Olivier Le Pape
email: olivier.le.pape@agrocampus-ouest.fr

Sylvain Bonhommeau

tel. Olivier Le Pape

Philippe Riou

Camille Gilliers

Caroline Kostecki

Sébastien Rochette

Benoit A Archambault

Sophie Pasquier

The food limitation hypothesis for juvenile marine fish

Keywords: Estuaries and coasts, food limitation, habitat functionality, juvenile fish growth, sizedependent mortality, trophic capacity of nursery habitat

Coastal zones are productive areas that serve as nursery grounds for a large number of marine species. However, the processes involved in survival success during the juvenile phase are not wellknown. Some authors suggest that the availability of prey is important to support the production of prerecruit fish whose fitness is enhanced through optimal feeding conditions. Accordingly, recruitment is limited by the carrying capacity of the nursery habitat. In contrast, other authors state that the carrying capacity of the nursery grounds is not fully exploited, suggesting that there is no effect of food limitation. This study combines an overview of the literature, focused on flatfish that are especially dependent on coastal and estuarine nursery grounds, an extension to other marine fishes and a modelling approach on growth and survival of juvenile fish to explore the controversy of food limitation in their nursery grounds. We demonstrate that the relative lack of growth limitation observed for young marine fishes at the individual scale is related to an observational bias: fish have been affected by size-selective mortality linked to food limitation, but only surviving individuals are observed. As the population is skewed towards the faster-growing juveniles, the growth of survivors remains close to optimal, even when food resources are limited. Food limitation is of major influence in determining the carrying capacity of the nursery habitat. To sustain marine fish populations and related fisheries, management action is needed to protect coastal and estuarine areas and maintain or restore nursery productivity.

Introduction

The life strategy of most marine teleost fish species is characterized by high fecundity, the production of large amounts of small pelagic eggs and the lack of parental care [START_REF] Juanes | Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes[END_REF]. This strategy leads to high mortality in early life stages (eggs, larvae and juveniles). Survivalto-maturity rates as low as 1:100,000 are common in many marine fish populations (Table 1). This low survival rate is specific to marine fish, as freshwater and anadromous species exhibit higher likelihood of surviving from egg to adult (e.g., 1% survival for Atlantic salmon (Salmo salar, Salmonidae) populations; [START_REF] Hutchings | Life history variation and growth rate thresholds for maturity in Atlantic salmon, Salmo salar[END_REF]. A life strategy with high and highly variable mortality makes the survival of eggs, larvae [START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF], 2008[START_REF] Cushing | Population production and regulation in the Sea: a fishery perspective[END_REF][START_REF] Bakun | Patterns in the ocean: Ocean processes and marine population dynamics[END_REF] and juveniles [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF]) strongly dependent on abiotic and biotic environmental factors. This, in turn, results in high variability in the recruitment and mortality of early life stages with dramatic influence on the abundance of fish populations [START_REF] Gallego | Understanding and quantifying mortality in pelagic, early life stages of marine organisms -Old challenges and new perspectives[END_REF]. Most of the recruitment variability of marine fishes (10-fold interannually and 100fold in overall variability; [START_REF] Houde | Emerging from Hjort's shadow[END_REF]) is explained by larval and juvenile survival rates [START_REF] Levin | Habitat triage for exploited fishes: can we identify essential fish habitat? Estuarine[END_REF]. These stages represent a bottleneck in the dynamics of fish populations and small changes in the survival rates of these stages can cause large differences in recruitment [START_REF] Levin | Habitat triage for exploited fishes: can we identify essential fish habitat? Estuarine[END_REF][START_REF] Daewel | Life history strategy and impacts of environmental variability on early life stages of two marine fishes in the North Sea: an individual based modelling approach[END_REF]. Recruitment variability and the associated large fluctuations in fish populations have been a focus of marine and fisheries science since in the early 20 th century [START_REF] Hjort | Fluctuations in the year classes of important food fishes[END_REF]) and continue to be important areas of research [START_REF] Sinclair | Recruitment in fish populations: the paradigm shift generated by ICES Committee A[END_REF][START_REF] Houde | Emerging from Hjort's shadow[END_REF][START_REF] Gallego | Understanding and quantifying mortality in pelagic, early life stages of marine organisms -Old challenges and new perspectives[END_REF].

The egg and larvae stage and the juvenile stage both exhibit low survival and contribute to the large recruitment variability:

-The variability-generating processes that occur at the egg and larval stages are of critical importance to population levels [START_REF] Hjort | Fluctuations in the year classes of important food fishes[END_REF], van der Veer et al. 2000a[START_REF] Rochette | Coupling hydrodynamic and individual-based transport models to simulate long-term larval supply on coastal nursery area[END_REF]; Table 1). During these life stages, complex and varied mechanisms influence both growth and survival and are important determinants of recruitment success. These include the drift of eggs and larvae, temperature control over early life dynamics (i.e., life stage duration, growth and mortality), food availability for larvae and predation. These mechanisms interact to generate recruitment variability that can fluctuate by an order of magnitude [START_REF] Houde | Emerging from Hjort's shadow[END_REF]).

-Mortality rates of the juvenile stage are also high (Table 1), though significantly lower than the larval stage (van der Veer et al. 2000a). Processes occurring in the nursery habitat are important determinants of population density [START_REF] Holbrook | Spatial patterns in abundance of a damselfish reflect availability of suitable habitat[END_REF]. [START_REF] Minto | Survival variability and population density in fish populations[END_REF] investigated the link between survival variability and population density from stock recruitment relationships using both a modelling approach and a meta-analysis of wild fish populations. They show that the interannual variability of progeny survival increases at low adult abundance. This pattern is consistent with density-dependent mortality in the juvenile phase which follows stochastic density-independent mortality in the egg and larval stages. Thus, density-independent and -dependent effects on settlement, growth and mortality in the nursery habitat influence recruitment success and variability (van der Veer et al. 2000a[START_REF] Peterson | Synthesis of linkages between benthic and fish communities as key to protecting essential fish habitat[END_REF][START_REF] Peterson | A conceptual view of environment-habitat-production linkages in tidal river estuaries[END_REF][START_REF] Levin | Habitat triage for exploited fishes: can we identify essential fish habitat? Estuarine[END_REF][START_REF] Fodrie | Use of population fitness to evaluate the nursery function of juvenile habitats[END_REF] and are important in regulating year-class strength (Scharf 2000, Stottrup and[START_REF] Stottrup | Can stock enhancement enhance stocks?[END_REF]. As described in the concentration hypothesis, recruitment variability is lower in populations with large density-dependent effects [START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF] related to the capacity and features of the nursery habitat [START_REF] Johnson | Habitat complexity modifies post-settlement mortality and recruitment dynamics of marine fish[END_REF]. This is especially verified for flatfishes [START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF], Le Pape et al. 2003c[START_REF] Rooper | Application of the concentration hypothesis to English sole in nursery estuaries and potential contribution to coastal fisheries[END_REF]). Thus, nursery habitats are particularly important for many marine fish species [START_REF] Peterson | Synthesis of linkages between benthic and fish communities as key to protecting essential fish habitat[END_REF][START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF][START_REF] Fulford | An ecological model of the habitat mosaic in estuarine nursery areas: Part I-Interaction of dispersal theory and habitat variability in describing juvenile fish distributions[END_REF]) and can act as habitat bottlenecks.

Though growth limitation and mortality on nursery grounds are thought to contribute to recruitment variability [START_REF] Rauck | On the nursery-aspects of the Wadden sea for some commercial fish species and possible long term changes[END_REF][START_REF] Karakiri | Growth differences in 0-group plaice Pleuronectes platessa as revealed by otolith microstructure analysis[END_REF][START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF], 6 Grover et al. 2002[START_REF] Duncan | Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks Sphyrna lewini in a nursery habitat[END_REF], survival processes of the juvenile phase are still not well known and remain controversial in regards to their contribution to recruitment variability.

-According to many analyses, prey availability is important to sustain production of pre-recruit fishes and juveniles. Coastal and estuarine (C&E) habitats (mudflats, salt marshes, kelp forests, seagrass beds, mangroves, coral reefs, upwelling regions, etc; Vasconcelos et al. in press), but also other productive habitats, serve as nursery grounds for many marine fish species [START_REF] Able | Habitat quality for shallow water fishes in an urban estuary: the effects of man-made structures on growth[END_REF][START_REF] Elliott | The structure and components of European estuarine fish assemblages[END_REF], Holbrook et al. 2000[START_REF] Grover | Effects of the 1997-1998 El Niño on early-juvenile Pacific hake Merluccius productus: age, growth, abundance, and diet in coastal nursery habitats[END_REF][START_REF] Jones | Patterns of resource use by fishes and macroinvertebrates in Barataria Bay, Louisiana[END_REF][START_REF] Laegdsgaard | Why do juvenile fish utilise mangrove habitats[END_REF][START_REF] Peterson | A conceptual view of environment-habitat-production linkages in tidal river estuaries[END_REF][START_REF] Mclusky | The Estuarine Ecosystem; ecology, threats and management, 3rd Edn[END_REF][START_REF] Elliott | The guild approach to categorizing estuarine fish assemblages: a global review[END_REF][START_REF] Franco | Life strategies of fishes in European estuaries: the functional guild approach[END_REF][START_REF] Selleslagh | Environmental factors structuring fish composition and assemblages in a small macrotidal estuary (eastern English Channel)[END_REF], and especially flatfishes [START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Meng | Use of fish index to assess habitat quality in Narragansett Bay, Rhode Island[END_REF], Le Pape et al. 2003b). Fishes aggregate in these productive areas where their fitness is enhanced through optimal growth from better feeding conditions [START_REF] Blaber | Factors affecting the distribution of juvenile estuarine and inshore fish[END_REF][START_REF] Miller | Patterns, mechanisms and approaches to the study of migrations of estuarine dependent fish larvae and juveniles[END_REF][START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Friedland | Formation and seasonal evolution of atlantic menhaden juvenile nurseries in coastal Estuaries[END_REF][START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF][START_REF] Houde | Emerging from Hjort's shadow[END_REF]. The interannual distribution of food availability and juvenile fish biomass are synchronous [START_REF] Fujii | Interactions between released and wild Japanese flounder (Paralichthys olivaceus) on a nursery ground[END_REF][START_REF] Walsh | Life history and ecology of long rough dab Hippoglossoides platessoides (F) in the Barents Sea[END_REF][START_REF] Vinagre | Niche overlap between flatfishes, Platichthys flesus and Solea solea, in a southern European estuary and adjacent coastal waters[END_REF][START_REF] Wouters | Are flatfish nursery grounds richer in benthic preys[END_REF]). Thus, food resources are often mentioned as a limiting factor in the capacity of nursery habitats (van der Veer and Witte 1993, [START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Craig | Density dependent growth and mortality in an estuary-dependent fish: an experimental approach with juvenile spot Leiostomus xanthurus[END_REF][START_REF] Nash | The influence of nursery grounds processes in the determination of year-class strength in juvenile plaice Pleuronectes platessa L. in Port Erin Bay, Irish Sea[END_REF], Nash et al. 2007).

