Hematodinium perezi (Dinophyceae: Syndiniales), parasite of an invasive blue crab: on the African Atlantic coast

INTRODUCTION: Invasive non-native species may carry invasive parasites and/or enhance native parasites, leading to a loss of native biodiversity and to disease/mortality of indigenous species as well as risks to human health and the economy. Callinectes sapidus, native to the western Atlantic, has been established in various Moroccan coastal ecosystems since 2017, hosts several parasites both in native and introduced areas. In this study, we document the first report of H. perezi on the African Atlantic coast. This is also the first parasite record in the invasive non-native blue crab C. sapidus in Morocco. METHODOLOGY: In winter 2023, 36 specimens of C. sapidus were sampled from two Ramsar sites on the Moroccan Atlantic, namely Merja Zerga and Oualidia Lagoons. All 36 specimens were screened to detect the presence of parasites in their hemolymph by staining fresh hemolymph smears and by PCR based on the amplification of the parasite’s first internal transcribed spacer region (ITS1). RESULTS: Based on staining fresh hemolymph smears, 19 blue crab individuals were infected by the parasite, with a prevalence of 75% in Merja Zerga Lagoon and 25% in Oualidia Lagoon. The PCR-based method proved to be more accurate in diagnosing the Hematodinium, as certain stages can be very difficult to detect in fresh hemolymph smears due to their resemblance to hemocytes. PCR analysis revealed that 13 C. sapidus individuals were infected in Merja Zerga (prevalence: 65%) and four in Oualidia (25%). Comparison with the previously published DNA sequences confirmed the presence of H. perezi. Ultimately, in-depth studies are desirable to understand the interactions between blue crab and its parasites in Morocco's coastal zones, and to assess their effects on native biodiversity, associated marine diseases and human health risks. In addition, screening native crabs in Morocco will enable us to verify parasite spillover and spillback events.