Ontogenic changes in habitat and trophic ecology in the Antarctic squid Kondakovia longimana derived from isotopic analysis on beaks

The life histories of cephalopods are still not well described. Stable isotopic analysis of cephalopod beaks is an effective method to study thehabitat and trophic ecology of this group of organisms. As beaks grow continuously throughout squid's life without replacement, we hypothesised that analysing different sections along the beak will provide information on the ontogenetic shifts during the individual's lifetime. Here we used the Southern Ocean squid Kondakovia longimana as a model species to test the reliability of this method along the beaks of Antarctic species. Growing patterns show that beaks grow throughout the squid lifetime by a continuous deposition of material. This new material can influence the results of the stable isotopic analysis. C-13 and N-15 values (from -26.3 to -20.6 parts per thousand and from +3.2 to +8.2 parts per thousand, respectively) from different beak regions indicated that K. longimana inhabits regions spanning a wide latitudinal range, and the trophic level at which it feeds increases throughout its lifetime. Stable isotopic analysis of different sections of the cephalopod beak is a reliable technique to study habitat and trophic ecology throughout Antarctic squid's lifetime. Stable isotopic results showed an increase in N-15 values from the tip of the rostrum to the end of the hood and crest, in the upper beak, and to the free corner of lateral wall and wing in the lower beak. Our results also suggested that the upper beak is the best beak to study ontogenetic shifts, mainly in initial stages of the cephalopods' life, presenting lower values of N-15 than the lower beak.