Differentiation of trophic niches of four common octopus species in East China Sea based on stable isotopes

To clarify the resource allocation strategies of four types of economic octopuses in the East China Sea (Amphioctopus fangsiao, A. ovulum, Octopus minor, and O. sinensis), we conducted a systematic analysis of their nutritional ecological niches using stable isotope techniques (δ¹³C and δ¹⁵N). We selected 193 octopus samples collected from the northern East China Sea during 2021—2022. According to the δ¹³C and δ¹⁵N values, as well as the differences in sex among different species, we constructed the ecological niche standard ellipses for the four octopus species, and their intra-species male and female populations. Through the analysis of standard ellipse area and overlap rates, we observed the inter-species and intra-species differentiation characteristics of nutritional ecological niches. The results show significant differences in δ¹³C values among the four octopus species (p<0.01), with O. minor [(−17.08±0.88)‰] and O. sinensis [(−16.52±0.87)‰] showing significantly lower values than A. fangsiao [(−17.87±0.87)‰] and A. ovulum [(−17.37±0.84)‰], reflecting distinct feeding preferences. Furthermore, there were significant differences in δ¹⁵N values among the four species (p<0.01), indicating clear nutritional level stratification. The ecological niche width of O. sinensis was the largest, possessing the greatest standard ellipse area (SEAc) and demonstrating a diverse resource utilization approach, while O. minor relied on a singular benthic food resource. Sexual differences were significant in certain species, particularly in O. sinensis, where a significant difference in δ15N values was observed between male and female individuals (p<0.01), indicating considerable disparities in their nutritional levels. The study concludes that the four octopus species in the East China Sea achieved coexistence through source differentiation (δ¹³C) and the differences in nutritional levels between male and female O. sinensis (δ¹⁵N), with a niche overlap rate of 27.74%.