Trophic ecology of the Atlantic blue crab Callinectes sapidus as an invasive non-native species in the Aegean Sea

Invasive non-native crustaceans are a biodiversity and management concern in the Mediterranean Sea. The Atlantic blue crab (Callinectes sapidus) was first recorded in the Mediterranean Sea in 1949, but may have arrived as early as in the 1930's. Blue crabs in the Mediterranean Sea are of concern due to their presumed potential for negative consumptive and competitive interactions with native fauna. The aim of this study was to provide a first assessment of the trophic ecology of non-native blue crab in the Northern Aegean Sea using stable carbon (delta C-13) and nitrogen isotope (delta N-15) analysis. We found limited isotopic niche overlap between blue crabs and seven native species examined at Gokceada Island in April, June, and August of 2017. In addition, the range of calculated trophic positions of blue crabs at Gokceada Island (2.0 to 4.4), while broad, is in general agreement with prior studies in both native and non-native ranges. We also observe that trophic position declined and the relative importance of pelagic carbon sources to blue crabs increased from April to August. However, we also found that differing assumptions as to the number and type of food web baselines and trophic discrimination factors led to differing estimates of trophic position in blue crabs at Gokceada Island by as much as one to two trophic levels. These methodical differences make it challenging to directly compare results within and between studies, and thus limit our ability to assess negative consumptive and competitive interactions of invasive blue crab with native coastal species in the Mediterranean Sea.

Automated summary

Invasive non-native Atlantic blue crabs in the Mediterranean Sea present a concern due to potential negative interactions with native species. A study in the Northern Aegean Sea found limited isotopic niche overlap with native species, and observed changes in trophic positions and diet sources of blue crabs over time. Methodological differences in estimating trophic position limit the ability to assess interactions of invasive blue crabs with native species.