-Other studies show that juvenile growth is not affected by trophic conditions in nursery habitats, indicating that there is no effect of food limitation [START_REF] Curran | Annual stability in the use of coves near inlets as settlement areas for Winter Flounder (Pseudopleuronectes americanus)[END_REF][START_REF] Ross | The relative value of different estuarine nursery areas in North Carolina for transcient juvenie marine fishs[END_REF][START_REF] Hampel | Feeding habits of young predatory fishes in marsh creeks situated along the salinity gradients of the Shelde estuary, Belgium, The Netherlands[END_REF][START_REF] Diaz | Nutritional condition of Argentine anchovy Engraulis anchoita larvae in connection with nursery grounds properties[END_REF][START_REF] Selleslagh | Comparison of macrobenthic assemblages of three fish estuarine nurseries and their importance as foraging grounds[END_REF] and suggesting that the carrying capacity of nursery areas is not reached [START_REF] Rogers | Populations density and growth rate juvenile sole Solea solea (L.)[END_REF][START_REF] Shi | Growth and survival of 0 super (+) English sole, Pleuronectes vetulus, in estuaries and adjacent nearshore waters off Washington[END_REF], van der Veer et al. 2000a, Vinagre and Cabral 2008). Van der Veer et al. (2000b) and [START_REF] Manderson | Predator prey relations between age-1+ summer flounder (Paralichthys dentatus, L.) and age 0 winter flounder (Pseudopleuronectes americanus, Walbaum): predator diets, prey selection, and effects of sediments and macrophytes[END_REF] propose predation as the main factor in the variability of juvenile mortality and recruitment success, suggested for various species [START_REF] Mcerlean | Abundance, diversity and seasonnal patterns of estuarine fish populations[END_REF][START_REF] Blaber | Factors affecting the distribution of juvenile estuarine and inshore fish[END_REF][START_REF] Riley | On the factors influencing the distribution of 0-group demersal fish in coastal waters[END_REF][START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Levin | Interactive effects of habitat selection, food supply and predation on recruitment of an estuarine fish[END_REF][START_REF] Wennhage | Influence of food supply and a potential predator (Crangon crangon) on settling behaviour of plaice (Pleuronectes platessa)[END_REF][START_REF] Halpin | Habitat use by an intertidal salt-marsh fish: trade offs between predation and growth[END_REF][START_REF] Lewis | Trade-offs between growth and survival responses of freshwater snails to predacious crayfish[END_REF][START_REF] Wennhage | Settlement patterns of newly settled plaice (Pleuronectes platessa) in a non tidal Swedish fjord in relation to larval supply and benthic predators[END_REF][START_REF] Hixon | Competition, predation and density-dependent mortality in demersal marine fishes[END_REF][START_REF] Baker | Redefining the piscivores assemblage of shallow estuarine nurseery habitats[END_REF], White and Caselles 2008[START_REF] Sheaves | Consequences of ecological connectivity: the coastal ecosystem mosaic[END_REF]. Predators and their short-term response [START_REF] Stier | Predator desnity and timing of arrival affect reef community assembly[END_REF] to juvenile fish densities generate density dependent mortality [START_REF] Johnson | Habitat complexity modifies post-settlement mortality and recruitment dynamics of marine fish[END_REF][START_REF] Juanes | Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes[END_REF]), helping to explain why recruitment is dampened during the juvenile stage on nursery grounds.

This controversy is illustrated (Table 2) by several well-studied cases of numerous species of the juveniles of commercial flatfish off the Western coasts of Europe (Fig. 1) and other temperate and subarctic areas. In many studies, measures of growth, nutritional condition and body condition indicate almost no food limitation or links to prey availability of the juveniles collected on C&E nursery grounds during the summer growth period. Moreover, these juveniles appear to be protected from interspecific competition by the process of food partitioning. However, for the same species, study areas and periods, other studies indicate (i) nutritionally-limiting conditions during metamorphosis, (ii) a small decrease in growth, (iii) an overlap between the juvenile distribution of benthic species and their potential prey and synchronous spatio-temporal variations, (iv) a link between recruitment and food production and (v) density-dependent distribution of juveniles, with an increased range into the open sea for stronger year classes, related to the extension of enriched productive areas. As a consequence, the influence of food limitation on juvenile fishes in their C&E nursery grounds remains unanswered.

The primary aim of this synthesis is to shed light on this question by focusing on temperate and subarctic flatfish (Table 2) that are especially dependent on C&E nursery grounds [START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF], and extending this focus to other marine fishes (pelagic, demersal and reef associated round fish and sharks, from tropical to subarctic ecoregions). We estimate the influence of trophic limitation on the density-dependent processes involved in year-class regulation during the juvenile stage of marine fishes in their nursery grounds. Solving this question has implications to understanding the main processes involved in the renewal of fish stocks during the juvenile stage. If food resources are an important regulating factor, the regulation of year-class strength during the juvenile stage depends, at least partly, on the productivity of consumable resources and the related capacity of nursery habitats [START_REF] Hayes | Linking fish habitat to their recruitment dynamics[END_REF]. In this case, maintaining the quality and productivity of essential nursery habitat is critical for the renewal of sustainable fish populations.

The question of food limitation in nursery grounds: the controversy from individual to population scale Different and complementary approaches have been used to evaluate the impacts of food limitation on the survival of juvenile fish, from laboratory experiments and mesocosms to in situ gradients at different biological scales: individual (growth, condition), population size (density and distribution) and multispecific scales. Differing results are observed when comparing the different approaches used to analyze the effect of food limitation on nursery grounds.

Experimental approach in the laboratory

Laboratory experiments enables us to estimate the influence of abiotic factors (e.g., temperature and salinity; Fonds 1975) as well as biotic factors (e.g., the effect of food intake on the growth of young flatfishes). These experiments allow us to develop models (e.g., the metabolic scope for growth, [START_REF] Fonseca | Ecophys.Fish perspectives on growth of juvenile soles, Solea solea and Solea senegalensis, in the Tagus estuary, Portugal[END_REF], or the Dynamic Energy Budget models, [START_REF] Kooijman | Dynamic Energy and Mass Budgets in Biological Systems[END_REF][START_REF] Van Der Veer | Body size scaling relationships in flatfish as predicted by Dynamic Energy Budgets (DEB theory): implications for recruitment[END_REF] to estimate juvenile flatfish growth with regard to the food supply (Table 2). These models are useful for further comparisons between in situ growth and estimates of growth based on controlled conditions. The experimental approach demonstrates that food quantity and quality affect juvenile flatfish growth. Limited food resources reduce growth, energy storage and the condition of juvenile flatfish after a few days, with important consequences on juvenile growth and survival, even for short-term events. Accordingly, a meta-analysis of starvation-induced changes in the early stages of fishes from laboratory-controlled experiments, including seven marine species (six round fishes, one flatfish) showed a general rapid exponential decrease of biogeochemical conditions with starvation, immediately followed by death [START_REF] Meyer | On the edge of death: Rates of decline and lower threshholds of biogeochemical condition in food-deprived fish larvae and juveniles[END_REF], thus extending previous mentioned results to round fishes.

Field experiments

Field experiments are less controlled experimental systems which provide favourable habitats in terms of the main factors governing juvenile fish growth, i.e., hydrodynamic exposure, food availability, predation and water temperature [START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF]. They can serve to bridge the gap between field studies with the inherent difficulties of control, and laboratory experiments that can be standardized and replicated but suffer from a lack of environmental realism [START_REF] Laffargue | Growth performances of juvenile sole Solea solea under environmental constraints of embayed nursery areas[END_REF]). Similarly, caging experiments that consist of stocking fishes in cages placed in the natural environment enables the comparison of growth rates in different habitats and living conditions [START_REF] Able | Habitat quality for shallow water fishes in an urban estuary: the effects of man-made structures on growth[END_REF][START_REF] Ciotti | Development, validation and field application of an RNA-based growth index in juvenile plaice Pleuronectes platessa[END_REF]. However, growth rates of fishes in enclosures or from in situ experiments must be interpreted with caution, as fish movements and the threat of predation may be influential but are not realistically represented [START_REF] Stunz | Growth of newly settled red drum Scianeops ocellatus in different estuarine habitats types[END_REF].

