Response of Petroleum Seep Mussels to Changing Environmental Conditions: Parasite Transmission, Infection Intensification, and Health

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Coastal Sciences, Gulf Coast Research Laboratory


Ocean Science and Engineering


© 2020 Elsevier Ltd. Trematode sporocyst and rickettsia weighted prevalences were found to be extremely high in Gulf of Mexico petroleum seep mussels, Bathymodiolus childressi, in comparison to shallow-water mytilids. Understanding the role that parasites might play in mussel population dynamics and health requires an understanding of the rapidity with which parasite infections and physiological condition respond to changes in host population structure and environment. To evaluate the influence of the seep environment on B. childressi, a transplant experiment was conducted between several donor (population of origin) and receiver (population of transplant) populations from three seep sites on the continental slope of the Gulf of Mexico. Donor and receiver populations varied significantly in prevalence and infection intensity for many parasites and often varied in physiological condition for most physiological indices. Transplanted populations came into equilibrium with the receiver populations relatively fast for single-celled parasites; trematode sporocysts responded less often and more slowly. In a few cases, these transplanted populations retained the donor population condition, most frequently for the trematode sporocysts and rarely for the single-celled parasites. Of the physiological indices, gonadal stage came into equilibrium with all receiver populations in one year. Mussels lost condition rapidly in cases where the receiver population had lower condition but gained condition more slowly in the opposite case. Digestive gland atrophy and gill tissue atrophy responded rapidly in most cases where the transplanted mussels varied initially from the receiver populations. Transmission rates could be approximated from changes in prevalence for gill rickettsia and the trematode sporocysts. For gill rickettsia, transmission rates varied between 0.36 and 0.45 yr−1. Loss rates were much higher, estimated at 1.95 yr−1, suggesting a short life span for any individual rickettsial body and that infection intensity is a balance between rapid rates of proliferation and loss. Transmission rates for the trematodes, likewise approximated, were slower: 0.13 to 0.29 yr−1; nevertheless, infection intensification was rapid, in one case reaching 3 on a 0-to-4-point semiquantitative scale in one year. Apparent loss rates were minimal in one case but reached 1.25 yr−1 in another. Mussels live for a relatively long time and the transmission rates measured for the trematode sporocysts are relatively high, yet population prevalences are often well below 100%. One possibility is that these trematode sporocysts have life spans considerably shorter than their hosts, a fact that is of some consequence because while infected, the mussels lose any capacity to reproduce. The alternative is that infected mussels have a relatively high mortality rate.

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Deep-Sea Research Part I: Oceanographic Research Papers

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