Size fractions of mesozooplankton (Copepoda and Appendicularia) in relation to first feeding larvae of anchovy (Engraulis anchoita) during spring of 2004 at the frontal system of Peninsula Valdes (42-44ºS), Argentina

SPINELLI, M; MARCELO PáJARO; MARTOS P; ESNAL G. B. ; CAPITANIO, F

Pucon

Congreso; 5th International Zooplankton Production Symposium; 2011

A frontal tidal system occurs at the north Patagonian coastal area during spring-summer which maintains several commercial fishes such as anchovy (Engraulis anchoita). We investigated the spatial distribution in abundance of different size fractions of copepods and appendicularians in relation to the distribution of first feeding larvae in the different sectors of this front. Twelve samples of zooplankton and ichthyoplankton were collected with Mini- Bongo (67µm) and Pairovet (200µm) nets along two transects crossing the front; CTD profiles were also recorded. Stratified and homogeneous waters were distinguished taking into account the distribution of the Simpson stability Index. Total abundance was higher in homogeneous waters, mainly at the southern transect. Mesozooplankton was divided into three size categories. As a whole, we observed that the dominance of the smallest fraction of mesozooplankton (<500ìm) at coastal stations coincided with the highest larval abundance (max. 6,000ind. 10m-2), while the dominance of the largest fractions (500-1,000ìm and >1,000ìm) at outside stations coincided with the highest egg abundance (max. 50,000 eggs 10m-2). The largest calanoids (2,100µm), cyclopoids (1,700µm) and nauplii (600µm) were found at the outside stations but the largest appendicularians (1,500µm) were found at the coastal stations. The physical structure of this front seems to enhance food availability for first feeding larvae, with calanoid and cyclopoid copepods the main food items, followed by nauplii and appendicularians. The abundance of such mesozooplankton food is likely to be important for the survival and growth of fish larvae in this frontal system.commercial fishes such as anchovy (Engraulis anchoita). We investigated the spatial distribution in abundance of different size fractions of copepods and appendicularians in relation to the distribution of first feeding larvae in the different sectors of this front. Twelve samples of zooplankton and ichthyoplankton were collected with Mini- Bongo (67µm) and Pairovet (200µm) nets along two transects crossing the front; CTD profiles were also recorded. Stratified and homogeneous waters were distinguished taking into account the distribution of the Simpson stability Index. Total abundance was higher in homogeneous waters, mainly at the southern transect. Mesozooplankton was divided into three size categories. As a whole, we observed that the dominance of the smallest fraction of mesozooplankton (<500ìm) at coastal stations coincided with the highest larval abundance (max. 6,000ind. 10m-2), while the dominance of the largest fractions (500-1,000ìm and >1,000ìm) at outside stations coincided with the highest egg abundance (max. 50,000 eggs 10m-2). The largest calanoids (2,100µm), cyclopoids (1,700µm) and nauplii (600µm) were found at the outside stations but the largest appendicularians (1,500µm) were found at the coastal stations. The physical structure of this front seems to enhance food availability for first feeding larvae, with calanoid and cyclopoid copepods the main food items, followed by nauplii and appendicularians. The abundance of such mesozooplankton food is likely to be important for the survival and growth of fish larvae in this frontal system.