Trophic ecology of the invasive marbled crayfish in ephemeral streams of semi-arid environments

The marbled crayfish (Procambarus virginalis) is an invasive, parthenogenetically reproducing species that has spread to freshwater ecosystems in more than 24 countries across North America, Europe, Africa, and the Middle East. To date, the trophic ecology of the marbled crayfish has been studied only in European lentic and lotic perennial ecosystems. This study aimed to shed light on the trophic ecology of the marbled crayfish in ephemeral streams of semi-arid environments in the Middle East. Three distinct habitats were compared using δ¹³C and δ¹⁵N stable isotope analysis to evaluate spatial variation in trophic position and resource use. A diet regime experiment was also conducted to test the impact of herbivorous and omnivorous diets on crayfish survival. In agreement with studies elsewhere, the analysis confirmed that P. virginalis functions as a flexible omnivore, occupying an intermediate trophic level (trophic position: 2.3–2.9), with the highest values observed during summer. The diet regime experiment indicated that juveniles can survive on various diets, with only small differences in survival rates among the three diets tested. The highest survival rate was observed under the poor plant-based diet. Adults and sub-adults also showed high survival rates under all tested diets, as well as some extent of cannibalism, which was amplified when they were fed purely plant-based diets. Cannibalism was primarily directed at small-sized juveniles (0–2 months old). In contrast, cannibalism among adults and sub-adults was very limited, even when they were reared at high densities.