristina Grela Docal for helping with leaf chemical analyses, and Fernando Hiraldo (former director of EBD-CSIC) for his support. The study was funded by start-up funds from the Donana Biological Station (EBD-CSIC, Spain) and from Ikerbasque to LB, the Fundacao para a Ciencia e Tecnologia (FCT) strategic project ID/MAR/04292/2013 granted to MARE (Portugal), the 'BIOFUNCTION' project (CGL2014-52779-P) from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER to LB and J. Pozo, and Basque Government funds (IT302-10) to J. Pozo

Riparian Plant Litter Quality Increases With Latitude

Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107°) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce ‘syndromes’ resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen:phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams

Conservation of highland streams in Kenya: the importance of the socio-economic dimension in effective management of resources

Conservation of streams in Africa cannot be considered separately from their importance as water sources for local people.  Humans and livestock interact daily with flowing water and its associated riparian vegetation, giving these landscape features social and economic importance.  Despite the destruction that these activities cause, they provide opportunities for imaginative approaches to conservation.  Issues focusing on resources other than water itself should be considered; for example, use of riparian vegetation for collection of medicinal herbs, firewood, timber for construction and as sites for spiritual, cultural and recreational activities.  To address these concerns, Kenyan streams and their catchments are given as examples in this paper, with the assumption that they are typical of streams and catchments in many parts of Africa.  These streams are used extensively for small scale abstraction, washing, livestock watering and exploitation of riparian vegetation.  All of these activities occur with little regulation or management, despite the riparian zones nominally being protected government property.  Effective management requires an understanding of patterns of supply and demand for water, which is seasonal, and for vegetation resources, which is continuous and increasing.  Challenges for effective management are identified as: politically- and tribally-mediated insecurity; ineffective governance, particularly with respect to enforcing protective legislation; different use of resources by different ethnic groups; division of labour along gender and age lines; poverty and the inability to diversify resources; traditions and neglect of traditional ecological knowledge; and inadequate formal education.  We propose that effective conservation of water and riparian resources – and therefore of essential ecosystem services – is best achieved by a combination of law enforcement and engagement of local communities with the resource upon which they depend.  Understanding the importance of the resource and engendering a spirit of community ‘ownership’ will help to avoid the current ‘tragedy-of-the-commons’, in which uncontrolled exploitation is increasing in a totally unsustainable fashion in tropical Africa

Organic matter processing in tropical streams

Organic matter derived from many sources provides a basis for stream food webs. In terms of weight, leaves from the surrounding land constitute the largest allochthonous source of energy for stream consumers, but other items, including fruits, flowers, wood and twigs, and terrestrial insects, are also important. Timing of allochthonous inputs can vary markedly due to the phenology of the riparian vegetation, retention mechanisms in the aquatic-terrestrial transition zone, and local climate (especially the incidence of high-rainfall events), but seasonality of litter inputs is different, and often much less marked, than is typical of streams in temperate latitudes. As in such streams, litter decomposition rates depend on the interaction of physical factors (flow, temperature), water chemistry (dissolved nutrients), and biological agents (micro-organisms and detritivores especially shredding invertebrates). Because vascular plant biodiversity in the tropics is high, varied leaf characteristics (hardness, phenolic content, and other aspects of leaf chemistry) contribute to great variability in breakdown rate: fast-decomposing leaves persist for a few days only, whereas highly recalcitrant species take well over a year to decompose. In all the above cases, the decomposition process includes an initial rapid leaching phase when water-soluble compounds are lost, followed by colonization by micro-organisms (fungi and bacteria), and subsequent mechanical breakdown of the leaf structure by invertebrate shredder and hydraulic forces. Undecomposed leaves are sometimes exported downstream during flood events, and thence deposited in water-logged riparian zones or, in some cases, forming dense accumulations of peat that are important as carbon sinks and as habitat for specialized biota. Recent research indicates that the role of invertebrate shredders in processing organic matter in tropical streams is less than in temperate latitudes, and there may be a higher proportion of material that is recalcitrant and/or exported from streams (or stored as peat) before it is decomposed completely. Autochthonous energy sources may be particularly important to consumers in tropical streams, and there is some evidence of a lesser reliance on allochthonous organic matter than in temperate streams