Histopathology and Phylogeny of the Dinoflagellate Hematodinium perezi and the Epibiotic Peritrich Ciliate Epistylis sp. Infecting the Blue Crab Callinectes sapidus in the Eastern Mediterranean

Abstract

Bioinvasions constitute both a direct and an indirect threat to ecosystems. Direct threats include pressures on local trophic chains, while indirect threats might take the form of an invasion of a microorganism alongside its host. The marine dinoflagellate Hematodinium perezi, parasitizing blue crabs (Callinectes sapidus), has a worldwide distribution alongside its host. In Greece, fluctuations in the blue crab population are attributed to overexploitation and the effects of climate change. The hypothesis of the present study was that blue crab population reductions cannot only be due to these factors, and that particular pathogens may also be responsible for the fluctuations. To investigate this hypothesis, both lethargic and healthy blue crab specimens were collected from three different fishing sites in order to assess the health status of this important species. Together with the lethargic responses, the hemolymph of the infested crabs presented a milky hue, indicating the first signs of parasitic infestation with H. perezi. The histopathological results and molecular identification demonstrated the effect of the presence of H. perezi in the internal organs and their important role in the mortality of blue crabs. Specifically, H. perezi, in three different tissues examined (heart, gills, hepatopancreas), affected the hemocytes of the species, resulting in alterations in tissue structure. Apart from this dinoflagellate parasite, the epibiotic peritrich ciliate Epistylis sp. was also identified, infecting the gills. This study represents the first detection of H. perezi in the eastern Mediterranean, demonstrating that this is the main causative agent of blue crab mortality on Greek coastlines.

Hematodinium perezi (Dinophyceae: Syndiniales) in Morocco: The First Record on the African Atlantic Coast and the First Country Record of a Parasite of the Invasive Non-Native Blue Crab Callinectes sapidus

“…In the Mediterranean and north-eastern Atlantic, regions where C. sapidus invaded, H. perezi was reported as an endoparasite of C. sapidus in the Eastern Mediterranean, Greece, [34] and now also on the African Atlantic coast (this study) (Figure 1).…”

<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 perezi was documented in the American blue crab Callinectes sapidus for the first time in coastal Maryland and Virginia, USA [72] and afterwards in many habitats in the USA [62,[73][74][75][76][77]. In the Mediterranean and north-eastern Atlantic, regions where C. sapidus invaded, H. perezi was reported as endoparasite of C. sapidus in the eastern Mediterranean, Greece [33] and now also on the African Atlantic coast (this study) (Figure 2). 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.…”

“…15 ITS1 rDNA sequences were generated (13 sequences from Merja Zerga Lagoon and two from Oualidia Lagoon), and the alignment was 295 bp in length. The comparison of ITS1 rDNA sequences with those already present in the GenBank database using BLAST search confirmed the identification of our parasites' species sequences as being those of Hematodinium perezi, sharing 98.99% of similarity with the sequence having the accession number EF065716, 98.65% with EF065708 and EF065711, all of them from the host Liocarcinus depurator Linnaeus, 1758 (Polybiidae), harbour crab, collected from Rye Bay on the South Coast of England [56], and 98.32% with the sequence with accession number PP056127 from the host Callinectes sapidus Rathbun, 1896 (Portunidae), American blue crab, collected from Greece [33].…”

“…The uncorrected p-distances between Moroccan sequences varied between 0% and 0.6%, and the uncorrected p-distances between Moroccan sequences and published sequences generated from GenBank [33,56,57] (Table 2), varied between 0.6% from H. perezi in Liocarcinus depurator collected off the South Coast of England and 4% from H. perezi in Callinectes sapidus from the United States of America (Table 3).…”

“…Along invaded Mediterranean and north-eastern Atlantic coasts, although the blue crab constitutes an important model organism for studying invasions related to the spread of microorganisms, the majority of scientific research is focused on the population dynamics, structure, and fisheries of the species [32]. The occurrence of parasites in the species has been very little explored, even though it is an appreciated shellfish product in many countries such as Greece and Turkey, Italy, and Egypt [33].…”