Both types of field experiments demonstrate that patterns in food availability result in differences in growth rates for juvenile fish. They also show competition for food to be the underlying mechanism in determining juvenile growth and survival for various marine fish 10 species [START_REF] Sogard | Variability in growth rates of juvenile fishes in different estuarine habitats[END_REF][START_REF] Craig | Density dependent growth and mortality in an estuary-dependent fish: an experimental approach with juvenile spot Leiostomus xanthurus[END_REF]). In accordance with laboratory studies, field experiments confirm that, in spite of a trade-off with other factors and especially the threat of predation [START_REF] Sogard | Variability in growth rates of juvenile fishes in different estuarine habitats[END_REF][START_REF] Halpin | Habitat use by an intertidal salt-marsh fish: trade offs between predation and growth[END_REF], food availability on the nursery ground is a primary driver of habitat choice and juvenile fitness.

In situ analysis, individual scale

Many field studies have analyzed growth limitation for juvenile wild fishes from individual food intake, growth and individual condition with the primary objective to estimate habitat quality and the link between food availability and living conditions. At this individual scale, food limitation often appears to be of minimal importance for juvenile flatfishes (Table 2). Measures of growth, nutritional condition and body condition indicate neither significant food limitation, nor a link with prey availability or juvenile density. However, some limited signals of limitation can be observed from gut content, recent condition, body condition and lipid reserve, especially just after settlement, with advantages to the first-settled fishes. Juvenile flatfishes appear to be not food limited and comparisons between experimental models and in situ estimates show that coastal nurseries provide a maximal potential for food intake, without negative density-dependent growth. Food limitation in the sense of starvation, individual growth and consumption of the prey of juvenile flatfishes often suggests that the carrying capacity of nursery areas is not reached [START_REF] Van Der Veer | Impact of juvenile growth on recruitment in flatfish[END_REF]. Concerning other fish orders (i.e., round fishes), [START_REF] Diaz | Nutritional condition of Argentine anchovy Engraulis anchoita larvae in connection with nursery grounds properties[END_REF] provide evidence that the Argentinean anchovy (Engraulls anchoita, Engraulidae) may not be food limited in any of their nursery grounds; juvenile growth and condition do not differ between nursery habitats for two other round fish species [START_REF] Ross | The relative value of different estuarine nursery areas in North Carolina for transcient juvenie marine fishs[END_REF] and individual consumption indicates no effect of food limitation on European sea bass (Dicentrarchus labrax, Moronidae) [START_REF] Hampel | Feeding habits of young predatory fishes in marsh creeks situated along the salinity gradients of the Shelde estuary, Belgium, The Netherlands[END_REF]. On the contrary, some authors reach opposite conclusions from in situ approaches at the individual scale on local habitat. Indeed, significant differences in condition are observed at small scales for juvenile plaice (Table 2). Concerning round fishes, [START_REF] Islam | Nutritional condition, starvation status and growth of early juvenile Japanese sea bass (Lateolabrax japonicus) related to prey distribution and feeding in the nursery ground[END_REF] use RNA:DNA ratios, total protein and growth rates to estimate the proportion of starving juvenile Japanese sea bass (Lateolabrax japonicas, Lateolabracidae) and to show their dependency on prey availability. The condition of juvenile sea bass was not equal throughout the nursery grounds. Fishes in the upper river were in better condition than those in the lower estuary. Juvenile fishes living on prey-impoverished habitats have significantly higher metabolic costs, and thus higher foraging expenses [START_REF] Goto | Bioenergetic responses of a forage fish (Fundulus heteroclitus) to habitat degradation and altered prey commubity in polluted salt marshes[END_REF]. Lastly, when considering juvenile hammerhead shark (Sphyrna lewini, Sphyrnidae), a non-teleost species with parental care and much larger juvenile individuals, the link between starvation and body condition, i.e., the effect of food limitation, is highly significant [START_REF] Duncan | Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks Sphyrna lewini in a nursery habitat[END_REF].

In situ estimation, population scale

Contrary to studies of individuals, population-scale in situ studies generally conclude that growth limitation and density-dependent effects on abundance and distribution are linked to competition and mortality related to food limitation. Firstly, limited effects are revealed when flatfish growth is analyzed from the size of individuals in the population (Table 2). With regard to model estimates based on laboratory experiments or to optimal conditions in mesocosms, in situ observations show smaller sizes of flatfish juvenile during part of the growing season in the nursery grounds, with a slight decrease in regards to optimal estimates. A synthesis of Table 2 suggests growth rates that were close to experimental values after settlement but food limitation in summer for large juveniles that had settled a few months previously. These lower growth rates and the related density-dependent regulation suggest 12 competition for food during the summer growth period. Similarly, growth rates appear to be positively related to food quantity and quality in space and time. Estuarine habitats offer optimal opportunities for flatfish juvenile growth, at least partly due to higher food availability, as growth varies annually with the most important food source in the nursery ground. When considering juvenile round fishes, Phelan et al. (1999) demonstrated that the growth of juvenile tautogs (Tautoga onitis, Labridae) is faster where prey availability is higher. Moreover the average length of juvenile Atlantic cod [START_REF] Lekve | Length dynamics in juvenile coastal skagerrak cod: effects of biotic and abiotic processes[END_REF] and red drum (Sciaenops ocellatus, Sciaenida)e [START_REF] Scharf | Patterns in abundance, Growth, and Mortality of Juvenile red drum across estuaries on the Texas coast with Implications for recruitment and stock enhancement[END_REF] decrease with increased density, indicating density-dependent effects. By coupling analyses of growth and density in different estuarine habitats, [START_REF] Sogard | Variability in growth rates of juvenile fishes in different estuarine habitats[END_REF] concludes that juvenile fishes of various species are most abundant in habitats that support faster growth.

Alternatively, studies which focus on spatial distribution and recruitment success also point out a clear influence of bottom-up food limitation on juvenile flatfishes (Table 2). Especially, a significant relationship is found between fluvial discharge and the abundance of high densities of flatfish juveniles in ecosystems of freshwater influence. This indicates that the freshwater supply helps sustain the ability of estuarine nurseries to support juveniles. The freshwater particulate organic matter propagates up the food web to juvenile flatfish, showing the role of river discharge and terrigeneous subsidy input in the function of nurseries. Richness in organic matter impacts the settling of benthic communities preyed upon by juvenile flatfishes. The influence of terrestrial discharge on juvenile flatfish differs in intensity and spatial extent between years with relation to river inputs and is correlated to the seaward extent of high densities of these juveniles. High land-based run-off is favorable to the productivity of invertebrate prey and consequently to the productivity of flatfish species. Trophic enhancement related to river inputs at least partly influences recruitment. The influence of estuarine organic matter supply for the development of a community that is tolerant to low salinity and can provide suitable food for juvenile fish were confirmed for round fish species (Costa andBruxelas 1989, Pasquaud et al. 2008). Similarly, the density dependent distribution of juvenile, from estuaries to open waters, was also verified for round fishes [START_REF] Bacheler | Density-dependent habitat use and growth of an estuarine fish[END_REF]. For instance, juveniles of filter-feeding Atlantic menhaden (Brevoortia tyrannus, Clupeidae) are found to be associated with gradients of phytoplankton biomass in their estuarine nurseries along the Eastern coast of the USA [START_REF] Friedland | Formation and seasonal evolution of atlantic menhaden juvenile nurseries in coastal Estuaries[END_REF]. When densities of juveniles are pooled for all marine species, the maximum juvenile density is observed in the middle mesohaline region of estuaries [START_REF] Lobry | Functional diversity in European estuaries: Relating the composition of fish assemblages to the abiotic environment[END_REF]. The amount of organic matter is the highest in these areas and conditions are particularly suitable for the development of benthic invertebrate prey (Moore 1978, Elliott and[START_REF] Elliott | The production ecology of the subtidal benthos of the Forth Estuary, Scotland[END_REF]. This high abundance of benthic prey leads to high fish density, especially of juvenile marine species [START_REF] Courrat | Anthropogenic disturbance on nursery function of estuarine areas for marine species[END_REF]. Accordingly, a human-induced limitation of the river flow that lowered the primary production of the adjacent shelf is found to negatively impact the recruitment of the European anchovy population in the Gulf of Cadiz [START_REF] Ruiz | A Bayesian model for anchovy (Engraulis encrasicolus): the combined forcing of man and environment[END_REF]. Likewise, severe droughts can reduce primary productivity in estuaries, with cascading effects on higher trophic levels, food availability and juvenile survival for various fish species [START_REF] Wetz | Severe droughts reduce estuarine primary productivity with cascading effects on higher trophic levels[END_REF].

The relationship between food availability and juvenile flatfish abundance (Table 2) and distribution are also confirmed outside regions of freshwater influence. In coastal areas, the migrations of juvenile flatfish demonstrate the influence of foraging opportunities on daily movements. At larger (i.e., seasonal to annual) time scales, their distribution match the distribution of their prey. Similarly, the interannual variation of abundance and distribution of juvenile flatfish are synchronous with those of the macrobenthos (Table 2). The densitydependent distribution of juveniles that extends to deeper water when abundance increases in their C&E nurseries is also verified for Atlantic cod on North West Atlantic coast [START_REF] Swain | Age and density dependent bathymetric pattern of Atlantic cod (Gadus morhua) in the Southern Gulf of St Lawrence[END_REF].

