The functioning of the planktonic food web in a sub-polar marine ecosystem during spring-summer.

MARIELA SPINELLI; FABIANA CAPITANIO; ANDREA MALITS; VIRGINIA GARCÍA ALONSO

Simposio; CES/PICES 6th Zooplankton Production Symposium "New Challenges in a Changing Ocean"; 2016

Austral Patagonian waters in the South Western Atlantic Ocean are considered a very productive marine system where Atlantic, Pacific and Antarctic fauna can coexist. Within these waters, a submerged plateau which forms the westernmost segment of the North Scotia Ridge has recently been declared the Marine Protected Area Namuncurá-Burdwood Bank (MPA N-BB, 53°40´-55°S; 62°-58°40´W).The MPA N-BB is divided in nucleus, attenuation and transition zones with a minimum depth of 50 m and delimited by the 150 m isobath. South of the MPA N-BB the bathymetry falls abruptly until meeting the Yaghan abyssal plain at >3000 m depth. The bank supports numerous top predators and is a nursery area of commercial fishes. Within the governmental project Pampa Azul (MINCYT, Argentina), we investigated the spring-summer functioning of the planktonic food web from microorganisms to larvae of fishes during cruises performed in 2014 and 2015 years. As key drivers of the biological pump, zooplankton feed on autotrophic and heterotrophic organisms being the subject to either bottom-up and top-down controls. The spratt Sprattus fueguensis, a remarkable small pelagic fish in the MPA N-BB, feeds on zooplankton organisms throughout its life cycle. In order to understand the dominant control mechanism at the three zones of Burdwood bank, data about the spatial variability of plankton abundance (eg. calanoid and cyclopoid copepods, appendicularians, euphausiids, amphipods) and their size composition is provided suggesting the presence of a gradient along the bank between west- eutrophic to east- oligotrophic conditions probably related to oceanographic patterns.