DIET COMPOSITION OF THE PENAEID SHRIMP, MELICERTUS KERATHURUS (FORSKÅL, 1775) (DECAPODA, PENAEIDAE) IN THE AEGEAN SEA BY I. KARANI1,2), M.-S. KITSOS1),N.CHARTOSIA1) and A. KOUKOURAS1) 1) Department of Zoology, School of Biology, Aristoteleio University of Thessaloniki, GR-541 24 Thessaloniki, Greece ABSTRACT The diet composition of adult and juvenile individuals of the penaeid shrimp, Melicertus kerathurus was determined, based on the analysis of 145 and 48 specimens, respectively, collected off and inside Pinios estuary (N.W. Aegean Sea). The adult individuals displayed a diversified diet, mainly based on Mollusca, Crustacea, and Polychaeta. The diet of the juvenile individuals is also diverse, with Crustacea being the most dominant prey category. Feeding activity of the juvenile M. kerathurus, which are also active predators, seems to be higher than that of the adults. Multidimensional analyses demonstrated that the diets of the juvenile and adult individuals were significantly different. This should probably be attributed to corresponding differences in the composition of the benthic assemblages of the open sea (adult individuals) and inside Pinios estuary (juveniles), as well as to developmental differences between the adults and the juveniles that affect their feeding behaviour. RÉSUMÉ Le régime alimentaire des adultes et des juvéniles de la crevette pénéide Melicertus kerathurus a été établi à partir de 145 et 48 spécimens provenant, respectivement, du large et de l’intérieur de l’estuaire de Pinios (partie nord-ouest de la mer Egée). Les adultes ont montré un régime alimentaire diversifié, contenant principalement des mol- lusques, des crustacés et des polychètes. Le régime alimentaire des juvéniles est également diver- sifié, les crustacés étant la catégorie dominante de proies. L’activité de nutrition des juvéniles de M. kerathurus, qui sont aussi des prédateurs actifs, semble être plus élevée que celle des adultes. Des analyses multidimensionnelles ont démontré que les régimes alimentaires des individus juvéniles et adultes différaient signiflcativement. Elles pourraient être attribuées à des différences correspondantes dans la composition des assemblages benthiques de pleine mer (adultes) et dans l’estuaire de Pinios (juvéniles) ainsi qu’à des différences liées au développement entre stades juvéniles et adultes, qui influencent leur comportement de nutrition. 2) Corresponding author; e-mail through: [email protected] © Koninklijke Brill NV, Leiden, 2005 Crustaceana 78 (4): 385-396 Also available online: www.brill.nl 386 I. KARANI ET AL. INTRODUCTION The penaeid shrimp, Melicertus kerathurus (Forskål, 1775) is a characteristic species of sandy sediments in shallow marine and estuarine waters (Holthuis, 1987). This species has been reported from all Mediterranean areas, including the Aegean Sea, from depths of 0.5-90 m (Zariquey Alvarez, 1968; Števciˇ c,ˇ 1990; d’Udekem d’Acoz, 1996, 1999; Koukouras et al., 1992). Due to its commercial importance, M. kerathurus has been a target species for a number of studies (e.g., Klaoudatos, 1978, 1984; Rodriguez, 1981, 1986; Faranda et al., 1984), which were mainly focused on its growth, reproduction, migration, and physiology. In contrast, the existing information on the diet composition and feeding habits of M. kerathurus, in its various developmental stages, is limited and has been mainly given by Scalera Liaci et al. (1980, 1982), from the N.W. Ionian Sea, San Feliu et al. (1973) from the Ebro estuary (N. Iberian Peninsula), and Rodriguez (1987) from the gulf of Cadiz, while Lagardère (1971) has given some more general information from the coasts of Morocco. In respect of the Aegean Sea, no information was available on the diet of this species until now. The aim of this study is to give new information on the diet composition of adults and juveniles of Melicertus kerathurus in the Aegean Sea, and to compare these two diets. MATERIAL AND METHODS Adult specimens of Melicertus kerathurus were collected with hanging nets (mesh-size 20 mm) deployed at a single station in October 2002. The station was located off Pinios estuary (N.W. Aegean Sea) at a depth of 12 m (A; fig. 1). In the same period, juvenile specimens of this species were collected inside Pinios estuary at a depth of 0.5 m (B; fig. 1) with a specially designed, triangular dredge (mesh size’ 5 mm). All samplings were carried out during night time. In the laboratory, carapace length (posterior margin of the eye orbit to terminal border of the carapace), total length (tip of the rostrum to tip of the telson) and sex were determined for each specimen. The stomach content of each individual examined was washed through a 125 µm sieve. All prey items were identified to the lowest possible taxonomic level, and counted. To analyse the data that resulted from the stomach content analysis, the methods described by Hyslop (1980), Williams (1981), and Kelleher et al. (2000) were used, and the following indices were calculated: Frequency of occurrence (F ): F = n100/Ns Percentage of prey (N): N = n 100/Np.