The aim of this paper is to analyse the emergence of functional response of a predator–prey system startingfrom diverse simulations of an Individual-Based Model of schooling fish. Individual characteristicscan, indeed, play an important role in establishing group dynamics. The central question we address iswhether or not aggregation influences predator–prey relationships.To answer this question, we analyse the consequences of schooling when estimating functional responsein four configurations: (1) no schooling of either prey nor predators; (2) schooling of prey only; (3)schooling of predators only; and (4) schooling of both prey and predators. Aggregation is modelled usingthe rules of attraction, alignment and repulsion.We find important differences between the various configurations, highlighting that functional responseis largely affected by collective behaviour. In particular, we show: (1) an increased predation efficiencywhen prey school and (2) different functional response shapes: Holling type II emerges if prey do notschool, while Holling type III emerges when prey aggregate.

Mnemiopsis leidyiis an invasive comb jelly which has successfully establisheditself in European seas. The speciesis known to produce spectacular blooms yet it is holoplanktonic and not much is known about its populationdynamics in between. One way to gain insight on howM. leidyimight survive between blooms and how it canbloom so fast is to study how the metabolism of this species actually responds to environmental changes infood and temperature over its different life-stages. To this end we combined modelling and data analysis tostudy the energy budget ofM. leidyiover its full life-cycle using Dynamic Energy Budget (DEB) theory andliterature data.An analysis of data obtained at temperatures ranging from 8 to 30 °C suggests that the optimum thermaltolerance range ofM. leidyiis higher than 12 °C. FurthermoreM. leidyiseems to undergo a so-called metabolicacceleration after hatching. Intriguingly, the onset of the acceleration appears to be delayed and the data donot yet exist which allows determining what actually triggers it. It is hypothesised that this delay confers a lotof metabolicflexibility by controlling generation time.We compared the DEB model parameters for this species with those of another holoplanktonic gelatinouszooplankton species (Pelagia noctiluca). After accounting for differences in water content, the comparisonshows just how fundamentally different the two energy allocation strategies are.P. noctilucahas an extremelyhighreservecapacity,lowturnovertimesofreservecompoundsandhighresistancetoshrinking.M.leidyiadoptsthe opposite strategy:ithas a low reserve capacity, highturnover ratesofreserve compounds and fastshrinking

Parameters for the standard Dynamic Energy Budget (DEB) model were estimated for the purple mauve stinger,Pelagia noctiluca, using literature data. Overall, the model predictions are in good agreement with data coveringthefulllife-cycle.Theparametersetweobtain suggeststhatP.noctilucaiswelladaptedto survivelong periods ofstarvation sincethepredictedmaximum reservecapacity isextremelyhigh.Moreover wepredict that therepro-ductive output of larger individuals is relatively insensitive to changes in food level while wet mass and lengthare.Furthermore,theparametersimplythateveniffoodwerescarce(ingestionlevelsonly14%ofthemaximumforagiven size) an individual would still mature and be able to reproduce. We present detailed model predictions forembryo development and discuss the developmental energetics of the species such as the fact that the metabo-lism of ephyrae accelerates for several days after birth. Finally we explore a number of concrete testable modelpredictions which will help to guide future research. The application of DEB theory to the collected data allowedustoconcludethatP. noctilucacombinesmaximizing allocation toreproduction with rather extreme capabilitiesto survive starvation. The combination of these properties might explain whyP. noctilucais a rapidly growingconcern tofisheries and tourism.

Biotic indices, which reflect the quality of the environment, are widely used in the marine realm. Sometimes, key species or ecosystem engineers are selected for this purpose. This is the case of the Mediterranean seagrass Posidonia oceanica, widely used as a biological quality element in the context of the European Union Water Framework Directive (WFD). The good quality of a water body and the apparent health of a species, whether or not an ecosystem engineer such as P. oceanica, is not always indicative of the good structure and functioning of the whole ecosystem. A key point of the recent Marine Strategy Framework Directive (MSFD) is the ecosystem-based approach. Here, on the basis of a simplified conceptual model of the P. oceanica ecosystem, we have proposed an ecosystem-based index of the quality of its functioning, compliant with the MSFD requirements. This index (EBQI) is based upon a set of representative functional compartments, the weighting of these compartments and the assessment of the quality of each compartment by comparison of a supposed baseline. The index well discriminated 17 sites in the north-western Mediterranean (French Riviera, Provence, Corsica, Catalonia and Balearic Islands) covering a wide range of human pressure levels. The strong points of the EBQI are that it is easy to implement, non-destructive, relatively robust, according to the selection of the compartments and to their weighting, and associated with confidence indices that indicate possible weakness and biases and therefore the need for further field data acquisition.

Phytoplankton is a key component in marine ecosystems. It is responsible for most of the marine primary production, particularly in eutrophic lagoons, where it frequently blooms. Because they are very sensitive to their environment, the dynamics of these microbial communities has to be observed over different time scales, however, assessment of short term variability is often out of reach of traditional monitoring methods. To overcome these limitations, we set up a Cytosense automated flow cytometer (Cytobuoy b.v.), designed for high frequency monitoring of phytoplankton composition, abundance, cell size, and pigment content, in one of the largest Mediterranean lagoons, the Berre lagoon (South-Eastern France). During October 2011, it recorded the cell optical properties of 12 groups of pico-, nano-, and microphytoplankton. Daily variations in the cluster optical properties were consistent with individual changes observed using microscopic imaging, during the cell cycle. We therefore used an adaptation of the size-structured matrix population model, developed by Sosik et al. (2003) to process the single cell analysis of the clusters and estimate the division rates of 2 dinoflagellate populations before, during, and after a strong wind event. The increase in the estimated in situ daily cluster growth rates suggest that physiological changes in the cells can prevail over the response of abundance.

Biotic indices, which reflect the quality of the environment, are widely used in the marine realm. Sometimes, key species or ecosystem engineers are selected for this purpose. This is the case of the Mediterranean seagrass Posidonia oceanica, widely used as a biological quality element in the context of the European Union Water Framework Directive (WFD). The good quality of a water body and the apparent health of a species, whether or not an ecosystem engineer such as P. oceanica, is not always indicative of the good structure and functioning of the whole ecosystem. A key point of the recent Marine Strategy Framework Directive (MSFD) is the ecosystem-based approach. Here, on the basis of a simplified conceptual model of the P. oceanica ecosystem, we have proposed an ecosystem-based index of the quality of its functioning, compliant with the MSFD requirements. This index (EBQI) is based upon a set of representative functional compartments, the weighting of these compartments and the assessment of the quality of each compartment by comparison of a supposed baseline. The index well discriminated 17 sites in the north-western Mediterranean (French Riviera, Provence, Corsica, Catalonia and Balearic Islands) covering a wide range of human pressure levels. The strong points of the EBQI are that it is easy to implement, non-destructive, relatively robust, according to the selection of the compartments and to their weighting, and associated with confidence indices that indicate possible weakness and biases and therefore the need for further field data acquisition.

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