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L'unité BIOEMCO est devenue IEES en janvier 2014.; International audience; These last twenty years have seen the development of an abundant literature on the influence of soil macrofauna on soil structure. Amongst these organisms, earthworms, termites and ants are considered to play a key role in regulating the physical, chemical and microbiological properties of soils. Due to these influential impacts, soil ecologists consider these soil macro-invertebrates as 'soil engineers' and their diversity and abundance are nowadays considered as relevant bioindicators of soil quality by many scientists and policy makers. Despite this abundant literature, the soil engineering concept remains a 'preach to the choir' and bioturbation only perceived as important for soil ecologists. We discussed in this article the main mechanisms by which soil engineers impact soil structure and proposed to classify soil engineers with respect to their capacity to produce biostructures and modify them. We underlined the lack of studies considering biostructure dynamics and presented recent techniques in this purpose. We discussed why soil engineering concept is mainly considered by soil ecologists and call for a better collaboration between soil ecologists and soil physicists. Finally, we summarized main challenges and questions that need to be answered to integrate soil engineers activities in soil structure studies.

The design of sustainable agroecosystems requires knowledge of plant species impacts on soil functioning. To address this need, we manipulated plant species diversity in pastures of eastern Amazonia. Four plant species (Arachis pintoi, Brachiaria brizantha, Leucaena leucocephala and Solanum rugosum) were grown alone and in every possible combination on experimental plots within three replicate farms. After 28 months, soils were sampled to determine impacts on 5 categories of variables: soil macrofauna, aggregate morphology, chemical fertility, water storage and compaction. No clear effects of plant species richness were observed on any of the soil properties measured. However, individual plant species had significant impacts on variables in all 5 categories. Most notably, the herbaceous legume, A. pintoi, promoted both earthworm and ant densities and a corresponding 87% increase in biogenic aggregates in plots with vs. without A. pintoi. Meanwhile, B. brizantha increased the proportion of root-derived aggregates, while negatively impacting ant densities. Significant covariation was observed among many of the 5 data sets (categories), namely soil aggregate morphology and soil macrofauna, as well as aggregate morphology and soil compaction. This research demonstrates that plant species composition can impact soil properties through faunal-mediated effects, and stresses the necessity of considering soil macrofauna in agroecosystem management.

In Brazilian Amazonia there are 26 million hectares of degraded pastures. One of the causes of degradation is assumed to be alterations in soil structure that is partly determined by a reduction in soil macrofauna diversity. The objective of this case study was to identify the consequences of altered macrofaunal diversity on soil structure and hydrological processes. After forest clearing for pasture establishment, the diversity of soil macroinvertebrates decreased strongly. Tensiometric measurements showed the formation of a superficial groundwater table in a 4-year-old pasture (P4), and a deeper groundwater table in an abandoned pasture (Pa), that was an exceptional situation. The forest soil, in contrast, was almost never water-saturated due to its microaggregate structure. Once the pasture was abandoned, the soil macrofauna was dominated by a single earthworm species, Pontoscolex corethrurus , which may modify, in the course of a few years, the morphology and hydrological functioning of soils. By placing very wet castings on the pasture soil surface, P. corethrurus can form a continuous layer that is relatively impermeable to air and water. Although initially limited to the surface layer, the episodic conditions of water saturation and anoxia may also occur in deeper horizons, favoring the development of hydromorphic conditions, even though the surface soil structure may be regenerating due to the activity of other macrofaunal groups such as termites, after reduction of P. corethrurus populations.

The Mid-Atlantic Ridge is the target of an emerging international ecosystem study under the Census of marine life programme. This pilot project shall gather new knowledge on biodiversity, distribution patterns, and ecological processes, and the overriding aim is "to describe and understand the patterns of distribution, abundance and trophic relationships of the organisms inhabiting the mid-oceanic North Atlantic, and identify and model ecological processes that cause variability in these patterns". The project will focus on pelagic, benthopelagic and epibenthic macrofauna, and analyse distribution and abundance patterns in relation to the abiotic and biotic environment, as well as trophic relationships and life history strategies. Fish, crustaceans, cephalopods and gelatinous plankton and nekton have the highest priority in the study. A major challenge of the project is to overcome observation difficulties at large depths and in rugged terrain. A central aim is thus to utilise modern remote sensing technology (acoustics, optics) using advanced instrument carriers (e.g. towed vehicles, ROVs, AUVs, etc.). The project will be carried out as a multi-ship operation in 2003-2005, and the ongoing planning is a collaborative effort involving many nations around the North Atlantic. The project will work on the Mid-Atlantic Ridge and in adjacent waters from the Azores to Iceland, both by surveying large areas by acoustics and mid-water trawling, and by focusing on three selected sub-areas for intensive sampling and observation by traditional and novel methods and technology. Overlapping with the field seasons, the period 2004-2008 will be an analytical phase, also including submission of data to OBIS., La ride médio-atlantique est la cible d’une étude internationale naissante de son écosystème, dans le cadre du programme de Recensement de la vie marine. Ce projet-pilote doit rassembler les connaissances nouvelles sur la biodiversité, la distribution et les processus écologiques. L’objectif assigné est de « décrire et comprendre les types de distribution, l’abondance et les relations trophiques des organismes vivant dans la partie centrale de l’Atlantique Nord, d’identifier et de modéliser les mécanismes écologiques qui régulent la variabilité de cette organisation ». Ce programme, centré sur la macrofaune pélagique, benthopélagique et épibenthique, doit analyser la distribution et l’abondance en relation avec l’environnement biotique et abiotique aussi bien que les relations trophiques et les différentes stratégies dans les cycles de vie. Les études portant sur les poissons, les crustacés, les céphalopodes, le plancton fragile et le necton sont prioritaires. Un des défis majeurs que ce programme doit relever est de dépasser les difficultés de l’observation en grande profondeur et en terrain accidenté. Un point-clef est donc de s’appuyer sur les techniques modernes de télédétection (acoustiques et optiques) utilisant les véhicules récents (par exemple des véhicules remorqués, des ROV, des AUV, etc.). Ce projet s’appuiera sur une opération à plusieurs navires en 2003-2005 impliquant un effort coopératif de nombreux pays du pourtour de l’Atlantique Nord. La zone d’étude est la ride médio-atlantique et les eaux adjacentes, des Açores à l’Islande ; elle sera étudiée aussi bien à grande échelle par les techniques acoustiques et le chalutage semi-pélagique que par des études fines sur trois zones-clefs avec un échantillonnage intensif et une observation s’appuyant sur les techniques classiques et modernes. Débordant sur ces campagnes de terrain, la période 2004-2008 constituera la phase d’analyse comprenant la soumission des données à la base Obis.

