Benthimermithid nematode parasites of the amphipod Hirondellea dubia in the Kermadec Trench
Parasitic nematodes have evolved to exploit a wide variety of hosts living in a range of marine environments. Benthimermithid nematodes occur deeper than any other nematode parasites (down to 5880 m depth) but are mostly known from free-living adult stages living in the sediments, and parasitic juveniles are seldom encountered. In the present study, the benthimermithid Trophomera cf. marionensis was discovered in the body cavity of the lysianassoid amphipod Hirondellea dubia sampled between 7018 and 10,005 m depths in the Kermadec Trench. The nematode specimens, which could be readily observed through the transparent exoskeleton of freshly caught amphipods, were up to twice the length of T. marionensis specimens described from the Atlantic and East Pacific Oceans but were otherwise morphologically identical. Because of its wide geographical and water depth distribution (almost 10,000 m), T. marionensis likely consists of several cryptic species. The prevalence of Trophomera parasites among the host population was estimated to be substantially less than 1 %; such a low proportion of parasitised hosts could help explain why so few Trophomera specimens have been obtained from their host so far. The present study demonstrates that parasites can occur throughout the entire ocean depth and that they likely occur in other hadal trenches where H. dubia and other lysianassoid amphipods also dominate.
KeywordsSouth-West Pacific Hadal Scanning electron microscopy Benthimermithidae Trophomera cf. marionensis
Funding was provided by NIWA’s Coasts and Oceans Centre Research Programme ‘Marine Biological Resources’ and the project ‘Impact of resource use on vulnerable deep-sea communities’ (CO1X0906). We are grateful to Tim Shank (WHOI), Alan Jamieson (University of Aberdeen), Ashley Rowden and Malcolm Clark (both NIWA), principal investigators of the HADES project (HADal Ecosystem Studies, funded by the National Science Foundation, NSF-OCE 1130712, 1130494 and 1131620) and to the officers, crew and scientific personnel of RV Thomas G. Thompson (voyage TN309) and ROV Nereus engineers and technicians. We thank an anonymous reviewer for providing constructive criticisms on the manuscript.
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