Cephalopods habitat and trophic ecology: historical data using snares penguin as biological sampler

Abstract

In the Southern Ocean and adjacent waters, early stages of cephalopods play an important role in food webs as prey to top predators, but few is known regarding their biology and availability. Snares Penguin, Eudyptes robustus, is a top predator endemic to Snares Islands (New Zealand) that feed on cephalopods. As historical data on diet are rare for this species, Snares Penguins were used as biological samplers to evaluate the cephalopod component of its diet, where habitat and trophic level of cephalopods around the Snares Islands was assessed through stable isotope analysis. Moreover, ontogenic changes of juvenile squid were evaluated. Data collection were carried out during the breeding season 1986–87 and its analysis revealed that penguins fed on three juvenile cephalopod species: two squids (Nototodarus sloanii and Moroteuthopsis ingens) and one octopod (Octopus campbelli). Nototodarus sloanii was the most important species in frequency of occurrence and mass, whereas M. ingens was the most important in number. Juvenile squid species showed similar δ13C values, suggesting both occupied similar habitats on the Snares shelf, whereas juvenile O. campbelli showed lower δ13C values. Moreover, O. campbelli fed on higher trophic level (δ15N) prey relative to squid species. Lower diversity and larger sizes of cephalopods were found when compared with data from 2002. This study shows that Snares Penguin can be a good local biological sampler of juvenile cephalopods during their breeding season, providing both essential biogeographic information of cephalopod diversity and relevant historical information for the conservation of this endemic penguin species.