Submesoscale distribution of Antarctic krill and its avian and pinniped predators before and after a near gale
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ORIGINAL PAPER
Submesoscale distribution of Antarctic krill and its avian and pinniped predators before and after a near gale Joseph D. Warren · Jarrod A. Santora · David A. Demer
Received: 3 December 2007 / Accepted: 25 November 2008 / Published online: 16 December 2008 © Springer-Verlag 2008
Abstract We conducted two ship-based surveys of the nearshore ecosystem north of Livingston Island, Antarctica during 2–10 February 2005. Between the two surveys, a low-pressure system (963 mbar) passed through the area providing the opportunity to measure ecosystem parameters before and after a near gale. A ship-based multiplefrequency acoustic-backscatter survey was used to assess the distribution and relative abundance of Antarctic krill (Euphausia superba). Net tows, hydrographic proWles, and meteorological data were collected to measure biological and physical processes that might aVect the krill population. During the survey, the distribution and behavior of several krill predators [chinstrap penguins (Pygoscelis antarctica), cape petrels (Daption capense), and Antarctic fur seals (Arctocephalus gazella)] were measured from the vessel by visual observations. The survey encompassed an area of roughly 2,500 km2, containing two submarine canyons with one to the west and one to the east of Cape ShirreV, which had diVerent abundances of krill and predators. Several aspects of the nearshore ecosystem changed after the near gale including: hydrography of the upper 100 m of the
Communicated by U. Sommer. J. D. Warren (&) School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11974, USA e-mail: [email protected] J. A. Santora Biology Department, College of Staten Island, City University of New York, Staten Island, NY 10314, USA D. A. Demer Southwest Fisheries Science Center, 8604 La Jolla Shores Dr, La Jolla, CA 92037, USA
water column, phytoplankton biomass, the abundance and distribution of krill, and the distribution of some krill predators. DiVerences in these parameters were also measured between the two canyons. These changes in the physical and biological environment during the survey period are quantiWed and show that the ecosystem exhibited signiWcant changes over relatively short spatial (tens of kilometers) and time (tens of hours) scales.
Introduction The Scotia Sea is a highly productive area of the Southern Ocean where Antarctic krill (Euphausia superba) serves as a key prey species for many animals (Marr 1962; Siegel 2000; Croxall et al. 2002). Measuring the abundance and distribution of the krill population is important for ecological studies and the management of the commercial krill Wshery (Agnew 1997; Jones and Ramm 2004). In conjunction with krill surveys, visual surveys can be used to study predator–prey relationships by measuring the abundance and distribution of important krill predators including penguins, petrels, other sea birds, fur seals, and other marine mammals (Santora et al. 2008; Veit 1999). If abundance measurements of krill and its predators are made over
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