Prey contribution to the diet of Octopus insularis (Leite and Haimovici, 2008) using stable isotopes and stomach content analysis in the Western Gulf of Mexico

Abstract

Octopus insularis is an active and opportunistic predator, its diet depends on the habitat in which it develops and the abundance and distribution of the species it preys on. Despite its importance for fisheries, little is known about the trophic relationships of this octopus. For this reason, the main objective of this study was to describe its diet in the southern Gulf of Mexico combining stable δ13C and δ15N isotopes and stomach content analysis. Stable δ13C and δ15N isotope analysis were performed in muscle tissue of octopuses and their prey. In addition, stomachs were analyzed to identify consumed prey and to obtain percentages of numerical and gravimetric importance, the frequency of occurrence and the index of relative importance. The diet did not show differences between year, sex, or size. Eight crustacean and three fish genera were identified as the main components in the diet. Crustaceans appeared as the main prey group, and the most important prey within this group was Mithraculus sp., and for the fish group it was Anchoa sp. The isotope analysis indicates a high contribution to predator´s muscle tissue from both crustaceans and fish. In one hand, results indicate that crustaceans as prey are important for the octopus population in the whole distribution area. On the other hand, isotope values positioned O. insularis as an intermediate trophic level predator, placing it as an efficient vehicle of energy transfer between lower to higher trophic levels in the ecosystem.