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 over 24 countries across North America, Europe, Africa, and the Middle East. To date, the trophic ecology of the marbled crayfish has only been studied in European lentic and lotic perennial ecosystems. This study aims to shed light on the trophic ecology of the marbled crayfish in ephemeral streams of semi-arid environments in the Middle East, using δ ¹³ C and δ ¹⁵ N stable isotope analysis. We also conducted a diet regime experiment to test the impact of herbivorous and omnivorous diets on crayfish survival. In agreement with studies elsewhere, our analysis confirmed that P. v irginalis 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 showed that juveniles can survive on various diets, with only small differences in survival rates among the three diets that were tested. Surprisingly, the highest survival rate was observed when the crayfish were fed a 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 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 reared at high densities.