White Band Disease (type I) of endangered caribbean acroporid corals is caused by pathogenic bacteria

Abstract

Diseases affecting coral reefs have increased exponentially over the last three decades and contributed to their decline, particularly in the Caribbean. In most cases, the responsible pathogens have not been isolated, often due to the difficulty in isolating and culturing marine bacteria. White Band Disease (WBD) has caused unprecedented declines in the Caribbean acroporid corals, resulting in their listings as threatened on the US Threatened and Endangered Species List and critically endangered on the IUCN Red List. Yet, despite the importance of WBD, the probable pathogen(s) have not yet been determined. Here we present in situ transmission data from a series of filtrate and antibiotic treatments of disease tissue that indicate that WBD is contagious and caused by bacterial pathogen(s). Additionally our data suggest that Ampicillin could be considered as a treatment for WBD (type I).

Figure 1. Photographs of the in situ filter and antibiotic experiments with (A) showing the coral fragments in clips on cinder blocks with the different experimental treatments applied (B) close-up of previously healthy A. cervicornis fragment with sterile gauze with WBD filtrate showing the beginning of disease progression (C) close-up A. cervicornis fragment with sterile cotton gauze with WBD filtrate treated with 100 ug/ml tetracycline that blocked WBD disease progression.

Figure 2. Frequency of WBD infections when sterile gauze containing 5 ml of the different experimental treatments was attached to healthy A. cervicornis fragments.

WBD homogenate was airbrushed coral with active WBD, 0.45 μM was the filtrate that passed through a 0.45 μM filter, and 0.22 μM the filtrate that passed through a 0.22 μM filter. The tetracycline treatment was active WBD homogenate that was treated with 100 μg/ml Tetracycline with 20 μg/ml imidocarb diproprionate for two hours prior to attachment, the Ampicillin treatment was treated with 100 μg/ml for two hours, and the controls were 5 ml of airbrushed tissue from healthy A. cervicornis colonies. Disease progression was scored two days after attachment of treatments and treatments were scored as transmitting WBD if there was more than 1 cm of dead tissue that progressed along the coral branch over time. In this figure treatments with (a) were statistically different from the controls (p<0.0001, Fisher-exact tests with Bonferroni adjustments), and those with (b) were not (p>0.1, Fisher-exact tests with Bonferroni adjustments).