which increased the taxonomic assignment success from 23.7 to 50.5 %. When the communities were studied along with environmental variables, similar spatial and temporal trends of taxonomic diversity were observed for metabarcoding and microscopic studies of zooplankton, but not for phytoplankton. This is most likely attributable to the lack of representative sequences for phytoplankton species in current databases. In addition, there was high correspondence in community composition when comparing abundances estimated from metabarcoding and microscopy, suggesting semiquantitative potential for metabarcoding. Furthermore, metabarcoding allowed the detection and identification of two non-indigenous species (NIS) found in the study area at abundances hardly detectable by microscopy. Overall, our results indicate that metabarcoding is a powerful approach with excellent possibilities for use in plankton monitoring, early detection of NIS and plankton biodiversity shifts.

Morote, E., Olivar, M. P., Villate, F., and Uriarte, I. 2010. A comparison of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) larvae feeding in the Northwest Mediterranean: influence of prey availability and ontogeny. – ICES Journal of Marine Science, 67: 897–908. The feeding ecology of the larvae of the two most important small pelagic species in the western Mediterranean, anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus), is investigated. Samples were collected in early summer (anchovy) and autumn (sardine). Composition of the diet and prey selectivity were compared over the course of ontogeny in anchovy (2.7–14.5 mm standard length, SL) and sardine (5.5–15.8 mm SL) larvae. Anchovy larvae begin feeding on prey items >150 µm at smaller sizes than sardine larvae, and the diets of both species are based mainly on copepod nauplii and postnauplii. Seasonal differences in the composition of the plankton influenced the contributions of prey types to the diets of the two species, e.g. the cladoceran Evadne spp. in anchovy and the tintinnid Codonellopsis sp. in sardine. Although copepod eggs are generally present in the diets of larval clupeoids, they were not major components of the diets of the species considered here. Despite morphological similarity, selection patterns were different between the species and changed through ontogeny.

In the northwestern Mediterranean, most fish species reproduce in early summer and fewer in the autumn mixing period. This study analyses and compares larval fish assemblages (LFA) in both seasons, and is the first attempt to characterize LFA structure for the autumn period. We analyze horizontal and vertical distribution of fish larvae and the micro‐ and mesozooplankton biomass and abundance of the main zooplankton groups. The oceanographic situation was analyzed through the study of data from CTD, Nν‐Shuttle and ADCP surveys. LFA were determined by ordination analyses based on larval abundance, and the relationships between larval assemblages and environmental variables were investigated through canonical correspondence analysis. The importance of some hydrographic variables (temperature, salinity and stability of the water column), current fields (along‐shelf and across‐shelf transport) and the abundance of zooplankton are discussed as important factors shaping the structure of larval assemblages. In early summer, LFA were mainly structured by a combination of bathymetry and trophic components, although sea surface temperature also played a role in shaping the horizontal larval distributions. In autumn, trophic variables were the main factors influencing the shelf‐dwelling species assemblage. Larvae of oceanic species, on the other hand, were not related to trophic variables but were more affected by current fields.

The bullet tuna Auxis rochei, Risso 1810, is a small tuna widely distributed in tropical and temperate Seas. The present study reports on the first attempt to jointly monitor diet and food selection in larvae of this species and to assess the influence of the ontogenetic development of feeding-related organs on the diet. A. rochei larvae from 2 to 7 mm long are diurnal feeders and highly active predators, with high values of feeding incidence, gut fullness and number of ingested prey items. The rate of change in prey item size in relation to larval size was higher than in other species. Only small, non-motile prey items are eaten at the onset of feeding. Rapid mouth development and the early appearance of teeth allow larvae from 3 to 5 mm long to ingest a wide range of prey. However, niche breadth decreases at 5 mm, when larvae avoid small prey items in favour of larger ones with a higher carbon content. Chesson's selectivity index indicated that small larvae (from 2 to 3 mm long) selected a variety of small prey items, mainly copepod nauplii. Larvae measuring 3 to 5 mm selectively ate cladocerans and appendicularians, and larvae with lengths ≥5 mm preferred appendicularians and fish larvae. Precocious body development (mouth, teeth, and onset of stomach and caudal fin development) and improved visual acuity (larger lens diameter and angular cone density) are factors that contribute to the feeding success of larvae of this species.

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