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Setting the record straight on drivers of changing ecosystem states


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This short communication is a response to the critique by Greene (2012), who puts forward the argument that the dynamics of northwest Atlantic continental shelf ecosystems are strongly influenced by changes in Arctic climate, as indexed by surface salinity. The argument, in its essence, discounts any indirect effects from over-exploitation of top predators on lower trophic levels in northwest Atlantic ecosystems. Frank et al. (Science 308, 2005, 1621; Nature 477, 2011, 86) reported the existence of cascading trophic interactions with particular emphasis on the eastern Scotian Shelf. Greene argues that the events occurring in the Gulf of Maine/Georges Bank region are representative of all Northwest Atlantic shelf systems, despite previous research (Frank et al. Trends Ecol. Evol. 22, 2007, 236; Petrie et al. Fish. Oceanogr. 18, 2009, 83) that has shown a differential pattern of forcing ranging from top-down in species-poor, cold water systems to bottom-up in warmer, more species-rich systems, including Georges Bank.