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We used a new experimental approach involving thin aquaria, luminophores, time lapse photography and image analysis to assess sediment reworking in 2 closely related bivalves, Abra ovata and A. nitida. The method proved efficient based on the highly significant correlation between the concentrations of luminophores assessed using image analysis and direct counting of sediment slices. A. ovata and A. nitida exhibited different sediment reworking behaviours. A. ovata remained immobile within the sediment and transferred luminophores within the sediment through its siphonal activity, which resulted in the creation of typical inverse conical structures. A. nitida moved within the sediment and reworked a thinner sediment layer. Both A. ovata and A. nitida were characterised as biodiffusers. Biodiffusion coefficients (D b ) were maximal at intermediate food concentration in A. ovata and at high food concentration in A. nitida. This new approach allowed assessment of the effects of spatial scale and vertical grid size on the computation of D b . In both species D b decreased with spatial scale up to 3.750 cm and then remained constant. It is suggested that this pattern partly resulted from heterogeneity linked to: (1) the mode of sediment reworking (A. ovata) and (2) the relative proportion of reworked sediment surface (A. nitida). Vertical grid size > 0.250 cm resulted in a significant overestimation of D b in A. nitida, due to the low thickness of the sediment layer reworked by this species. The implications of these results on the main characteristics (duration, spatial scale, vertical grid size) of classical luminophore experiments are discussed. KEY WORDS: Sediment reworking · Image analysis · Food availability · Scaling · Luminophores · Abra ovata · Abra nitida Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 319: [135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153] 2006 metal-doped sediment, chlorophyll a, luminophores) have been used to estimate sediment reworking by benthic fauna (Robbins 1982, Krezoski et al. 1984, Smith et al. 1986, White et al. 1987, Sharma et al. 1987, Sun et al. 1991, Wheatcroft 1992, Gérino et al. 1998. These tracers are indicative of sediment reworking occurring at different timescales. Luminophores (i.e. fluorescent particles) have been widely used in laboratory (Mahaut & Graf 1987, Gérino et al. 1998, Ouellette et al. 2004, Mermillod-Blondin et al. 2005 and in situ experiments (Mahaut & Graf 1987, Gérino 1990, Gérino et al. 1994, 1998, Biles et al. 2002, Mugnai et al. 2003, Solan et al. 2004b. Experiments classically consist of spreading luminophores at the surface of experimental sediment cores containing test organisms at time 0 and then incubating those cores for a known amount of time. At the end of the experiments, the cores are sliced horizontally and the vertical profiles of luminophore concentration assessed. The profiles are fitted to mathematical models that allow computat...

A Lagrangian stochastic larva tracking model based on a 3-dimensional (3D) high resolution wind-driven coastal circulation model is used to study the dispersal of benthic larvae. The larva tracking model includes 3D advection and turbulence, and a species-specific larval swimming behaviour that accounts for ontogenic changes, sensitivity to light exposure and inter-individual variability. Larval mortality can also be included. The dispersal model is applied to Owenia fusiformis larvae, whose swimming behaviour description is based on both existing data and new complementary measurements. Larval velocities (resulting from both settling and swimming behaviour) were measured with actographic equipment and ranged between -1 and 0.9 mm s -1. Measured swimming activity rates were lower than 50%. The sensitivity study of larval dispersal in March-April 1999 showed that: (1) the dispersal of neutrally buoyant passive larvae is more sensitive to the physical forcings resolution, because of both advection and diffusion processes, than to the variability of spawning locations within neighbouring grid cells (up to 1 km apart) in Banyuls Bay (France, NW Mediterranean); and (2) a physical barrier, located at 20 m deep in Argelès (France, NW Mediterranean) and 30 m deep in Banyuls Bay, separated nearshore and offshore larval dispersal in 1999. The final positions and local retention of larvae released in Banyuls Bay and Argelès result from: (1) the balance between the 3D turbulence, larval settling velocity (~0.8 mm s -1 ) and swimming activity rate; and (2) natural mortality, although the effect is not proportional to survival rates. High resolution larvae dispersal patterns for O. fusiformis in Banyuls Bay suggest that self-recruitment was low in the Banyuls population during spring 1999 and confirm that post-settlement deposit patterns observed there in May 1999 were insignificant. In addition, interconnections between the Argelès and Banyuls populations can exist. KEY WORDS: Larval dispersal · 3D numerical modeling· Lagrangian/Eulerian models · Owenia fusiformis · Wind-driven currents Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 311: [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] 2006 behaviour, what population dynamics emerge? Benthic population dynamics is a major issue in the management of nearshore regions. Some benthic species are fished directly and others are used to assess the biochemical quality of the environment since their sedentary adult stage integrates bio-chemical environmental changes throughout their lifetime. The use of some of these populations as bio-indicators is questionable if their dynamics are unstable due to larval dispersal.Pioneering larval dispersal studies have tried to identify physical retention structures (which are generally highly predictable) relative to the duration of the animal's larval stage, e.g. tidal estuaries for a short larval stage (de Wolf 1974, Chen et al. 1997 or a general ther...

This review lists and discusses the different methods currently available to assess sediment reworking by benthic infauna. Direct methods are used to estimate the amount of sediment transported by infauna at the sediment-water interface during a given period of time. Particle-tracer methods are used to quantify the vertical distribution of particle tracers within the sediment column. Tracers are classified based on their mode of introduction at the sediment -water interface (i.e. whether they occur naturally or are deliberately introduced at the onset of the experiment). The main characteristics of each method, including modelling aspects, are presented, and their respective advantages and drawbacks are outlined with a particular emphasis on their accuracy, spatial (i.e. both horizontal and vertical) and temporal resolutions. Direct and particle-tracer methods assess different components of sediment reworking. Selection of the most appropriate approach depends on the specific question(s) to be answered, as well as other factors, including the behaviour of the organisms studied, the spatial and temporal scales considered, and whether the experiments are carried out in situ or under controlled laboratory conditions.