Food-web traits of the North Aegean Sea ecosystem (Eastern Mediterranean) and comparison with other Mediterranean ecosystems K. Tsagarakis a, b, * , M. Coll c, d , M. Giannoulaki a , S. Somarakis a , C. Papaconstantinou a , A. Machias a a Hellenic Center for Marine Research, Former American Base, Gournes, 71003 Heraklion, Greece b Department of Biology, University of Crete, P.O. Box 2208, 71409 Heraklion, Greece c Institut de Ciències del Mar (ICM-CSIC), Passeig Marítim de la Barcelonesa, 37e49, Barcelona 08003, Spain d Dalhousie University, Biology Department, 1355 Oxford Street, Halifax, B3H 4J1, Canada article info Article history: Received 2 December 2009 Accepted 9 April 2010 Available online 18 April 2010 Keywords: ecopath food-web model network analysis fisheries pelagic environment ecosystem structure Greece Mediterranean Sea 40  0 0 e41  0 0 N, 23  8 0 e26  0 0 E abstract A mass-balance trophic model was built to describe the food-web traits of the North Aegean Sea (Strymonikos Gulf and Thracian Sea, Greece, Eastern Mediterranean) during the mid-2000s and to explore the impacts of fishing. This is the first food-web model representing the Aegean Sea, and results were presented and discussed in comparison to other previous ecosystems modelled from the western and the central areas of the basin (South Catalan and North-Central Adriatic Seas). Forty functional groups were defined, covering the entire trophic spectrum from lower to higher trophic levels. Emphasis was placed on commercial invertebrates and fish. The potential ecological role of the invasive ctenophore, Mnemiopsis leidyi, and several vulnerable groups (e.g., dolphins) was also explored. Results confirmed the spatial productivity patterns known for the Mediterranean Sea showing, for example, that the total biomass is highest in N.C. Adriatic and lowest in N. Aegean Sea. Accordingly, food-web flows and several ecosystem indicators like the mean transfer efficiency were influenced by these patterns. Nevertheless, all three systems shared some common features evidencing similarities of Mediterranean Sea ecosystems such as dominance of the pelagic fraction in terms of flows and strong benthicepelagic coupling of zooplankton and benthic invertebrates through detritus. The importance of detritus highlighted the role of the microbial food-web, which was indirectly considered through detritus dynamics. Ciliates, meso- zooplankton and several benthic invertebrate groups were shown as important elements of the ecosystem linking primary producers and detritus with higher trophic levels in the N. Aegean Sea. Adult anchovy was shown as the most important fish group in terms of production, consumption and overall effect on the rest of the ecological groups in the model, in line with results from the Western Mediterranean Sea. The five fishing fleets considered (both artisanal and industrial) had high impacts on vulnerable species and numerous targeted groups given the multispecies nature of the fisheries in the N. Aegean Sea. Several exploitation indices highlighted that the N. Aegean Sea ecosystem was highly exploited and unlikely to be sustainably fished, similarly to other Mediterranean marine ecosystems. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Mediterranean fisheries are multispecies and multi-gear in nature with numerous small-to-medium size boats. This creates difficulties in fisheries management which is still at an early stage of development in the whole basin (Papaconstantinou and Farrugio, 2000). Several fish stocks in the Mediterranean are reported to be fully- or overexploited (Lleonard and Maynou, 2003). The ecosystem is under a regime of rapid ecological degradation due to anthropogenic and climatic influence. Fishing (e.g., Jackson et al., 2001) and coastal eutrophication caused by human activi- ties such as aquaculture and sewage discharge (e.g., Cloern, 2001) among others, affect target and non-target marine species. More- over, biological invasions (in the Mediterranean several Lessepsian immigrants; e.g., Galil, 2000), favoured by climate change (Walther et al., 2002; Lejeusne et al., 2010), alter food-web structure. These should be taken into account within the framework of an integrated ecosystem-based fisheries management (Garcia et al., 2003). Ecosystem modelling integrates available information to study direct and indirect trophic interactions among ecosystem * Corresponding author. Hellenic Center for Marine Research, Former American Base, Gournes, 71003 Heraklion, Greece. E-mail addresses: kontsag@her.hcmr.gr (K. Tsagarakis), mcoll@icm.csic.es (M. Coll), marianna@her.hcmr.gr (M. Giannoulaki), somarak@her.hcmr.gr (S. Somarakis), pap@ath.hcmr.gr (C. Papaconstantinou), amachias@ath. hcmr.gr (A. Machias). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2010.04.007 Estuarine, Coastal and Shelf Science 88 (2010) 233e248