For flatfishes, local population density is a trade-off between larval supply and high mortality rates [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF]). Accordingly, competition for a limited food resource is one of the main causes of restocking failure in coastal stock enhancement programs [START_REF] Stottrup | Can stock enhancement enhance stocks?[END_REF]. The survival rate of hatchery-reared fish is first related to the number of larvae released and then to the total (wild and hatchery-reared) recruitment intensity, indicating that there are limits in the carrying capacity of nursery grounds [START_REF] Goto | Stock size fluctuations and recruitment characteristics of Japanese flounder Paralichthys olivaceus in the coastal waters off Iwate Prefecture Pacific coast of northern Honshu, Japan[END_REF]. White and Cazelles (2008) examine the effect of density-dependent processes linked to larval supply and habitat capacity on post-settlement interactions in juvenile reef fish. They estimate that the abundance of juvenile fish is not limited by the larval supply at low densities of recruits, but by density-dependent competition for food resources and shelter at high densities of recruits. However, other studies that estimate total consumption in C&E nursery grounds using growth, daily food consumption and density find that food is abundant enough to sustain juvenile growth for flatfish (Table 2), suggesting that the carrying capacity of nursery areas is not reached.

Thus, using population approaches, even if opposite conclusions are sometimes reached, density-dependent growth and mortality related to food availability appear to be major factors controlling recruitment success of juvenile stages [START_REF] Juanes | Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes[END_REF].

In situ, interspecific competition

Many studies of C&E flatfish nurseries demonstrate that if numerous species use the same nursery area, they develop strategies of resource partitioning to avoid food limitation and niche overlap. Species, but also different cohorts or age groups of a given species, had specialized their feeding behavior, with only a moderate niche overlap. Differences in feeding rhythms, habitat use, and food preference reduce food competition (Table 2). More generally, when all fish species are considered, niche overlaps vary: they are higher between species of the same family but remain limited (Pasquaud et al. 2010b). Juvenile fish of different species avoid competing for food resources even if competition is observed between resident species [START_REF] Lafaille | Composition of fish communities in a European macrotidal salt marsh (the Mont Saint Michel Bay, rance)[END_REF].

Resource partitioning, indicative of competition [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF], is a strategy to optimize food availability and appears as an adaptation to limited food resources that allows coexistence of species within the nursery zone. Such partitioning results from the long term natural selection of a trophic strategy. Indeed, there is no need to avoid niche overlap if food supply exceeds the need of the different species. This conclusion is reinforced by ontogenic shifts from higher overlap in diets of larval fish, to lower overlap in diets of juvenile fish, enabling competition avoidance between different size and age classes of the same species [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. [START_REF] Geange | Order of arrival affects competition in two reef fishes[END_REF] analyze the timing of settlement on coral reef systems and find that species survive best in the absence of competitors and that survival declines when species enter the community later than their competitors. These interspecific effects related to settlement time provide additional evidence of the importance of competition in nursery areas.

In spite of some intra-scale discrepancies, different approaches that measure common parameters such as growth, condition, density or distribution allow us to draw different conclusions about food limitation. Laboratory and field experiments, in situ studies at population scales and interspecific competition show a significant influence of food limitation on juvenile fish growth and survival. In situ studies that focus on individuals lead mainly to opposite conclusions; growth of juvenile fishes, especially small juvenile fishes, on the nursery grounds does not appear to be food limited. These opposing conclusions are obvious for populations of juvenile flatfishes on C&E areas (Table 2). However, they are verified 16 elsewhere for other fish species in different types of nursery habitats, from tropical to subarctic ecoregions.

Bridging the gap between the different approaches and scales and their opposing conclusions

Size-selective mortality in juvenile stages of teleost fish is critical [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF]. If direct evidence of density-dependent competition for food is weak [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF], especially on an individual scale, the influence of food limitation on juvenile fish growth and survival becomes obvious when changes in the size distribution associated with mortality are distinguished from changes due to individual growth.

Size-dependent mortality during juvenile life stages

A range of daily mortality as high as 5-40%, with a mean of 18% [START_REF] Selleslagh | Fonctionnement des nourriceries intertidales et estuariennes: influence de l'environnement sur la dynamique et les performances physiologiques de l'ichtyofaune[END_REF], is observed for the Eastern Channel plaice during the highly sensitive post-settlement period [START_REF] Geffen | The cost of metamorphosis in flatfishes[END_REF][START_REF] Nash | Mortality through the early life-history of fish: What can we learn from European Plaice (Pleuronectes platessa L.)?[END_REF]. The same level of mortality is estimated for tropical reef fishes (9-20%; Juanes 2007). Such high mortality rates for newly-settled larvae are far from specific to flatfishes and reef fishes, i.e., Atlantic cod shows even higher mortality rates at the juvenile stage [START_REF] Houde | Mortality. In: The unique contributions of early life stages[END_REF]; Table 1).

These high mortality rates during the juvenile stages appear to select the faster growing individuals [START_REF] Hovenkamp | Growth dependent mortality of larval plaice Pleuronectes platessa in the North Sea[END_REF][START_REF] Houde | Patterns and consequences of selective processes in teleost early life histories. Early life history and recruitment in fish populations[END_REF][START_REF] Marchand | Responses of European flounder Platichthys flesus populations to contaminant in different estuaries along Atlantic coast of France[END_REF][START_REF] Craig | Density dependent growth and mortality in an estuary-dependent fish: an experimental approach with juvenile spot Leiostomus xanthurus[END_REF][START_REF] Juanes | Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes[END_REF][START_REF] Selleslagh | Fonctionnement des nourriceries intertidales et estuariennes: influence de l'environnement sur la dynamique et les performances physiologiques de l'ichtyofaune[END_REF]). Natural mortality rates decline dramatically with increasing body size [START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF][START_REF] Miller | Larval size and recruitment mechanisms in fishes: Toward a conceptual framework[END_REF][START_REF] Conover | Nets versus nature[END_REF], leading to size-selective processes: as individuals grow rapidly, they spend less time in the smallest size classes that are most vulnerable to predation [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF]. For example, growth of anchovies in the Bay of Biscay was investigated using the otolith growth data collected during repeated larval and juvenile surveys on spawning and nursery grounds [START_REF] Allain | The selection process from larval to juvenile stages of anchovy (Engraulis encrasicolus) in the Bay of Biscay investigated by Lagrangian simulations and comparative otolith growth[END_REF]. The surviving juveniles show much faster growth rates during their larval period than the pool of larvae from which they originate, indicating dramatic growth-selective survival. Similarly, Atlantic cod have a high potential for growth-and starvation-induced mortality (Daewell et al. 2011). [START_REF] Lekve | Length dynamics in juvenile coastal skagerrak cod: effects of biotic and abiotic processes[END_REF] demonstrate that the size distribution of juvenile Atlantic cod is skewed to the larger size classes on nursery grounds, indicating size-selective mortality. This skewness increases with increased density in relation to density-dependent processes. More generally, size distribution of juvenile fish within a cohort is strongly influenced by intraspecific competition for resources, often leading to skewed frequency distributions [START_REF] Ohlberger | Biotic and abiotic effects on cohort size distributions in fish[END_REF]. The aforementioned studies and numerous others mentioned in [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF] provide evidence that body size during the juvenile stages is a major determinant of survival. Thus, the disproportionate removal of small fish causes an overestimation of growth rates if it is based only on survivors [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF].

Two explanations have been proposed to explain this size-selective mortality.

-Firstly, survival of larger fish is enhanced because larger members of a cohort can better tolerate physical extremes and endure longer periods without food [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF]. A lack of food affects energetic reserves of individuals and makes them more sensitive to other sources of mortality [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF]). Faster growing juveniles gain survival advantages via resistance to starvation and also through the ability of larger individuals to ingest a wider variety of prey [START_REF] Salgado | Feeding ecology of the gobies Pomatoschistus minutes (Pallas, 1770) and Pomatoschistus microps (Kroyer, 1838) in the upper Tagus estuary, Portugal[END_REF][START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. Rapid growth provides a size advantage in which larger fish have stronger competitive effects [START_REF] Geange | Order of arrival affects competition in two reef fishes[END_REF].

-Secondly, predation is a significant size-selective process, especially for early stages, as predation mortality is directly determined by fish size, with decreasing mortality rates with the increasing size (van der [START_REF] Van Der Veer | Impact of juvenile growth on recruitment in flatfish[END_REF]. Slow-growing and small fish remain vulnerable to predation for a longer period (i.e., the stage duration hypothesis; Sheperd and [START_REF] Shepherd | A mechanism for density-dependent survival of larval fish as the basis of a stock-recruitment relationship[END_REF][START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF][START_REF] Anderson | A review of size dependent survival during pre-recruit stages of fishes in relation to recruitment[END_REF]. For example, individuals of newly metamorphosed demersal fish, e.g., plaice [START_REF] Gibson | The behavioural basis of predator-prey size relationships between shrimp (Crangon crangon) and juvenile plaice (Pleuronectes platessa)[END_REF][START_REF] Gibson | Piscine predation on juvenile fishes on a Scottish sandy beach[END_REF], are subject to strong size-selective predation by crangonid shrimp (Crangon crangon, Crangonidae) [START_REF] Burrows | Shrimp predation on 0group plaice: contrasts between field data and predictions of an individual based model[END_REF], which primarily consume fish < 30 mm (van der [START_REF] Van Der Veer | Size-selective predation on juvenile North Sea flatfish and possible implications for recruitment[END_REF]. Accordingly, [START_REF] Ellis | Size-selective predation of O-group flatfishes on a Scottish nursery ground[END_REF] estimate that flatfish reaching 45 mm are at much lower risk from predators. More generally, after the dramatic decline in natural mortality with increasing size in early life stages, a lower but steadier density level is maintained for large juveniles of marine fish species [START_REF] Conover | Nets versus nature[END_REF][START_REF] Dingsor | Density dependence and density independence during the early life stages of four marine fish stocks[END_REF]). Thus, growth limitation influences body size and affects resistance to unfavorable environment factors and to food limitation. It also affects foraging ability and vulnerability to predation, which in turn influence individual fitness [START_REF] Ohlberger | Biotic and abiotic effects on cohort size distributions in fish[END_REF]) and recruitment.

