Molecular characterization and prevalence of Halarachne halichoeri in threatened southern sea otters (Enhydra lutris nereis)

Abstract

Parasitism, particularly in concert with other sublethal stressors, may play an important, yet underappreciated role in morbidity and mortality of threatened species. During necropsy of southern sea otters (Enhydra lutra nereis) from California submitted to the Marine Wildlife Veterinary Care and Research Center's Sea Otter Necropsy Program between 1999 and 2017, pathologists occasionally observed nasopulmonary mites infesting the respiratory tracts. Infestation was sometimes accompanied by lesions reflective of mite-associated host tissue damage and respiratory illness. Our objectives were to estimate prevalence of nasopulmonary mites, determine the taxonomic identity of the observed mites, and create a DNA reference for these organisms in southern sea otters as an aid in population management. Using unique morphological characteristics discerned via light and scanning electron microscopy (SEM), we identified the mites as Halarachne halichoeri, a species typically associated with harbor seals (Phoca vitiluna). The 18S, 16S, 28S and ITS1-2 genetic regions were sequenced and submitted to GenBank. We observed H. halichoeri mites in 25.6% (95% CI 19.9-33.4%). of southern sea otters from a subset of necropsies performed between 2012 and 2017. This is the first documentation of H. halichoeri in southern sea otters and is suggestive of parasite exchange between sea otters and harbor seals.

Keywords: Acarology; Enhydra lutris; Halarachne halichoeri; Halarachnidae; Marine parasites; Sea otter.

Graphical abstract

Fig. 1

(A) Scanning electron microscopy of adult Halarachne halichoeri showing opisthosoma (abdomen) with slight constriction only at the anterior end and dorsal shield broader posteriorly than anteriorly with linguiform caudal tip. (B) Scanning electron microscopy of larvae Halarachne halichoeri with postanal setae (bristles) longer than adanal setae.