The Southern Ocean around Antarctica is among the most rapidly warming regions on Earth, but has experienced episodic climate change during the past 40 million years. It remains unclear how ancient periods of climate change have shaped Antarctic biodiversity. The origin of antifreeze glycoproteins (AFGPs) in Antarctic notothenioid fishes has become a classic example of how the evolution of a key innovation in response to climate change can drive adaptive radiation. By using a time-calibrated molecular phylogeny of notothenioids and reconstructed paleoclimate, we demonstrate that the origin of AFGP occurred between 42 and 22 Ma, which includes a period of global cooling approximately 35 Ma. However, the most species-rich lineages diversified and evolved significant ecological differences at least 10 million years after the origin of AFGPs, during a second cooling event in the Late Miocene (11.6-5.3 Ma). This pattern indicates that AFGP was not the sole trigger of the notothenioid adaptive radiation. Instead, the bulk of the species richness and ecological diversity originated during the Late Miocene and into the Early Pliocene, a time coincident with the origin of polar conditions and increased ice activity in the Southern Ocean. Our results challenge the current understanding of the evolution of Antarctic notothenioids suggesting that the ecological opportunity that underlies this adaptive radiation is not linked to a single trait, but rather to a combination of freeze avoidance offered by AFGPs and subsequent exploitation of new habitats and open niches created by increased glacial and ice sheet activity.Notothenioidei | Icefish | Percomorpha | molecular clock | buoyancy

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Distance, currents, deep water and sub-zero temperatures isolate the waters of the Antarctic continental shelf from other shelf areas in the Southern Hemisphere. The Antarctic shelf is an insular evolutionary site for a variety of marine organisms. The fish fauna is relatively small and unusual in composition, consisting of 213 species with higher taxonomic diversity restricted to 18 families. Ninety-six species of perciform notothenioids comprise 45% of the fish fauna. However in many areas of the shelf, including the highest latitudes, notothenioids make up 77% of the species and 90-95% of fish abundance and biomass. Notothenioids are morphologically and ecologically diverse and have diversified into niches in the water column. Antarctic notothenioids were evaluated using criteria employed for assessing freshwater species flocks. Although monophyly is in question, notothenioids exhibit the disproportionate speciosity (5·6-fold more Antarctic than non-Antarctic species) and high endemism (97%) characteristic of a species flock. Notothenioids are one of the first recognized examples of a species flock of marine fishes. Notothenioids are compared with some freshwater species flocks and calculations made of the time required for speciation (TFS) for notothenioids of the family Channichthyidae. Estimates of TFS are slower than for most lacustrine species flocks but similar to estimates for island radiations of birds and arthropods. 2000 The Fisheries Society of the British Isles

Investigations in recent years of the ecological structure and processes of the Southern Ocean have almost exclusively taken a bottom-up, forcing-by-physical-processes approach relating various species' population trends to climate change. Just 20 years ago, however, researchers focused on a broader set of hypotheses, in part formed around a paradigm positing interspecific interactions as central to structuring the ecosystem (forcing by biotic processes, top-down), and particularly on a "krill surplus" caused by the removal from the system of more than a million baleen whales. Since then, this latter idea has disappeared from favour with little debate. Moreover, it recently has been shown that concurrent with whaling there was a massive depletion of finfish in the Southern Ocean, a finding also ignored in deference to climaterelated explanations of ecosystem change. We present two examples from the literature, one involving gelatinous organisms and the other involving penguins, in which climate has been used to explain species' population trends but which could better be explained by including species interactions in the modelling. We conclude by questioning the almost complete shift in paradigms that has occurred and discuss whether it is leading Southern Ocean marine ecological science in an instructive direction.

14We report analyses of a dataset spanning 38 years of near-annual fishing for Antarctic toothfish 15 Dissostichus mawsoni, using a vertical setline through the fast ice of McMurdo Sound, 16

Antarctica is a continental island and the waters of its shelfand upper slope are an insular evolutionary site. The shelf waters resemble a closed basin in the Southern Ocean, separated from other continents by distance, current patterns and subzero temperatures. The benthc fish fauna of the shelf and upper slope of the Antarctic Region includes 213 species with higher taxonomic diversity confined to 18 families. Ninety-six notothenioids, 67 liparids and 23 zoarcids comprise 45%, 32% and 11% of the fauna, a combined total of 88%. In high latitude (71-78"s) shelf areas notothenioids dominate abundance and biomass at levels of 90-95%. Notothenioids are also morphologically and ecologically diverse. Although they lack a swim bladder, the hallmark of the notothenioid radiation has been repeated diverslfication into water column habitats. There are pelagic, semipelagic, cryopelagc and epibenthic species. Notothenioids exhbit the Qsproportionate speciosity and high endemism characteristic offish species flock. Antifreeze glycopeptides originating from a transformed trypsinogen gene are a key innovation. It is not known when the modem Antarctic shelffauna assumed its current taxonomic composition. A late Eocene fossil fauna was taxonoinically diverse and cosmopolitan. There was a subsequent faunal replacement with little carryover of families into the modem fauna. Basal notothenioid clades probably diverged in Gondwanan shelf locations during the early Tertiary. Dates inferred from molecular sequences suggest that phyletically derived Antarctic clades arose 15-5 n1.y.a.

The RV Nathaniel B. Palmer was used for bottom trawling at depths of 100–1200 m during two recent cruises in the south-western Ross Sea. Although only 10 of 20 trawls were completely successful, a diverse collection of 979 specimens was obtained representing 47 species (36 notothenioids and 11 nonnotothenioids) and eight families. The collection included four new species, a new colour morph of a known species and eight rare species. The collection also established four new locality records, three second occurrences, three most southerly records and eleven new depth records for fish in the Ross Sea. Good taxonomic coverage for some groups was indicated by collection of all four species of Artedidraco, nine of ten bathydraconids and seven of eight channichthyids occurring in East Antarctica. The most abundant species were Trematomus scotti (29.7%), Bathydraco marri (10.4%), Trematomus eulepidotus (8.7%) and Dolloidraco longedorsalis (6.1%). Fish biomass was determined at two stations. The fish fauna of the Ross Sea south of the 1000-m isobath includes at least 80 species – 54 notothenioids and 26 non-notothenioids, approximately the same number as the Weddell Sea. Species diversity (H′ = 1.88) was higher than both the Weddell Sea and boreal regions. This collection indicates that, even in relatively shallow water, knowledge of specific and intraspecific diversity in the Ross Sea fauna is incomplete.