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Aubert, A., Antajan, E., Lynam, C., Pitois, S., Pliru, A., Vaz, S., et al. (2018). No more reason for ignoring gelatinous zooplankton in ecosystem assessment and marine management: Concrete cost-effective methodology during routine fishery trawl surveys. Mar. Pol., 89, 100–108.
Résumé: Gelatinous zooplankton, including cnidarians, ctenophores, and tunicates (appendicularians, pyrosomes, salps and doliolids), are often overlooked by scientific studies, ecosystem assessments and at a management level. Despite the important economic consequences that they can have on human activities and on the marine food web, arguments often related to the costs of monitoring or their coordination, or simply negligence, have resulted in the absence of relevant monitoring programs. A cost-effective protocol has been applied on trawling from existing fishery surveys conducted by national laboratories in England and France. The testing phase has successfully demonstrated the adequacy of such a tool to sample macro- and mega-zooplankton gelatinous organisms in a cost-effective way. This success has led to the acceptance of this protocol into the French implementation of the EU's Marine Strategy Framework Directive (MSFD). Here, a protocol which can be applied to any trawl-based fishery survey and in any new large-scale monitoring program is provided. As an ecosystem approach to marine management is currently adopted, exemplified by the MSFD in Europe, gelatinous zoo plankton should be monitored correctly to prevent a knowledge gap and bias to ecosystem assessments in future.
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Bachiller, E., Albo-Puigserver, M., Gimenez, J., Grazia Pennino, M., Mari-Mena, N., Esteban, A., et al. (2020). A trophic latitudinal gradient revealed in anchovy and sardine from the Western Mediterranean Sea using a multi-proxy approach. Sci Rep, 10(1), 17598.
Résumé: This work combines state-of-the-art methods (DNA metabarcoding) with classic approaches (visual stomach content characterization and stable isotope analyses of nitrogen (delta N-15) and carbon (delta C-13)) to investigate the trophic ecology of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) at high taxonomic and spatial resolution in the Western Mediterranean Sea. Gut contents observed are in accordance with the dietary plasticity generally described for anchovy and sardine, suggesting a diet related to the opportunistic ingestion of available prey in a certain area and/or time. Genetic tools also showed modest inter-specific differences regarding ingested species. However, inter-specific and intra-specific differences in ingested prey frequencies and prey biomass reflected a latitudinal signal that could indicate a more effective predation on large prey like krill by anchovy versus sardine, as well as a generalized higher large prey ingestion by both species southwards. In fact, both species presented lower delta N-15 in the northernmost area. This latitudinal gradient indicates changes in the trophic ecology of anchovy and sardine that coincide with previously described better biological conditions for fish in the southern part of the study area as well as higher landings of both species in recent years.
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Brosset, P., Le Bourg, B., Costalago, D., Banaru, D., Van Beveren, E., Bourdeix, J. - H., et al. (2016). Linking small pelagic dietary shifts with ecosystem changes in the Gulf of Lions. Mar. Ecol.-Prog. Ser., 554, 157–171.
Résumé: Since 2008, a severe decrease in size and body condition together with a demographic truncation has been observed in the sardine (secondarily in anchovy) population of the Gulf of Lions (NW Mediterranean Sea). In parallel, sprat biomass, which was negligible before, has increased tenfold. All of these changes have strongly affected the regional fisheries. Using trophic and isotopic data from contrasting periods of low versus high growth and condition, we investigated potential changes in diet and interspecific feeding interactions through time. Evidence of resource partitioning was found between sprat and both anchovy and sardine in 2004 and 2005. Since 2010, the isotopic niches of the 3 species have tended to overlap, suggesting higher risk of competition for food resources. Moreover, the wider trophic niche of sprat indicates higher variability in individual diets. Anchovy and sardine diet varied through time, with a high proportion of large copepods or cladocerans in periods of high growth and condition (1994 and 2007, respectively) versus a dominance of small copepods in the present (2011-2012). Furthermore, an important reduction in prey diversity was also identified in the diet of both anchovy and sardine during the most recent period. Our results support the hypothesis that changes in small pelagic fish growth, size and body condition and ultimately biomass could be due to bottom-up control characterized by changes in food availability and increasing potential trophic competition.
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CORMON, X., LOOTS, C., VAZ, S., VERMARD, Y., & MARCHAL, P. (2014). Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) in the North Sea. Ices Journal Of Marine Science, 71(6), 1342–1355.
Résumé: Spatial interactions between saithe (Pollachius virens) and hake (Merluccius merluccius) were investigated in the North Sea. Saithe is a well-established species in the North Sea, while occurrence of the less common hake has recently increased in the area. Spatial dynamics of these two species and their potential spatial interactions were explored using binomial generalized linear models (GLM) applied to the International Bottom Trawl Survey (IBTS) data from 1991 to 2012. Models included different types of variables: (i) abiotic variables including sediment types, temperature, and bathymetry; (ii) biotic variables including potential competitors and potential preys presence; and (iii) spatial variables. The models were reduced and used to predict and map probable habitats of saithe, hake but also, for the first time in the North Sea, the distribution of the spatial overlap between these two species. Changes in distribution patterns of these two species and of their overlap were also investigated by comparing species' presence and overlap probabilities predicted over an early (1991–1996) and a late period (2007–2012). The results show an increase in the probability over time of the overlap between saithe and hake along with an expansion towards the southwest and Scottish waters. These shifts follow trends observed in temperature data and might be indirectly induced by climate changes. Saithe, hake, and their overlap are positively influenced by potential preys and/or competitors, which confirms spatial co-occurrence of the species concerned and leads to the questions of predator–prey relationships and competition. Finally, the present study provides robust predictions concerning the spatial distribution of saithe, hake, and of their overlap in the North Sea, which may be of interest for fishery managers.
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Elleouet, J., Albouy, C., Ben Rais Lasram, F., Mouillot, D., & Leprieur, F. (2014). A trait-based approach for assessing and mapping niche overlap between native and exotic species: the Mediterranean coastal fish fauna as a case study. Diversity and Distributions, 20(11), 1333–1344.
Résumé: Aim We propose a trait-based approach for assessing and mapping potential niche overlap between native and exotic species at large spatial scales. Location The Mediterranean Sea. Methods We developed two complementary indices based on ecological, biological and ecomorphological similarities between native and exotic species. The first index (FNNr) allows identifying areas where native species are the most at risk in terms of potential ecological interactions with exotic species. The second index (FGO) is species-specific and allows identifying native species that display the broadest functional niche overlap and range overlap with exotic species. We illustrated our approach using the Mediterranean coastal fish fauna as a case study. Results We found that endemic and exotic fishes had a similar global functional niche at the Mediterranean scale, that is, they filled the same functional space defined by trait axes. FNNr hotspots were found to be moderately congruent with exotic species richness hotspots. Higher values of FNNr were observed along the coasts of the Levantine Sea. The computation of the FGO index showed that the geographical range of a given endemic species overlapped in average with 52 exotic species. Species showing the highest FGO values displayed localized and/or fragmented distributions in the eastern Mediterranean basin. Main conclusions Our findings suggest that the number of exotic species alone cannot be used as a broad-scale indicator of potential impact because this metric does not account for functional relatedness between native and exotic species. The trait-based indices developed in this study can be used for other taxa in both aquatic and terrestrial ecosystems and should help environmental managers to set up local-scale studies on areas where the potential impact of exotic species on native biodiversity is the highest.
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