Posición trófica y fuentes de alimentación de larvas del stock bonaerense de Engraulis anchoita en el Océano Atlántico Sudoccidental

The existing literature has classified Engraulis anchoita larvae as exclusively zooplanktophagous, with copepod eggs and nauplii larvae as their main prey. However, there is evidence that other plankton components that have not been identified by intestinal content analysis may be a part of their diet. The objective of this work was to explore trophic positions and main food sources of E. anchoita larvae by analyzing stable nitrogen and carbon isotopes (δ15N and δ13C) with respect to other plankton components (particulate organic material, calanoid copepods, and chaetognaths) at a fixed sampling station close to the coast of the Province of Buenos Aires, Argentina, southwest Atlantic. Samples were collected at different times of the year between the end of 2016 and the beginning of 2018. By averaging δ15N and δ13C values of all surveys, it was found that the anchovy larvae in their three development stages coincided with the same trophic position as chaetognaths, suggesting that their diets overlap. When surveys carried out in autumn were analyzed separately, trophic levels of anchovy larvae differed in a staggered manner among their stages, being situated between the positions of copepods and chaetognaths. Compared to other stages of development, anchovy larvae in the preflexion stage consumed a higher proportion of particulate organic material rather than small copepods. These findings suggest that anchovy larvae may consume a variety of food items and shift their trophic position in response to environmental conditions.