The link between size-dependent mortality and growth explains the hidden effect of food limitation at individual scales

Average growth rates of fish larvae and juveniles are lower under food-limited conditions [START_REF] Houde | Emerging from Hjort's shadow[END_REF]. As demonstrated for larvae in the stage duration hypothesis (Sheperd and [START_REF] Shepherd | A mechanism for density-dependent survival of larval fish as the basis of a stock-recruitment relationship[END_REF][START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF], mortality rates of juvenile fish are inversely related to size and linked to growth. According to the "bigger is better hypothesis", mortality and predation during young fish stages are related to nutritional deficiencies [START_REF] Miller | Larval size and recruitment mechanisms in fishes: Toward a conceptual framework[END_REF][START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF][START_REF] Suthers | Bigger? Fatter? Or is faster growth better? Considerations on condition in larval and juvenile coral-reef fish[END_REF].

This link could explain why food limitation effects are not obvious for very young fishes. If there is high mortality of starving juveniles, a disproportionate removal of small fish causes an overestimation of the population mean growth rate from the size of survivors, which could be misleading [START_REF] Houde | Emerging from Hjort's shadow[END_REF]. As the population is skewed toward faster growing i,a inf 1 inf 1 0 juveniles, the growth of survivors could be close to experimental values under optimal conditions (Table 2), even when food limitation is important. The relationship between food availability and size-dependent mortality hinders variability in growth by selecting fastergrowing individuals and dampening recruitment variability. This also helps explain why the relationship between the mean length of a cohort and the year class strength appears to be relatively weak [START_REF] Van Der Veer | Impact of juvenile growth on recruitment in flatfish[END_REF], even if food limitation alters growth performance (dynamic self-thinning, [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF]). Similarly, this could explain why estimates of the total food consumption by juvenile fish over the summer period suggest that food is abundant enough to sustain juvenile growth (Table 2). The juvenile population size, in abundance, is adapted to the available food after the high mortality period during the first post-settlement stages. Growth limitation is more obvious for larger fish with lower mortality rates, e.g., 1 year old juvenile common sole (Le Pape et al. 2003a) or sharks [START_REF] Duncan | Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks Sphyrna lewini in a nursery habitat[END_REF].

Testing the food limitation hypothesis using simulations

Using a simulation framework, we test if, in conditions of limited food, the growth curve that is observed at the population scale during the first months of juvenile growth differs from the theoretical optimal growth curve. For illustrative purposes, we choose the life history traits of common sole and simulate a population of one million larvae. Model Individuals of the population grow according to a von Bertalanffy equation: 21

L =L . ε (a )-( L . ε (a)-L ) . e (-k . t . ε 2 (a))
where t is the time (in months), Li,a is the length (in cm) of the individual i at age a (in months since metamorphosis), Linf is the maximal length (i.e., 54 cm; Fishbase.org), L0 is the length at metamorphosis (0.5 cm; Fonds 1979), k is the growth rate (0.26; Fishbase.org). ε1(a) and ε2(a) 20 i,a are random noise that have a normal distribution with a mean equal to 1 and a standard deviation equal to 0.1 (i.e., 10% noise). This random noise is added to k and Linf to account for inter-individual variability. The growth of one million fish over their first year (from metamorphosis in the spring to the end of the year) is described in the size-at-age matrix (Li,a). Two scenarios are developed: (S1) there is no food limitation and the growth is simulated as in Eq. 1. Ten thousand individuals are then randomly sampled in the population to simulate a survey. (S2) Food limitation is simulated. As food limitation is shown to decrease the maximal length (e.g., Kooijman 2010), a negative offset is subtracted from the infinite length. This offset corresponds to 20% of the maximal length (Linf, = 43.2). Individuals die following a size-related natural mortality as defined by [START_REF] Gislason | Size, growth, temperature and the natural mortality of marine fish[END_REF]. This mortality is defined for each individual for each age in a mortality-at-age matrix (Mi,a):

M i,a = 0. 55-1 . 61. log ( L i,,a ) +1 .44 . log ( L inf ) +log (k )
where Mi,a is the instantaneous mortality rate per year of the individual i at age a (in months) and for its size, Li,a.

The probability of survival of each individual per month is directly calculated from the mortality-at-age matrix with the equation S = e -M i,a . Over the first six months of the juvenile stage, the estimate of survival is about 10%, which is in accordance with estimates for the common sole [START_REF] Rochette | A bayesian state-space model approach to integrate the whole life cycle in marine fish population model[END_REF]). The survival probability, Si,a, is then used to define the probability that an observer would sample the larva i at age a in the wild. Ten thousand fish were sampled within the whole population using the survival probability as a weighting.

Results

For the two scenarios, the sampled population has an estimated mean length within the same range as the theoretical growth curve (Fig. 2). If sampling occurs over the whole population without accounting for the individual mortality (S1), the length of individuals is randomly distributed over the theoretical growth curve. As only survivors are observed or sampled in S2 (food limitation scenario; Fig. 2b), individuals having a slower growth rate due to food limiting conditions are not sampled or are sampled less often. The mean length of sampled individuals in S2 is very similar to the theoretical growth curve but the distribution is less variable and skewed, with lower a longer tail towards higher lengths, corresponding to the observation made for Atlantic cod by [START_REF] Lekve | Length dynamics in juvenile coastal skagerrak cod: effects of biotic and abiotic processes[END_REF]. This simulation demonstrates the bias of in situ sampling; as only survivors are observed, i.e., juveniles with the fastest growth; thus, the sampling is biased towards fast-growing individuals (Fig. 2b). This shows that even in food-limited conditions, one observes individuals close to the theoretical growth curve.

Thus, the synthesis of different approaches and scales demonstrates both the trophic limitation in C&E nursery areas and the lack of an obvious signal when food limitation is observed on survivors at the individual scale. Though the present approach is at first focused on temperate and subarctic flatfish, further extension to other marine fishes (pelagic, demersal and reef associated round fish, from tropical to subarctic ecoregions) allows us to broaden these conclusions. As hypothesized by [START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF], food appeared to be the main factor affecting juvenile fish concentration in nursery grounds. Juvenile fish growth is related to food availability, and its limitation interacts with other factors, such as size-(growth) dependent predation [START_REF] Wennhage | Vulnerability of settling plaice Pleuronectes platessa to predation: effects of developmental stage and alternative prey[END_REF] and mortality [START_REF] Sogard | Size-selective mortality in the juvenile stage of teleost fishes: a review[END_REF]) to determine survival rates. Moreover, the negative relationship between growth and the duration of life stages increases the period when mortality and predation are higher for food limited juveniles. Thus, food limitation affects both the duration of the juvenile stage and the survival during this stage (Sheperd and [START_REF] Shepherd | A mechanism for density-dependent survival of larval fish as the basis of a stock-recruitment relationship[END_REF][START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF][START_REF] Van Der Veer | Impact of juvenile growth on recruitment in flatfish[END_REF].

The influence on fish populations of trophic limitation and habitat capacity in C&E nursery grounds

An obvious but variable dependency of juvenile fish on the productivity of C&E essential habitats

