The 2022 Diadema antillarum die-off event: Comparisons with the 1983-1984 mass mortality

Abstract

The 1983-1984 die-off of the long-spined sea urchin Diadema antillarum stands out as a catastrophic marine event because of its detrimental effects on Caribbean coral reefs. Without the grazing activities of this key herbivore, turf and macroalgae became the dominant benthic group, inhibiting coral recruitment and compromising coral reef recovery from other disturbances. In the decades that followed, recovery of D. antillarum populations was slow to non-existent. In late January 2022, a new mass mortality of D. antillarum was first observed in the U.S. Virgin Islands. We documented the spread and extent of this new die-off using an online survey. Infected individuals were closely monitored in the lab to record signs of illness, while a large population on Saba, Dutch Caribbean, was surveyed weekly before and during mortality to determine the lethality of this event. Within four months the die-off was distributed over 1,300 km from north to south and 2,500 km east to west. Whereas the 1983-1984 die-off advanced mostly with the currents, the 2022 event has appeared far more quickly in geographically distant areas. First die-off observations in each jurisdiction were often close to harbor areas, which, together with their rapid appearance, suggests that anthropogenic factors may have contributed to the spread of the causative agent. The signs of illness in sick D. antillarum were very similar to those recorded during the 1983-1984 die-off: lack of tube feet control, slow spine reaction followed by their loss, and necrosis of the epidermis were observed in both lab and wild urchins. Affected populations succumbed fast; within a month of the first signs of illness, a closely monitored population at Saba, Dutch Caribbean, had decreased from 4.05 individuals per m2 to 0.05 individuals per m2. Lethality can therefore be as high as 99%. The full extent of the 2022 D. antillarum die-off event is not currently known. The slower spread in the summer of 2022 might indicate that the die-off is coming to a (temporary) standstill. If this is the case, some populations will remain unaffected and potentially supply larvae to downstream areas and augment natural recovery processes. In addition, several D. antillarum rehabilitation approaches have been developed in the past decade and some are ready for large scale implementation. However, active conservation and restoration should not distract from the primary goal of identifying a cause and, if possible, implementing actions to decrease the likelihood of future D. antillarum die-off events.

A scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea

“…We term this mass mortality “ D. antillarum scuticociliatosis (DaSc).” It is currently unknown whether DaSc was involved in the 1980s D. antillarum mass mortality. The association between DaSc and calm water ports and harbors, and the proximity of some sites where the condition initially occurred to river mouths, is of particular interest since these habitats may foster enhanced productivity of microorganisms in general ( 15 ). However, subsequent emergence at sites away from ports and harbors suggests that other host population characteristics or dispersal factors, potentially including currents, eddies, Sargassum rafts, migratory fish, or seabirds, may influence spread of the ciliate.…”

“…In late January 2022, D. antillarum began experiencing another mass mortality event. The condition was first observed in St. Thomas [U.S. Virgin Islands (USVI)] and, by late March, had been found at nine more insular Caribbean jurisdictions across the Lesser Antilles, Jamaica, and the Mexican Caribbean ( 15 ). By June 2022, the condition had also been reported in most of the Greater Antilles, Florida, and Curaçao ( 15 ).…”

“…The condition was first observed in St. Thomas [U.S. Virgin Islands (USVI)] and, by late March, had been found at nine more insular Caribbean jurisdictions across the Lesser Antilles, Jamaica, and the Mexican Caribbean ( 15 ). By June 2022, the condition had also been reported in most of the Greater Antilles, Florida, and Curaçao ( 15 ). Gross signs in affected urchins began with detachment from vertical surfaces, loss of spine movement/reaction to stimuli, loss of tube foot control, using spines for locomotion instead of tube feet, and forming a stellate spine arrangement ( Fig.…”

“…1 ). Within days, urchins with these signs catastrophically lost spines leading to epidermal tissue loss and exposure of underlying test which progressed rapidly (~2 days) to death ( 15 ). The loss of spines, in particular, led to predation by nearby fishes ( Fig.…”

Design and validation of a PCR protocol to specifically detect the clade ofPhilastersp. associated withDiadema antillarumscuticociliatosis

“…The long spined Caribbean urchin, Diadema antillarum experienced mass mortality across the Caribbean starting in spring 2022 (Hylkema et al 2023). This mass mortality echoed an earlier event which decimated D. antillarum population densities from 1983-1984 and triggered a phase shift from coral to algal-dominant environments in the region (Lessios 2016).…”