We compared the sediment and its community on the Celtic continental slope (Goban Spur) with those in a branch of the nearby Whittard Canyon in search for evidence of canyon mediated transport of (labile) organic matter. We studied the megabenthos and macrobenthos biomass and taxonomic composition, measured in situ sediment community oxygen consumption and determined sediment concentrations of particulate organic carbon, phytopigments, and nucleic acids. While the sediment community and activity on the canyon fan was similar to that on the abyssal station near Goban Spur, the sediment within the canyon had relatively enhanced sediment community oxygen consumption rates and higher levels of phytopigments. particulate organic carbon and nucleic acids, particularly towards the canyon head. However, near-bottom sediment traps and transmissometre readings gave no sign of enhanced particle fluxes. Most likely this enrichment is supplied periodically through lateral transport as suggested by increased numbers of filter-feeding macrobenthos. Markedly higher concentrations of sedimentary pigments were found in a second branch of the Whittard Canyon illustrating the complexity of canyon systems and the need for a much more extensive study., Nous avons comparé le sédiment et sa communauté de la pente continentale celtique (Goban Spur) avec ceux dˈune branche du canyon voisin de Whittard, pour mettre en évidence le transport relatif de matière organique (labile) par le canyon. Nous avons étudié la biomasse et la composition taxonomique du megabenthos et du macrobenthos, mesuré la consommation dˈoxygène in situ de la communauté sédimentaire, et déterminé les concentrations de carbone organique particulaire, des pigments végétaux et des acides nucléiques. Alors que la communauté sédimentaire et lˈactivité au pied du canyon sont similaires à la station abyssale près de Goban Spur, le sédiment du canyon présente une consommation dˈoxygène plus élevée, et des concentrations supérieures de pigments végétaux, de carbone organique particulaire et dˈacides nucléiques, particulièrement vers la tête de canyon. Cependant, les données des pièges à particule et les mesures de transmission près du fond nˈindiquent pas un rehaussement du flux de particules. Cet enrichissement périodique est dû au transport latéral, comme lˈindiquent les densités supérieures de macrobenthos à régime alimentaire de filtreurs. Des concentrations de pigments nettement plus élevées ont été trouvées dans une deuxième branche du canyon de Whittard, ce qui illustre la complexité des systèmes de canyon et la nécessité dˈune étude beaucoup plus approfondie.

The carbonates associated with the macrofauna of shallow fine sands have been evaluated at six stations located at five different sites on the French Mediterranean coast. The carbonate content of forty species or zoological groups has been estimated. At each station the mean calcimass has been calculated during a year-long cycle, showing the participation of the different zoological groups, mainly molluscs and echinoderms. The comparison of calcimass and associated biomass shows that CaCO3/AFDW ratio fluctuates between 1.6 to 19.3. These values are similar to those obtained in some rocky bottom communities. Calcimass values usually largely exceed biomass ones; therefore the carbon linked to carbonates cannot be excluded from the carbon balance including macrofauna, which are usually represented only by biomass organic matter. According to mean longevity of species providing CaCO3, the annual carbonate production by macrobenthos in Mediterranean fine sands can be roughly estimated as being one third of its calcimass value., Les carbonates associés à la macrofaune des sables fins littoraux ont été évalués à six stations réparties dans cinq sites différents des côtes de Provence, en Méditerranée nord-occidentale. La teneur en calcaire d'une quarantaine d'espèces ou de groupes zoologiques a été déterminée. La calcimasse moyenne par station est estimée sur un cycle annuel portant sur les quatre saisons et montrant la participation respective des différents groupes zoologiques, mollusques, échinodermes et crustacés, les deux premiers étant les principaux contributeurs. La comparaison des calcimasses et des biomasses montre que le rapport CaCO3/PSSC varie de 1,6 à 19,3, valeurs comparables à celles données pour certains peuplements de substrats durs. Les valeurs des calcimasses excèdent le plus souvent largement celles des biomasses, ce qui indique que les bilans de carbone incluant la macrofaune doivent prendre en compte le carbone lié aux carbonates et ne plus se limiter à la matière organique de la biomasse. Compte tenu de la longévité moyenne des principales espèces productrices de calcaire, la production annuelle de carbonates est estimée au tiers de la calcimasse dans les sables fins littoraux en Méditerranée nord-occidentale.