Comparison of the biophysical and trophic characteristics of the Bering and Barents Seas

Journal of Marine Systems 109–110 (2013) 22–42 Contents lists available at SciVerse ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys Comparison of the structure and function of Southern Ocean regional ecosystems: The Antarctic Peninsula and South Georgia E.J. Murphy a, ⁎ , E.E. Hofmann b , J.L. Watkins a , N.M. Johnston a , A. Pinones b , T. Ballerini b , S.L. Hill a , P.N. Trathan a , G.A. Tarling a , R.A. Cavanagh a , E.F. Young a , S.E. Thorpe a , P. Fretwell a a b British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK Center for Coastal and Physical Oceanography, Old Dominion University, Norfolk, Virginia, USA a r t i c l e i n f o Article history: Received 12 September 2011 Received in revised form 26 March 2012 Accepted 28 March 2012 Available online 5 April 2012 Keywords: Ecosystem comparison Southern Ocean South Georgia Antarctic Peninsula Model Food web, climate change Krill a b s t r a c t The ocean ecosystems around the west Antarctic Peninsula and South Georgia are two of the best described regional ecosystems of the Southern Ocean. They therefore provide a useful basis for developing comparative analyses of ocean ecosystems around the Antarctic. There are clear and expected differences in seasonality and species composition between the two ecosystems, but these mask an underlying similarity in ecosystem structure and function. This similarity results from the two ecosystems being part of a continuum, from more ice covered regions in the south to open water regions in the north. Within this continuum the major factors affecting ecosystem structure and function are the sea ice, the biogeochemical conditions and the connectivity generated by the ﬂow of the Antarctic Circumpolar Current. Antarctic krill are central to the food web in both ecosystems, but the other species of plankton and predators present are different. These different species provide alternative pathways of energy transfer from primary production to the highest trophic levels. The relative dominance of these species can provide indicators of change in ecosystem structure and function. Both ecosystems are changing as a result of physically and biologically driven processes, and the ecological responses being observed are complex and variable across different species and within the two regions. Species in parts of the northern Antarctic Peninsula are being replaced by species that currently dominate farther north in more oceanic areas such as at South Georgia. The similarity of structure and strong connectivity, mean that projections of future change will require generic models of these ecosystems that can encompass changes in structure and function within a connected continuum from ice covered to open water in winter. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Southern Ocean ecosystems are changing as a result of some of the most rapid regional warming that has been observed anywhere on the planet and further major physical and chemical changes are expected to occur in the coming decades (Costa et al., 2010; Meredith and King, 2005; Montes-Hugo et al., 2009; Schoﬁeld et al., 2010; Trivelpiece et al., 2011; Vaughan et al., 2003). These ecosystems are also of global importance in biogeochemical cycles, in contributing to food security through major ﬁsheries and in maintaining unique biological diversity. Changes in their structure and function will, therefore, have consequences for human society, which makes the development of the basis for predicting the responses of these ecosystems to change an urgent requirement (Murphy et al., 2008). Understanding the factors that generate differences in ecosystems that exist in different regions of the circumpolar Southern Ocean is crucial ⁎ Corresponding author. E-mail address: e.murphy@bas.ac.uk (E.J. Murphy). 0924-7963/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2012.03.011 for the development of models that provide useful projections of ecosystem level responses to the changes in physical processes (affecting ocean temperatures, circulation patterns and sea ice), chemical processes (affecting nutrients, carbon dioxide concentrations and pH) and direct human impacts (ﬁsheries and tourism), which are expected to occur in the coming decades (Murphy et al., 2008; Trathan and Agnew, 2010; Trivelpiece et al., 2011; Turner et al., 2009). Recent development of a strategic basis for generating the models required to produce such predictions has emphasised the requirement for a range of ocean-scale models of Southern Ocean ecosystems (Murphy et al., in press). Generating these models, with the appropriate space and time scales and processes, requires knowledge of the controls on the structure and function of Southern Ocean ecosystems at regional scales. This in turn requires development of comparative views of how properties of ecosystems can be characterised so that differences or changes can be distinguished (Megrey et al., 2009b; Murawski et al., 2009; Sydeman and Bograd, 2009). The western Antarctic Peninsula (wAP) and the northern Scotia Sea around South Georgia (Figs. 1 and 2; Ducklow et al., 2007; Murphy et al., 2007b; Hofmann et al., 2011) are the most studied regions of the