Paradigm misplaced? Antarctic marine ecosystems are affected by climate change as well as biological processes and harvesting

Abstract

A recent review by Ainley et al. has suggested that recent investigations of the ecological structure and processes of the Southern Ocean have "almost exclusively taken a bottom-up, forcing-by-physicalprocesses approach relating individual species' population trends to climate change". We examine this suggestion and conclude that, in fact, there has been considerable research effort into ecosystem interactions over the last 25 years, particularly through research associated with management of the living resources of the Southern Ocean. Future Southern Ocean research will make progress only when integrated studies are planned around well structured hypotheses that incorporate both the physical and biological drivers of ecosystem processes.

Effects of Whaling on the Structure of the Southern Ocean Food Web: Insights on the “Krill Surplus” from Ecosystem Modelling

“…This is particularly true for small pelagics, cephalopods and most planktonic groups, and less so for large air-breathing predators. While the massive depletion of rorquals [1], [4], [38], the current recovery of Antarctic fur seals [40] and humpback whales [1], as well as recently observed changes in seabird numbers [21], [22], can be approached with some confidence, the existing field data on the “krill surplus” is incomplete and often contradictory [4], [5], [14], [15]. For this reason, ecosystem modelling is one of the few available tools that can shed light on these poorly known events in the historical ecology of the Southern Ocean.…”

“…This was due partly to an increasing emphasis on physical factors and climate change in Antarctic science [4], [13], and partly to a growing recognition that while both top-down and bottom-up factors were most likely involved, currently available data on trends in the abundances of the species concerned may not be reliable enough to conclusively determine the validity of this hypothesis [4], [5], [14], [15]. Several studies [16], [17] also pointed to a lack of consistency between species and regions in the purportedly increasing biomass trends for krill-eating pinnipeds, penguins and flying seabirds, which had been usually cited as evidence of a “krill surplus.” Fraser et al [17] have also noted the importance of intraspecific, as opposed to interspecific, competition in seabirds, including penguins.…”

Effects of climate change and fisheries bycatch on Southern Ocean seabirds: a review

“…These physical changes may have had profound effects on several components of the Southern Ocean ecosystems and across a range of trophic levels (Forcada et al 2006, Nicol et al 2007). For example, in the southern Atlantic Ocean, long-term surveys suggest a 38 to 81% decline in krill stocks since the mid-1970s (Atkinson et al 2004).…”

“…Although the relative importance of bottom-up or top-down processes on the effect of fish and whale harvesting on Southern Ocean top predators such as seabirds are highly debated (Ainley et al 2007, Nicol et al 2007, Ainley & Blight 2008, Barbraud & Cotté 2008, Ainley et al 2010b, it is at present difficult to quantify the effects of either process given the lack of long-term data that incorporate both physical and biological drivers of ecosystem processes. Better documented are the direct interactions between seabirds and fisheries, and more particularly bycatch, which may have been implicated in population declines of several species of seabirds in the Southern Ocean (e.g.…”

Antarctic Futures

“…In 2007, CCAMLR tasked SC-CAMLR with addressing climate change in the context of conserving Antarctic marine living resources (CCAMLR 2007;Nicol et al 2007;Trathan and Agnew 2010). In 2007, CCAMLR tasked SC-CAMLR with addressing climate change in the context of conserving Antarctic marine living resources (CCAMLR 2007;Nicol et al 2007;Trathan and Agnew 2010).…”