Sediment reworking by marine benthic species from the Gullmar Fjord (Western Sweden): Importance of faunal biovolume

In order to compare and quantify sediment reworking activities by different species/functional groups of macrofauna, a laboratory experiment was carried out with species from the Gullmarsfjord (Western Sweden). Monospecific communities of Amphiura filiformis, Echinocardium cordatum, Scalibregma inflatum and Abra nitida were introduced in experimental mesocosms, with identical densities (795 ind. m−2), for 10 days. Sediment reworking was studied by quantifying downward and upward movements of fluorescent inert tracers (luminophores). Luminophores with different colour were initially deposited both at the sediment surface and within the sediments. Population biomass and biovolume were also determined. Surface tracers reworking coefficients ranged from 0.6 to 2.2 cm2 y−1 and 0.9 to 4.1 y−1, respectively for the biodiffusive-like and non-local transports. Calculated biodiffusive-like coefficient was between 1.0 and 2.3 cm2 y−1 for the deep tracers. For both tracers, the E. cordatum population presented the highest reworking coefficients. Among the morphological and/or ethological parameters that could determine overall patterns of reworking and differences between species, results have shown a direct relationship between the apparent biodiffusive mixing and the biovolume of the individuals (Db=0.35 ⁎ Biovolume). This suggests that the biovolume of macrofauna may allow a rough estimate of the biodiffusive-like reworking intensity of particles deposited on the sediment surface

Biodiversity of benthic invertebrates and organic matter processing in shallow marine sediments : an experimental study

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Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

International audience1. Invertebrate bioturbation can strongly affect water-sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U-shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water-sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments

Ecosystem engineering at the sediment-water interface : bioturbation and consumer-substrate interaction

International audienceIn soft-bottom sediments, consumers may influence ecosystem function more via engineering that alters abiotic resources than through trophic influences. Understanding the influence of bioturbation on physical, chemical, and biological processes of the watersediment interface requires investigating top-down (consumer) and bottom-up (resource) forces. The objective of the present study was to determine how consumer bioturbation mode and sediment properties interact to dictate the hydrologic function of experimental filtration systems clogged by the deposition of fine sediments. Three fine-grained sediments characterized by different organic matter (OM) and pollutant content were used to assess the influence of resource type: sediment of urban origin highly loaded with OM and pollutants, river sediments rich in OM, and river sediments poor in OM content. The effects of consumer bioturbation (chironomid larvae vs. tubificid worms) on sediment reworking, changes in hydraulic head and hydraulic conductivity, and water fluxes through the watersediment interface were measured. Invertebrate influences in reducing the clogging process depended not only on the mode of bioturbation (construction of biogenic structures, burrowing and feeding activities, etc.) but also on the interaction between the bioturbation process and the sediments of the clogging layer. We present a conceptual model that highlights the importance of sediment influences on bioturbation and argues for the integration of bottom-up influence on consumer engineering activities

Macro-invertebrates functional groups in freshwater and marine sediments: a common mechanistic classification.

Functional group definitions in aquatic ecology vary depending on the type of ecosystem (e.g., marine compared to fresh water ecosystems, stream compared to lake ecosystems). Since the benthic environment functions as the major storage and recycling compartment for virtually all material that flows in the aquatic system, biological processes that take place there are interesting models for identification of the different invertebrate functions. The accurate species function includes the effects of an organism on the abiotic as well as the biotic properties of the habitats. Therefore, a functional group may be defined as a group of species that share common biogeochemical and interspecific attributes. The main difficulty of applying this definition in aquatic ecosystems comes from the high diversity of organism functions (compared to terrestrial systems) that potentially exist at different levels: i) interspecific diversity supported by the large morphological and behavioural diversity of organisms, reinforced by a low degree of species redundancy; ii) intraspecific functional diversity due to changes in life history strategy during the life cycle, and enhanced by optimal foraging theory. The major question remains to find accurate functional group sizes and classifications that permit the distinction of the different biological activities involved in ecosystem key processes without missing other biological functions. After reviewing some of the problems in current functional classifications of benthic invertebrates, we propose a classification system based on the mechanical activities that characterize each species rather than consideration of the multiple consequences of these activities. This sorting strategy will result in a sub-classification of classical feeding groups into more precise functional groups. Such groups as bioturbation groups or functional feeding groups may be composed of representative taxa in both marine and freshwater environments