Juvenile fish of many species aggregate in productive C&E nursery areas in order to enhance their fitness [START_REF] Blaber | Factors affecting the distribution of juvenile estuarine and inshore fish[END_REF][START_REF] Miller | Patterns, mechanisms and approaches to the study of migrations of estuarine dependent fish larvae and juveniles[END_REF][START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF]. Habitat suitability, which is linked to production and food quality and availability, is highly influential on the spatio-temporal patterns of juvenile fish [START_REF] Holbrook | Spatial patterns in abundance of a damselfish reflect availability of suitable habitat[END_REF][START_REF] Nicolas | Relationship between benthic macrofauna and habitat suitability for juvenile common sole (Solea solea, L.) in the Vilaine estuary (Bay of Biscay, France) nursery ground[END_REF]. Though trophic limitation is a primary factor in determining the suitability of nursery habitat, juvenile fish-habitat interactions are complex [START_REF] Fulford | An ecological model of the habitat mosaic in estuarine nursery areas: Part I-Interaction of dispersal theory and habitat variability in describing juvenile fish distributions[END_REF]. Habitat suitability is a trade-off between habitat selection, foraging quality and predator avoidance [START_REF] Sogard | Variability in growth rates of juvenile fishes in different estuarine habitats[END_REF][START_REF] Wennhage | Influence of food supply and a potential predator (Crangon crangon) on settling behaviour of plaice (Pleuronectes platessa)[END_REF][START_REF] Laegdsgaard | Why do juvenile fish utilise mangrove habitats[END_REF][START_REF] Able | A re-examination of fish estuarine dependence: Evidence for connectivity between estuarine and ocean habitats[END_REF][START_REF] Sheaves | Consequences of ecological connectivity: the coastal ecosystem mosaic[END_REF]). The level of juvenile dependence on trophic limitation varies with time, among cohorts (i.e., density-dependent variations related to interannual variations in settled larvae; Fig. 3) and even among subcohorts during the settlement period [START_REF] Fonseca | Growth variability of juvenile soles Solea solea and Solea senegalenses, and comparison with RNA: DNA ratios in the Tagus estuary; Portugal[END_REF][START_REF] Geange | Order of arrival affects competition in two reef fishes[END_REF][START_REF] Nash | Mortality through the early life-history of fish: What can we learn from European Plaice (Pleuronectes platessa L.)?[END_REF][START_REF] Geffen | Sub-cohort dynamics of 0group plaice, Pleuronectes platessa L., in the Northern Irish Sea: Settlement, growth and mortality[END_REF]. This dependence varies at small spatial scales and between different nursery habitats of the same population [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF][START_REF] De Raedemaecker | Spatial variability in diet, condition and growth of juvenile place (Pleuronectes platessa) at sandy beach nursery grounds on the south-west coast of Ireland[END_REF], with relations to juvenile density and food availability. It also varies between different populations of the same species, e.g., the influence of food limitation appears significantly higher for plaice in the Irish Sea [START_REF] Nash | The influence of nursery grounds processes in the determination of year-class strength in juvenile plaice Pleuronectes platessa L. in Port Erin Bay, Irish Sea[END_REF] relative to those in the North Sea [START_REF] Van Der Veer | Immigration, settlement and density-dependent mortality of a larval and early post-larval 0-group plaice (Pleuronectes platessa) population in the western Dutch Wadden Sea[END_REF] or in the Wadden Sea (van der Veer et al. 2000a). Finally, it varies from one species to another, even in the same area, e.g., in the North Sea, trophic dependence is important for common sole [START_REF] Van Der Veer | The nursery function of the intertidal areas in the western Wadden Sea for 0-group sole Solea solea (L.)[END_REF]) but limited for plaice [START_REF] Van Der Veer | Immigration, settlement and density-dependent mortality of a larval and early post-larval 0-group plaice (Pleuronectes platessa) population in the western Dutch Wadden Sea[END_REF]).

An influence on marine fish population renewal

For a fish population to persist, habitat must be available to sustain all periods of development [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]). As such, the capacity of nursery habitats is a key contributor to the overall population fitness [START_REF] Fodrie | Use of population fitness to evaluate the nursery function of juvenile habitats[END_REF], stability and extinction risk [START_REF] Ohlberger | Biotic and abiotic effects on cohort size distributions in fish[END_REF]. [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF] provide evidence of self-thinning for plaice at the local population scale: when juvenile population density is high, food limitation depends on the number of individuals that settle relative to the productivity of the nursery ground. Populations that strictly depend on limited nursery habitats approach the carrying capacity of the habitat, at least when settlement is high. Post-settlement survival depends on nursery habitat size and productivity, in relation to the amount of larval settlement [START_REF] Rooper | Application of the concentration hypothesis to English sole in nursery estuaries and potential contribution to coastal fisheries[END_REF][START_REF] Johnson | Habitat complexity modifies post-settlement mortality and recruitment dynamics of marine fish[END_REF], Nash et al. 2007). Thus, fish populations are limited by the quantity and quality of habitat and food available for juvenile fishes [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. Food dependent size-selective mortality dampens the variability in size distribution and reduces among-year variability in recruitment strength [START_REF] Van Der Veer | Impact of juvenile growth on recruitment in flatfish[END_REF], Le Pape et al. 2003b[START_REF] Minto | Survival variability and population density in fish populations[END_REF]). Accordingly, habitat bottlenecks have been identified for juvenile fish stages of species or populations for which the variation in habitat quality has a disproportionate effect on renewal [START_REF] Fulford | An ecological model of the habitat mosaic in estuarine nursery areas: Part I-Interaction of dispersal theory and habitat variability in describing juvenile fish distributions[END_REF]. This dependence appears especially important for C&E nursery dependent flatfish species [START_REF] Iles | A review of stock-recruitment relationships with reference to flatfish populations[END_REF], but is also of important concern for many other fishes. [START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF] demonstrate that nursery-dependent species at high spawning stock biomass have asymptotic stock recruitment relationships, with a maximum recruitment level hiding a linear relationship to spawning biomass (i.e., the concentration hypothesis). These species depend on the capacity of nursery habitats for their recruitment (Fig. 3): density-dependent processes are at least partly linked to prey resources that regulate recruitment strength and dampen 24 recruitment variability [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF], van der Veer et al. 2000a, Le Pape et al. 2003c[START_REF] Houde | Emerging from Hjort's shadow[END_REF][START_REF] Minto | Survival variability and population density in fish populations[END_REF].

Thus, if variability-generating processes operating at the egg and larval stages are of major importance, processes occurring during the juvenile stage are also important in determining recruitment strength (van der Veer et al. 2000a) and variability [START_REF] Iles | A review of stock-recruitment relationships with reference to flatfish populations[END_REF]Beverton 2000, Minto et al. 2008). Among these juvenile processes, density-dependent effects related to food limitation appear to be a main governing factor [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF]. Nevertheless, food limitation influence differs for different species, populations, cohorts, nursery habitats, and years in relation to the balance between juvenile density and food availability (van der Veer et al. 2000a[START_REF] Nash | The influence of nursery grounds processes in the determination of year-class strength in juvenile plaice Pleuronectes platessa L. in Port Erin Bay, Irish Sea[END_REF], Nash et al. 2007).

The critical first juvenile stages

The present synthesis provides evidence of trophic limitation on juvenile marine fishes in their C&E nursery grounds but the question remains for which juvenile stage(s) this limitation constrains the recruitment strength.

The transition phase, after the last larval metamorphosis [START_REF] Geffen | The cost of metamorphosis in flatfishes[END_REF], is demonstrated to be a critical stage [START_REF] Juanes | Role of habitat in mediating mortality during the post-settlement transition phase of temperate marine fishes[END_REF], and thus demands thorough attention [START_REF] Nash | Mortality through the early life-history of fish: What can we learn from European Plaice (Pleuronectes platessa L.)?[END_REF]. Indeed, for the juvenile stages, density-dependent processes in young fish survival decline as they grow [START_REF] Dingsor | Density dependence and density independence during the early life stages of four marine fish stocks[END_REF], with an especially dramatic decline of mortality with increasing body size [START_REF] Houde | Fish early life dynamics and recruitment variability[END_REF][START_REF] Miller | Larval size and recruitment mechanisms in fishes: Toward a conceptual framework[END_REF]). Size-selective mortality appears to be mainly restricted to the first year of life (van der Veer et al 1994) and is especially high during the first juvenile stages. Indeed, during ontogeny at young stages, both improvements in vision and swimming performances and increases in gape size lead to shifts in diet composition and a larger choice of prey [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. The density-dependent regulation of a cohort derived from a reduction in prey resources is hypothesized to occur at a critical size and/or weight following the larval settlement [START_REF] Van Der Veer | Immigration, settlement and density-dependent mortality of a larval and early post-larval 0-group plaice (Pleuronectes platessa) population in the western Dutch Wadden Sea[END_REF][START_REF] Houde | Patterns and consequences of selective processes in teleost early life histories. Early life history and recruitment in fish populations[END_REF][START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF][START_REF] Nash | Mortality through the early life-history of fish: What can we learn from European Plaice (Pleuronectes platessa L.)?[END_REF]. Fish are most vulnerable in the period following the larval settlement, as the lack suitable prey due to their limited predation abilities, potentially leading to either reduced growth or starvation, reduce survival [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. This limitation occurs when densities of fish populations and consumption of resources remain high relative to the prey density and the replenishment rate [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF], Nash et al. 2007), and before the shift in resource use [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF] and the drop in vulnerability. At young stages, the decline in prey density by juvenile consumption is large enough to result in density-dependent effects, as is demonstrated in several cases studies [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF].

In summary, after an exponential decrease in mortality with body size/weight [START_REF] Conover | Nets versus nature[END_REF], fish reach a body size related both to lower predation and to an increase in prey size, energy content and availability (i.e., a larger choice of species item and size spectra, [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF], and mortality is dramatically reduced (Ellis and[START_REF] Gibson | The behavioural basis of predator-prey size relationships between shrimp (Crangon crangon) and juvenile plaice (Pleuronectes platessa)[END_REF]. Thus, a dramatic regulation of the size of a population occurs for the lowest juvenile size [START_REF] Dingsor | Density dependence and density independence during the early life stages of four marine fish stocks[END_REF]) during the critical period [START_REF] Houde | Emerging from Hjort's shadow[END_REF] when mortality is high enough to sharply modulate the population via limited food resources (Fig. 3). Indeed, density-dependent processes influence year-class strength mainly during the first weeks after settlement in the nurseries [START_REF] Van Der Veer | Immigration, settlement and density-dependent mortality of a larval and early post-larval 0-group plaice (Pleuronectes platessa) population in the western Dutch Wadden Sea[END_REF][START_REF] Rijnsdorp | Recruitment of sole stocks, Solea solea (L.), in the northeast Atlantic[END_REF].

