Stony coral tissue loss disease decimated Caribbean coral populations and reshaped reef functionality

Abstract

Diseases are major drivers of the deterioration of coral reefs and are linked to major declines in coral abundance, reef functionality, and reef-related ecosystems services. An outbreak of a new disease is currently rampaging through the populations of the remaining reef-building corals across the Caribbean region. The outbreak was first reported in Florida in 2014 and reached the northern Mesoamerican Reef by summer 2018, where it spread across the ~450-km reef system in only a few months. Rapid spread was generalized across all sites and mortality rates ranged from 94% to <10% among the 21 afflicted coral species. Most species of the family Meandrinadae (maze corals) and subfamily Faviinae (brain corals) sustained losses >50%. This single event further modified the coral communities across the region by increasing the relative dominance of weedy corals and reducing reef functionality, both in terms of functional diversity and calcium carbonate production. This emergent disease is likely to become the most lethal disturbance ever recorded in the Caribbean, and it will likely result in the onset of a new functional regime where key reef-building and complex branching acroporids, an apparently unaffected genus that underwent severe population declines decades ago and retained low population levels, will once again become conspicuous structural features in reef systems with yet even lower levels of physical functionality.

Structure-from-motion photogrammetry demonstrates variability in coral growth within colonies and across habitats

“…astreoides suggest that the ability to rapidly occupy space has helped these weedy species to become dominant on today’s (and likely tomorrow’s) Caribbean reefs. As these species are small and do not notably contribute to reef structure or community calcification, the functional integrity of coral reefs in the region continues to decline [ 5 , 8 , 30 ]. The effects of shifting community composition on reef functions may however vary on small spatial scales, as we show that growth rates clearly differ between closely spaced habitats, probably as a function of locally variable environmental conditions.…”

“…In January 2020, 52 colonies of the species Orbicella faveolata , Porites astreoides , Siderastrea siderea , Pseudodiploria strigosa , Agaricia agaricites and Agaricia tenuifolia were tagged and photographed at two reef sites close to Puerto Morelos, Quintana Roo, Mexico ( Fig 1 ). These corals are among the most common Caribbean species and were still present after the SCTLD severely impacted reefs across the Mexican Barrier Reef [ 5 ]. The two surveyed reef sites represent two different habitats with distinct environmental conditions.…”

“…severely impacted reefs across the Mexican Barrier Reef [5]. The two surveyed reef sites represent two different habitats with distinct environmental conditions.…”

“…In the Caribbean, a combination of disease, overfishing, pollution and climate change over the past decades has led to a region-wide decline in coral cover [ 1 ], reef complexity [ 2 ] and calcium carbonate budgets [ 3 ]. Critically, many reef communities are shifting towards assemblages dominated by slow-growing, non-framework-building taxa [ 4 ], a trend exacerbated by the recent Stony Coral Tissue Loss Disease (SCTLD) outbreak [ 5 ]. The key metric to quantify the functional impacts of these changes is coral growth, underpinning reef health indices such as the ReefBudget method [ 6 , 7 ] and the Reef Functional Index [ 8 ].…”

Mixtures of genotypes increase disease resistance in a coral nursery

“…The highly transmissible white band disease (WBD) 11 , for example, led to the near complete collapse of dominant reef-building Acropora cervicornis and Acropora palmata coral populations 8 , 12 . More recently, stony coral tissue loss disease (SCTLD) threatens the existence of numerous other reef-building corals around the Caribbean 10 , 13 , 14 . While the etiology of SCTLD is still unknown, the application of antibiotics has been effective at a colony scale 15 – 20 , but cannot keep pace with continued infections and reinfections on the reef scale.…”