title: Reduced disease in black abalone following mass mortality: phage therapy and natural selection.
abstract: Black abalone, Haliotis cracherodii, populations along the NE Pacific ocean have declined due to the rickettsial disease withering syndrome (WS). Natural recovery on San Nicolas Island (SNI) of Southern California suggested the development of resistance in island populations. Experimental challenges in one treatment demonstrated that progeny of disease-selected black abalone from SNI survived better than did those from naïve black abalone from Carmel Point in mainland coastal central California. Unexpectedly, the presence of a newly observed bacteriophage infecting the WS rickettsia (WS-RLO) had strong effects on the survival of infected abalone. Specifically, presence of phage-infected RLO (RLOv) reduced the host response to infection, RLO infection loads, and associated mortality. These data suggest that the black abalone: WS-RLO relationship is evolving through dual host mechanisms of resistance to RLO infection in the digestive gland via tolerance to infection in the primary target tissue (the post-esophagus) coupled with reduced pathogenicity of the WS-RLO by phage infection, which effectively reduces the infection load in the primary target tissue by half. Sea surface temperature patterns off southern California, associated with a recent hiatus in global-scale ocean warming, do not appear to be a sufficient explanation for survival patterns in SNI black abalone. These data highlight the potential for natural recovery of abalone populations over time and that further understanding of mechanisms governing host-parasite relationships will better enable us to manage declining populations.
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA.
authors.forename: Carolyn S
authors.initials: CS
authors.lastname: Friedman
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Wight
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Crosson
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Seattle, WA, USA ; Washington Cooperative Fish and Wildlife Research Unit, U.S. Geological Survey, University of Washington Seattle, WA, USA.
authors.forename: Glenn R
authors.initials: GR
authors.lastname: Vanblaricom
authors.affiliation: Western Ecological Research Center, U.S. Geological Survey, c/o Marine Science Institute, University of California at Santa Barbara Santa Barbara, CA, USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Lafferty
keywords: Haliotis; abalone; endangered; histology; phage; rickettsial; selection; withering syndrome