Implication of food limitation for management of essential nursery habitats

The need to preserve the functionality of C&E nursery habitats for marine fish population renewal

The present synthesis focuses on the important influence of the biotic habitat capacity, i.e., food availability, on the early life stages of fish (Rijndorp et al. 1992, Schmitt and Holbrook 2000[START_REF] Johnson | Habitat complexity modifies post-settlement mortality and recruitment dynamics of marine fish[END_REF], Nash et al. 2007[START_REF] Hayes | Linking fish population dynamics to habitat conditions: insights from the application of a process-orienter appoach to several Great lakes species[END_REF]). Recruitment strength and population dynamics are strongly determined by the productivity and food resources in C&E nursery habitats. Maintaining large and high quality nursery habitats should be a primary focus to preserve fish species whose population range depends on the trophic capacity of their habitat at the juvenile stage [START_REF] Hodgson | Habitat area, quality and connectivity: striking the balance for efficient conservation[END_REF][START_REF] Van De Wolfshaar | Effect of habitat productivity and exploitation on populations with complex life cycles[END_REF]. There is a need for protection of the quality and productivity of nursery habitats to maintain fish stock renewal. The nutrient supply from C&E areas stimulates primary production, which supplies food sources for larvae and juveniles, consequently, sustains the related fisheries [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF][START_REF] Lamberth | The effects of altered freshwater inflows on catch rates of non estuarine dependent fish in multispecies nearshore fisheries[END_REF][START_REF] Sheaves | Consequences of ecological connectivity: the coastal ecosystem mosaic[END_REF]. Quantitative and qualitative factors related to anthropogenic disturbances influence the capacity of C&E nurseries and, thus, the recruitment and the renewal of populations [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF][START_REF] Meng | Using winter flounder growth rates to assess habitat quality in Rhode Islands coastal lagoons[END_REF][START_REF] Peterson | Synthesis of linkages between benthic and fish communities as key to protecting essential fish habitat[END_REF][START_REF] Peterson | A conceptual view of environment-habitat-production linkages in tidal river estuaries[END_REF], Phelan et al. 2000[START_REF] Scharf | Patterns in abundance, Growth, and Mortality of Juvenile red drum across estuaries on the Texas coast with Implications for recruitment and stock enhancement[END_REF][START_REF] Rochette | Effect of nursery habitat degradation on flatfish population: Application to Solea solea in the Eastern Channel (Western Europe)[END_REF]. It is important to maintain a high ecological quality of essential nursery habitat in C&E areas in order to sustain marine populations and fisheries. Measures aiming at improving or preserving the capacity of juvenile habitat are the most effective for improving adult biomass of populations regulated by density dependence during the juvenile phases (van de [START_REF] Van De Wolfshaar | Effect of habitat productivity and exploitation on populations with complex life cycles[END_REF]. Preservation and rehabilitation measures should be designed to provide nursery habitats for fishes and enhance their food base [START_REF] Nunn | The foraging ecology of larval and juvenile fishes[END_REF]. Nursery function must be accounted for in monitoring systems of C&E waters to maintain high ecological status [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF] and especially for the establishment of MPAs to provide and export juveniles, to enhance fishing yields [START_REF] Pelletier | Dynamics of a migratory population under different fishing effort allocation schemes in time and space[END_REF][START_REF] Gell | Benefits beyond boundaries: the fishery effects of marine reserves[END_REF][START_REF] Kaplan | Fish life histories and marine protected areas: an odd couple?[END_REF]) and benefit the fisheries [START_REF] Mesnildrey | Marine Protected Areas and fisheries management: some criteria for ecological efficiency[END_REF].

Estimating habitat suitability from large juvenile fish growth and density: an appropriate tool

The density, growth and condition of juvenile fishes are relevant indicators to estimate the ecological quality of nursery habitats (e.g., [START_REF] Guindon | Growth potential of juvenile southern flounder, Paralichthys lethostigma, in low salinity nursery areas of Pamlico Sound, North Carolina, USA[END_REF][START_REF] Suthers | Bigger? Fatter? Or is faster growth better? Considerations on condition in larval and juvenile coral-reef fish[END_REF], Able et al. 1999[START_REF] Duffy-Anderson | Effects of municipal piers on the growth of juvenile fishes in the Hudson river estuary: a study across pier edge[END_REF], Phelan et al. 2000;[START_REF] Selleslagh | Effect of starvation on condition and growth of juvenile plaice Pleuronectes platessa: nursery habitat quality assessment during the settlement period[END_REF]. However, as starving and newly-settled juveniles are removed from the population by high mortality rates, growth rates are overestimated for very young stages and cannot be used as indicators of the nursery function. With regards to high mortality rates of post-settlement juvenile fishes in relation to the nutritional deficiencies of their nursery grounds (i.e., the food limitation hypothesis, Fig. 3), it could be misleading to determine essential nursery habitats and estimate their quality from the density and growth of newly post-settled fish.

In contrast, large juveniles experience dramatically lower mortality and it is more reliable to collect data on larger juvenile fish to identify nursery habitat and estimate its ecological status. Indeed, density is less variable, food limitation is more obvious [START_REF] Duncan | Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks Sphyrna lewini in a nursery habitat[END_REF], and growth is less biased due to size-dependent selection [START_REF] Meng | Using winter flounder growth rates to assess habitat quality in Rhode Islands coastal lagoons[END_REF], Le Pape et al. 2003a[START_REF] Gilliers | Growth and condition of juvenile sole (Solea solea L.) as indicators of habitat quality in coastal and estuarine nurseries in the Bay of Biscay with a focus on sites exposed to the Erika oil spill[END_REF], Amara et al. 2007, Amara et al., 2009;[START_REF] Selleslagh | Effect of starvation on condition and growth of juvenile plaice Pleuronectes platessa: nursery habitat quality assessment during the settlement period[END_REF]. Nevertheless, biased and incorrect decisions regarding habitat quality can still be made when using a growth-based assessment without identifying factors, such as temperature and density, that may underlie differences in growth rates [START_REF] Searcy | Is growth a reliable indicator of habitat quality and essential fish habitat for a juvenile estuarine fish?[END_REF].

A given habitat is considered a nursery if it contributes disproportionately to the size and number of adults relative to other juvenile habitats [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF]. The most environmentally-sensitive fish populations are those whose nursery areas are restricted to a few coastal sites [START_REF] Parrish | Nursery habitat in relation to production of juvenile snapper Pristipomoides filamentosus in the Hawaian Archipelago[END_REF]. The identification of these sites is an important consideration for coastal management [START_REF] Cogan | The role of marine habitat mapping in ecosystem based management[END_REF], Vasconcelos et al. 2011, Vasconcelos et al. in press). During the settlement period, the high spatiotemporal variability in juvenile abundance linked to both the pulses of larval supply and high mortality rates [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF]) leads to spurious estimates of juvenile abundance and habitat capacity. On the contrary, the abundance of juvenile fish is dramatically less variable after larval settlement and the huge decline in mortality caused by the dampening effects of density-dependent processes [START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF][START_REF] Rooper | Application of the concentration hypothesis to English sole in nursery estuaries and potential contribution to coastal fisheries[END_REF][START_REF] Johnson | Habitat complexity modifies post-settlement mortality and recruitment dynamics of marine fish[END_REF]. At this older juvenile stage, the habitat contribution to the population, i.e., the total biomass of individuals added to adult populations [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF]) from a given habitat, can be estimated from juvenile abundance. It is possible to quantify essential and effective juvenile habitats (i.e., the overall contribution from specific habitats to the adult population; [START_REF] Dahlgren | Marine nurseries and effective juvenile habitats: concepts and applications[END_REF], from habitat suitability models [START_REF] Norcross | Habitat models for juvenile pleuronectids around Kodiak Island, Alaska[END_REF], 1999[START_REF] Guisan | Predictive habitat distribution models in ecology[END_REF][START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF], Le Pape et al. 2007[START_REF] Stoner | Flatfish-habitat associations in Alaska nursery grounds: Use continuous video records for multiscale spatial analysis[END_REF][START_REF] Dahlgren | Marine nurseries and effective juvenile habitats: concepts and applications[END_REF]) and related mapping approaches (Le Pape et al. 2003b[START_REF] Fodrie | Availability, usage and expected contribution of potential nursery habitats for the California halibut[END_REF], Rotenberry et al. 2006, Trimoreau et al. in press). Such procedures can be based on populations but can also be estimated from a multimetric index for a more general definition of the essential fish habitats of C&E ecosystems [START_REF] Courrat | Anthropogenic disturbance on nursery function of estuarine areas for marine species[END_REF][START_REF] Delpech | Development of a fish-based index to assess the ecological quality of transitional waters: The case of French estuaries[END_REF]. Policy objectives, such as the sustainability of fish resources, ecosystem health or the design of MPAs, should be based on quantitative maps of essential fish habitats [START_REF] Cogan | The role of marine habitat mapping in ecosystem based management[END_REF][START_REF] Johnson | Linking temperate demersal fish species to habitat: scales, patterns and future directions[END_REF]2012). Furthermore, quantitative indices of habitat suitability can be useful tools to assess the vulnerability of fishes to various anthropogenic disturbances [START_REF] Steizenmuller | Towards spatially explicit risk assessment for marine management; assessing the vulnerability of fish to aggregate extraction[END_REF], such as habitat loss and degradation linked to xenobiotics [START_REF] Rochette | Effect of nursery habitat degradation on flatfish population: Application to Solea solea in the Eastern Channel (Western Europe)[END_REF] or invasive species [START_REF] Kostecki | Reduction of flatfishes habitat as a consequence of the proliferation of an invasive mollusc[END_REF].

