Data for Sea urchin mass mortalities 40 years apart further threaten Caribbean coral reefs

In 1983-1984, a mass mortality caused a Caribbean-wide, >95%
population reduction of the echinoid grazer, Diadema antillarum. This led
to blooms of algae contributing to the devastation of scleractinian coral
populations. Since then, D. antillarum exhibited only limited and patchy
population recovery in shallow water, and in 2022 was struck by a second
mass mortality reported over many regions in the Caribbean. Half a century
of time-series analyses of populations of this sea urchin from St. John,
US Virgin Islands, reveal that the 2022 event has reduced population
densities by 98.00% compared to 2021, and by 99.96% compared to 1983. In
2021, coral cover throughout the Caribbean was approaching the lowest
values recorded in modern times. However, prior to 2022, locations with
small aggregations of D. antillarum produced grazing halos in which weedy
corals were able to successfully recruit and become the dominant coral
taxa. The 2022 mortality has eliminated these halos on St. John and
perhaps many other regions, thereby increasing the risk that these reefs
will further transition into coral-free communities.