Zooplankton plays a pivotal role in marine ecosystems and the characterisation of its biodiversity still represents a challenge for marine ecologists. In this study, mesozooplankton composition from 46 samples collected in summer along the western Adriatic Sea, was retrieved by DNA metabarcoding analysis. For the first time, the highly variable fragments of the mtDNA COI and the V9 region of 18S rRNA genes were used in a combined matrix to compile an inventory of mesozooplankton at basin scale. The number of sequences retrieved after quality filtering were 824,148 and 223,273 for COI and 18S (V9), respectively. The taxonomical assignment against reference sequences, using 95% (for COI) and 97% (for 18S) similarity thresholds, recovered 234 taxa. NMDS plots and cluster analysis divided coastal from offshore samples and the most representative species of these clusters were distributed according to the dominant surface current pattern of the Adriatic for the summer period. For selected sampling sites, mesozooplankton species were also identified under a stereo microscope providing insights on the strength and weakness of the two approaches. In addition, DNA metabarcoding was shown to be helpful for the monitoring of non-indigenous marine metazoans and spawning areas of commercial fish species. We defined pros and cons of applying this approach at basin scale and the benefits of combining the datasets from two genetic markers.

Ontogenetic variation in the diet of Engraulis encrasicolus (L.) was examined in the northern Adriatic Sea, off the River Po delta, by stomach contents analysis. Anchovy (10 to 130 mm total length) were collected during a 1 wk cruise in October 2002. Feeding activity was mainly diurnal in all the length classes: stomach fullness, calculated for each 10 mm size class, was always higher during the day than at night, with maximal values measured for the 40 to 49 and 50 to 59 mm size classes. All analysed life stages of E. encrasicolus had a strictly zooplanktivorous diet based on a few species of copepods. The principal prey of E. encrasicolus were small-sized copepods, measuring about 0.2 to 0.3 or 0.5 to 0.6 mm in prosoma length. The copepods Euterpina acutifrons and Oncaea spp. dominated anchovy diet during the day, both in terms of frequency, number and biomass, in all anchovy size classes. During the night, bivalve larvae were also important dietary items, with Oncaea spp. and E. acutifrons making up > 69% of total prey number for all anchovy size classes. Within the considered size range, the dimensions of particles does not seem to be a limiting factor in food selection, and no relationship was found between anchovy length and the maximal dimension of ingested prey. Ivlev's electivity index confirmed that European anchovy was able to select specific food items and preferred small copepods such as E. acutifrons and Oncaea spp., and bivalve and decapod larvae. KEY WORDS: Anchovy · Late larvae · Stomach contents · Prey selection · ZooplanktonResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 392: 193-209, 2009 Several studies on Engraulis species have demonstrated that anchovy can feed by filtering or particulate feeding (O'Connell 1972, James 1987, James & Findlay 1989, van der Lingen 1994, Bulgakova 1996, van der Lingen et al. 2006, 2009. The ability to switch between these feeding modes makes anchovy highly opportunistic and flexible foragers, which are able to maximize their energy intake through employing the feeding mode most appropriate to a particular food environment. Given this ability, the diet of anchovy, which is generally comprised of mesozooplanktonic prey, may also include smaller particles such as phytoplanktonic cells (King & Macleod 1976, Mikhman & Tomanovich 1977, Bulgakova 1996. The feeding behaviour of anchovies and the resulting variability or breadth in their food intake make field and laboratory studies regarding selectivity the only means of predicting their diet in any particular ecosystem. Robert et al. (2008) recently pointed out the importance of carrying out field studies coupling fish gut contents analysis and prey availability assessment. In fact, the knowledge of prey availability is essential in order to understand the relative importance of food categories and to assess prey selectivity. Moreover, Robert et al. (2008) stressed the importance of obtaining high taxonomical resolution in the identification of prey in sel...

European anchovy Engraulis encrasicolus, with total lengths ranging from 40Á0 to 132Á5 mm, were sampled during October 2002 and May 2003 in the northern Adriatic Sea in order to estimate their energy densities (E D ). A highly significant (P < 0Á001) relationship between E D (y) (J g À1 wet mass) and per cent dry mass (x) was found: During the last few decades, interest in energy density (E D ) has increased with the growing use of bioenergetics models that link basic animal physiology and behaviour with environmental conditions and are used in studies on fish ecology and in fish management (Brandt & Hartman, 1993;Hartman & Brandt, 1995). Energy density is used to measure fish growth and food consumption. Energy density of prey items can also affect fish gastric evacuation rates (Andersen, 1999) and thus should be considered in the gastric evacuation models to obtain food consumption estimates. Fish E D may change with ontogeny (Arrhenius, 1998; Paul et al

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Anchovies represent the largest world’s marine fish catches and the current threats on their populations impose a sustainable exploitment based on sound scientific information. In the European anchovy (Engraulis encrasicolus), the existence of several populations has been proposed but a global view is missing. Using a multidisciplinary approach, here we assessed the divergence among different ecotypes and its possible causes. SNPs have revealed two functionally distinct ecotypes overlapping in the Central Mediterranean, with one ecotype confined near the river estuaries. The same SNPs outliers also segregated two distinct populations in the near Atlantic, despite their large spatial distance. In addition, while most studies suggested that adaptation to low salinity is key to divergence, here we show that the offshore ecotype has higher environmental tolerance and an opportunistic feeding behaviour, as assessed by the study of environmental conditions, anchovy diet and trophic levels, and passive egg dispersal. These results provide insights into the anchovy evolutionary history, stressing the importance of behaviour in shaping ecotypes.