Habitat degradation increases interspecific trophic competition between three spiny lobsters in Seychelles

Abstract Spiny lobsters (P. penicillatus, P. longipes and P. versicolor) are heavily dependent on habitats like coral reefs, known to be highly vulnerable to climate change-driven degradation. Yet, little is known about their trophic ecology and their adaptive capacity to a changing environment. In this study, we used fatty acids (FA) analysed in the hepatopancreas and δ13C and δ15N stable isotopes analysed in tail muscle of three spiny lobster species from Seychelles coastal waters to (1) infer habitat usage, dietary patterns and potential for resource competition and (2) investigate the effects of reef type and coral bleaching on their trophic niche metrics. We found that there was a potential for interspecific competition between the three species, shown by their high dietary overlap (FA niche overlap ranging from 71.2% to 99.5% for P. longipes and P. versicolor in P. penicillatus) and similar habitat use (δ13C value ranges). P. penicillatus was more a generalist than the two other species (i.e., had larger FA niche) and P. versicolor seemed to feed on smaller/earlier life stage prey than P. longipes (based on differences in δ15N values), possibly allowing for their coexistence. The potential for resource competition of Seychelles spiny lobsters appeared higher in granite than carbonate reefs and in post-2016 coral bleaching reefs. Our results suggest that P. penicillatus could have a greater adaptive capacity to climate change due to its higher dietary plasticity and that competition between Seychelles spiny lobsters may increase in the future as the frequency and severity of bleaching events is predicted to increase with climate change.