Although cephalopods play a critical role in marine food webs both as predators and prey, there is a limited knowledge of several basic aspects of their ecology, including their habitat and trophic level, in the Southern Ocean. We examined the ecological role of several Southern Ocean cephalopod species by analyzing δ N values were more variable among species, ranging from 2.4 to 13.3 ‰, a difference of ~11 ‰ that represents approx. 3 trophic levels. Differences among islands in isotope ratios in the same cephalopod species (higher δ 15 N and lower δ 13 C values in South Georgia) were attributed to regional oceanographic processes. Antarctic cephalopods occupy niches similar to those found in some pelagic fish, seabirds and marine mammals. As cephalopods are key components in Southern Ocean food webs, these results greatly advance our understanding of the structure, energy and carbon flows in this polar ecosystem.

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Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms Journal of Sea Research 83 (2013) 9-29 ☆ Given his role as Guest Editor, Joao-Carlos Marques had no involvement in the peer-review of this article and has no access to information regarding its peer-review. Full responsibility for the editorial process for this article was delegated to Angel Borja.⁎

34The present study aims to review the current biological knowledge on the largest 35 (heaviest) living invertebrate, the colossal squid Mesonychoteuthis hamiltoni 36 (Robson, 1925). This squid is known to be endemic off the Southern Ocean (SO),