Similarities and Differences Between Two Deadly Caribbean Coral Diseases: White Plague and Stony Coral Tissue Loss Disease

Abstract

For several decades, white plagues (WPDs: WPD-I, II and III) and more recently, stony coral tissue loss disease (SCTLD) have significantly impacted Caribbean corals. These diseases are often difficult to separate in the field as they produce similar gross signs. Here we aimed to compare what we know about WPD and SCTLD in terms of: (1) pathology, (2) etiology, and (3) epizootiology. We reviewed over 114 peer-reviewed publications from 1973 to 2021. Overall, WPD and SCTLD resemble each other macroscopically, mainly due to the rapid tissue loss they produce in their hosts, however, SCTLD has a more concise case definition. Multiple-coalescent lesions are often observed in colonies with SCTLD and rarely in WPD. A unique diagnostic sign of SCTLD is the presence of bleached circular areas when SCTLD lesions are first appearing in the colony. The paucity of histopathologic archives for WPDs for multiple species across geographies makes it impossible to tell if WPD is the same as SCTLD. Both diseases alter the coral microbiome. WPD is controversially regarded as a bacterial infection and more recently a viral infection, whereas for SCTLD the etiology has not been identified, but the putative pathogen, likely to be a virus, has not been confirmed yet. Most striking differences between WPD and SCTLD have been related to duration and phases of epizootic events and mortality rates. While both diseases may become highly prevalent on reefs, SCTLD seems to be more persistent even throughout years. Both transmit directly (contact) and horizontally (waterborne), but organism-mediated transmission is only proven for WPD-II. Given the differences and similarities between these diseases, more detailed information is needed for a better comparison. Specifically, it is important to focus on: (1) tagging colonies to look at disease progression and tissue mortality rates, (2) tracking the fate of the epizootic event by looking at initial coral species affected, the features of lesions and how they spread over colonies and to a wider range of hosts, (3) persistence across years, and (4) repetitive sampling to look at changes in the microbiome as the disease progresses. Our review shows that WPDs and SCTLD are the major causes of coral tissue loss recorded in the Caribbean.

Coral disease outbreak at the remote Flower Garden Banks, Gulf of Mexico

“…Coral reefs provide numerous ecosystem services including support of robust fisheries and tourism industries. Over the last half-century, however, natural and anthropogenic stressors including pollution, overfishing, disease, and ocean warming have contributed to widespread degradation of coral reefs throughout the Tropical Western Atlantic (Eakin et al, 2010;Woodley et al, 2016;Gil-Agudelo et al, 2020;Croquer et al, 2021). Flower Garden Banks National Marine Sanctuary (FGBNMS) is a high coral cover reef ecosystem in the northwest Gulf of Mexico that has shown remarkable resilience despite declines in coral reef health elsewhere (Aronson et al, 2005;Johnston et al, 2016).…”

“…Disease outbreaks are of increasing concern, especially as the Caribbean region is a hotspot of coral diseases (Weil et al, 2006;Ruiz-Moreno et al, 2012;van Woesik and Randall, 2017), experiencing recurring disease outbreaks such as white plague from the 1970s through the mid-2000s (reviewed in Croquer et al, 2021). White plague produces lesions at colony margins leading to rapid tissue loss and mortality (Richardson et al, 1998;Bythell et al, 2004).…”

“…White plague produces lesions at colony margins leading to rapid tissue loss and mortality (Richardson et al, 1998;Bythell et al, 2004). White plague affects nearly 40 species and is now considered endemic to much of the Tropical Western Atlantic (Croquer et al, 2021). Despite identification of Aurantimonas coralicida in white plague (Type II)affected corals, a universal white plague pathogen has not been confirmed, and it has been hypothesized that white plague signs may be caused by multiple etiologies.…”

“…SCTLD constitutes an ongoing epizootic event in the Caribbean, and is currently in an epidemic phase at some locations and an endemic phase in others (Aeby et al, 2021;Croquer et al, 2021). SCTLD's etiology remains unknown, yet both direct and waterborne transmission routes are hypothesized to occur (Aeby et al, 2019;Muller et al, 2020;Studivan et al, 2022a;Studivan et al, 2022b).…”

Differences in the progression rate of SCTLD in Pseudodiploria strigosa are related to colony size and morphology

“…SCTLD resembles the Caribbean White Plague (WP) diseases, because of the tissue loss they produce in their hosts; however, the progression rate can be several orders of magnitude faster than lesions usually produced by WP (Croquer et al, 2021). A clearer diagnostic sign of SCTLD is the presence of one or multiple lesions and the presence of a bleaching front between the apparently healthy tissues and the recently exposed coral skeleton (Croquer et al, 2021). Generally, a band is observed initially showing the white skeleton of the coral, which increases in size over time until the whole colony dies within a few weeks or months.…”