Genotypic variation in disease susceptibility among cultured stocks of elkhorn and staghorn corals.

Margaret W Miller,Esther C Peters,Dana E Williams,Allan J Bright,Emma Pontes,Philip J Colburn,Xaymara M Serrano

doi:10.7717/peerj.6751

Abstract

Disease mortality has been a primary driver of population declines and the threatened status of the foundational Caribbean corals, Acropora palmata and A. cervicornis. There remain few tools to effectively manage coral disease. Substantial investment is flowing into in situ culture and population enhancement efforts, while disease takes a variable but sometimes high toll in restored populations. If genetic resistance to disease can be identified in these corals, it may be leveraged to improve resistance in restored populations and possibly lead to effective diagnostic tests and disease treatments. Using a standardized field protocol based on replicated direct-graft challenge assays, we quantified this important trait in cultured stocks from three field nurseries in the Florida Keys. Field tests of 12 genotypes of A. palmata and 31 genotypes of A. cervicornis revealed significant genotypic variation in disease susceptibility of both species measured both as risk of transmission (percent of exposed fragments that displayed tissue loss) and as the rate of tissue loss (cm2 d–1) in fragments with elicited lesions. These assay results provide a measure of relative disease resistance that can be incorporated, along with consideration of other important traits such as growth and reproductive success, into restoration strategies to yield more resilient populations.

Highlights

Disease constitutes an existential threat to coral persistence (Walton, Hayes & Gilliam, 2018), and this threat is exacerbated by its worsening with thermal stress (Randall & Van Woesik, 2015)
A. palmata and A. cervicornis, are both designated as critically endangered by the IUCN and threatened under the US Endangered Species Act (ESA) with disease cited as a primary driver of their high extinction risk (Aronson & Precht, 2001; NMFS, 2006)
All assays were performed on segregated, experimental coral nursery “trees” (Nedimyer, Gaines & Roach, 2011) at the nursery operated by the Coral Restoration Foundation off Tavernier, Florida, USA

Summary

Introduction

Disease constitutes an existential threat to coral persistence (Walton, Hayes & Gilliam, 2018), and this threat is exacerbated by its worsening with thermal stress (Randall & Van Woesik, 2015). Genotypic variation in disease susceptibility among cultured stocks of elkhorn and staghorn corals. A. palmata and A. cervicornis, are both designated as critically endangered by the IUCN and threatened under the US Endangered Species Act (ESA) with disease cited as a primary driver of their high extinction risk (Aronson & Precht, 2001; NMFS, 2006). The strong association of climate change related thermal stress and disease is welldocumented in both these species (Muller et al, 2008; Randall & Van Woesik, 2015), lending little expectation of abatement under expected continued warming

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