The benthic production of prey seems to be one of the main drivers among many environmental factors that influence the quality of fish nurseries and potentially limit their carrying capacity. However, the contribution of food availability in the growth and survival of juveniles is still controversial. The Available Benthic Energy Coefficient (ABEC) aims to assess the trophic profitability of benthic invertebrate prey; this concept reflects the combination of energy richness and availability of prey. A value of the coefficient was associated with each prey species. This value was calculated from the product of 4 components: (1) mass energy, (2) productivity, (3) regeneration, and (4) accessibility. Thus, this coefficient is expressed as a quantity of energy per unit of weight and per year. From this coefficient, it is simple to calculate the annual production of profitable energy for the fish community in a delimited nursery; it only needs information about the biomass of benthic invertebrates via a standard sampling method. This tool appears to be decisive in properly estimating the carrying capacity of such a fish nursery. Prey classifications based on taxonomy or trophic guilds are widely used in predator−prey studies; comparison with a classification based on ABEC highlighted the energetic heterogeneity of these groups. ABEC can also be used as an index of profitable energy, thereby substituting the usual classifications of prey in trophic studies.

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Despite their importance for species conservation and sound management of exploited living resources, the density-dependent mechanisms that regulate wild populations are among the least understood process in ecology. In many marine fish species, there is strong evidence that regulation occurs at the juvenile stage, when individuals concentrate in spatially restricted nurseries. However, little is known about the underlying mechanisms. Whether competition for food resources determines fish growth and survival is particularly controversial. We investigated whether food supply may have limited juvenile fish production (integrating both growth and survival) in a coastal and estuarine nursery in western Europe. Using a recent bioenergetics-based approach, we calculated annual macrobenthic food production (FP) and annual food consumption (FC) by juvenile fish and predatory invertebrates for three consecutive years (2008)(2009)(2010). We also calculated exploitation efficiency (FC:FP) and used it as an index of food limitation. Results revealed substantial interannual variations in FP (FP ∼2-3 times higher in 2008 and 2010 than in 2009). FC by young-of-the-year fish followed a fairly similar pattern. In addition, predatory invertebrates consumed as much food as juvenile fish, highlighting the need to consider all dominant epibenthic predators when estimating the overall predation pressure on macrobenthic prey. Lastly, exploitation efficiency of the entire epibenthic predator community reached ∼30% in 2009, which is relatively high despite the conservative modeling approach. Overall, these results suggest that food supply may have limited juvenile fish production during the study period, at least in 2009. Nonetheless, further studies based on longer time-series and/or other study sites are required to strengthen these findings.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

International audienceSoft sediments in coastal shallow waters constitute nursery habitats for juveniles of several flatfishes. The quality of a nursery is defined by its capacity to optimize the growth and the survival of juvenile fish. The influence of biotic factors, such as food availability, is poorly studied at the scale of a nursery ground. Whether food availability limits juvenile survival is still uncertain. A spatial approach is used to understand the influence of food availability on the distribution of juvenile fish of various benthic and demersal species in the Bay of Vilaine (France), a productive nursery ground. We quantified the spatial overlap between benthic macro-invertebrates and their predators (juvenile fish) to assess if the latter were spatially covering the most productive areas of the Bay. Three scenarios describing the shapes of the predator prey spatial relationship were tested to quantify the strength of the relationship and consequently the importance of food availability in determining fish distribution. Our results underline that both.food availability and fish densities vary greatly over the nursery ground. When considering small organisational levels (e.g., a single fish species), the predator prey spatial relationship was not dear, likely because of additional environmental effects not identified here; but at larger organisational level (the whole juvenile fish community), a strong overlap between the fish predators and their prey was identified. The evidence that fish concentrate in sectors with high food availability suggests that either food is the limiting factor in that nursery or/and fish display behavioural responses by optimising their energetic expenditures associated with foraging. Further investigations are needed to test the two hypotheses and to assess the impact of benthic and demersal juvenile fish in the food web of coastal nurseries. (C) 2015 Elsevier B.V. All rights reserved