Conclusion and suggestions for future research

The aim of the present synthesis is to shed light on the controversy of food limitation for juvenile fishes in their C&E nursery grounds and to analyze the related consequences for survival and future recruitment. We demonstrate that the relative lack of observed growth limitation for young fishes at the individual scale in their nursery grounds is at least partly related to size-selective mortality affecting food-limited and newly-settled fishes [START_REF] Sogard | Variability in growth rates of juvenile fishes in different estuarine habitats[END_REF]. This synthesis confirms the conclusions of studies that use different approaches (i.e., experiments on individual juvenile fishes and in situ observations at the population scale) and enhances the understanding of the strategy of food partitioning developed between age groups and between species to limit competition for food resources. Though the present approach focuses on temperate and subarctic flatfish for illustration purposes, a large amount of references to other marine fishes allows us to extend these conclusions to other fish species, and especially to the large proportion of C&E nursery dependent fishes [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF].

The food limitation hypothesis is such: juveniles aggregate in C&E productive areas where their fitness is enhanced through better feeding conditions and optimal growth [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF]. Food limitation is of major importance in determining the nursery habitat capacity [START_REF] Nash | Dynamics of shallowwater juvenile flatfish nursery grounds: application of the shelf-thinning rule[END_REF]). Nevertheless, this influence can vary between species, populations, cohorts (and even subcohorts), locations and years (van der Veer et al. 2000a). Habitat structure, refuge opportunities and connectivity between habitats modulate this ecological function [START_REF] Able | A re-examination of fish estuarine dependence: Evidence for connectivity between estuarine and ocean habitats[END_REF][START_REF] Sheaves | Consequences of ecological connectivity: the coastal ecosystem mosaic[END_REF].

This synthesis provides enough information to demonstrate the influence of the productivity of C&E nursery habitats on the recruitment of fish populations [START_REF] Rijnsdorp | Recruitment of sole stocks, Solea solea (L.), in the northeast Atlantic[END_REF][START_REF] Gibson | Impact of habitat quality and quantity on the recruitment of juvenile flatfishes[END_REF][START_REF] Iles | The concentration hypothesis: the statistical evidence[END_REF]. After the nursery stage, juvenile fish move out of C&E ecosystems to join and sustain fish populations on the continental shelf [START_REF] Beck | The role of nearshore ecosystems as fish and shellfish nurseries[END_REF][START_REF] Sheaves | Consequences of ecological connectivity: the coastal ecosystem mosaic[END_REF]. Breaking closure of life history cycle causes severe problems and C&E habitat degradation is one of the most serious threats to the recovery of fish stocks. There is a need to maintain and restore the ecological function of C&E nursery grounds to sustain marine fish populations and related fisheries [START_REF] Hall | The effects of fishing on marine ecosystems and communities[END_REF][START_REF] Elliott | The guild approach to categorizing estuarine fish assemblages: a global review[END_REF]. Spatial and temporal relationships between fisheries species and habitats must be included in fisheries management plans [START_REF] Peterson | A conceptual view of environment-habitat-production linkages in tidal river estuaries[END_REF]. In this context, an important challenge is to account for nursery function in MPA designs to protect juvenile fish from various anthropogenic pressures. To that aim, observations of in situ density and growth of relatively large and old juvenile fish could provide useful tools when density estimates become reliable and sizeselective mortality is not hindered by food limitation. Data on these large juveniles could be used to develop habitat suitability models to identify and map essential nursery habitats and to estimate indicators of ecological status for these essential fish habitats.

Nevertheless, the underlying ecological processes are still unknown and further studies are needed for young juvenile stages when food limitation is mostly influential [START_REF] Cowan | Is density dependent growth in young of the year fishes a question of critical weight?[END_REF], Juanes 2007, Vasconcelos et al. in press;Fig. 3). It is critical to investigate the dependence level of recruitment on food availability and the variability of this dependence (e.g., interannual or interspecific). In forthcoming research, there is a need to focus on the young post-settlement stage to understand the trophic dependence of juvenile fish on their nursery grounds [START_REF] Able | A re-examination of fish estuarine dependence: Evidence for connectivity between estuarine and ocean habitats[END_REF], as this is one life stage that has not received enough study (Nash and Geffen 2012, Vasconcelos et al. in press). However, the study of food availability for these very young fish remains a challenge and requires a fine analysis of biological and ecological processes to determine the critical stage and to understand the trophic limitation. The uncertainty of the precise life stage on which to focus, the high spatiotemporal variability in both larval supply and mortality (and, thus, density) and the high turnover rate of fish and small invertebrate prey during the first juvenile stages requires data with small time steps [START_REF] Fonseca | Growth variability of juvenile soles Solea solea and Solea senegalenses, and comparison with RNA: DNA ratios in the Tagus estuary; Portugal[END_REF][START_REF] Geange | Order of arrival affects competition in two reef fishes[END_REF][START_REF] Nash | Mortality through the early life-history of fish: What can we learn from European Plaice (Pleuronectes platessa L.)?[END_REF] and fine spatial scales [START_REF] De Raedemaecker | Spatial variability in diet, condition and growth of juvenile place (Pleuronectes platessa) at sandy beach nursery grounds on the south-west coast of Ireland[END_REF]Johnson et al. 2012). Moreover, as the main governing process varies among species and even among populations (Van der Veer et al. 2000a), solving the problem with a general explanation may be an unrealistic goal. Numerous specific case studies are necessary before drawing generic conclusions on the trophic limitations of fish populations.

1 European anchovy (Engraulis encrasicolus, Engraulidae) Bay of Biscay 10 -5 10 -3 -2

Calculated from [START_REF] Allain | The selection process from larval to juvenile stages of anchovy (Engraulis encrasicolus) in the Bay of Biscay investigated by Lagrangian simulations and comparative otolith growth[END_REF][START_REF] Allain | Modélisation biophysique pour la prévision du recrutement[END_REF] Altantic cod (Gadus morhua, Gadidae) North Sea 10 -7 -10 -8 10 -5 -10 -6 -2

Houde 2002

Common sole (Solea solea, Soleidae) Bay of Biscay Eastern Channel 10 -5 10 -5 10 -3 10 -3 -2 -2 calculated from [START_REF] Koutsikopoulos | The role of coastal areas in the life history of sole (Solea solea L.) in the Bay of Biscay[END_REF][START_REF] Koutsikopoulos | Cross-well dispersion of dover sole (Solea solea (L.)) eggs and larvae in Biscay Bay and recruitment to inshore nurseries[END_REF][START_REF] Rochette | A bayesian state-space model approach to integrate the whole life cycle in marine fish population model[END_REF].

Plaice (Pleuronectes platessa, Pleuronectidae) North Sea Irish Sea English Channel 10 -5 -10 -6 10 -5 10 -5 10 -3 -10 -4 10 -3 10 -3 -2 -2 -2

Geffen et al. 2007

Calculated from [START_REF] Harding | Recent studies on the eggs and larvae of the plaice (Pleuronectes platessa L.) in the Southern Bight[END_REF][START_REF] Harding | Recent studies on the eggs and larvae of the plaice (Pleuronectes platessa L.) in the Southern Bight[END_REF][START_REF] Talbot | The dispersal of plaice eggs and larvae in the Southern Bight of the North Sea[END_REF] Winter flounder (Pseudopleuronectes americanus, Pleuronectidae)

All or whole 10 -5 -10 -6 10 -3 -10 -4 -2

Rose et al. 1996 Atlantic eel (Anguilla Anguilla, Anguillidae) All or whole 10 -4 3.10 -4 0.3 [START_REF] Bonhommeau | Estimates of the mortality and the duration of the trans-Atlantic migration of European eel leptocephali using a particle tracking model[END_REF] Atlantic bluefin tuna (Thunnus thynnus, Scombridae) All or whole 10 -4 4.10 -4 0.3 [START_REF] Simon | Effects of Stochasticity in Early Life History on Steepness and Population Growth Rate Estimates: An Illustration on Atlantic Bluefin Tuna[END_REF] Pacific bluefin tuna (Thunnus orientalis, Scombridae) All or whole 6-8.10 -5 4.10 -4 0.1-0.2 [START_REF] Iwata | Reconsideration of natural mortality of age 0 Pacific bluefin tuna and its variability relative to fish size[END_REF][START_REF] Polacheck | Updated estimates of mortality rates for juvenile SBT from multi□year tagging of cohorts[END_REF][START_REF] Whitlock | Estimating fishing and natural mortality rates for Pacific bluefin tuna (Thunnus orientalis) using electronic tagging data[END_REF] Southern bluefin tuna (Thunnus macoyii, Scombridae) All or whole 2.10 -5 4.10 -4 0.06 Figure legends Fig. 1: Location of the regional seas in Western Europe where many of the studies in this review have taken place. Fig. 2: Comparison of the theoretical growth curve of the common sole after settlement during their first year (grey line) and simulations of sampling carried out each month for 10,000 (out of 1,000,000) juvenile common sole that experienced a) no food limitation and b) food-limited conditions (i.e., maximal length reduced by 20% in the model). Fig. 3: Processes involved in the food limitation hypothesis: consequences of the limited trophic capacity of nursery habitats during the settlement and post-settlement period on the recruitment variability of marine fishes (pluriannual variability in cohort abundance is represented for two different life stages, larval / large juveniles, before and after the stage of food limitation).

For

Revie w

Table 1 :

 1 Mortality during the pre-adult life phases in some marine fish populations 2

	Species

Table 2 :

 2 Analysis of food limitation in temperate and subarctic juvenile flatfish: species, location, methods and conclusions 2

	Tsuji (1998)

Acknowledgements