Diversity of Parasitic Animals in Hypersaline Waters: A Review

Hypersaline waters are unique polyextreme habitats, where the salinity limits species richness. There are main patterns of a relationship between salinity and the species richness of free-living aquatic animals, but for parasitic organisms, general regularities have not yet been established. There are quite numerous data on parasites in hypersaline waters worldwide; however, they have not been summarized before. This review tries to fill this gap by summarizing the available data. All parasites, 85 species and forms, found in hypersaline waters belong to five phyla: Platyhelminthes, Nematoda, Acanthocephala, Cnidaria, and Arthropoda. Platyhelminthes are the most diverse phylum with the highest species richness in class Cestoda. Most species were noted in hypersaline waters with a salinity of no more than 100 g·L−1. The total number of parasitic species decreases exponentially with an increase in salinity. The number of free-living animal species inhabiting waters with a salinity from 35 to 210 g·L−1 is approximately 12 times higher than that of parasitic ones in all intervals of this salinity range. Salinity influences parasite richness and composition in two ways—directly and through the availability of hosts. Free-living crustaceans were hosts of most parasite species in hypersaline waters. Artemia spp., the most halotolerant animals, are an intermediate host for 22 species and unidentified forms of parasites.