Ontogenetic variation of trophic habitat for sympatric benthic octopods in East China Sea derived from isotopic analysis on beaks

Abstract Sympatry is commonly observed in marine species, and always accompanied by high competition. Octopus consists of large amount of species and also widely distributed in the neritic area of the sea. As typical benthic species, octopus tend to live in the similar habitat with less movement during its lifetime. It is important to understand the trophic ecology of sympatric octopod species, which play an irreplaceable role in marine ecosystem. In this study, four neritic octopus species in the East China Sea (Amphioctopus fangsiao, Amphioctopus ovulum, Octopus minor and Octopus sinensis) were chose, we used stable isotope analysis (SIA) to analyze the variation of δ13C and δ15N derived from beak to assess the trophic variation among species and maturity stages. O. sinensis has the largest body and beak size than other species, and this species also had highest mean δ13C, δ15N value among species. The result of ANOVA showed that significant differences existed among four species for isotopic values. The overlaps among species were also calculated by standard ellipse area (SEAc). Isotopic overlap was decreased from immature stage to mature stage. The trophic niches were shrunk from immature to mature for all the four octopods species except for A. ovulum, which presented an expansion tendency. Trophic overlaps between specific two species in different groups were also calculated with distribution and mean values based on Bayesian model. The highest and lowest isotopic overlap occurred between O. minor and A. ovulum in immature group, A. fangsiao and O. sinensis in mature group, respectively. The four octopods species had very different trophic niches during ontogeny.