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

FABIANA L. CAPITANIO; MARIELA L. SPINELLI; VIRGINIA GARCIA ALONSO; ANDREA MALITS

Bergen

Simposio; 6th ZOOPLANKTON PRODUCTION SYMPOSIUM; 2016

Austral Patagonian waters in the South Western Atlantic Ocean are considereda very productive marine system where Atlantic, Pacific and Antarctic fauna cancoexist. Within these waters, a submerged plateau which forms thewesternmost segment of the North Scotia Ridge has recently been declared theMarine 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 transitionzones with a minimum depth of 50 m and delimited by the 150 m isobath. Southof the MPA N-BB the bathymetry falls abruptly until meeting the Yaghan abyssalplain at >3000 m depth. The bank supports numerous top predators and is anursery area of commercial fishes. Within the governmental project Pampa Azul(MINCYT, Argentina), we investigated the spring-summer functioning of theplanktonic food web from microorganisms to larvae of fishes during cruisesperformed in 2014 and 2015 years. As key drivers of the biological pump,zooplankton feed on autotrophic and heterotrophic organisms being the subjectto either bottom-up and top-down controls. The spratt Sprattus fueguensis, aremarkable small pelagic fish in the MPA N-BB, feeds on zooplanktonorganisms throughout its life cycle. In order to understand the dominant controlmechanism at the three zones of Burdwood bank, data about the spatialvariability of plankton abundance (eg. calanoid and cyclopoid copepods,appendicularians, euphausiids, amphipods) and their size composition isprovided suggesting the presence of a gradient along the bank between westeutrophic to east- oligotrophic conditions probably related to oceanographicpatterns.