Lack of Hematodinium microscopic detection in crustaceans at the northern and southern ends of the Wadden Sea and an update of its distribution in Europe

<em>Hematodinium perezi</em> (Dinophyceae: Syndiniales) in Morocco: First Record on the African Atlantic Coast, and First Country Record of a Parasite of the Invasive Blue Crab <em>Callinectes sapidus</em>

“…Hematodinium is considered to be a generalist parasite [34,56,69], reflecting its host range as well as its ability to switch between host species, allowing it to maintain a presence in the environment when the preferred host may become scarce. Positive infections of Hematodinium were reported in 13 crustacean species belonging to two orders, Decapoda and Amphipoda [78]. Several factors affect the epidemiology of Hematodinium, including environmental conditions such as salinity and temperature.…”

“…It is known that this parasite tends to infect hosts in high salinity waters [79]. For example, in Europe (Wadden Sea), no detection of Hematodinium in 1252 individuals of eight crustacean species from six sites was reported due to lower salinity [78]. Epidemics of these parasites have damaged commercial stocks of Nephrops norvegicus (Linnaeus, 1758) langoustines, Chionoecetes opilio (Fabricius, 1788) snow crabs, Chionoecetes bairdi Rathbun, 1924 Tanner crabs, C. sapidus American blue crabs and Necora puber (Linnaeus, 1767) velvet swimming crabs [34].…”

“…In the present research, diagnosis of infection by representatives of Hematodinium in C. sapidus was performed using the fresh hemolymph smear essay with neutral red and molecular analysis (PCR-based method and sequencing). The hemolymph smear assay with neutral red has been used as an initial assessment tool due to its cost-effective and time-efficient diagnostic method for detection of members of Hematodinium [78] as well as to its specificity and sensitivity [81]. The active absorption of neutral red by Hematodinium lysosomes results in distinct staining, providing visual contrast to host hemocytes [34].…”

“…It was revealed to be more accurate in identifying crabs parasitized by Hematodinium than histological methods. The difference in parasite prevalence between Merja Zerga (65%) and Oualidia Lagoon (25%) could be explained by environmental factors [60,78,80] or biological factors [66,87]. According to [80], several studies have shown that temperature and salinity conditions favor the invasion of Hematodinium.…”

“…According to [80], several studies have shown that temperature and salinity conditions favor the invasion of Hematodinium. The prevalence of Hematodinium decreased at lower temperatures [80], and lower salinity can also limit the distribution of the parasite [78]. For example, the highest prevalence (69%) of the parasite in blue crab collected from the USA was found at salinities of 26 PSU to 30 PSU and water temperature >25 °C and no infected crabs were found in salinities below 11 PSU [60].…”