Interranual variability in horizontal patterns of larval fish assemblages in the northeastern Aegean Sea (eastern Mediterranean) during early summer Stamatina Isari a, * , Nina Fragopoulu a , Stylianos Somarakis b a Laboratory of Zoology, Department of Biology, University of Patras, 26500 Rio, Patras, Greece b Hellenic Centre for Marine Research, PO Box 2214, 71003 Heraklion, Crete, Greece article info Article history: Received 28 March 2008 Accepted 2 June 2008 Available online 7 June 2008 Keywords: fish larvae ichthyoplankton horizontal distribution community composition continental shelves eastern Mediterranean Greece northeastern Aegean Sea abstract Larval fish community structure was studied in the northeastern Aegean Sea (NEA) over an area influ- enced by the advection of Black Sea water (BSW). Sampling was carried out in early summer during a period of 4 years (2003–2006). Taxonomic composition and abundance presented high variability in space that remained relatively constant among years. Tow depth and indicators of trophic conditions in the upper water column (i.e., zooplankton displacement volume, fluorescence) explained significantly the structure of larval assemblages during all surveys. The northern continental shelf (Thracian and Strymonikos shelf), where a large amount of enriched, low salinity BSW is retained, was dominated by larvae of epipelagic species, mainly anchovy (Engraulis encrasicolus). Interannual changes in horizontal extension of the BSW seemed to match closely observed changes in the distribution of anchovy larvae. Mesopelagic fish larvae were particularly abundant beyond the continental shelf (over the North Aegean Trough) where a strong frontal structure is created between the low salinity waters of BSW origin and the high salinity waters of the Aegean Sea. Larvae of certain mesopelagic species (e.g., Ceratoscopelus maderensis) may occasionally be transported inshore when the prevailing current meanders towards the coast or feeds anticyclonic gyres over the continental shelf. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Spatiotemporal patterns of ichthyoplankton communities, with respect to abundance, distribution and species composition, have been traditionally a basic topic of scientific research in fisheries oceanography (Govoni, 2005). Ichthyoplankton surveys provide useful data for the assessment of important parameters of commercially important fish populations (i.e. spawning stock biomass, recruitment), but can also improve our knowledge on the agents structuring larval assemblages. Looking beyond the single species level may facilitate our understanding on fundamental ecological and evolutionary aspects of fish faunas (Moser and Smith, 1993). A large number of biological and physical factors contribute to the formation, maintenance and disruption of larval fish assem- blages as has been pointed out for several coastal systems around the world’s oceans since the early 90’s (e.g. Boehlert and Mundy, 1993; Doyle et al., 1993). The biotic and abiotic environment controls the mesoscale distribution patterns of fish larvae either indirectly, by affecting the timing and location of adult egg pro- duction, or, directly, by influencing larval advection, mortality and behavior (Moser et al., 1993). Regarding the Mediterranean waters, research on the structure of larval fish communities has been progressively developed in the last two decades. A large amount of information has been published concerning the western part of the Mediterranean Sea (Catalan Sea, Balearic Archipelago), which has recently been reviewed by Sabate ´ s et al. (2007a). Latitudinal and vertical distributions of fish larvae in relation to short-term me- soscale variability have also been examined in the western Alboran Sea (Vargas-Ya ´ nez and Sabate ´s, 2007). In the central and eastern Mediterranean information on ichthyoplankton assemblage struc- ture and distribution is scant (straits of Sicily: Cuttitta et al., 2004; northern Aegean Sea: Somarakis et al., 2000, 2002). The present study was directed towards an improvement of our understanding of the factors that determine distribution patterns of fish larvae in the northeastern Aegean Sea (NEA). NEA is a topo- graphically and hydrologically complex Sea, consisting of a set of three relatively broad continental shelf areas (Thracian shelf, Stry- monikos shelf and Lemnos plateau) separated by the deep North Aegean Trough (Fig. 1). Enriched, low salinity Black Sea water (BSW) enters into the NEA and largely affects water column structure and circulation in the region (Zervakis and Georgopoulos, 2002; Isari et al., 2006). NEA is characterized by relatively high levels of pro- ductivity (e.g., Siokou-Frangou et al., 2002; Isari et al., 2006, 2007), abundant fish stocks (especially small pelagic species) (Stergiou * Corresponding author. E-mail address: misari@upatras.gr (S. Isari). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2008.06.001 Estuarine, Coastal and Shelf Science 79 (2008) 607–619