Trophic ecology of Octopus insularis: methodological comparisons and new perspective through the use of stable isotopes
Cephalopoda, diet, trophic level, Octopodidae, food web
Octopuses are mollusks that play a significant role in marine food webs, not only for their importance as prey to top predators, but also because they are carnivorous consumers of the benthic environment. For this reason, their feeding ecology has been studied using multiple methodologies applied to a variety of species of the group. However, there is no consensus on which technique would be more effective in this type of research, or even if there is only one "ideal and self-sufficient" method. Another issue relates to the positioning of the octopus in the marine food webs. It is known that they feed on a wide variety of crustaceans, mollusks, fish and other organisms and that they serve as food for many top consumers, but their ecological function remains undefined, making it difficult to predict the effects of their increase or decrease in shallow water marine communities. Therefore, in order to bring answers to these two questions, this study aims to compare three distinct quali-quantitative methods to characterize the food habits of octopuses (i.e. analyses of gut contents, of prey remains in midden piles and of stable isotopes) and to identify the trophic position of these cephalopods and their importance as prey and predators. The study object is the Octopus insularis, the most frequent octopus on the northeast coast of Brazil and its oceanic islands, and which have already being regularly exploited by artisanal fisheries in the country. The study areas are the Rocas Atoll Biological Reserve, an insular, pristine and unique environment in terms of Southern Hemisphere; and Rio do Fogo, a costal environment with human presence and fisheries impact