Coexistence mechanism between sympatric snapper species revealed by stomach contents analysis and stable isotope analysis in the central Gulf of California, Mexico

Sympatric species can overlap in different ecological niche dimensions, which can increase interspecific competition for resources. The objective of this study was to assess the trophic interactions between two sympatric snapper species (Lutjanus guttatus and Lutjanus peru) coexisting in the area of Santa Rosalía, Central Gulf of California. Interactions were analyzed using two complementary techniques: stomach contents analysis and stable isotope analysis (δ¹³C and δ¹⁵N). Specimens were captured from June 2016 to October 2017 and were separated into three categories: sex, size group (1, 2, and 3), and season (warm or cold). A total of 187 L. guttatus stomachs and 397 L. peru stomachs were analyzed; 43 L guttatus and 45 L. peru muscle samples were also obtained for isotopic analysis. Results showed that L. guttatus consumed 28 prey items, whereas L. peru consumed 30 prey items. The %PSIRI showed that the sardines S. sagax (L. guttatus: 34.78% and L. peru 37.42%) and H. thrissina (L. guttatus: 34.61% and L. peru: 24.92%), and the euphausiid N. simplex (L. guttatus: 9.66% and L. peru: 15.20%) were the most important prey in the diet. However, secondary prey differed between snapper species. The PERMANOVA showed significant differences (p < 0.05) for most categories, except for size groups 1 and 3. L. guttatus δ¹⁵N values were higher (18.00‰–19.90‰) than those of L. peru (17.71‰–19.51‰), showing the importance of fish in the L. guttatus diet; lower L. peru values could reflect a greater consumption of crustaceans. δ¹³C values indicated that the two species occupied a coastal habitat with possibility of movements towards the pelagic area, especially for L. peru. Trophic and isotopic niches of the two species were narrow, showing an opportunist strategy. The trophic level showed that the two species could be considered linking species within the trophic web. The mixing models (SIMMR) showed that sardines and myctophids were the best assimilated prey. Interspecific competition between L. guttatus and L. peru was reduced; the two species shared trophic resources that are abundant in different proportions, as a coexistence mechanism.