Natural disease resistance in threatened staghorn corals

Abstract

Disease epidemics have caused extensive damage to tropical coral reefs and to the reef-building corals themselves, yet nothing is known about the abilities of the coral host to resist disease infection. Understanding the potential for natural disease resistance in corals is critically important, especially in the Caribbean where the two ecologically dominant shallow-water corals, Acropora cervicornis and A. palmata, have suffered an unprecedented mass die-off due to White Band Disease (WBD), and are now listed as threatened under the US Threatened Species Act and as critically endangered under the IUCN Red List criteria. Here we examine the potential for natural resistance to WBD in the staghorn coral Acropora cervicornis by combining microsatellite genotype information with in situ transmission assays and field monitoring of WBD on tagged genotypes. We show that six percent of staghorn coral genotypes (3 out of 49) are resistant to WBD. This natural resistance to WBD in staghorn corals represents the first evidence of host disease resistance in scleractinian corals and demonstrates that staghorn corals have an innate ability to resist WBD infection. These resistant staghorn coral genotypes may explain why pockets of Acropora have been able to survive the WBD epidemic. Understanding disease resistance in these corals may be the critical link to restoring populations of these once dominant corals throughout their range.

Figure 1. Resistance to White Band Disease (WBD) in the staghorn coral Acropora cervicornis.

(A) WBD transmission to a coral fragment occurs rapidly as illustrated by the progress of the advancing white band of disease after three days of direct contact (grafting) with an infected coral fragment. (B) In situ transmission experiments identified five staghorn coral genotypes that did not contract WBD. (C) Field surveys of WBD prevalence identified ten genotypes that were not observed in the field with WBD. (D) Integrated field surveys and experimental transmission results show that three staghorn coral genotypes were resistant to WBD infection.